sort of stumble at idle

[John Robinson]

Stay tuned

I have found a cracked plug in #8 today but the really big discovery is with the new wires I put on when I changed the plugs. On #8 & #6 GM used a straight boot to cover the plug. the new set of wires had two wires with straight boots and were the right length for these two plugs. The problem I discovered today is that the straight boots are too long and therfore the plug does not go into the solid connector inside the boot. I will be correcting this problem tommorrow by cutting off at least 5/8" from the length of the boot. I hope this will be the answear to my miss when it gets hot. I am not an engine engineer but I think I heard somewhere that when the engine is cold it takes less spark to fire the cylinder but when it gets hot it requires a hotter or stronger spark. If this is true then it would explain why the miss came on at 190F.

 

[Toms007]

John, I certainly hope that this fixes your problem. Amazing what you find when you dig into things isn't it?

 

[John Robinson]

could not wait

Well I went out and looked again at the wires and the real problem is the boot had slid on the wire pulling the hard connection too far back into the boot. My answear was to use this to my advantage by covering the wire with dialectric grease and sliding the boot back up the wire to expose the metal connector. I put it on the plug good and tight and then slid the boot back over the plug.

I have to do a lot of work yet to drive the car but I had to try to start it and it ran without a miss. I can't wait to be abel to drive it and get it hot and see what happens. I will keep you posted. I hate to

 

[Steve40th]

I am not able to read the entire thread, but I will tell you something I learned about the IAC. GM does not have a code for it. You will not get a code/check engine light etc. ANy software that monitors your engine will show ONLY what the ECM is telling the IAC to do, period. It will not show you what the IAC is actually doing.
I went three years troubleshooting with the best of them, and some ol fart showed me the way, Sure enough, I did a resistance check and the IAC was bad. It worked, but not until certain criteria was met, but I purchased another one and my idle , off idle etc was cured. I have a speed density 396 LT1 with a medium 230 cam, and it purrs now with ac on too.

 

[John Robinson]

No Luck

Well I am getting to the place that I am pretty sure that the plugs and wires are not my problem. Currently I have the EGR off the car and am trying to figure out how to clean it up. the pin seemed to be stuck just short of being fully extended when I took it out. I have sprayed it with CRC and wiped out the area around the pin. I also found a glaze on the shaft of the pin and used CRC to get rid of it. Now when I push the diaphragm down it returns the pin slowly to its top position I guess the next thing to do is buy the gasket with the screen in it and see if this solves my problem.

When I ran the car today it was missing badly at low rpm's but if I put it into second gear and kept the rpm's above 3000 it ran fairly good and occasionally did not have the miss. If I put it back into a higher gear and let the rpm's drop the miss became very pronounced.

If this was happening back in the old days when all we had was a carburetor, points and a distributor I would be looking at the carb accelerator pump because it acts just like the fuel to air ratio is way lean at low rpm's

 

[Steve40th]

Was the Opti looked at through this whole thread? Optis do strange things, even new ones.

 

[Toms007]

Steve, I am having a new MSD opti installed...as you said opti's do funny things and my mechanic found that mine (less than 6000 miles) had issues.

 

[Steve40th]

MSD and any opti is only as good as the install. Any time you install a new one, ensure all things line up properly. The splines for the 92-94 is important, as you can possibly put it in one tooth off, and it wont run right.
ALso, If I had the opti off, I would rebuild (as I have) or replace the pump. And dont go cheap on the water pump, get an AC DELCO.

 

[Toms007]

Replaced the pump (with AC/Delco) less than 6000 mile back when I put the last opti in.

 

[LT4man]

Well I am getting to the place that I am pretty sure that the plugs and wires are not my problem. Currently I have the EGR off the car and am trying to figure out how to clean it up. the pin seemed to be stuck just short of being fully extended when I took it out. I have sprayed it with CRC and wiped out the area around the pin. I also found a glaze on the shaft of the pin and used CRC to get rid of it. Now when I push the diaphragm down it returns the pin slowly to its top position I guess the next thing to do is buy the gasket with the screen in it and see if this solves my problem.

When I ran the car today it was missing badly at low rpm's but if I put it into second gear and kept the rpm's above 3000 it ran fairly good and occasionally did not have the miss. If I put it back into a higher gear and let the rpm's drop the miss became very pronounced.

If this was happening back in the old days when all we had was a carburetor, points and a distributor I would be looking at the carb accelerator pump because it acts just like the fuel to air ratio is way lean at low rpm's

If your EGR valve was not reacting quick enough (pintle stuck in an open position) way too much air would be entering and causing an extremely lean condition at low rpms.

If the pintle now retracts completely, you might have found the cause of your stumble.

Reinstall the EGR valve and drive your Vette enough to put it through its paces.

SAVE THE GOSH DARN

 

[John Robinson]

War and Peace

This is like a saga or book that just never ends. The EGR was cleaned but when I filled the cavity around the pintle the fluid went straight through to the other chamber. I must have a bad seat for the pintle. I put it back into the car and it ran much different than before the miss was not as harsh but the engine ran what I call soft no neck snapping power. I think the next thing is to buy a new EGR and see if that is the fix.:L

By the way LT4Man do you think you could send me the number of that Chevy dealer you get parts from. Or better yet a new EGR

 

[LT4man]

This is like a saga or book that just never ends. The EGR was cleaned but when I filled the cavity around the pintle the fluid went straight through to the other chamber. I must have a bad seat for the pintle. I put it back into the car and it ran much different than before the miss was not as harsh but the engine ran what I call soft no neck snapping power. I think the next thing is to buy a new EGR and see if that is the fix.:L

By the way LT4Man do you think you could send me the number of that Chevy dealer you get parts from. Or better yet a new EGR

John, I think you found your answer. The EGR valve is only supposed to work under deceleration! Never at idle. Never upon acceleration.

If the EGR valve is putting air into the exhaust manifolds at the wrong times (in front of the O2 sensors) the O2 sensors are getting wayyyyyy too much oxygen. The sensors send the incorrect information to the PCM and the PCM tries to correct for the mistake. End result: your engine does NOT run like it was programmed by the engine engineers! (Redundant? Maybe, but right! :L)

Try Chris May at Superior Chevrolet in Kansas. 1-800-728-8267 Tell him Gregory in Chicago told you to call. Also tell him you are on the Corvette Action Center website.

SAVE THE GOSH DARN , WILL YA?

 

[John Robinson]

Pulled codes tonight

Hey guys and gals I pulled the codes tonight and had the following codes in History

41

22


43

64

72

Other than the code 22 which is the TPS and I pulled the voltage on it and it was .49 at closed throttle and went up to 4.09 at WOT

I would guess the others are reactions to what is causing the miss

Any thoughts ?:ugh

 

[G Winter]

John, I think you found your answer. The EGR valve is only supposed to work under deceleration! Never at idle. Never upon acceleration.

If the EGR valve is putting air into the exhaust manifolds at the wrong times (in front of the O2 sensors) the O2 sensors are getting wayyyyyy too much oxygen. The sensors send the incorrect information to the PCM and the PCM tries to correct for the mistake. End result: your engine does NOT run like it was programmed by the engine engineers! (Redundant? Maybe, but right! :L)

Try Chris May at Superior Chevrolet in Kansas. 1-800-728-8267 Tell him Gregory in Chicago told you to call. Also tell him you are on the Corvette Action Center website.

SAVE THE GOSH DARN , WILL YA?

Greg, you are usually right about things you post but I think you have the EGR confused at the moment with the air injection pump.
The EGR [ exhaust gas recirculating ] valve allows exhaust gas to be introduced into the intake manifold under deceleration,which I believe cools the combustion temp. You are correct that it should never do this at idle.

Glenn

 

[Toms007]

ALRIGHT, here's is the final chapter as far as mine is concerned.....

The Optispark cap and rotor were toast! I just got home about an hour ago and the Vette ran like a striped @ss ape. She's back. He got the oil leak as well (I hope, as she didn't lose a drop on the drive home and I got it up on the lift and she's dry still after the 40 minute drive. When talking to the mechanic he said "There's no doubt that the cap and rotor are shot. Just take a look at the inside of that cap and you'll see where it was misfiring. I'm actually surprised it was running as well as it was." I have taken some pictures of the cap.

I think that the rest of the opti is fine, but this would need a new cap and rotor to be nearly good as new.

 

[Steve40th]

Opti, Here was mine. I went to DELTEQ after this one broke.

 

[LT4man]

Greg, you are usually right about things you post but I think you have the EGR confused at the moment with the air injection pump.
The EGR [ exhaust gas recirculating ] valve allows exhaust gas to be introduced into the intake manifold under deceleration,which I believe cools the combustion temp. You are correct that it should never do this at idle.

Glenn

One of my posts was censored here and I think I lost my head for awhile! :W

You are absolutely correct. The Air Injection Pump is responsible for introducing air into the exhaust manifolds. EGR introduces air into the intake manifold. I do not believe it cools the combustion chamber. Just makes for more complete burning of the fuel.

I stand corrected! Except for when I am sitting down!

WHILE YOU ARE AT IT, COULD YOU SAVE THE ?

 

[LT4man]

ALRIGHT, here's is the final chapter as far as mine is concerned.....

The Optispark cap and rotor were toast! I just got home about an hour ago and the Vette ran like a striped @ss ape. She's back. He got the oil leak as well (I hope, as she didn't lose a drop on the drive home and I got it up on the lift and she's dry still after the 40 minute drive. When talking to the mechanic he said "There's no doubt that the cap and rotor are shot. Just take a look at the inside of that cap and you'll see where it was misfiring. I'm actually surprised it was running as well as it was." I have taken some pictures of the cap.

I think that the rest of the opti is fine, but this would need a new cap and rotor to be nearly good as new.

Tom, did he shed any light on why those components failed?

JUST SAVE THE GOSH DARN

 

[Toms007]

Tom, did he shed any light on why those components failed?

JUST SAVE THE GOSH DARN

Gregory, he couldn't say why he thought it did that, just the fact that you won't believe it could run at all. So my fingers are crossed that this has fixed that issue as well.

 

[Steve40th]

Tom, did he shed any light on why those components failed?

JUST SAVE THE GOSH DARN

These things are notorious for carbon arcing. If you have an MSD type box on it it is even worse. They were a great design, just not executed well, especially the 92-94 LT1's. The 95and on LTx engines received a better design, and little vacuum lines to assist in the other issue of moisture within the Opti.