91 ZR-1 Cutting Out Under Load

[GregCrowe]

Put the coils on Sunday, now the car runs even worse. I'm so disgusted.

I need to rip it all apart and see if I goofed something up. Now the car starts up and idles just fine. When in park, giving it gas makes it rev slowly with hesitation. I even got it to backfire once. I took it out for a drive and it just felt down on power, engine didn't run smooth, slight stumble all the time. I never even got the car hot enough to see if the original problem was still there. I don't know that I could have even told.

[XfireZ51]

Originally Posted by GregCrowe

Put the coils on Sunday, now the car runs even worse. I'm so disgusted.

I need to rip it all apart and see if I goofed something up. Now the car starts up and idles just fine. When in park, giving it gas makes it rev slowly with hesitation. I even got it to backfire once. I took it out for a drive and it just felt down on power, engine didn't run smooth, slight stumble all the time. I never even got the car hot enough to see if the original problem was still there. I don't know that I could have even told.

Forgive me but are
plug wires on correctly?

[GregCrowe]

Originally Posted by XfireZ51

Forgive me but are
plug wires on correctly?

I'm sure they are, I did one coil at a time. The car starts and idles smoothly.

If I can find some time, maybe this coming weekend, I'm going to take it apart and see if I messed anything up. If I don't find anything wrong, I'm going to go buy a set of the cheapest coils at O'Reilly and put it back together. My worry now is that I'm going to have to take it apart 5 more times to test things and find out what's wrong.

Dumb question: Is there any way to put the long electrical connector on the bottom of the plenum(held in with the screw), in 180 degrees off?

Not so dumb question: How do you test the coils with a volt meter ?

[tomtom72]

Okay fwiw the description of how it runs reminds me of what used to happen back in the days of distributors. If ya missed a coupla teeth on the way back in the motor usually ran as you describe. Or...a more ominious thought just crossed my mind, skipped teeth on the timing gear set, but I don't think that applies to an LT5, I hope.

Disclaimer: I'm okay with a 70's sbc, I'm not fluent in LT5 yet.

My first impression was exactly what XfireZ51, miss placed plug wires. I can go look up the firing order in my Helm if need be? See I told ya I'm not fluent in LT5, heck I don't even remember the firing order on my 72 LT-1 that I had a long time ago (I'm also getting senile!).

I would wonder if a scan tool would diagnoise a problem with the DIS box? That's the only other thing I can think of, unless there is a insulation problem with the harness that connects the coil plate to the DIS box? Can the plate go bad?

I shouldn't even post this as I'm lost on diagnoising your issue.


Tom

I know you don't want to hear this Greg, but simplest things first. Firing order, bridged plugs, wires okay, coils seated properly, DIS wiring I believe is "Keyed" so you really can't put individual harnesses in the wrong spots or 180* off (I'm fairly sure on that point). I know there used to be a lot of defect issues with aftermarket coils a long time ago the experienced guys said to stay with GM coils. That's all I can think of right now. Sorry for my lack of help.

Originally Posted by GregCrowe

Dumb question: Is there any way to put the long electrical connector on the bottom of the plenum(held in with the screw), in 180 degrees off?

Greg, I would double check the plug wire orientation. I always label the plug wires with either collars or paint.

Also check the DIS module for a possible bent pin. And no, you can not install the connector 180 off. It is keyed to go in one way only.

[GregCrowe]

Sunday is my only day I have a few hours I can work on my own car. I just took it apart again. Here's some pics.

Jeff, take a look at the pic of the DIS module. This is with the plenum laying upside down. Can you please tell me if any of the pins are missing? It looks fine to me. Given that you're looking at the module mounted to the plenum and the plenum is upside down, there is 7 slots for pins, the screw, and then 7 more slots for pins. Looking at the pic, the pins slots are as:

1. empty
2. empty
3. empty
4. pin
5. pin
6. pin
7. pin
SCREW
1. pin
2. pin
3. pin
4. pin
5. pin
6. empty
7. pin

Here's the confusing part:

Looking at the DIS module, there are 4 pins in the first set of 7 slots and 6 pins in the second set of 7 slots.

Looking at the DIS modue connector, there are only 4 electrical female slots on each side for the pins in the module. It doesn't match up...... 6 pins and 4 female slots for those 6 pins on the right side. Do I take it that 2 of those pins on the right side are just there for no reason and not used?

I don't think I have a broken or bent pin. I really don't see anything wrong.

Also, I double and triple checked the plug wire orientation. It is all correct.

Originally Posted by GregCrowe

Sunday is my only day I have a few hours I can work on my own car. I just took it apart again. Here's some pics.

Jeff, take a look at the pic of the DIS module. This is with the plenum laying upside down. Can you please tell me if any of the pins are missing? It looks fine to me. Given that you're looking at the module mounted to the plenum and the plenum is upside down, there is 7 slots for pins, the screw, and then 7 more slots for pins. Looking at the pic, the pins slots are as:

1. empty
2. empty
3. empty
4. pin
5. pin
6. pin
7. pin
SCREW
1. pin
2. pin
3. pin
4. pin
5. pin
6. empty
7. pin

Here's the confusing part:

Looking at the DIS module, there are 4 pins in the first set of 7 slots and 6 pins in the second set of 7 slots.

Looking at the DIS modue connector, there are only 4 electrical female slots on each side for the pins in the module. It doesn't match up...... 6 pins and 4 female slots for those 6 pins on the right side. Do I take it that 2 of those pins on the right side are just there for no reason and not used?

I don't think I have a broken or bent pin. I really don't see anything wrong.

Also, I double and triple checked the plug wire orientation. It is all correct.

Pins look fine on the DIS module. And yes there are only 8 active connections on the DIS. 4 wires going in on each side of the bolt/screw.


I'm still thinking you have a spark issue, and it's cutting out.

[GregCrowe]

Originally Posted by Jeffvette

Pins look fine on the DIS module. And yes there are only 8 active connections on the DIS. 4 wires going in on each side of the bolt/screw.


I'm still thinking you have a spark issue, and it's cutting out.

OK, thanks Jeff. Since it got worse with the new Summit coils I'll go pick up some coils from O'Reillys and slap them on. If that fixes it I'm going to have a pretty upset conversation with Summit Racing.

[XfireZ51]

Originally Posted by GregCrowe

OK, thanks Jeff. Since it got worse with the new Summit coils I'll go pick up some coils from O'Reillys and slap them on. If that fixes it I'm going to have a pretty upset conversation with Summit Racing.

Greg,

Have you checked plug wires? Meaning have you checked for open circuit or ohm's them?

[GregCrowe]

Originally Posted by XfireZ51

Greg,

Have you checked plug wires? Meaning have you checked for open circuit or ohm's them?

They have less than 20 miles on them. That was the first thing I tried almost 3 years, new plugs and wires. The car did the exact same thing before and after the plug/wire change.