The dreaded P0300 CAUTION LONG POST
 

Greetings all,
I will try to make a long story short, but I'm afraid that it's not going to turn out that way. But here goes anyway. First things first, I am attempting to locate the cause of a DTC #PO300 (Random/Multiple Cylinder Misfire). I know, it's the absolute worst code to diagnose but it's the hand I've been dealt.
The vehicle in this case is a 2001 s-10 Blazer 2wd with a 4.3 (W) 5 spd (NV3500) with 103000 miles. My wife bought it new just before we met so I know the complete history of this vehicle. About six months ago on the way to work it suddenly started to buck and surge and then just died. It felt like a fuel delivery issue, likethe pump quit. It would crank fine, but would sputter and die and wouldn't rev over about 5-600rpm. trailered it home and started looking for the problem. Turns out it was a bad ignition module and a weak coil. (no codes and the pump testedfine)Replaced bothalong with thespark plugs, cap and rotor (all ac delco parts) and plug wires (msd) Figured while I was at it might as well change the fuel filter.
About 4 months ago I started to notice a slight intermittent miss (no codes) from then until now it has gotten progressively worse. Now I have a serv eng soon light, and the missfire can be quite severe at times, but it seemsto happen mostly under part/light throttle conditions, and not so much if at all under acceleration, or idle. It was a little sluggish from idle to about 1000 rpm but would pick up from there all the way to red line. But at cruising speed (55-65 mph, 1900-2400 rpm) you could feela surge, almost like a cylinder dropping out then refiring. So Thinking maybe the fuel system was getting dirty I changed the filter again, ran some fuel system cleaner through it (3times with a filter change in between each) and got no improvement. Given the fact that I live on the gulf coast where humidity is a real BIG issue I also ran some HEET (water evaporater) through it as well.
That didn't cure the problem (not that I REALLY thought it would) that would be too easy.
I have checked the following as well, theTPS, MAF, and MAP sensorsI replaced the IAT sensor thinking that be cause the problem was more pronounced at a lower ambient air temp it might help,....NOPE!
This weekend I upgraded to the MFI Spider (THE BEST THING I HAVE DONE TO THIS TRUCK THUS FAR, BAR NONE!!!!!! THANKS BLAZER FORUM!!!!!!) No I haven't checked my fuel pressure yet, (can't find my guage) but with the cost to have the injectors etc. pro cleaned, plus parts I figured I'd be money ahead.( Was it necessary,......WELL, I won't argue with the end result, It runs better than it ever has!) The throttle responce(sp) is incredible,....got the old girl sideways last night, WHOO HOO! Anyway the part throttle misfire is still there. Cleaned pcv and the EGR valve and tube (not that it needed it, was really quite clean actually) No improvement, as of yet I have found no vacuum leaks (BTW don't vacuum leaks SUCK?! ;p I pulled the spark plugs and they looked ok, (minor amount of high speed glazingn ,not bad but I will replace them)
So I'm thinking I either have a unlocated vac leak or may be a bad O2 sensor or two. It seems that after theinitial warm up,....for the O2 sensors (couple of mins) the missfire starts,but as I said it's only at part throttle/ cruise rpm, not under accelleration. I'm assuming (Ya, I KNOW)that the truck is going into open loop in reasponce to bad O2 sensor(s). How often should they be replaced I mean is there a scheduled replacement interval, or is it a replace at failure deal. Speaking of which how can I test the sensors with a multimeter ( I didn't have much luck earlier, not my strong suit sorry to say) Please correct me if I'm wrong but If I were having issues with fuel pressure or volume wouldn't accelleration be affected more so than part throttle/ cruise? I guess I'm just trying to find a way out of having to buy a new guage to test my pump.
I'm sorry that this post has turned into the latest version of War and Peace but I just want to give you all the information that I can in one shot in the hopes that WE can solve this issue without having to post/ reply muliple times.

Thank you in advance for ANY ideas you my have to help me resolve this issue.

Gator

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Looks like you've got a lot of experience trouble shooting vehicles! You've done pretty much everything right. I would have inspected the O2 sensors before replacing the spider, but with 103k miles on the clock and your justification (I did the same thing), the new spider was money well spent.

For me, it's easy to take a look at the sensors and what the vehicle is doing while the misfire occurs, but I have a scan tool capable of showing me whatever it is I want to see. For this type of problem I would look at the O2 sensor trace, cross counts, as well as long and short term fuel trims. This information would tell me if a sensor has become lazy to a point of affecting performance/efficiency or maybe point me in another direction.

Without a scan tool capable of delivering this data, your choices are really quite limited. AC Delco O2 sensors aren't exactly cheap, but in my experience with O2 sensors for GM vehicles, there isn't another that beats it. At 103k miles, the O2 sensors very well could be the culprit.

Hope this helps!!

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Boy does this thread seem familiar. [8D]

My P0300 turned out to be cap, rotor, and plug wires. All replaced within a year of the problem. Don't rule them out. Still got the old wires, swap them and see what happens. Pull the cap off and look for corrosion. Try spraying the cap with water while the engine is running, see if she purrs differently.

I need to do some research into the MFI change thingy. Anybody got a link to a thread on it?

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Thanks for the quick reply,

Just for giggles, if I were to disconnect the O2 sensor(s) (upstream of the cat; for diagnositic purposes only) would that tell me if I had a bad or marginal one? I.E. force the computer to stay in open loop. Short of taking it to a dealer to diagnose them and not being sure exactly how to test them with a multimeter am at a loss. I really don't want to through money at the problem until I stumble on the cure.

Just a straw to grab

Thanks again,

Gator

Thanks,

Gator

RE: The dreaded PO300 CAUTION LONG POSTas123
 

I had a similar problem with my blazer, P0302 code I believe, Cylinder 2 misfire, I had just changed the plugs and wires so I just ruled them out. Turns out the problem was a faulty wire or plug, I just changed both and the truck has never run better. Dont over look the simple crap, thats what I did for 2 whole months. [:@]

RE: The dreaded PO300 CAUTION LONG POSTas123
 

yea, you could disonnect the O2 sensor. The puter only read the sensor after the engine is up to operating temp. Once up to temp it reads the sensor and makes adjustments to the air/fuel ratio to hit that perfect ratio. If the O2 sensor is disconnected teh puter will stay in open loop, trip a code, and go into some default programming. If it runs smoother, your O2 is at fault. If nothing changes, you haven't found the problem yet.

Disclaimer: with the O2 disconnected the engine will get horrible gas mileage, and if you let it go long enough it could plug up a cat.

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Thats what I was thinking, and yes I am aware of the adverse effects of disconnecting the sensors. I would only disconnect them to rule them out as a possible cause for the current condition. But as I'm sure you are aware O2 sensors ( AC Delco) aren't CHEAP. I'm wondering though in order to make it a valid test I have to disconnect all (3) at once correct? If it clears up how do I determine which one is the culprit,...replace two of them, buy a third and just keep changing it's position ? Or should the smart thing to do be just bite the bullit and replace them all at once. Gee that was a STUPID question !!!! (Tripping over dollars to save nickels)
Thank you so much for pointing out the detrimental effects of disconnecting the sensor(s) as I realize that others who may not know also read these post! I'm am so greatfull to everyone on this site for their help. As soon as I can figure this mess out I will most definately post the results so that others may benefit as well.
Please keep the ideas coming.

Thanks again,

Gator

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Only the upstream (B1S1 & B2S1) sensors influence fuel delivery and these sensors are located before the catalytic converter. The post-cat or downstream sensor B1S2 is a catalyst monitoring sensor only and should only be replaced if a code is present and repeatable (ie. comes back if you clear it).

So since you are experiencing an engine drivability concern, the only sensors of interest would be the upstream sensors, B1S1 & B2S1. You can disconnect them independant of each other. Driving around for a day with an O2 sensor disconnected should not significantly impact the life or performance of the catalytic converter.

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Thank you so much for clearing that up for me. I'll try it and see if it helps.

I did run across onther post in a different section that sounds carbon copy to my situation, that I will reinvestigate (i.e. TPS) I did check it but I might have missed a flat spot. HUMMMM come to think about it my rolloff truck (MACK) did the same thing and it was the TPS. I'll get back to you

Thanks again,

Gator

P.S. Nice reply to goat6500 : )

RE: The dreaded PO300 CAUTION LONG POSTas123
 

Nuts,

Disconnected all (3) O2 sensors, 1 at a time and,.........no change. Oh well, I guess it's not all bad. I haven't found the problem,............yet, but at least I don't have to spend big$$$$ on O2 sensors. The battle continues.

Gator

RE: The dreaded PO300 CAUTION LONG POSTas123
 

I feel your pain.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

The battle continues,.............and I'm still fighting but not making much headway.

Changed the TPS and the MAP sensors today, the throttle response has improved but the code and the random miss is still there. All the parts I have tested and or replaced have helped the overall drivability to the point that it runs better than it ever has( bought it new from the dealer)
I've reached the point where I've run out of altitude, air speed and ideas. I could change plugs, cap and rotor again ( but the problem occured BEFORE I changed them the first time) so I don't really think changing them again is the answer.
Tomorrow I will go through all my grounds again, so far all the wiring and electrical componants have checked out fine or have been replaced. Everything I have done up to this point has helped but not cured the problem, and is found in previous post.
I have in the past taken this vehicle to more than one dealership ( under warranty) but in most cases they could never find the problems ( things like a siezed throwout bearing, 2 sticking rear calipers etc.)that were
discribed. So I'd come home order the parts and repair the problems myself, and up until now I've been pretty sucessful. Is it just me or do dealerships really hate to do warranty work? Its not like they have to do it for free (correct me if I'm wrong, but dosen't the factory reimburse the dealer for warranty work?)
Sorry,...... my train of thought derailed. (Somebody call the NTSB)
I would really like to solve this problem, without removing the radiator cap and driving a new truck under it.
I'm open to any and all suggestions even if they have been covered in this post before. I'm missing something,.........somewhere,.......and I'll bet it's so simple that it's easy to overlook. The question is what.

Thanks in advance,

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

what about the distributor itself in general maybe its slipping gear thats the only suggestion i haven't heard yet and so maybe thats causing the misfire check that out you never know

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Man does this post sound familiar.
I too pulled out my distriburtor, it wasn't the problem.

Got a test for ya.
Turn off the lights in the garage, start the truck and look for arcing from teh plug wires to surrounding metal. Also verify that your plugs are on al the way, and in the correct locations. At this point, start with the basics and run through them again.

Can you get a to the data stored in the puter? See if you can get the readings whent he code was set. I am drawing a blank on the technical term for them. Howver when a fualt code is triggered the puter stores the engine readings at the exact moment of the fualt. Post those up.

One other thing. Bang on your cat, under the truck, does it rattle?

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

The battle still wages on,.....and I'm short on ammo.
Checked / cleaned and reinstalled all the grounds (execpt pass side head to body,........I'll add one from the engine to frame before I tackle that nightmare!) They all looked as good as the day the factory hooked them up. (no change) I guess i'll throw some more money at it tomorrow ( cap, rotor, and plugs) even though I don't think it will make any difference. Plug wires checked out fine (multimeter) and no signs of arcing to ground by sight or sound (checked last night)
All the wife's cats are inside so I had to wait for the neighbor's cat to walk under the truck before I could (bang on it) it didn't rattle,.........it just hissed. :D(NOTICE TO PETA,...........IT'S A JOKE!) I love cats,......(They taste like chicken) (NOTICE TO PETA,........SEE ABOVE):eek:
Sorry it's been a REALLY long day.
As for the distributor I inspected it while it was out during the MFI spider upgrade and it appeared to be fine, nothing worn, cracked, broken etc.standard production tolerences (excessive shaft end play, corrected with a moroso shim and a new roll pin) I haven't checked the ignition pick up yet ,.......hmmm, I wonder..... ( I'll check that tomorrow) I don't remember is it a magnetic or hall effect style?

Any other ideas?

Again thanks to all the wonderful people on The Blazer Forum!

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

deffinitly check the pickup coil and see if thats bad that could be possibly the problem its one of the few last things on the check list. Dont worry about ammo we got a surplus of it!!!

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Anyone got any rope?,.....cause I'm about at the end of mine! Spent this morning replacing vaccum lines as some were starting to deteteriorate. As luck would have it it didn't help. Replaced the pick-up in the distributor, and as I feared,..... no change.
I have never in my life had this much difficulty in diagnosing a problem. Stupid me for thinking I was intelligent enough to fix this myself! [email protected]#$%! I'm really starting to hate late model stuff! Nothing is easy, or cheap! I could dam near rebuildanyone of my big blocksfor what I've spent trying to fix this misfire (ok I'm exaggerating somewhat,........but right now it doesn't seem like it!)
Don't get me wrong, everything I have done to this point has helped. The difference is almost night and day, and except for the missfire it runs great. I haven't just thrown money and parts at it hoping that I'll somehow figure it out, but it sure seems like it. Every part I have replaced has made a difference how ever slight, but it to this point it still hasn't corrected the issue that I was attempting resolve, (PO300)
I'm so tempted at this point to rip out the 4.3 and stuff a 383 that I have built in to it! (with a carb and a magnetic distributor) I was planning to do that anyway but I'm not ready just yet and I was wanting to use factory F.I. instead of an aftermarket system. (stealth factor, avalibility of replacement parts etc.) I felt if I didn't solve the issue before I performed the conversion then it would come back to haunt me. Now a large portion of the budget for the conversion is gone, and I'm no closer to fixing the problem than when I started.
Should I have taken it to a shop (dealer, independant, etc.) hard to say. Past dealings around here have proven less than fruitful. (If someone knows of a really good shop in NW Florida I'd love to hear about it)
I can honestly say that I have learned alot during this adventure, and have had the pleasure of talking with some really great people on the Blazer Forum !!!! Thanks so much.
Have I given up,.......NO WAY! Now it's personal!!!!So where do I go from here?

Thanks again,
Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

you changed the plugs did you gap them just want to help rule even more stuff out? what about hhmm timing i don't know if i asked or if anyone has but is it in time maybe?

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Plugs are gapped to 060 (as specified by lable)

I have not checked the timing (with a timing light) because I was under the assumption that the computer was responsible for timing and that it was not adjustible, i.e. the distributor housing doesn't rotate when the bolt is loosened. That being said I haven't looked to see if there is even a timing tab on the front cover. I'm sure that there is a probe holder for a magnetic pick up type timing light, but all I have is a snap-on inductive style. If there is a timing tab I could check,(if just to rule out any timing issues) I don't believe that it is a timing issue as the miss is during light/ part throttle cruise only.( usuallybetween approx 18-2400? rpm/ 50-65mph)Under idle/ acceleration etc. it doesn't seem to be a factor. In my understanding if it was a timing or valve train event, like a weak spring for example it would start at low rpm and get progressively worse no matter what kind of load was present. I'm still leaning toward an electrical system issue or vaccum leak. Doesn't mean that I won't check to rule them out, thanks for the ideas. Anything else?

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Man gator, I wish you were closer! At this point I am out of ideas as far as i can suggest without actually being there and feeling/hearing/seeing what is truely going on. With my scantool (autoenginuity), we could look at the freeze frame data and the actual event where the misfire occurs. That would allow us to try to narrow things down... But I'm afraid that I am out of ideas on how to help in this problem...

Could you run down what you have replaced and/or tested thus far? And what the results of the tested components were? Just kind of a summary sequence of events. It's not that I am too lazy to read back through this post, its just that I don't have a bunch of time right now.

I hope I(we) can help you get this resolved!!

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

I was thinking that would be a good idea as well, I'll get to work on a summary,and............Thanks to everyone! You all, oops (y'all) are great!

(I LOVE THE BLAZER FORUM!!!!)

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

we as a forum will give you all the ammo you need to help get this taken care of don't worry the more we narrow it down without it costing you alot to no money the better sorry its taking so long to help but just to let you know were here for you

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

so the missfire only happens under light trottle at 55-65 mph? Does it happen in any other gear at the same rpms?

Is this a 4x4, if so, drop it into 4lo and see if you can get the missfire to happen at the same rpms?

It could the the coil. Have you tested it, and did you replace it, if so with what Brand?

I doubt its your timing, could be a streched chain, but not likely. Typically with timing, it works or it don't, its not really an intermittent problem.

Did you replace teh cap, rotor, and plug wires?

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

The following is a summary of components tested and or replaced while searching for the cause of a DTC. Code PO300 (random multiple cylinder missfire)

The subject vehicle is a 2001 Chevrolet s-10 blazer 2wd with 103000 miles
H.O.4.3L v-6 (L35)
NV3500 5sp (M-50)
8.5 rear axle with 3.42 (GU6) and positraction (G80)

The following has occured within the past 6-9 months (approx)

Ignition module replaced (defective)
Ignition coil replaced ( weak)
Spark plug wires replaced
Spark plugs replaced (x2 no change)
Distributor cap replaced
rotor replaced
Inlet air temp sensor replaced (tested marginal)
TPS replaced (flat spot)
MAP sensor replaced (tested marginal)
Fuel filter replaced (x3 nochange)
Fuel system cleaner added (x3 nochange)
SCFI (spider assy) MFI upgrade
Distributor shaft end play corrected (shim kit)
Pick-up (distributor) replaced (no effect)
EGR valve/ supply tube cleaned (no effect)
Vacuum lines (hoses) replaced ( dry rot)
O2 sensor(s) disconnected (no change)
' ' reconnected&cleared codes
Ground wires inspected/cleaned
Positive cable inspected/cleaned
Electricle leads/connect inspected/cleaned

The above is the short list (ya right!) of parts inspected,tested,or replaced while searching for the cause of the missfire. Bear in mind this missfire occures during light/ part throttle (cruise) and doesn't occur at idle or while accellerating. At times it is barely noticeable, other times it can be quite severe (can't narrow down specific temp/wheather conditions that if at all apply) Dry verses wet, hot verses cold, etc. Fuel consumption is not to bad, approx 20mpg (but I used to get on average approx 25mpg, believe it or not) when I can FINALLY solve this missfire issue I know the mileage will return. The plugs appear fine no fouling, good color (for unleaded fuel anyway) no excessive deposits, no signs of detonation, etc. As for fuel I have tried different brands, (although I haven't tried a higher grade) and to this point have noticed no improvement. I could be mistaken but I don't believe I have a fuel delivery problem (pressure or volume) as it starts, idles, and accellerates fine. I suppose I should test for pressure if for nothing else to rule it out. Still haven't found my gauge ( I guess the best way to find it is go out and buy a new one LOL)
I have worn out my best fine tooth comb looking for the cause of this missfire. The only code that has ever come up is PO300. Maybe I should just bite the bullit and go buy a really good scan tool like what kyle linked to me, but I really hate to because this is the only vehicle I own that even has a computer. But what is the alturnative, pay someone else every time (I really hope this is the last) I have a problem, or keep throwing time, money, and parts at it. Would I really be time and or money ahead if I had just taken it to a dealer in the first place? Maybe yes,.......maybe no,..... that remains to be seen. As I have said before everything that has been done up to this point has helped, except for the missfire. To be honest I think it runs better now than it ever has, and it was purchased new from a dealer with 3 miles on it.

I think I've covered everything up until now, so I guess we'll see what happens! Sorry again for the longgggggg post.

Thank you all for your continuing help and support.

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

The missfire seems dependant on rpm not mph, same rpm spread in all gears (1-5) I agree with you about the timing issue, and I don't think it's a worn Timing chain. Short of pulling the cover an checking, or hooking up a timing light and watching for a traveling timing mark (at the harmonic balancer) I could not say with 100% certanty(sp). It's something to think about but,........not very likely. I'm willing to entertain any ideas at this point, and will not refuse any.

Thanks
Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Have you attempted an upper intake tract cleaning? A bottle of seafoam (or GM top engine clean which is more expensive) will only cost you a few dollars and shouldn't hurt anything that you have already done. I posted the procedure in another thread. You really should change the oil after words. It may help.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

When I did the MFI conversion I cleaned the living stuff out ofthe intakeall the way down into the heads with carb cleaner and engine cleaning brushes. It wasactually pretty cleani.e. no carbon etc. just the typical synthetic oil discoloration.Removed the excess rags, shop vac,( waited until everything evaporated first--didn't want to blow myself up)and finally compressed air, looked into each one with a light and a mirror. When I got done it looked brand new like the day it was cast. Then I pulled all the spark plugs and spun the engine over to make sure I got anything that might have gotten past a valve pushed out. Re installed the plugs and changed the oil and filter. So do you think I should dump some Sea Foam , or G.M. top engine cleaner down it any way? If you think it would help I'll do it.

Thanks

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

The top engine cleaner (Seafoam or GM stuff) will clean the valve stems in the intake & exhaust tracts as well as clean up the combustion chambers. The carbon buildup in the combustion chamber is if interest here. If there is carbon buildup, it could cause preignition which the computer could misinterpret as a misfire. But this should be more promenant the harder you push the motor... I'm just running out of ideas here.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

i agree with swartlkk its worth a shot right? i don't know what else to advise about and swartlkk even said it himself runnin outta ideas but hey were the blazerforum we can do it just have to dig deep into everything that could be linked to a misfire. try the seafoam like swartlkk said and see if it changes anything if it doesn't work let us know we will try something else hopefully by then we think of something else

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

just some other feedback.
http://www.obd-codes.com/trouble_cod...e-detected.php
http://www.aa1car.com/random-misfire/

Since your sure of the other stuff.
Check that cat, vacumm and do a compression test.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Kyle,
Last night after I posted a reply (ref; upper intake cleaning) where as I explained that I did a thorough cleaning during the MFI conversion, I got to thinking. Why would you ask about an intake tract cleaning, what was I missing here. Then after much tossing and turning, (didn't sleep last night) it hit me like a ton of bricks!! Carbon in the chambers, which combined with a lean fuel mixture (by design) could lead to detonation. It was then I understood where you were headed, the knock sensors were detecting detonation due to carbon deposits ( glow plug effect;for lack of a better way of explaining it) and the computer tried to adjust spark lead (retard timing) to compensate. The computer then saw unburned fuel as a result and concluded there was a missfire, at which time a code was set. It made sense (at 2:30 am anyway)
This morning before I left for work I checked the forum, just to see if there were any new replies and I found your post which confirmed the conclusion I reached earlier that morning. The more that I thought about it the more it made sence, except for one thing. Correct me if I'm wrong but doesn't the death rattle(detonation) increase as the load increases. This appears to me as a lean missfire. Or is what is happening is the mixture is at it's leanest( part throttle high vacuum signal ) as is programed in to the ecm to achieve the highest fuel economy with the least amount of emisions, and because of the detonation the computer backs off the timing and adds additional fuel to compensate ( to cool the intake charge below the threashold of detonation)? To me it makes sense, is this what you were trying to express?
I actually had not thought too seriously in this direction for the simple reason that when I checked the spark plus they didn't show any indication of detionation ( little fly specks on the insulators) or deposits (carbon) on the electrodes. But I have changed my thinking in this direction because it makes sense. I have to remember that unleaded fuel doesn't burn or color plugs like leaded or race fuel. I loaned out my spark plug viewer out and never got it back, so I have been trying to read plugs with the naked eye.
I guess the point that I'm trying to make is that I dismissed a diagnostic theory (tool) too quickly (STUPID) Is this the answer I've been looking for? It very well could be, it's something that I will most deffinately persue. Like I said in a previous post I have a feeling that this problem is going to come down to something so very simple that it would be easily overlooked. Detonation due to poor additive package in the gas we are forced to live with now?,....Go figure.
Even if this tends not to be the answer, I have to say that it is still a fantastic diagnostic idea, that I dismissed too quickly early on ( trying to make a mountain out of a mole hill) THANKS KYLE!!!!
I do remember reading the post you mentioned (ref; sea foam) don't remember where it was but a search shouldn't take long. I will deffinately put this advise to good use, and will post the results. It will most likely be towards the end of the week. One question though in regards to using sea foam as an intake (upper engine cleaner) should I remove my O2 sensors before hand. I just concerned that if this proceedure loosens up and removes excess carbon from the combustion cambers it has to go out through the exhaust system. Wouldn't the deposits end up coating the O2 sensors (causing an additional problem) or will it clean them as well? Same question in reference to the cat.

Any way again, Thanks fora Great idea

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

I had thought the same thing when I originally was typing up that response, but the combustion process is quite complex and often fickle to say the least and an upper intake cleaning is cheap! Also, it is very difficult to diagnose detonation by reading the spark plugs on these newer, knock sensor equipped vehicles. The PCM cuts timing so quickly after detonation is detected that often you cannot even hear the detonation and must use a scan tool to watch the knock sensor active counts to diagnose such a problem.

The O2 and cat should be ok with the upper intake cleaning. I have never had a problem with either after doing this procedure on any of the vehicles that I have done this on. Although the possibility does exist, it could be that age old saying, "The straw that broke the camels back" type scenario. With a healthy cat & O2 sensors, you should be fine.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

The rope is so short now, that I don't even have enough to hang myself.

Tried the upper intake cleaning, (Sea Foam) and talk about a difference! ( It really runs like S--- now!) Ok to be fair I kind of expected it to, sometimes things have to run their course. (get worse before they get better) I followed the steps That I found on the Blazer Forum, which were very close to the instrutions on the can. I'll spare the details, but when I got to the point of adding the Sea Foam until the engine died, it wouldn't (even with the key off) it just dieseled. It concerned me to say the least, as all I needed was to bend a rod or break a crankshaft.(It was that violent!) So I let it sit about 25-30 min. and hoped that no damage was done. I pulled the coil wire and tried to turn the engine over, andto my reliefit spun over fine. Reconnected the coil wire and tried to start it. It took quite a bit to get it fired and when it did, the smoke show began.( was like a misquito spraying truckfrom the old days) Anyway, I drove it like a getaweay car after robbing Fort Knox! The smoke only lasted about half a block, then was gone. Still I couldn't resist so I drove the hell out of it for about 25 miles. It felt like the plugs were fouled so I pulled them all out and none of them were, but Ireplaced them anyway. The miss was still presant, so given the fact that the situation didn't change from the previous, (before the Sea Foam treatment) I don't think that carbon was the culprate. But on the plus side now I have very little if any carbon build up in the chambers, and one more variable has been removed from the equation.
I really didn't want to spend the $ to add another pressure gauge to my tool inventory (cause I already have one,....... somewhere):eek:but I did.What follows is a summery of the findings.I hooked it up and gave it a shot. Key on, cycled until pump stopped (approx 1-2 seconds) 62psi. Turned the key and started the engine, 58 psi. Tied the gauge to the wiper arm and drove home (approx 10 miles on the highway, 65 mph) during the trip the pressure was steady at 56-58 psi (no fluctuations) Under light trottle, pressure was 54-56 psi. Any throttle application would bring an increase in observed pressure, up to as high as 62 psi. Off throttle it never dropped below 54 psi.
So now what?..... static test? Ok, here it is. Key on (no start) 60-62 psi, first 5 min, no drop. Key off after 5min. went from 60-58 psi. After10 mins. down to 56 psi. After 15mins. down to 50 psi. After 20 mins. down to 45 psi. soforth and so on. After 1 hr total loss was 34 psi. So after the first 5 mins.(holds pressure for the first 5 mins.)then drop starts and continues at a rate of about 2psi every 5 mins. I did check all connections and retested just to be sure (verify test) no change in results.
Now BEFORE we blame the FPR please remember that the spider was replaced (upgraded to MFI) less than 4wks ago. I know that just because a part is new dosen't mean that it is good, but the problem (the missfire) exsisted before the spider was upgraded. I pulled the Throttle body and the inside of the intake was dry as a bone, so I'm ruling out a leak from the FPR, metering block, injectors etc. The metering block came with O rings (for the supply and return lines) installed from the factory. If they were leaking wouldn't fuel be visable from the out side (pressurized) or is the rate of bleed off so small that the fuel would evaporate faster than it would collect or otherwise be seen? What amount of leak down if any is acceptable, over what period of time? Is there a check valve in the system (in the tank etc. ) that could be causing the bleed off. Or am I making a mountain out of a mole hill again?
I'm almost to the point of putting this truck out of my misery, I'm down to one bullet,.........which one gets it? Me or my Blazer

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Have you tried different gas stations??

Have you ruled out the possibility of water/condensation in your tank by trying some dry-gas?

Man I'm really running out of ideas without telling you to come north to our soon to be winter wonderland so I can plug it into my scantool and have a look at those O2 sensor readings as well as record the pertinent operating parameters while it's acting up...

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Kyle,

In answer to your questions,.......yes and yes. Both are things that I've tried before and had no success with. I'm sorry to keep posting questions about this problem, but I'm at a loss. I am coming to the conclusion that without a proper scan tool I'm SOL trying to diagnose this. I really hate to take her to anybody to figure out whats wrong. But I've run out of ideas, and I'm affraid that I've bored everyone here to the point where I'll soon be receiving boxes of bullets. (for me and my truck)
I cannot thank everyone here enough for trying to help me, I'm so very sorry that this has gone as long as it has. Everone here has been great and provided me with lots of ideas, and support. I did get a recommendation for an independant shop today, so I guess I'll take my a--whipping like a man, and let somebody else figure it out.:(If and or when I can get this issue resolved I'll post a follow up, so at least maybe someone else can benefit without having to take a loan out on their soul.

Again Thanks to everyone for putting up with me.

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Like I said way back when. P0300 is the worst code there is., and now you too have joined the lucky ranks of us poor souls to live through the ordeal.:D

I highly recommend a dealer service tech. Fork out hte $80 and let them do a complete diagnostic.

I'll give you $50 for the truck. :)

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

MY BUDDY HAD THIS PROBLEM ONCE BEFORE, AND IT TURNED OUT TO BE THE COIL. HE THOUGHT IT WAS FINE, BECAUSE IT WAS BRAND NEW. HE TOOK THAT ONE BACK AND STARTED RUNNING FINE AFTER THAT. IT MAY NOT HELP, BUT I HAVENT SEEN ANYTHING ABOUT YOU CHECKING YOUR AIR FILTER. GOOD LUCK.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Matt,
Thanks for the imput. As for the coil it's been replaced once (along with the module waaaaayyyy back in the begining) and I don't think that it's the culprit. It is something that I will definately take into consideration and retest. Usually a coil either works or it doesn't,......usually. I'm to the point where I either buy myself a really killer scan tool ( Kyle hooked me up with a really sweet web site link,........Thanks Kyle!!) or take it to a guy my parts supplier recommended and have him run a full system scan and see what he thinks. Then maybe I'll take it to the dealer and have them do the same. (just to compare the two) I still haven't made up my mind. If I buy the scaner, then I'll have it forever. But right now the blazer (the 01) is the ONLY thing I have that is computer controlled ( I kinda like it that way:D) So it's a matter of where do I spend the cash,.............tough call.
As for the air filter It's a K/N drop in (stock air box) and no it wasn't over oiled, and yes I've cleaned and tested the MAF sensor at least twice. I hope that a full system scan (whether by me or someone else )will finally show where the problem lies. God knows I've already worn out at least 3 fine tooth combs. But as I've said before I will take ANY suggestions,.........Don't want to miss the forest for the trees, so to speak.
Again thanks for the imput and I'll test the coil again just to be sure.

Gator

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

I'm still sticking to cap & rotor or plug wires.:D

It's in your spark circuit.

RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
 

Is the War over?[sm=patriot.gif]
If it is I'm not going to know how to act. I really hate to say anything for fear of jinxing myself, but here goes.
I took hanr3's advise an changed the cap, rotor and plugs,.......AGAIN, and saw little to no improvement. I was going to take the old girl in and have a diagnostic done, but it was so nuts at work this week that it wasn't possible.
I stopped by the parts store on the way home to pick up a new fuel filter( who knows what the sea foam dislodged in the fuel tank) and as I was walking out I saw it............Dielectric grease!
Ok, I know it sounds silly, but give me a minute and I'll try to explain. Back in the very begining I mentioned that the truck died on the way to work.( the very first post) The fix turned out to be a new coil, and a new..........module. This is the part where I admit to being REALLY STUPID[sm=headbang.gif]The new module did not come with any dielectric grease. In my haste to try to fix the problem I took a short cut,........I scraped the grease off the old module and reapplied it to the new one.[sm=icon_beat.gif]At the time I fully intended to pull it back apart and do it right. Of course when themodule replacement cured the no run situation I was so happy that I forgot to go back correct the short cut. Today I corrected that mistake,.........and the missfire is gone!
To be honest I'm afraid that I'm getting my hopes up, but after months of fighting this problem, to do something (anything) that seems to have cured the problem is a HUGE deal. Is it wishful thinking? I sure hope not! Time will tell, I'll know for sure in the morning.
In a way it makes no sense, in a way it does. Why would it (the missfire) only show up under part or lite throttle. Does the grease isolate the module from heat soaked up from the bracket? Or does it keep the module from grounding out on the bracket? I don't really understand why the factory located it (along with the coil) in one of the worst places you could find for radiant heat. (top of a valve cover above an exhuast manifold)
I know it sounds strange but so far it is what it is. If this indeed cures the problem I'll be happier than a tornado in a trailer park!!!!!!!!![sm=happybounce.gif]

I'll keep yall posted.

Gator