Hi all...time to resurect this one.

2000 4wd LS Blazer
120k miles

Same issues here. So far, I've been chasing potential, ignition control, spark, and fuel issues. I have...
[ul][*]Changed the fuel pump - 1 year ago[*]Changed the fuel filter - a few months ago[*]Changed the fuel injector assembly (multiport spider including FPR) - a few months ago[*]Inspected vacuum lines and replaced suspects - a few months ago[*]Changed y-pipe, cat, and oxygen sensors (all OE OBDII certified)- a few months ago[*]Changed MAF sensor - 1 year ago[*]Changed spark plugs - last week[*]Changed PVC valve - last week[*]Changed cap and rotor - last week[*]Cleaned MAF - last week[*]Cleaned EGR valve and port - last week[*]Changed air filter - last week[*]Installed new muffler - last week[*]verified proper trans fluid level - last week[*]Verified proper running fuel pressure (on cycle and idle) - last week[/ul]

Well...I'm getting better gas mileage all the time. But the surging is still present. I call it surging...not sure if someone else would. It could also be described as lagging. It feels like a boat towing a waterskier when the rope slack is taken up fully. There's a sharp jerk back and then a jerk forward.Anyway...that's about what I've got going on. I'm not sure that this is a torque converter issue, a fuel pump circuit issue, a fuel pressue issue...or something I haven't even thought about.

Some other specifics (and reasons why those things come to mind)...

It's worse when it rains. It's actually barely detectable during dry weather. It is most noticeable after some rain. I've gone down the spark path and the air path...which makes me think fuel. The fuel pump is relatively new, and cycle fuel pressure and no load idle fuel pressure check out, but I don't have a way to check running loaded fuel pressure without installing an additional gauge. I may do that he soon.

My gas mileage has improved drastically with last weeks efforts. In fact, I'm getting about 20 MPG AVERAGE (verified over the last 961 miles). This is up from about 16 MPG average historically. 20 MPG isactually better than manufacturers advertised fuel economy, if I'm not mistaken. Which makes me wonder if I'm lean...back to fuel pressure.

This current bout all started with a P0300 (multiple cylinder random misfire) code. I started with a cap and rotor...and have not seen the code again. But, i still have the surging issue...or lagging...whichever. I have no fuel leaks, vacuum leaks, or suspect lines that I can find. I have no pending, hard, or historical codes...other than the P0300. I have tried varying grades of gas, as well as fuel injector and fuel system treatments...and see no correlation between thier use and surging.

I should also point out that, although I have had symptoms of misfiring and general `rough running` for about...ever...this surging and P0300 business didn't become prevalent until a couple of months ago. Basically, everything from changing spark plugs down (in my list of stuff done) was done in direct response to this surging issue. In other words,the issuedidn't pop up after doing one of these things...or after doing anything in particular that I can identify.

I see the MAP, TPS, and IAC sensors come up in conversation...but, I don't think I have all of them. I think I have an IAC and TPS sensor...but, I'm not sure where they are or how to go about testing them or cleaning them.

Any input, guidance, other ideas would be greatly appreciated.

Thanks!

Icarus

 

I had the surging/stumble that you describe with my old Bravada and never did find a source. I ran with the hood off and a fuel pressure gauge zip tied to the windsheild wiper for a few days. Had my scan tool attached recording every parameter I could to no avail. One thing I did notice is that the surging is MUCH less prevalent when the A/C was switched off. I could barely feel it.

I just finally chalked it up to "one of those things" and moved on. It never impacted my fuel mileage that I could tell. Running with the A/C off never really did gain me any extra MPG...

 

Hmm...thanks for the quick response. Not quite the prognosis I was hoping for...but maybe I can stand to chill a bit on it. How long did your run like that without breaking down...a long time?

Are there some other quick checks / procedures that I could try? I can't imagine there's much left. If there are just a couple more things that I could do...I'd just as well do them...just to give it a fair chance of being knocked out.

As another point of interest...I did check running fuel pressure again when I got home from work. It is running at about 52 - 53psi. If my memory serves me, it ran at about 59psi when I last checked it. It seems odd to me that I should see a 6-7 psi drop over such a short period. 7 psi (in my mind) is a substantial amount of fluid pressure....especially to be lost.

Not sure if you remember...but, I've still got that weird condition where fuel pressure drops right off after cycling the pump. In other words, it doesn't hold...which is part of the reason for replacing the FI spider and FPR. But, that was no help.

I've got an itch to drop the tank now. I've got a bad feeling that there's a bunch of crap in there that the guys who replaced the pump last didn't get rid of. Of course, crap in the tank wouldn't make fuel pressure bleed off. My hunch has been thatthe bleed offhas been because of the pump. Maybe this new stuff is the incentive I need to have a look.

Is it a big deal to drop the tank...hadn't been there...yet.

Thanks,

Icarus

 

Just an update...

The problem has gotten much worse. The vehicle is now barely drivable. It spits, sputters, and nearly dies every other second. I don't dare drive it more than a few miles at a time.

I haven't done anything new, other than observe. I have not seen the P0300 code again, my gas milage is back down to miserable, and now I am seeing P1345 (camshaft and crankshaft out of sync). I'm willing to bet that I've already burned that new rotor I put in a couple of months ago.

I started to look into problem symptoms, and replacement procedures for the camshaft and crankshaft sensors. I think the most likely problem, between these two sensors is the crankshaft...partly because it looks like a pain to replace.

I also came across information that suggests that my problem may be a timing chain, or a worn distributor gear.

Any thoughts, suggestions?

 

sounds like your engine is out of time. get it timed and see what happens.

typically your cam and crank sensors work or they dont. if they are saying they are out of sync, that sounds like your timing is off to me. maybe skipped a tooth on the timing chain.

 

Don't know if this will help, but
Check the following items:
[*]A loose CMP sensor causing a variance in the sensor signal.[*]Excessive free play in the timing chain and gear assembly.[*]Incorrectly installed distributor -- 1 tooth off in either advance or retard positions.[*]A loose distributor rotor on the distributor shaft.[*]A loose or missing distributor hold down bolt. [/ul]
An intermittent may be caused by any of the following conditions:
[*]A poor connection[*]Rubbed through wire insulation[*]A broken wire inside the insulation [/ul]

 

I've been told that the computer adjusts timing as necessary based on sensor signals. Is this not the case? If it is, I'm not sure how I wouldset the timing. I would think that even if I could, the computer would put it right back.

I'd thought more about this last night, and identifieda couple more things to do to eliminate some variables.

When I went through the long list of "stuff done", I did not change plug wires because the wires I had were only a couple years old. But, I suppose those could be arcing (the problem is worse when it rains). I don't see them arcing in the dark, though. I figured I'd also change the camshaft sensor since it's cheap, quick, and easy to do so. If those don't cure it, when I have a bit more time, I'll pull the distributor to inspect the gear for wear.

Some other details that might spark some imperical knowledge...

The truck starts and idles OK, but runs like garbage under load almost all the time. ONCE IN A WHILE, when it's very dry, the truck will run OK for a little bit...but, as I said, it's much worse when it's wet. This makes me think plug wires, or electrical distribution to and from the sensors.

I've also had a problem, in the past,starting the vehicle when it's below 30 degrees, and the vehicle has sat for more than one day. Don't know if these might be related or not.

Theforth mechanic to tell me that he's stumped (last night), told me that, under the P0300 code, cylinder 5 is the most frequent offender. He must have a fancier OBDII scanner than I do. I'm not quite sure how to utilize this information, except for that if it were a sensor issue (camshaft or crankshaft) I would expect the the misfire be truely random. The mechanic mentioned that cylinder 5 has misfired 5:1 on any other cylinder.

The plugs are brand new, but I'll pull plug 5 to inspect. Stupid question, I know, but how do I identify plug 5? I think the distributor cap might be marked, but I'm not sure on that.

***Edit***

Found this on the forum:

------------
F|2---4---6|/--\
F|----------|DS|
F|1---3---5|\--/
------------

Probably would have been in my haynes manual too, duh.

Thanks,

Icarus

 

PLEASE DO keep us posted on what s going on with this. My 95 is the same cloned problem as yours!

 

Ah more information.

P0300 is a bitch to fix. Ask around and you will get the smae answer.

To set timing you simple need to pull the distributor and put it back in correctly.
Make sure #1 is at TDC (top dead center) and Haynes should get you on with the distributor ion most cases.
Yes the puter controls timing, too some extent. However if your base timing is off, its off. Teh coputer adjusts timing for numerous contidtions, none of which are base timing.

Spark plugs is a good canditdate, cap and rotor are too (especially if the problem gets worse in wet warther), and verify you have the correct gap on those plugs and they are AC Delco plugs. These engines are very picky about plugs, wires, and cap & rotor. They are highly tuned high performance engines, they require good parts, not cheap parts, not average parts, good parts. Like OEM or better parts. Ignition is the one area you cannot skimp on. Been there fought it for 3 months (P0300). Fixed it!!!!

 

Thanks Hanr3.

Idid use bosch platinum plugs (the 2 prong ones) when I changed plugs. These plugs do not require gapping. Some people told me not to do this because the engine is picky, and some people told me I would have no problems but thatI would see an increase in gas mileage and power. Every auto shop lists these plugs as aviable replacement for this vehicle.

I did initially see an increase in gas mileage and power, but now (obivously) I have troubles. The troubles, though, existed well before the spark plug change. In fact, this has been going on for a year now...slowly progressing. Granted, the progression is occuring more quicklysince the plug change...but I'm not convinced that plugs are the issue. Don't get me wrong...I'm not ruling it out either.

More recently, I've been told that the platinum plugs foul more easily...so that may be a contributor here.

As soon as I can get a few quality hours in the garage, I'll be going through inspecting all of the things I mentioned. Iwill go back to normal, everyday, ACDelco plugs if I see evidence of plug problems. I may anyway...just to eliminate a variable.

From a reporting aspect, it's difficult to distinuish what exactly is important and what is not. So, I'm sure as this goes more details will fall out. From time to time I get the feeling that most all the troubles I've had, and asked for assistance with on this forum, have been related to some degree. I may be wrong there.

Something else that may be useful...

When I changed the cap and rotor (about2 months ago), the rotor was badly burned. With the new plugs and other TLC, I saw improved performance for a short time. Now, I'm obviously worse off than I was. I will be checking it soon, but based on how I'm running, I'd be willing to bet that the new rotor is burned. If it is, I imagine that would help isolate contributors. I imagine there is a relatively small subset of situations that would burn a new rotor up on short order.

Thanks all for your attention and help.

Icarus