L98 Pinging Problem
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 804
Likes: 5
From: Fresno CA
L98 Pinging Problem
I just replaced all the gaskets on the top end of my 85 L98 car and put it back together and timed it (6 BTDC) and checked fuel pressure (38 psi) and it runs great..except when the engine temps are below about 170 the engine pings really bad at WOT..if you drive it for awhile and it gets warmer..like above 170 or 180 then the pinging goes away...no codes in the computer either...any ideas?
Instructor
Joined: Nov 2002
Posts: 107
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From: clarendon hills il
EGR problem?
Check your egr system. My 91 would ping at WOT because my EGR was not opening. In my case I did have a code, but maybe your case something is malfunctioning that does not throw a code. I would for starters check all EGR hoses and put a vacuum pump on the egr valve to see if holds vacuum.
good luck
good luck
Pro
Joined: Jan 2005
Posts: 686
Likes: 62
From: San Jose Ca
Originally Posted by howdo
Check your egr system. My 91 would ping at WOT because my EGR was not opening. In my case I did have a code, but maybe your case something is malfunctioning that does not throw a code. I would for starters check all EGR hoses and put a vacuum pump on the egr valve to see if holds vacuum.
good luck
good luck
Instructor
Joined: Nov 2002
Posts: 107
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From: clarendon hills il
Maxlean,
You're right. Putting the vacuum pump on the egr valve will not work if it is a negative backpressure type. Also, thinking back to my problem of pinging, I now remember it was really at moderate to hard acceleration, not wot. After replacing the egr valve, the pinging went away. You got me thinking, so I checked my Saturday Mechanic book: "A defective EGR system will almost always cause spark knock". It sounds like the reason is due to the higher combustion chamber temps.
Anyways, I know there are other possible causes ( incorrect ignition timing, etc) but I still think it would be a good idea to check the egr function.
You're right. Putting the vacuum pump on the egr valve will not work if it is a negative backpressure type. Also, thinking back to my problem of pinging, I now remember it was really at moderate to hard acceleration, not wot. After replacing the egr valve, the pinging went away. You got me thinking, so I checked my Saturday Mechanic book: "A defective EGR system will almost always cause spark knock". It sounds like the reason is due to the higher combustion chamber temps.
Anyways, I know there are other possible causes ( incorrect ignition timing, etc) but I still think it would be a good idea to check the egr function.
Team Owner
Joined: Sep 2003
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
Originally Posted by 85 500 horse
Also, make sure you're running super unleaded.
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Safety Car
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From: Glenbeulah Wi
You need to check your computer chip to see what temperature the knock sensor is enabled at. On GM cars the knock sensor is disabled until the temperature reachs a pre set temperature. That temperature is usually in the low 100's. It sounds to me like you have a non stock chip that may be disabeling the sensor until the water temperature is up to 170 degrees. This is only a educated guess there may be other reasons why this may happening.
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Cruise-In I-II-III Veteran
Originally Posted by eguyett1985
I'll look at that this weekend. The car has a Hypertech Thermomaster Chip in it with a 160 stat and 4026 secondary fan switch.
You have an '85 and a Hypertech chip? I know for a fact that the hypertech chip for that year has way too much timing advance in it. Do you still have the stock chip? If so, swap that into it, reset the ECM and see how it runs.
Also, check all your vacuum tubes. I had a broken one that went to an EGR switch on my '90 and had massive pinging problems. I went from being able to use 87 octane fuel with no pinging to pinging even when using 93 octane. After discovering that broken tube, and fixing it, so far no more pinging. I had even programmed my chip with a lot less timing advance trying to compensate. I put the stock timing back in and still no pinging. I'll put regular gas back in next tank and see how it does.
The vacuum tube on my '90 is a little different than what is on your '85, but check them all out, especially the one leading to the EGR under the plenum and anything that connects to that tube.
