NEED HELP! I cant find whats wrong!
Thread Starter
Intermediate
Joined: Oct 2004
Posts: 30
Likes: 0
From: Macclenny FL
NEED HELP! I cant find whats wrong!
I have a modified 90 l98 with a problem. When I go to drive it the rpms will jump up and down and will slow the car down. I also hear a slight back fire from the exhaust. I checked the plugs, wires, cap & rotor, all new. I checked the fuel pressure and it was at a constant 41 psi. I took it to a dealership they had it for over a week, and said that there wasnt a problem, only that it did it every once in a while and that they cant find a problem. So any help would be nice.
Thread Starter
Intermediate
Joined: Oct 2004
Posts: 30
Likes: 0
From: Macclenny FL
i was about to change the fuel filter to see what it would do. also the tech at the dealership said that they were getting weird readings, but they said it was because of the aftermarket parts on the engine.
Also i have notice on the information display where it shows the mpg it was flashing system.
Also i have notice on the information display where it shows the mpg it was flashing system.
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
Originally Posted by 90pologreen
i was about to change the fuel filter to see what it would do. also the tech at the dealership said that they were getting weird readings, but they said it was because of the aftermarket parts on the engine.
Also i have notice on the information display where it shows the mpg it was flashing system.
Also i have notice on the information display where it shows the mpg it was flashing system.
Thread Starter
Intermediate
Joined: Oct 2004
Posts: 30
Likes: 0
From: Macclenny FL
I grounded the A B slots and the check engine light flash 12 over and over again, but when i ground A and G on the display I get H72, H74. I should get the code 33 because i have no egr vavle but i got nothing. Any help would do.
Drifting
Joined: Oct 2005
Posts: 1,259
Likes: 0
From: bakersfield cali
possible help
have you tried to check the setting on the idle air control valve? Have you checked for vacuum leaks? You say that your egr is not even there, did you remove completely, what did you do with the sensor that goes between the exhaust and the intake tube?
If your mods were listed, it could help us help you to diagnose the problem better.
Do your mods include a hotter lopey camshaft?
If your mods were listed, it could help us help you to diagnose the problem better.
Do your mods include a hotter lopey camshaft?
Last edited by 86VX1; Nov 16, 2005 at 02:30 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Intermediate
Joined: Oct 2004
Posts: 30
Likes: 0
From: Macclenny FL
mods- long tubed header, bigger injectors, ajustable fuel pressure regulator, k & n filter, polished and ported heads, 52 mm throttle body, 3 wire heated O2 sensor, stock cam, throttle body coolent bypass, removed frisbee. rebuilt engine with 30,000 miles on it. i have replaced every sensor, hose, belt. it just started this 3 weeks ago, i have check for vacuum leaks, tomorrow i will replaced fuel filter and check to see if the iac valve it set right at 1 3/8th inch i only listed the mods on the engine not the trans, rear, or chassie.
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
Not much you can do to test the ECM other than change it out with a known good one and see if the problem persits. You may get the code 12's and still have an ECM with intermittent failures. They are about $100 at most parts stores these days, but as it is an electronic part, usually no return policy.
When mine went bad it was intermittent so I chased my tail and replaced a bunch of sensors/relays before replacing the ECM.
Best of Luck. BTW, those mods should not cause too much of a "weird" reading on your scanner, other than EGR trouble code possibly if removed.
When mine went bad it was intermittent so I chased my tail and replaced a bunch of sensors/relays before replacing the ECM.
Best of Luck. BTW, those mods should not cause too much of a "weird" reading on your scanner, other than EGR trouble code possibly if removed.
Le Mans Master
Joined: Apr 2000
Posts: 6,341
Likes: 1
From: Shelton CT
Double and triple check your districutor.. Make sure it is not off a tooth or even 180degrees installed by accident.. Mine did the same thing as yours years ago the first time I had re-insalled my distributor in the engine wrong.
GB
GB
Thread Starter
Intermediate
Joined: Oct 2004
Posts: 30
Likes: 0
From: Macclenny FL
i check the disributor it is good and i did not remove it it is installed corrected. Every time I change something it runs fine for awhile then back the same. Now it is dropping it rpm and then reviving back. The drop is about 1500 rpm and then back up it makes the car shot forward and the stops and shots forward again. It looks like I cant drive a stick.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
A scan would help - might be reacting to a funky a/c signal which would push it up and down at idle. Check Targeted vs. Actual, IAC Counts vs. Load, A/C request On/Off, Park/Neutral status, etc. That should narrow it down to component vs. an ECM problem. Hard to believe the Dealer didn't do this while the problem was present or if they did, time to find another Dealer (or better yet, just buy your own scanner).
