1985 corvette L98 engine knock
10-09-2015, 11:35 AM
#1
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; 10-09-2015 at 12:33 PM.
10-09-2015, 12:10 PM
#2
Le Mans Master
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?
10-09-2015, 12:50 PM
#5
Team Owner
Member Since: Sep 2003
Location: Freedom is never more than one generation away from extinction.
Posts: 20,161
Received 639 Likes
on
443 Posts
St. Jude '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-‘19-'20-'21-'22-'23-'24
Time to pull the pan for an inspection
10-09-2015, 01:26 PM
#6
Le Mans Master
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?
The following users liked this post:
Banksysvette (10-09-2015)
10-09-2015, 02:08 PM
#7
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; 10-09-2015 at 02:19 PM.
