Please help with bad pinging problem in 85
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
Please help with bad pinging problem in 85
I just got back from Carlisle and discovered my engine pings very noticably under load.
I noticed pinging in the past and recently had the timing checked by a mechanic our Corvette Club president says is good with L98's. He could not set it at 6 degrees with the wire off as recommended without casing rough idling, but got it as close as he could.
This is the first time in a long time I drove any real distance with the roof on, radio off, and windows up so I don't know how long it has been doing this.
Other details:
1985
117,000 miles
The guy I bought it from 10 years ago said it had just had a mild cam installed. I have a receipt but could not get specs on the cam. Also at that time: valve job, new injectors, adjustable fuel pressure regulator.
I run 93 octane gas and octane booster makes no difference.
It runs great otherwise. 24 MPG highway.
I have an intermittant issue with the instrument cluster blinking off and after speaking with Gordan Killebrew at Carlisle, believe I have a bad ground.
A had oil leaking from both valve covers, now fixed, but some wire connections on the engine may need cleaned.
No ECM codes.
It has duel exhaust (no cats) that was installed before I got it.
Air pump and related plumbing deleted.
Thanks for the help.
I noticed pinging in the past and recently had the timing checked by a mechanic our Corvette Club president says is good with L98's. He could not set it at 6 degrees with the wire off as recommended without casing rough idling, but got it as close as he could.
This is the first time in a long time I drove any real distance with the roof on, radio off, and windows up so I don't know how long it has been doing this.
Other details:
1985
117,000 miles
The guy I bought it from 10 years ago said it had just had a mild cam installed. I have a receipt but could not get specs on the cam. Also at that time: valve job, new injectors, adjustable fuel pressure regulator.
I run 93 octane gas and octane booster makes no difference.
It runs great otherwise. 24 MPG highway.
I have an intermittant issue with the instrument cluster blinking off and after speaking with Gordan Killebrew at Carlisle, believe I have a bad ground.
A had oil leaking from both valve covers, now fixed, but some wire connections on the engine may need cleaned.
No ECM codes.
It has duel exhaust (no cats) that was installed before I got it.
Air pump and related plumbing deleted.
Thanks for the help.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
I would guess that you are running the stock heads which are only about a 8.5 to 1 compression. Running 93 fuel is a waste if the heads are still stock. You could be running 87 without a problem. The reason to run high octane is when you have a high compression ratio that will cause the lower octane fuel to ignite (detonate) prior to full compression.
If the cam has been changed, there is no mention of a new tune for the engine. When ever you change the cam, 99% of the time you will need to have the computer chip re-worked. Sounds like this is the case and you are running too lean.....hence the PING.
If the cam has been changed, there is no mention of a new tune for the engine. When ever you change the cam, 99% of the time you will need to have the computer chip re-worked. Sounds like this is the case and you are running too lean.....hence the PING.
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 276
From: Melbourne, Victoria, Australia
Hi the 85 vette had 9.0:1 compression as per my 85 shop manual.
Even when standard my 85 would ping with high load unless i used premium fuel. And yes the timing was spot on. It was worse at around 220F and would be ok when the engine was cool below 190F.
I have removed my 85 350 engine a few weeks ago to fit my new 383, there was a lot of carbon build up on the heads, well the engine did 170,000 miles and she looked great bearings were all good just the rings were worn out. (note the 85 vettes had TRW forged pistons standard) so a little pinging should be ok me thinks.
In the old days we used to de carbon the engine by pouring a little water slowly down the carburetor with the engine running, with the TPI its not easy as i am sure the mass airflow sensor would be really upset and because they are so expensive will cease to work
So some sort of system would need to be worked out.
Even when standard my 85 would ping with high load unless i used premium fuel. And yes the timing was spot on. It was worse at around 220F and would be ok when the engine was cool below 190F.
I have removed my 85 350 engine a few weeks ago to fit my new 383, there was a lot of carbon build up on the heads, well the engine did 170,000 miles and she looked great bearings were all good just the rings were worn out. (note the 85 vettes had TRW forged pistons standard) so a little pinging should be ok me thinks.
In the old days we used to de carbon the engine by pouring a little water slowly down the carburetor with the engine running, with the TPI its not easy as i am sure the mass airflow sensor would be really upset and because they are so expensive will cease to work
So some sort of system would need to be worked out.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
I have little information on the cam. The previous owner told me it was a mild upgrade, but nothing about the chip. I doubt it was changed.
I've owned the car for ten years and put 18,000 miles on it. It has always had a little detonation on hard accelleration, but not this bad.
Maybe it now has carbon build up which has made the chip problem worse?
Where do I get a new chip and can anyone program one without cam specs?
How much damage has been done to the pistons?
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Pull some random spark plugs to see if they are burnt. If they are bright white its lean and pinging. If they are off-white, normal in color the problem is more ignition related like old wires, poor quality wires. I had new accels cause a bad ping/knock at high temps. After doing everything else, I reinstalled the stock wires and problem solved.
Check the EGR operation as well. Ping or knock is from excess combustion temps. EGR should stop that in coordination with the ESC retarding the timing briefly.
Check the EGR operation as well. Ping or knock is from excess combustion temps. EGR should stop that in coordination with the ESC retarding the timing briefly.
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Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
When my 1986 was all stock it would ping if the water temp reached 200 degrees with 93 octane fuel. The timing was correct and the care was tuned properly and the knock sensor worked. The only way I could eliminate the pinging was to run a 160 degree stat and a 176 degree fan switch and then it would not ping at WOT. I attritributed the pinging to the cast iron heads, high water temp, and lack of quench in the stock set-up.
The bottom line is that I could not stop it from pinging until I ran it cooler, after the change the car ran great.
The bottom line is that I could not stop it from pinging until I ran it cooler, after the change the car ran great.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
Thanks for the replies!
I pulled two plugs and they were white, but I Seafoamed the intake Sunday and only drove it a couple of miles to see if that helped. Not sure how that would effect the color of the plugs. Note to self: next time trying this, park car facing wind to avoid being engulfed in smoke. There must have been carbon build up, but spark knock was still there during the quick trial run afterwards.
How do I check EGR? There are no stored codes. Do I need to pull the plenum? Maybe I should pull the EGR valve out and clean it. I can do the thottle body as well.
We gave up on the numbers and tried timing it by ear. At 6, it won't idle. Now the timing has been advanced to the point the engine will idle, but it knocks.
Pull some random spark plugs to see if they are burnt. If they are bright white its lean and pinging. If they are off-white, normal in color the problem is more ignition related like old wires, poor quality wires. I had new accels cause a bad ping/knock at high temps. After doing everything else, I reinstalled the stock wires and problem solved.
Check the EGR operation as well. Ping or knock is from excess combustion temps. EGR should stop that in coordination with the ESC retarding the timing briefly.
Check the EGR operation as well. Ping or knock is from excess combustion temps. EGR should stop that in coordination with the ESC retarding the timing briefly.
I pulled two plugs and they were white, but I Seafoamed the intake Sunday and only drove it a couple of miles to see if that helped. Not sure how that would effect the color of the plugs. Note to self: next time trying this, park car facing wind to avoid being engulfed in smoke. There must have been carbon build up, but spark knock was still there during the quick trial run afterwards.
How do I check EGR? There are no stored codes. Do I need to pull the plenum? Maybe I should pull the EGR valve out and clean it. I can do the thottle body as well.
We gave up on the numbers and tried timing it by ear. At 6, it won't idle. Now the timing has been advanced to the point the engine will idle, but it knocks.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
When my 1986 was all stock it would ping if the water temp reached 200 degrees with 93 octane fuel. The timing was correct and the care was tuned properly and the knock sensor worked. The only way I could eliminate the pinging was to run a 160 degree stat and a 176 degree fan switch and then it would not ping at WOT. I attritributed the pinging to the cast iron heads, high water temp, and lack of quench in the stock set-up.
The bottom line is that I could not stop it from pinging until I ran it cooler, after the change the car ran great.
The bottom line is that I could not stop it from pinging until I ran it cooler, after the change the car ran great.
Melting Slicks
Joined: Nov 2005
Posts: 2,736
Likes: 0
From: WAY UPSTATE NY
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
That virtually guarantees that the harmonic balancer has slipped. That's how I discovered my first one had slipped -- couldn't set the timing. The second one walked into the timing chain cover and rubbed a hole in it. Oil poured out when the engine was running.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
I pulled all the plugs and tried to feel TDC on #1 to check the balancer. As near as I could tell the line was below the scale on the After side at TDC. I guessed at 6 degees advanced from there and set base timing. This seems to have fixed the problem. The car runs great and I only hear a half second of pinging when I floor it. This is what it used to do.
Cliff, did yours end up on this side of the scale? It seems that it should be on the Before side based on engine rotation.
Will it hurt to leave this balancer on the car or should I replace it?
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 276
From: Melbourne, Victoria, Australia
This appears to be the culprit.
I pulled all the plugs and tried to feel TDC on #1 to check the balancer. As near as I could tell the line was below the scale on the After side at TDC. I guessed at 6 degees advanced from there and set base timing. This seems to have fixed the problem. The car runs great and I only hear a half second of pinging when I floor it. This is what it used to do.
Cliff, did yours end up on this side of the scale? It seems that it should be on the Before side based on engine rotation.
Will it hurt to leave this balancer on the car or should I replace it?
I pulled all the plugs and tried to feel TDC on #1 to check the balancer. As near as I could tell the line was below the scale on the After side at TDC. I guessed at 6 degees advanced from there and set base timing. This seems to have fixed the problem. The car runs great and I only hear a half second of pinging when I floor it. This is what it used to do.
Cliff, did yours end up on this side of the scale? It seems that it should be on the Before side based on engine rotation.
Will it hurt to leave this balancer on the car or should I replace it?
I now have a race type harmonic ballancer that cannot move back or forward. Re your pinging check the knock sensor wire hasn't fallen of, i was driving my 85 today and had been adjusting the timing was having your problem of heavy pinging. The knock sensor wire had come of, fixed that and it pinged the ecm retarded the timing dramatically and it dropped performance noticeably. So it confirmed the spark retard worked, have corrected the timing and all ok again. Well it is not standard anymore so i tend to adjust the timing till it just stops pinging at full throttle. if your vette had heavy pinging the ecm should have retarded the ignition dramatically like it did to my vette?
Had a couple of code 43's stored. but none since
Last edited by gerardvg; Sep 6, 2012 at 07:24 AM.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
Yes replace the harmonic ballancer when you get a chance, i had two spin and slide into the timing cover. the first you will know is an oil leak I now have a race type harmonic ballancer that cannot move back or forward.
Re your pinging check the knock sensor wire hasn't fallen of, i was driving my 85 today and had been adjusting the timing was having your problem of heavy pinging. The knock sensor wire had come of, fixed that and it pinged the ecm retarded the timing dramatically and it dropped performance noticeably. So it confirmed the spark retard worked, have corrected the timing and all ok again. Well it is not standard anymore so i tend to adjust the timing till it just stops pinging at full throttle. if your vette had heavy pinging the ecm should have retarded the ignition dramatically like it did to my vette?
Had a couple of code 43's stored. but none since
I now have a race type harmonic ballancer that cannot move back or forward. Re your pinging check the knock sensor wire hasn't fallen of, i was driving my 85 today and had been adjusting the timing was having your problem of heavy pinging. The knock sensor wire had come of, fixed that and it pinged the ecm retarded the timing dramatically and it dropped performance noticeably. So it confirmed the spark retard worked, have corrected the timing and all ok again. Well it is not standard anymore so i tend to adjust the timing till it just stops pinging at full throttle. if your vette had heavy pinging the ecm should have retarded the ignition dramatically like it did to my vette?
Had a couple of code 43's stored. but none since
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
The plastic connectors on the knock sensor wire are known to get bridle and fail on our older cars. I had to replace mine because it fell apart when I pulled it off...The best way to check if your knock sensor and associated parts are working properly is to hook up to a scanner, then take a wrench and tap on your exhaust near the sensor.. You can then see if the knock counts are registering on the scanner and retarding the timing..I have also read of people using a timing light to check for the timing retarding when the exhaust manifold is tapped with a wrench.....WW
Last edited by WW7; Sep 6, 2012 at 08:07 AM.
1st Gear
Joined: May 2013
Posts: 1
Likes: 0
My tpi just started pinging for a second under heavy load. Baught a new knock sencor, didnt make a differencs. The book said it connects to the computer but the diagram shows it going to the ignition modual and pickup coil. I dont want to open the harness to trace it . It would be great to just run it directly with a new wire. Is there a pro out there that can save me some time by helping me bypass the harness completely ?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The knock sensor talks to the ESC (Electronic Spark Control). The ESC is what tells the ECM that there are knocks occurring. In early cars it's mounted on the passenger side next to the HVAC blower motor:
Later cars (I think starting in 1990 -- don't know exactly) have the ESC module mounted on the MEMCAL in the ECM (on the left):
Later cars (I think starting in 1990 -- don't know exactly) have the ESC module mounted on the MEMCAL in the ECM (on the left):