I feel your pain.

 

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

 

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

 

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?

 

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. (NOTICE TO PETA,...........IT'S A JOKE!) I love cats,......(They taste like chicken) (NOTICE TO PETA,........SEE ABOVE)
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

 

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!!!

 

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! !@#$%! 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

 

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?

 

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

 

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!!