RUNS BUT STILL SKIPS AFTER OPTI SPARK REPLACEMENT

[corvetterider84]

I recently replaced the opti spark on my 92 in hopes of getting rid of a skip that has been there since I bought the car. You may have seen my thread about what I went through replacing it, which really wasn't that bad but wasn't that good either. Anyways, long story short, the car still has the same skip after all that. So far, what I have done is new plugs, wires, opti, and waterpump. I'm going to buy a new fuel filter today to eliminate that as a possibility. The only two things that I think could be causing the skip are either the pressure regulator or one or more bad injectors. Does any one have any ideas? Any way to check to see if an injector is good or not (i've heard some talk about node lights?). ;help

 

[CAJUN C4]

How Many Miles on Her??

Which Brand of Gasoline Do You Use?

 

[Hib Halverson]

An expensive example of trial/error service procedure.

Typically a fuel filter will not cause a misfire characterized as a "skip". Same is true of the fuel pressure regulator. That said, if the filter has never been changed or has not been changed in the last 36,000 miles, I'd do that on GP.

When does the misfire occur?
All the time?
Light throttle only?
Wide open throttle and high rpm only

Is it a momentry miss just as you step into the throttle?

As for injectors, the first thing to do is run the fuel pressure tests in the FSM followed by the electrical tests in the FSM.

 

[corvetterider84]

An expensive example of trial/error service procedure.

Typically a fuel filter will not cause a misfire characterized as a "skip". Same is true of the fuel pressure regulator. That said, if the filter has never been changed or has not been changed in the last 36,000 miles, I'd do that on GP.

When does the misfire occur?
All the time?
Light throttle only?
Wide open throttle and high rpm only

Is it a momentry miss just as you step into the throttle?As for injectors, the first thing to do is run the fuel pressure tests in the FSM followed by the electrical tests in the FSM.

Its more on the take off.. When I give it the gas it stumbles (doesn't take the gas at all), sometimes backfires, and then catches up to how much I have the pedal pushed down. I usually have to "feather" the gas on take off just to get up to speed. Once I get going, say 35-40 mph, the miss is less pronounced, but still there. I do know that this is a costly example of trial and error, but with all the posts about bad optis I thought I might get lucky (obviously not). :bash

 

[corvetterider84]

How Many Miles on Her??

Which Brand of Gasoline Do You Use?

It has 104,000 on it and I use premium gas. The inspection sticker ran out in May and, since I just got it running again (but still skipping) I decided to go try and get it inspected..An obvious BAD MOVE on my part, but I just wanted to get the car legal again. Well it passed safety no problem, but bombed the emissions test: HC GPM: 13.16 (limit is 3.06) and CO GPM: 126.74 (limit is 30.99). I should have guessed it would have failed by the way its running but I took a gamble and lost! My uncle seems to think its one of the injectors, but I don't have a factory manual to figure out how to test them and they're 77 bucks a piece. ;help

 

[kcrick]

I'm assuming that you've checked the plugs and wires...that scenario sounds like a plug wire....is it throwing any codes? Maybe the O2 sensor??

 

[kcrick]

Hey, I'm sorry...I just saw that you replaced the plugs and wires....

 

[corvetterider84]

Hey, I'm sorry...I just saw that you replaced the plugs and wires....

No problem. Thanks for the reply.

 

[corvetterider84]

An expensive example of trial/error service procedure.

Typically a fuel filter will not cause a misfire characterized as a "skip". Same is true of the fuel pressure regulator. That said, if the filter has never been changed or has not been changed in the last 36,000 miles, I'd do that on GP.

When does the misfire occur?
All the time?
Light throttle only?
Wide open throttle and high rpm only

Is it a momentry miss just as you step into the throttle?

As for injectors, the first thing to do is run the fuel pressure tests in the FSM followed by the electrical tests in the FSM.

Hi, I don't have the factory manual, but I did some research online. I checked all my injectors with an ohms meter and they all checked out at about 13.5 ohms. Since it failed the smog test, could it be the catalytic converters or o2 sensors. I'm at a loss here. :confused Sorry I know I should probably just buy the manual.

 

[JimBobC4]

Hi, I don't have the factory manual, but I did some research online. I checked all my injectors with an ohms meter and they all checked out at about 13.5 ohms. Since it failed the smog test, could it be the catalytic converters or o2 sensors. I'm at a loss here. :confused Sorry I know I should probably just buy the manual.

The manual helps on these cars . I dont think a cataclismic
perverter or ummm catalytic converter would make it skip. O2 sensors maybe, but it would prolly throw an SES light.

My first step would be to read the codes from the ECM and see whats missing. (air,fuel or spark) and go from there. If your car is running as you say its most likely in open loop or limp mode. So your operating on a best guess of the computer because its missing information.

Next step for me would be to check fuel pressure, after I checked the codes

Also, lets clear something up ...

does it skip ALL the time ? throughout the RPM range ?

does it skip at idle and when revved when in park? all the way up to higher revs ?

Good luck ! keep us posted

 

[kcrick]

Hib....

Hey Hib! My 94 LT1 has been in the shop for 2 weeks now...after they replaced the head gasket, it's got a miss that they can't find...it's running way rich and they even replaced the cats....he's checked fuel pressure,changed spark plugs and wires and can't seem to find the miss...it's giving me a "odo err" on the dash meaning that the CCM is showing a fault, but it was running fine with this prior to the head gasket replacement. I'm trying NOT to do the throw parts at it method. It's now throwing and codes....any ideas?

As for injectors, the first thing to do is run the fuel pressure tests in the FSM followed by the electrical tests in the FSM.[/quote]

An expensive example of trial/error service procedure.

Typically a fuel filter will not cause a misfire characterized as a "skip". Same is true of the fuel pressure regulator. That said, if the filter has never been changed or has not been changed in the last 36,000 miles, I'd do that on GP.

When does the misfire occur?
All the time?
Light throttle only?
Wide open throttle and high rpm only

Is it a momentry miss just as you step into the throttle?

Hey Hib! My 94 LT1 has been in the shop for 2 weeks now...after they replaced the head gasket, it's got a miss that they can't find...it's running way rich and they even replaced the cats....he's checked fuel pressure,changed spark plugs and wires and can't seem to find the miss...it's giving me a "odo err" on the dash meaning that the CCM is showing a fault, but it was running fine with this prior to the head gasket replacement. I'm trying NOT to do the throw parts at it method. It's now throwing and codes....any ideas?

As for injectors, the first thing to do is run the fuel pressure tests in the FSM followed by the electrical tests in the FSM.

 

[Hib Halverson]

Hi, I don't have the factory manual, but I did some research online. I checked all my injectors with an ohms meter and they all checked out at about 13.5 ohms. Since it failed the smog test, could it be the catalytic converters or o2 sensors. I'm at a loss here. :confused Sorry I know I should probably just buy the manual.

Stop guessing and throwing parts.

Before you can solve the misfire, you need to fix the problem with the engine running rich.

1) Buy the factory service manual.
2) Buy a EFI pressure gauge and run the fuel pressure tests in the FSM. That will help determine if there's a leaking injector.
3) At 103K, if the O2s are original, I'd replace them. Good is OE, Best is Denso

Also, does the check engine light come on at bulb check. If so, have you seen the light on recently?

 

[Hib Halverson]

Hey Hib! My 94 LT1 has been in the shop for 2 weeks now...after they replaced the head gasket, it's got a miss that they can't find...it's running way rich and they even replaced the cats....he's checked fuel pressure,changed spark plugs and wires and can't seem to find the miss...it's giving me a "odo err" on the dash meaning that the CCM is showing a fault, but it was running fine with this prior to the head gasket replacement. I'm trying NOT to do the throw parts at it method. It's now throwing and codes....any ideas?

As for injectors, the first thing to do is run the fuel pressure tests in the FSM followed by the electrical tests in the FSM.

It sounds like the codes it's "throwing" are CCM codes which probably do not have anything to do with the engine problem, but, nevertheless should be addressed. Consult the 94 FSM to CCM code diagnosis.

If the engine is running rich, did they find any leaking injectors?

Why did they replace the cats if the engine was running rich?

Did they check the condition of the distributor? Of the ign. coil?

As for the misfire, can you be a little more specific as to when it occurs? Low rpm? High rpm? Light load? Heavy load?

 

[kcrick]

No the injectors aren't leaking...they replaced the cats because they thought they were clogged with all the smoke it was putting out when the coolant was leaking into the cylinders...they said they were glowing red hot, which could have been because they were clogged OR they were just trying to burn all that extra gas because it's running rich...to my knowledge, they have not checked the distributor since it's such a ***** to get off...but I was thinking it would throw at least one code if it was the distributor...I'm about to the point where I'm going to have to have it towed to a Chevy dealer....I have the FSM and took it to him...he's a good mechanic and knows this engine, but I don't know if he's worked on it in a vette...he said he had the plugs sitting on top of the engine and they were all firing...now, could they be firing and just not firing enogh? The previous owner had altered the chip in it with a hypertech and I took that thing to him too so he could reset it to factory settings....do you think the ECM could be bad?

 

[corvetterider84]

No the injectors aren't leaking...they replaced the cats because they thought they were clogged with all the smoke it was putting out when the coolant was leaking into the cylinders...they said they were glowing red hot, which could have been because they were clogged OR they were just trying to burn all that extra gas because it's running rich...to my knowledge, they have not checked the distributor since it's such a ***** to get off...but I was thinking it would throw at least one code if it was the distributor...I'm about to the point where I'm going to have to have it towed to a Chevy dealer....I have the FSM and took it to him...he's a good mechanic and knows this engine, but I don't know if he's worked on it in a vette...he said he had the plugs sitting on top of the engine and they were all firing...now, could they be firing and just not firing enogh? The previous owner had altered the chip in it with a hypertech and I took that thing to him too so he could reset it to factory settings....do you think the ECM could be bad?

Are you trying to hijack my thread??? Just kidding, but with mine I did replace the distributor (opti spark) and the problem still persists. I checked all my injectors and they all seem to have the correct ohms, so I'm leaning towards bad o2 sensors with mine. I just dropped it off at the mechanic down the road due to me not having enough patience or money to spend on parts I don't really need any more. I'll post the outcome.

 

[Hib Halverson]

If the cats were glowing red hot and the car flunked an emissions test, there is little doubt in my mind that at part throttle, it's running rich...maybe way rich.

Did the service shop replace the O2 sensors?

Has your mechanic scaned the ECM data stream and if so what are the short- and long-term fuel trim values...94s may display them as "block learn" and "integrator".

In your last post was the first mention of an aftermarket calibration. Did these problems start occuring before or after the ECM was reprogrammed to stock? Also, is this car modified in any way other than the Hypertech calibration?

As for the distributor setting a code which would be directly related to the misfire, well...it might and it might not. Interestingly, early in this thread were was reveference to a code 41, which, if it was an ECM code, sets when there is a short in the distributor or its wiring. However, later in the thread you ID'ed that code as a CCM code.

As for a "bad" ECM... understand that DvI (diagnosis via Internet) is often an imprecise method, but I'm going to guess that it's not.

I will close by suggesting that in the case of the first post in this thread and in the case of the last one, both situations are demonstrating techs who may be limited in diagnostic skills. Be careful.

 

[kcrick]

Are you trying to hijack my thread??? Just kidding, but with mine I did replace the distributor (opti spark) and the problem still persists. I checked all my injectors and they all seem to have the correct ohms, so I'm leaning towards bad o2 sensors with mine. I just dropped it off at the mechanic down the road due to me not having enough patience or money to spend on parts I don't really need any more. I'll post the outcome.

Hey rider! I'm sorry...not trying to steal your thread...but we have similar probs.....let's both be sure to post the outcome so maybe it will help someone!!

 

[corvetterider84]

Hey rider! I'm sorry...not trying to steal your thread...but we have similar probs.....let's both be sure to post the outcome so maybe it will help someone!!

Picked my vette up today from the mechanic (i hated the idea of bringing it to someone). Low and behold, problem has been solved. Turns out it was a bad map sensor. The mechanic told me that he fixed the skip but the check engine light was still on. Apparently it is throwing a code 36, which is supposed to mean bad opti or bad harness going to the opti. I informed him that I had replaced both already.. He ran emissions and it passed, but the light is still on...

Bottom line is my car runs like a race car now..No skips whatsoever. Its amazing what one little electrical part can do to these computer driven cars. I probably could've figured this out on my own if I ran the codes and had the factory manual, but after sinking a bunch of money into parts I didn't need, I wasn't gonna take any more chances. I'll have to look into the check engine light in the future, but for now I'm gonna enjoy it.

Thanks for the advice everyone.

 

[kcrick]

I wonder if mine has a MAP sensor! Mine's still at the shop....

 

[corvetterider84]

I wonder if mine has a MAP sensor! Mine's still at the shop....

I pretty sure it does, but someone else will probably chime in..