95 LT1 Problem -- Possessed by Satan
But seriously, check your grounds.
Take them off, one by one and clean them with a wire brush or sandpaper.
Do the same to the surface they mount against and re-install them.
Bad grounds have caused more issues around here than I can count and often leave people spending
themselves into a level of pissed off that you cannot imagine when they find the issue.
Take them off, one by one and clean them with a wire brush or sandpaper.
Do the same to the surface they mount against and re-install them.
Bad grounds have caused more issues around here than I can count and often leave people spending
themselves into a level of pissed off that you cannot imagine when they find the issue.
Thread Starter
Joined: Apr 2004
Posts: 1,634
Likes: 2
From: Macomb Twp, MI
Well - that was embarrassing. Apparently the vacuum line for the EGR (which has been deleted) was completely exposed. We found the rubber plug we had used and there was a crack running all the way from tip to head. It must have been allowing air in prior to the optispark swap but it was a small enough of a leak that the PCM could compensate.
When we did the optispark swap, I replaced the optispark harness and I must have knocked the rubber plug completely off the vacuum port and never noticed - the plug was sitting in the valley between the intake manifold and the valve cover.
Spraying carb cleaner around the engine bay exposed the issue real quick - as soon as I sprayed by the throttle body it became quite apparent that's where the issue was and then I realized what my dad and I both thought was a loud alternator whine was the damn vacuum port sucking air.
Lmao -- needless to say, damn embarrassed that we didn't catch that sooner.
Since the issue started last year - these are all the items that we found which were contributing to the problem:
1. Corrupt tune telling the PCM that the injectors were flowing 700+ lbs/hr.
2. One fuel injector was out of calibration by 15%
3. Bad o2 sensor
4. Bad optispark
5. Vacuum leak at the EGR port in the TB
Pretty nuts that we had all 5 of those gremlins that we were fighting all at once... no wonder we were so stumped that every time we thought we found the fix and there was still something wrong.
When we did the optispark swap, I replaced the optispark harness and I must have knocked the rubber plug completely off the vacuum port and never noticed - the plug was sitting in the valley between the intake manifold and the valve cover.
Spraying carb cleaner around the engine bay exposed the issue real quick - as soon as I sprayed by the throttle body it became quite apparent that's where the issue was and then I realized what my dad and I both thought was a loud alternator whine was the damn vacuum port sucking air.
Lmao -- needless to say, damn embarrassed that we didn't catch that sooner.
Since the issue started last year - these are all the items that we found which were contributing to the problem:
1. Corrupt tune telling the PCM that the injectors were flowing 700+ lbs/hr.
2. One fuel injector was out of calibration by 15%
3. Bad o2 sensor
4. Bad optispark
5. Vacuum leak at the EGR port in the TB
Pretty nuts that we had all 5 of those gremlins that we were fighting all at once... no wonder we were so stumped that every time we thought we found the fix and there was still something wrong.
TECH Enthusiast
Joined: Mar 2009
Posts: 680
Likes: 8
From: Clearwater
your "corrupt" tune was probably caused by the wrong definition file. there is an EE and an EEb (seen mostly with 94s). if you see those jacked up numbers then switch to the other definition file.
Thread Starter
Joined: Apr 2004
Posts: 1,634
Likes: 2
From: Macomb Twp, MI
The weird part is that since we discovered the "corrupt tune" we have replaced it with two other tunes. I've only used tunes which were done using the $EE definition and they run perfectly fine -- could the $EEb be part of the reason why the "corrupt tune" didn't run good? So not so much that the tune was corrupt, but that the tune was done with the wrong revision?
TECH Enthusiast
Joined: Mar 2009
Posts: 680
Likes: 8
From: Clearwater
that i could not answer. both my 94 and 95 are EE 6 speed cars and the EEB is from an automatic so i never bothered to experiment on it. i dont know if the "eeb tune" is specific to the operating system in the PCM, the effects of loading the opposite over top of it or even how to externally identify one without attempting to read it. for all i know it was just a changeup to deter anyone not affiliated with GM from screwing with it.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Launching!
Joined: Aug 2012
Posts: 259
Likes: 0
From: Johnstown, Pa
another way to check injectors. Pop them completely out and get a ohmeter. Jump the connections on the top and read them they should all be right around the same. If you have one that reads almost nothing theres your bad injector. Not sure exactly what our LT1'S readings are. But i figured out a mazda that had been giving us the same kinda problem for months with this test. Good Luck. also my lt1 bird is currently throwing a fit with backfireing and not running rite so let me know how you fare.
Hey ugod, you should check the date of the last post-in this case it was ten months ago. They probably have it fixed....by now.
I've been guilty of not date checking also...
I've been guilty of not date checking also...
Teching In
Joined: May 2012
Posts: 30
Likes: 0
ok i was told by everyone that the 95 pcm cant b tuned but the 96 and later can. Now i was also told that since the cams rpm rating is 1500-5500 the car really wont bring out the hp til it reaches 1500 rpm. but how can i tune it?
Incorrect. All PCM's can be tuned. In the world of fourth gen F-bodies, the 1993 was the odd guy out. 1994 and some 1995 cars were OBDI. Starting in 1995 and then out, they were OBDII.
Some '95 cars have what is unofficially considered OBD one and a half.
Some '95 cars have what is unofficially considered OBD one and a half.
TECH Fanatic
Joined: Sep 2010
Posts: 1,037
Likes: 2
My car has OBD1.5 its OBD1 with an OBD2 connector.
93 has to have chips burned.
94 - 95 use TunerCats
96+ HPTuners.
When an item says 1500 - 5500 rpm it means its going to make its best power between those rpms.
Under 1500 its not going to be making max power.
Spinning it over 5500 its going to drop off.
When you tune you are setting your spark timing and your injector pulse.
Spark 'generally' you are trying to run the highest spark advance you can without seeing knock. This means the mixture is igniting soon as it can thus burning all the fuel/air making the most power.
Injector pulse is just what you are using to control the amount of fuel for a given amount of air. So say your Wideband is reading lean because you put a new CAI on. You need to make your injector stay open longer in order to spray more fuel to richen the mixture up.
93 has to have chips burned.
94 - 95 use TunerCats
96+ HPTuners.
When an item says 1500 - 5500 rpm it means its going to make its best power between those rpms.
Under 1500 its not going to be making max power.
Spinning it over 5500 its going to drop off.
When you tune you are setting your spark timing and your injector pulse.
Spark 'generally' you are trying to run the highest spark advance you can without seeing knock. This means the mixture is igniting soon as it can thus burning all the fuel/air making the most power.
Injector pulse is just what you are using to control the amount of fuel for a given amount of air. So say your Wideband is reading lean because you put a new CAI on. You need to make your injector stay open longer in order to spray more fuel to richen the mixture up.
Thread Starter
Joined: Apr 2004
Posts: 1,634
Likes: 2
From: Macomb Twp, MI
What they probably meant was that they only have OBD2 tuning software at the shop. Even here in Detroit there's not too many tuners who tune OBD1 LT1s, most only do OBD2.
Thread Starter
Joined: Apr 2004
Posts: 1,634
Likes: 2
From: Macomb Twp, MI
We replaced/swapped the IAT sensor, optispark, MAF, throttle body, o2 sensors, injectors, ICM, coil, spark plugs, spark wires, MAP... Probably more. Tried different stock tunes found online, etc. In the end we never could figure out what the problem was and we ultimately gave up. Every time we changed something it *seemed* to get a little better but then it'd start backfiring again. My dad was so disheartened by the whole thing that he didn't care to work on it anymore or drive it at all, he only put about 1000 miles on the car (what WAS a semi-daily driver except in snow) so he ended up selling it. I know the guy who bought it and hopefully he'll figure it out.
