1985 corvette L98 engine knock
Thread Starter
Heel & Toe
Joined: Sep 2015
Posts: 15
Likes: 0
1985 corvette L98 engine knock
Looking for help please, running out of money for sensors.
Bought the car 3 mos. ago.
Noticed the knock right away but thought tune-up and timing, and all will be ok. WRONG!!
Did tune and wires, played with timing and put it back to 6 degrees.
Getting knock at almost wide open throttle and at WOT.
I understand knock sensor will retard timing but why am i getting knock in the first place. Done TPS adjust and idle air adjust according to corvette forum members advice. Removed and cleaned throttle body and cleaned carbon from iac. Rough idle at start-up and won't go over 500 rpm when first started until warm. Checked for vaccum leaks and none found. Every time i start it from cold it never starts or idles the same as the time previous. HELP please??
Bought the car 3 mos. ago.
Noticed the knock right away but thought tune-up and timing, and all will be ok. WRONG!!
Did tune and wires, played with timing and put it back to 6 degrees.
Getting knock at almost wide open throttle and at WOT.
I understand knock sensor will retard timing but why am i getting knock in the first place. Done TPS adjust and idle air adjust according to corvette forum members advice. Removed and cleaned throttle body and cleaned carbon from iac. Rough idle at start-up and won't go over 500 rpm when first started until warm. Checked for vaccum leaks and none found. Every time i start it from cold it never starts or idles the same as the time previous. HELP please??
Last edited by Banksysvette; Oct 9, 2015 at 12:33 PM.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
First, I would not rev the engine to 5000 RPM when cold.
With the car running I would use a automotive stethoscope to try and pin point the source of your knock. This sounds more like a internal issue, bad bearings, rod, piston slap or other issue. Use the stethoscope and move it around on the block to try an locate the noise.
Is it the sound of metal on metal? Ping and kind of a chugging? At all RPM or in a specific range?
With the car running I would use a automotive stethoscope to try and pin point the source of your knock. This sounds more like a internal issue, bad bearings, rod, piston slap or other issue. Use the stethoscope and move it around on the block to try an locate the noise.
Is it the sound of metal on metal? Ping and kind of a chugging? At all RPM or in a specific range?
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Sounds more like a problem with the distributor advancing and a lean condition with fuel. I would start by putting a fuel pressure gauge on the fuel rail. You can "borrow" from many auto parts stores. Attach the gauge and read the pressure with the car at idle. The pressure should be around 36-39 PSI. Now slowly increase the RPMs and watch the gauge. Does the pressure drop?
Next question, do you know if the engine is stock? Is there a stock computer chip in the computer?
Next question, do you know if the engine is stock? Is there a stock computer chip in the computer?
Thread Starter
Heel & Toe
Joined: Sep 2015
Posts: 15
Likes: 0
Sounds more like a problem with the distributor advancing and a lean condition with fuel. I would start by putting a fuel pressure gauge on the fuel rail. You can "borrow" from many auto parts stores. Attach the gauge and read the pressure with the car at idle. The pressure should be around 36-39 PSI. Now slowly increase the RPMs and watch the gauge. Does the pressure drop?
Next question, do you know if the engine is stock? Is there a stock computer chip in the computer?
Next question, do you know if the engine is stock? Is there a stock computer chip in the computer?
Last edited by Banksysvette; Oct 9, 2015 at 02:19 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
