You may have seen some of my previous posts about trying to find a miss. I think I finally fixed the problem 9 months and $1G later.

Here's the history: Last October my vette developed a miss during one day when I had a little trip of 3 70 mile legs. At cruising speed the Vette would just miss once or twice then be fine. It did this once on the first leg, three or four times on the second and third legs. The check engine light came on, it stored an O2 lean code. I replaced both O2 sensors and the code cleared, intermittent miss was still there.

I don't know if this had anything to do with it (I don't think so) but a week earlier I had hit a dead deer, it was laying down, I ran over it with my left side tires. Everything seemed fine after that incident, got the front end repainted.

Coming home from a 45 mile trip, near the end, the miss showed up real bad but I was able to throttle it away and make it home.
Ran a scanner and no codes were present except for 27 the QDM#2 which has always been there, I think it's because I disconnected the CAGS.

A fairly easy maintenance item would be spark plugs and wires, so I replaced them even though there were only 30K miles old.
Old wires and plugs looked just fine, miss was still there.

A friend of mine who owns a car repair shop took it for a ride and thought it was ignition. So based on that advice which was really a guess, I replace the Opti, the previous Opti was also only 30K miles old. The rotor and cap were in need of replacement as revealed taking the old one apart. I opted to use an MSD Opti as I have heard of recent OEM ones going bad shortly after installation. Didn't solve the problem, the miss is still there. I also installed an MSD coil at that time.

I connected a fuel pressure gauge and drove the Vette, when the miss showed up the pressure held.

I read up on some drivability issues in the FSM. I found the EVAP purge solenoid valve to be bad. Upon replacing it I found the line from the canister to be filled with charcoal bits. Bought a new canister and cleared the line, miss is still there.

You can hear the miss in the exhaust on the left side. I did a leak down test and a compression test on both sides. Leak down passed, and compression was 185 to 190, all OK.

I checked the resistance on the fuel injectors, they were all between 12.3 and 12.7 OHMS, OK I believe.

At this point I'm at the end of my rope, I decide to take it to a Corvette shop. Upon emailing them the history, they decline to take the car, saying I have done everything they would have. They suggest checking the EGR which I never did and then look at the computer then injectors.

EGR checks out OK, got a new computer and no miss runs great

I'm cautiously optimistic that is was the computer. I've taken her out on 3 local drives and she didn't miss a beat. I feel I need a few more local drives before I would again be comfortable on a long cruise. But waht a nightmare, hopefully it's over

 

After all of that time and money I sure hope you got it.

 

I had a similar problem on my 3800 V6 Minivan...it had a bad missed that nothing would fix.In the end we tracked it down to a bad ecm.

We did use a snap on scanner and once in a while when the missed occur,it was showing up as weak cylinder 3..even though it had all new ignition parts and injectors.We swapped the injector harness clip from 3 to 5 and the "weak" cylinder moved!

The computer was not firing the injectors or completing the cycle or whatever it was doing then...it was intermittent and drove me nuts trying to fix.

Like you,I even tried asking the Pros(the so called dealer in my case) to look at it,and all they suggested was to change all the parts I already had installed.Said froget that...so I did everything at home I could,I even kept the old parts to try back to back troubleshooting in case something was overlooked.

Just wanted to share the story...very similar and alot of money spent but the best thing that came out of it,was I got even better at diagnosing miss problems and using a scanner can be a great tool as well.Who wold have thought the ecm was the problem?

 

I had a strange one as well.
I have an 86, and I got it from my neighbor, and it would start up, run normal till I got off my street into traffic, the idle would increase to 1000 rpm, the digital dash displays all went to zeroes, the mileage distance remaining, and the mpg would reset to zero as well, about the time I would find a place to turn off the road, it all went back to normal, and no more problems. I went through everything that was temp related, cold start temp sensor, temp sensor, oil temp sensor, oxygen sensor, I even borrowed a maf sensor, and changed the maf relay and burnoff relay thinking ithe burnoff relay was defective, and turning on the burnoff cycle on it's own.
I changed the ecm, and it never came back.
I was sure it was temp related, but who would have guessed it was the ecm not being at warmed up temp that was causing the problem?

 

Wow,these ecm related stories are very interesting...I had an 86 Firebird years ago...the A/C quit cycling and overheated,and the repair shop could NOT find out what was wrong.I put alot of new parts and sensors etc,and it turned out the ecm was bad JUST for the a/c function.

ECM was not signalling the Fan to come on demand when the a/c was activated..the shop felt it was NOT the ecm but after I replaced a few parts per their suggestions,only trying a new ECM fixed it.

 

Rex, did you get a remanufactured ECM? Where did you get it?

just curious...... Hope this fixes your problem permenently!

 

My buddy who owns a shop got it for me. It's a reman, I believe ACardone is the mfg.

 

...would love to see some pics of your Ruby !!

 

A couple of observations.

When someone here posts that they are having "missing, stumbling, hesitation, etc. problems" they will usually get a plethora of "replace the opti" posts. Going back through similar threads, it looks like just about anything on these cars could be the actual culprit.

Second observation. I assume that you ordered the computer on your own and replaced the original. Do you think it could have been that maybe the connection to the computer was the culprit? In other words, did you try disconnecting and then reconnecting the harness that connects to the computer? Just a thought.

Anyway, it is great news that you finally solved.

Doug

 

on the plus side, your ignition system should be good for the next 100k miles.

(unless the water pump goes out)

 

Here's a good one!


No I did not try plugging and unplugging the ECM connection. If I had known my buddy could have returned an ECM I may have tried it a lot sooner. Good points, troubleshooting always looks easy with hind sight.

True. Quite a few little things that were bad or marginal were replaced which ultimately add reliability, I hope