Bad L98 HEI Module?
Thread Starter
Cruising
Joined: Oct 2003
Posts: 12
Likes: 0
From: Chandler AZ
Bad L98 HEI Module?
My 1991 L98 is running bad after it warms up, I have a feeling the HEI Module is bad. How will my car run if the HEI Module is bad? I've posted my problem on this site before, everyones help is greatly appreciated. I've tried all the suggestions and the problem still exists. Thanks
Racer
Joined: Feb 2004
Posts: 265
Likes: 1
From: Irwindale Ca
Re: Bad L98 HEI Module? (sdaztecs)
I dont think your car would even start. My hei module left me stranded in Sandiego and on my 76 my hei left me at the beach. I do however change them out at every tune up. routine maintenance so i wont get stuck anymore. Is it idling bad or no power with throttle? is it a erratic miss or a consistent miss? . My guess is you need to clean the trottle body and IAC because when cold your IAC lets more air in the plenum and when warm it chokes the air off leaning the car. In your case its choking it to extinction wth all the buildup. Its not hard to clean. I would clean the throttle body and Plenum while i was at it. Lots of previous posts oh how too. Im surprised noone has answered your post. Your on page four with no replies. Have you made enemies??? ive just noticed on your post that you have had other suggestions. Oh well for what its worth. :seeya
Team Owner
Joined: Aug 2000
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From: Sydney, Australia
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Re: Bad L98 HEI Module? (madmike)
When my HEI module went bad the car just plain died when things got warm - and it wouldn't restart until it cooled right down again. I would suggest looking elsewhere too.
Drifting
Joined: May 1999
Posts: 1,478
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From: Sacramento, CA Money can't buy happiness - but it's more comfortable to cry in a Corvette than a Yugo.
Re: Bad L98 HEI Module? (sdaztecs)
I agree with the previous posts. probably not the HEI. If the car starts and runs ok when cold, but gets worse when warm I'd check the O2 sensor and coolant temp sensor.
At cold start the PCM regulates fuel based upon tables built into the chip and coolant sensor readings. Once the engine reaches operating temp it goes into "closed loop" which is when the O2 sensor gets hot enough to send reliable feedback to the PCM for it to regulate fuel mixture. If the O2 sensor is bad it can send bad data to the PCM causing poor mixture. The O2 sensor is only used by the PCM when warmed up, not when cold. Until it fails completely a poorly performing O2 sensor can send bad data and never set a code.
If the coolant temp sensor reading is off, it will cause the PCM to make mixture adjustments that are for an engine temp that is incorrect. In my opinion it is less likely to be a bad or poorly reading coolant temp sensor than an O2 sensor, but it could be part of the problem
At cold start the PCM regulates fuel based upon tables built into the chip and coolant sensor readings. Once the engine reaches operating temp it goes into "closed loop" which is when the O2 sensor gets hot enough to send reliable feedback to the PCM for it to regulate fuel mixture. If the O2 sensor is bad it can send bad data to the PCM causing poor mixture. The O2 sensor is only used by the PCM when warmed up, not when cold. Until it fails completely a poorly performing O2 sensor can send bad data and never set a code.
If the coolant temp sensor reading is off, it will cause the PCM to make mixture adjustments that are for an engine temp that is incorrect. In my opinion it is less likely to be a bad or poorly reading coolant temp sensor than an O2 sensor, but it could be part of the problem
