First, I'm pretty mechanically inclined. I've pulled/rebuilt motors, built/designed racecars, etc... but I can't seem to figure this one out in the brief time I've had the problem.

I pull in last night from cruising around and having a little fun with the vette (more importantly, I fixed a vacuum leak so was 'test driving.') When I go to pull in the garage I have to stop and move my motorcycle out of the way, so the car gets turned off for two minutes. Restarting the car, the engine sounded like it was firing on half of it's cylinders!

She was able to pull into the garage for me, but it sounded god awful. Without a scanner, and her being a 1996, I can't easily access any codes in the PCM. I was hoping when she cooled off (I got her up to 230 water and 235ish oil while playing around) maybe the ICM or coil would have been the problem and issue resolved. This morning... nothing. I played with the spark plug wires, ran it with the lights off without seeing arcing, jiggled/cleaned/disconnected-reconnected any and all wires relating to the opti or ignition. This doesn't feel like a mechanical issue, you can smell the unburnt gas and she starts right up so I feel like some cylinders are firing properly... but again sounds horrible and does throw codes.

The spark plug wires are fairly old, and last tune-up (new plugs/clean filter included) was about 2000 miles ago with zero issues since then.

Next step will be a compression check, but I really don't want to go that far and pull the plugs if I don't have to... especially since the car pulled STRONG until I turned her off.

I'm just glad I have a bike I can still use to get to work, but what the crap? Any ideas?

 

sounds like you have some heat soaked injectors.
A while ago, I decided to rip through the gears. At high RPM, suddenly, it started missing and then a code, and before I could turn it off, it was missing on more cylinders.
I can only determine that I reached the saturation point of 3 of the injectors, and they stuck open.
Gas smell, cutting out, and black black smoke.
I changed injectors, and problem went away.

 

I purchased, four or five years ago, a generic OBD11 code reader for $38.00 from Harbor Freight. Might want to take a look at one.

 

Check the INJ 1 and INJ 2 fuses as well.

 

Yes, check the fuses. Each one controls a bank of injectors, and if one side is not getting juice, your car will run exactly like you described. My car did this once, both fuses were good, but one had some corrosion or oxidation on it not allowing it to make the connection to the fuse block. Just removing it and reinstalling it was the fix.

 

I'll check the fuses when I get home... hoping that's what's going on.

 

You can use the dash to pull the codes

here's how

http://s242.photobucket.com/albums/f...m/ccm%20codes/

 

Note on a 1996... well I can, but it won't let me talk to the PCM. So that means I can talk to the DDC (dash and internal car electronics) and the DERM (airbags... kinda scary talking to that module really.) I was able to go through what I could and had zero codes. Thank you for the response though!

 

Start by checking your codes, but off the top, I'd be suspecting the MAF sensor??

 

You just might have had a heat soaked ecm that wouldn't pulse one bank of injectors and after cooldown worked normally.

 

Update... looked at the injector fuses (and any other fuses really) yesterday and everything there looked ok but car still had the same problem... I'm going to borrow a code reader on Tuesday/Wednesday next week when I get back from traveling.

 

Got a scanner on it finally:
DTC P0300 - Random Multiple Cylinder Misfire Detected
Intermittent:
P0137 - 02S Low Volts 1/2
P0171 - System to Lean Bank 1
P1416 - AIR System Bank 2

The last three are not common, just background. The P0300 is clearly the right code for the condition. Time to start chasing it down...

 

I suspect a rather large vacuum leak, given that the ECM has detected a lean condition on bank 1. The ECM tries to compensate by richening the mixture which is why you're smelling unburnt fuel. Given that it's showing the lean condition on one bank only, there could be an intake gasket issue. The P0300 is what's happening, the secondary codes are why it's happening.

BUT....before doing anything, put a vacuum gauge on it and tell me what your readings are at idle. If it is going heavily lean on one bank, pull the plugs out on that bank and look for fuel fouling.

Run that test and post the results.

 

Vacuum's fine, I had a big leak that I fixed about two hours before the misfire occurred. Trust me, this is not a vacuum leak it's a full on ignition misfire. The smell of raw fuel is pretty pungent. Thank you for the suggestion though! The reason the codes are in there were from the big leak before. I haven't cleared any codes yet. I'll be diving into it this weekend at some point.

 

Ah....well, I feel better about my diagnostic skills now....I successfully troubleshot an issue you'd already fixed. Clear those codes before we do any more troubleshooting

Now...are you certain it's an ignition misfire? Noid the injectors and see how they're behaving. I'd like to rule out the injector drivers in the ECM. Also how many lbs of fuel pressure do you have? Let's give the entire fuel system a clean bill of health, then we know we're chasing the right demons moving on the ignition / emission systems.

Also, do pull the plugs and inspect them. Fuel fouling will go a long way to telling us where the problem resides....either fuel or ignition related.

Happy wrenching

PS...just out of curiousity...what was your big vacuum leak?

 

Ahh, beat you to one of the next punches. The plugs are about 2000 miles old and the car ran perfectly strong (no hesitation or missing) until I turned it off that one night....
I'll let you know regarding the other suggestions. Thanks again!

 

So I cleared the code a few times and was able to get one to come back... P0307 which signifies misfire on cylinder 7. I do not have a multimeter so I can't run through the FSM diagnostics... I pulled the plug which looks beautiful and double checked all the wires to ensure no chaffing from the opti back and still have the issue. I'm picking up a multimeter to check more tomorrow. The interesting thing is while I feel I narrowed it down to cylinder 7, after I cycle ignition on/off the code sets to P0300 (without running the engine again.) Wierd...

 

Have you checked the ohms on the injectors (hot)? Checked fuel presure for leakdown?

Waiting to hear the fix on this one.

 

Not yet, no multimeter to do the resistance check. Hopefully that will happen tomorrow...

 

Minor update: So in a drunken stupor one evening I decided to heck with it, the car has 140k on the clock with all oem components so I'm just going to redo the entire ignition system; new opti, new coil/icm, new plugs/wires (new gaskets for the 20k mile old water pump...) On top of that, I'm throwing new injectors from Jon at FIC at it because why not. Hopefully this will be good preventative maintenance for all the parts except the one that's broke...

My hungover plan the next day included swap out parts one (or eight for the injectors) at a time until I find the problem with the opti being the last of the bunch.

As of this evening, I swapped over the coil/ICM with the same issue so that rules them out... kinda wanted to keep tearing stuff apart but will be patient on the tear-down. Next up: injectors!

Disclaimer: Yes I may be a bit insane for replacing a lot without a confirmed diagnosis... but part of me was looking for a big project and part of me just wanted to replace the 'unknowns' from when I bought the car. Wish me luck!