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Idle After Closed Loop Hunts 5-- RPM to 750 RPM

 
Old 02-05-2019, 11:47 PM
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raya123_2000
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Default Idle After Closed Loop Hunts 5-- RPM to 750 RPM

1990 Corvette 6MT car idles great when cold but idles between 500 RPM and 750 RPM sometimes will die. I put a spark tester on the multiple spark plugs, and I found the tester showed a lot of time the spark plug either did not get spark or it was weak, I'll attach a video.

What I want to know is how much to replace.

1.) Coil
2.) The control module
3.) Pickup coil

What else?

Ray
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Old 02-05-2019, 11:53 PM
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raya123_2000
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Default Idle After Closed Loop Hunts 5-- RPM to 750 RPM

The video did not attach above.

Here it is.

Ray
Attached Files
File Type: mov
SparkGapTest-2-5-2019.MOV (1.45 MB, 16 views)
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Old 02-06-2019, 10:22 AM
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rharker
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Originally Posted by raya123_2000 View Post
1990 Corvette 6MT car idles great when cold but idles between 500 RPM and 750 RPM sometimes will die. I put a spark tester on the multiple spark plugs, and I found the tester showed a lot of time the spark plug either did not get spark or it was weak, I'll attach a video.

What I want to know is how much to replace.

1.) Coil
2.) The control module
3.) Pickup coil

What else?

Ray
I just had a coil go out and it definitely was intermittent till the end when it completely failed ... that and the ICM are my picks. Parts store can test your ICM. Look close to coil and check for arcing or burn through. Smell test for burnt smell. Also change your cap which is sure to be bad if it never has been changed. ICM =$30 coil=$35-60

Last edited by rharker; 02-06-2019 at 10:23 AM.
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Old 02-06-2019, 03:56 PM
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How are the plug wires? Are they leaking? How is the cap and rotor?
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Old 02-06-2019, 04:06 PM
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Bfenty
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Originally Posted by rharker View Post
I just had a coil go out and it definitely was intermittent till the end when it completely failed ... that and the ICM are my picks. Parts store can test your ICM. Look close to coil and check for arcing or burn through. Smell test for burnt smell. Also change your cap which is sure to be bad if it never has been changed. ICM =$30 coil=$35-60
Parts store can test the ICM but don't always trust their results. I've had it say it was good but through process of elimination determined it had to be faulty (and replaced and the car suddenly started working perfectly, so...)

Take those tests with a grain of salt.
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Old 02-06-2019, 06:14 PM
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Originally Posted by Bfenty View Post
Parts store can test the ICM but don't always trust their results. I've had it say it was good but through process of elimination determined it had to be faulty (and replaced and the car suddenly started working perfectly, so...)

Take those tests with a grain of salt.
Have them run the test 3 times. Any one time it fails, get a new unit.
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Old 02-06-2019, 09:59 PM
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Originally Posted by aklim View Post
How are the plug wires? Are they leaking? How is the cap and rotor?
I took the Distributor out today, and all the parts look good Coil measures Primary .6 ohms Secondary 7,880 ohms. Distributor bearing looks good

The camshaft gear is worn so I'll replace it.
The Capacitor I''ll replace.
The ICM i'll replace
The Coil I'll replace
The spark plug wires I'll replace.

The car has new plugs cap and rotor.

I am also going to replace the catalytic converter and the Y pipe w/o pre-cats.

Rock Auto has the parts from all then different venders. Are they a good place to buy from??

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Old 02-06-2019, 10:32 PM
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Originally Posted by raya123_2000 View Post
The camshaft gear is worn so I'll replace it.
The Capacitor I''ll replace.
The ICM i'll replace
The Coil I'll replace
The spark plug wires I'll replace.

The car has new plugs cap and rotor.

I am also going to replace the catalytic converter and the Y pipe w/o pre-cats.

Rock Auto has the parts from all then different venders. Are they a good place to buy from??
Why is the cam gear worn? Did something wear it out?

Why are you replacing so many things that haven't tested out bad? I really would solve this issue first before I go doing all that work. You introduce new variables into the equation. Best way is to do it step by step and replace only parts that are bad. Are you sure the gear is worn?
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Old 02-07-2019, 10:02 AM
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I don't know much about L98s, but if the car is running perfectly when in open-loop mode (cold), but then starts running badly in closed-loop mode (warmed up), then you're looking for a bad sensor of some sort. The ECM is getting bad data from a sensor, somewhere, that it normally ignores in closed-loop. A bad coil/distributor/ICM would all probably run badly from cold start (the ICM might be bad only when warm). Ditto plugs and wires (in fact, they should run worse when cold, since it's harder to fire the gas mixture when cold). And very much ditto the cats. I'd check O2 sensors, coolant temp sensor, etc.
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Old 02-07-2019, 11:56 AM
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raya123_2000
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Originally Posted by MatthewMiller View Post
I don't know much about L98s, but if the car is running perfectly when in open-loop mode (cold), but then starts running badly in closed-loop mode (warmed up), then you're looking for a bad sensor of some sort. The ECM is getting bad data from a sensor, somewhere, that it normally ignores in closed-loop. A bad coil/distributor/ICM would all probably run badly from cold start (the ICM might be bad only when warm). Ditto plugs and wires (in fact, they should run worse when cold, since it's harder to fire the gas mixture when cold). And very much ditto the cats. I'd check O2 sensors, coolant temp sensor, etc.
The main catalytic converter broke up and clogged the exhaust. It started with a ecm code H44, which indicated a low voltage on the Oxygen sensor. Then the cat broke up. Now something happened to send too much fuel to the cat.

I changed the injectors (they were 15 years old) the original injectors lasted 12 years. New temp and O2 sensor. Cap and rotor and plugs so far. Using a spark gap tester I notice good spark until it warmed up, when the car started to run bad I noticed I had bad spark showing on the tester. I suspect it's the capacitor. But why not rebuild the distributor

The gear has normal wear but came become a problem in 50K miles. I plan on keeping the car for a while, I brought it in 1990 when I was 41, I'm 70 now I hope I have another 20 years where I drive.

Ray
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