Oh no, it's not the Opti is it??

[dmd]

In the last few weeks my '96 LT4 has been developing a new problem. Below 1500rpm and at throttle inputs >~20%, it gets the hiccups. I don't want to call it a misfire, because it is much more severe. It is as if the ignition is being shut off for a fraction of a second and it's a very harsh jerk through the powertrain. The computer doesn't seem to see it, as it's not tripping the SES light when it happens. So thinking outside of things from which the ECM has feedback, I'm betting it's ignition related - so that would point to the Optispark starting to go, but these don't appear to be symptoms usually associated with its impending failure. So my question is, how likely is it to be an Optispark with those symptoms, and what else might it be?

 

[boomdriver]

In the last few weeks my '96 LT4 has been developing a new problem. Below 1500rpm and at throttle inputs >~20%, it gets the hiccups. I don't want to call it a misfire, because it is much more severe. It is as if the ignition is being shut off for a fraction of a second and it's a very harsh jerk through the powertrain. The computer doesn't seem to see it, as it's not tripping the SES light when it happens. So thinking outside of things from which the ECM has feedback, I'm betting it's ignition related - so that would point to the Optispark starting to go, but these don't appear to be symptoms usually associated with its impending failure. So my question is, how likely is it to be an Optispark with those symptoms, and what else might it be?

Fuel

 

[bgedz]

In the last few weeks my '96 LT4 has been developing a new problem. Below 1500rpm and at throttle inputs >~20%, it gets the hiccups. I don't want to call it a misfire, because it is much more severe. It is as if the ignition is being shut off for a fraction of a second and it's a very harsh jerk through the powertrain. The computer doesn't seem to see it, as it's not tripping the SES light when it happens. So thinking outside of things from which the ECM has feedback, I'm betting it's ignition related - so that would point to the Optispark starting to go, but these don't appear to be symptoms usually associated with its impending failure. So my question is, how likely is it to be an Optispark with those symptoms, and what else might it be?

I had a similar problem with my 93 Coupe. It was caused by a leaking water pump that trashed the Opti-Spark

 

[2VettesMike]

Very similar symptoms to when mine failed. Usually when the motor was hot and under sudden load.

Good luck,

Mike

 

[93Rubie]

In the last few weeks my '96 LT4 has been developing a new problem. Below 1500rpm and at throttle inputs >~20%, it gets the hiccups. I don't want to call it a misfire, because it is much more severe. It is as if the ignition is being shut off for a fraction of a second and it's a very harsh jerk through the powertrain. The computer doesn't seem to see it, as it's not tripping the SES light when it happens. So thinking outside of things from which the ECM has feedback, I'm betting it's ignition related - so that would point to the Optispark starting to go, but these don't appear to be symptoms usually associated with its impending failure. So my question is, how likely is it to be an Optispark with those symptoms, and what else might it be?

Your 96 is a OBDII car, if you are having an ignition misfire-you will not get a Check Engine Light, you will get a FLASHING CHECK ENGINE Light, if it is severe enough. OBDII runs a continuous misfire monitor. I'm not ruling out an ignition misfire-weirder things have happened.

The FSM has a section just on this symptom. For my 93 it is 6E3-B-10
However, I'm agreeing with boomdriver, FUEL. Your FSM is your best friend on this one.

Can you hear it backfire though the intake at all? Does it run better with more throttle opening, ok otherwise???

 

[dmd]

The more throttle I give it the worse it is, but otherwise there are no symptoms...

 

[dmd]

Very similar symptoms to when mine failed. Usually when the motor was hot and under sudden load.

Yep, that's exactly it. I don't think it's a leaking water pump causing it though, first because I don't think it's leaking and second because the '95-'96 units are sealed. Either way, I guess I'm on borrowed time with it now.

 

[boomdriver]

yep, that's exactly it. I don't think it's a leaking water pump causing it though, first because i don't think it's leaking and second because the '95-'96 units are sealed. Either way, i guess i'm on borrowed time with it now.

fuel.

 

[John Robinson]

Corroded electrical connector on the Opti

Bad ground - Clean all grounds

 

[Itshakes]

Opti???

Check/replace your coil wire from the Opti to the coil. Mine had a split in the boot at the Opti, and was shorting on the back of the water pump.

 

[catbert]

Where's LT4man? He kind of an Optispark guru.

 

[2VettesMike]

Yep, that's exactly it. I don't think it's a leaking water pump causing it though, first because I don't think it's leaking and second because the '95-'96 units are sealed. Either way, I guess I'm on borrowed time with it now.

Easy enough to replace the coil wire and plug wires. If it doesn't cure it then dig deeper into the opti. They all seem to act differently. I changed wires and got the symptoms to go away for a year or so, then it bucked, kicked, and died coming home one day never to start again until the opti was replaced. Not one of the easier repairs I've ever made...

Good luck,

Mike

 

[dmd]

All good suggestions. I am in the midst of another major repair project right now, but once that's back up and running I'll be diving deeper into this one and will report back with my findings. Thanks everyone.

 

[dmd]

Okay, so the car has been parked for a couple months and it took a lot longer than I thought to finish my other projects, but I finally took the front end of the engine apart enough yesterday to find that my water pump is indeed leaking. It had gotten so bad I couldn't back up my driveway without it jerking to a stall.

After retorquing the wp bolts to 30fp and topping off the coolant, several problems have been solved. This problem in particular has been reduced to the point of being unnoticeable in normal driving - I have to do something deliberate to force it to occur. Replacing the opti is inevitable for every long-term LT1/4 owner, but I've at least bought myself some more time before the big job.

 

[Schrade]

Easy enough to replace the coil wire and plug wires.

Huh? On an LT motor??? Have you replaced a lot of them?

 

[boomdriver]

Huh? On an LT motor??? Have you replaced a lot of them?

Might be one of those LT CP's.

 

[dmd]

So it actually turned out to be the MAF. Some codes finally appeared in the PCM last week for Mass Airflow and Bank 0/1 Too Rich. Sometimes these problems can take a long time for all the symptoms and clues to manifest themselves... then I had to drive it a few days to make sure it didn't come back. Interestingly, it was also triggering the Low Oil sensor despite having a full crankcase. I haven't looked at the wiring diagram to see how those two are connected, but I'm just glad it killed two birds with one stone.