ecm eprom chip
Thread Starter
Intermediate
Joined: Mar 2018
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ecm eprom chip
1985 corvette- l98 engine- I am having trouble getting the engine to run smooth at idle- it hunts around the rpms wont stay stable when im stopped at a red light a few times it has actually died I know it souns like a manifold leak but ive spent the last 3 years trying to find it- there is no vacume leak. the previouse owners did quite a few mods to the engine most of which i have undone. as a last resort before I pull the heads off to check the valve guides for excess wear, I decided to look at the ecm and check the connectors etc... the connecters look good and clean but it does have an after market prom chip that says super chip- have any of you had experience with these chips? could a bd prom chip cause unstable idle? it seems to run fine at anything above idle. any advice on where to send the ecm to be checked?
Team Owner
Joined: Jul 2004
Posts: 28,465
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From: Hartford WI
Supposedly, all the Superchips does is lighten your wallet and turn the fans on earlier and gives you "up to X HP". What mods have you NOT undone? Have you tried getting a scanner to see what the IAC counts are and set the min air rate with that? Any way you can get a stock chip? First thing I would try is the stock chip and cleaning the TB. Normally, I get new gaskets, take the TB off, take the top plate off, take the IAC valve off and the IAC housing off. Clean the TB with brake cleaner and all the passages on it. Spray a gentle spray on the pintle of the IAC and wipe it off GENTLY. Reinstall with new gaskets and see if there are any leaks. Way I like to check is to set the timing first, get the engine hot and with everything else off, see what the IAC counts are. If it is more than 30, turn the adjustment screw in, rev and recheck after it settles down. My target is 30 counts. IF it is less, turn the screw out, rev and recheck. This part is important. If you turn the screw out all the way and it still is at 0, you definitely have an air leak.
Team Owner
Joined: Sep 2003
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Since the modifications weren't done by you I'd maybe confirm 1st that the ECM is actually a 1985 GM# 1226870, many '85 owners changed to the later GM# 1227165 and that required some changes also. If you have a confirmed #1226870 then maybe you try to find an original PROM for the car. There are various 'correct' configurations BUT 1st I'd attempt to just confirm the ECM in the car.
There should be a label of some sort on the ECM housing that ID's the actual ECM.
There should be a label of some sort on the ECM housing that ID's the actual ECM.
Last edited by WVZR-1; Apr 17, 2021 at 05:27 PM.
Melting Slicks
Joined: Jun 2011
Posts: 2,383
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From: Leland , North Carolina
1985 corvette- l98 engine- I am having trouble getting the engine to run smooth at idle- it hunts around the rpms wont stay stable when im stopped at a red light a few times it has actually died I know it souns like a manifold leak but ive spent the last 3 years trying to find it- there is no vacume leak.
Mine had a manifold leak at the front where it seals to the block.Was hard to find. Failing MAF and fuel injector. I feel your pain.....
Oil Producer
Joined: Apr 2014
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i had an 85 auto like that.
after rsealing everything down to the headgaskets, it was still just slow to react and always chasing the proper idle.
years ago, wvzr1 informed me that there was infact an updated prom chip available for the 85 auto that was offered by gm very late. its chip designation is HLH3200.
If its an auto, it also fixes the stupid VERY early tcc lockup which feels like your car is shifting too early.
that gm, factory, HLH3200 chip made my 85 run P E R F E C T L Y.
ran exact same as my 87 auto
very few people talk about it here.
the last person who put one in his car that i know of got it from Nomake Wan on this forum.
after rsealing everything down to the headgaskets, it was still just slow to react and always chasing the proper idle.
years ago, wvzr1 informed me that there was infact an updated prom chip available for the 85 auto that was offered by gm very late. its chip designation is HLH3200.
If its an auto, it also fixes the stupid VERY early tcc lockup which feels like your car is shifting too early.
that gm, factory, HLH3200 chip made my 85 run P E R F E C T L Y.
ran exact same as my 87 auto
very few people talk about it here.
the last person who put one in his car that i know of got it from Nomake Wan on this forum.
