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Discussion Starter · #1 ·
LT1 from roadmaster with roller rocker heads.
Had a place in NY take emissions out of computer.

Runs rough at idle, check engine light on, painless wiring kit.

starts to back fire under load.

idle varies.

mit has a new opti-spark, new plugs, etc.

checked fuel pressure at 40

any ideas?
 

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Hates: Liver. Loves: Diesel
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Lifter preload incorrect is my stab in the dark guess.

New Optispark doesn't mean good optispark. Could also be an oops by the programmer. What emissions stuff was taken out?
 

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Get yourself an obd1 cable for computer and download scan9495, you will be able to see what codes are throwing check engine light on, plus monitor everything to see what’s happening, once you have cable you can also get adjustments made to the tune! I want to say the red river is the cable i have for my 94 lt1
 

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Discussion Starter · #7 ·
Update;
The painless kit came with obd2 even though 94 roadmaster was obd1. We are not able to get a code from code re

I rewired It obd1 style and to fit obd1 port, the check engine light stays solid.

many suggestions?
 

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What year is the pcm? If 94-95 it’s still
Obd1, 95 was obd1 with an obd 2 port. So you need to get an obd2 cord for computer, and get that scan9495 I mentioned, it’s a free program! It will putll your codes, most readers do no read the obd1 stuff with obd2 port! Without knowing your codes, everything is a guess
I would also suggest joining ltxtech forum and picking their brains! Also download wiring diagrams from Shbox.com. Those two sites helped me to no end when I did my lt swap into my jag
 

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Discussion Starter · #9 ·
Thanks, I’ll check those out.
Let me confirm; it is 94, but painless sent an obd2 port….but confirming, no obd2 scanner will get a code, correct? Because it is an obd1 computer, correct?
So why isn’t the engine light flashing a code when I hook up the obd1?
 

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Discussion Starter · #11 ·
We have two computers; so me with emissions deleted and one without for testing.
This one is from a 93 trans;Service #, 16188051,
I pulled it out of the car,

the other is a 94 roadmaster computer, I’m pulled that one too.

map given that, for certain I shouldn’t be trying to read it with obd2, correct?

mom sending my son down to get a new coil this morning to try to fix running, that’s the only part i haven’t replaced…
 

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Obd2 scanner will not read obd1 codes, and 94- 95 will not do the obd1 code flash with check engine light. Obd1 with an obd 2 port is generally known as obd1.5, but still uses the obd1 code, 93 computer is an ecm or engine control module, as it doesn’t control transmission, 94 and up is called a pcm power train control module as it does control trans, also, 93 cannot be reprogrammed via a flash like the 94 up, it will require a new chip being installed!
 

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Via an actual obd1 scanner for gm, or you need scan9495, which will not only scan your codes for you, let you reset them, it will also create a data log that can be read by some others and they will be able to tell you exactly where your issue lies, could be as simple as a failed fuel pressure regulator letting fuel be pulled through the vac line directly into manifold.
 
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