Help! 1988 pinging

[David Parker]

My 1988 Vette pings all the time when I accelerate medium to hard. I use premium gas and it does the same. Where do I start to solve this? Also only 51000 miles on it

 

[DonB]

My 1988 Vette pings all the time when I accelerate medium to hard. I use premium gas and it does the same. Where do I start to solve this? Also only 51000 miles on it

What is the base timing set to? I believe spec is 6*BTDC. My '90 is at 8* with no issues, but I like a little more advance. I check mine with engine cold(closed loop) before the computer takes over. You will need a timing light. Also try a different gas station. All premium gas is not the same. You might also try an octane fortifier but not till checking all the obvious things.

 

[Hib Halverson]

There are a number of reasons why the engine may ping.

Combustion chamber deposits
Poor fuel
Knock sensing not working properly

...are a few.

Is the check engine light on?

What is the base timing set to? I believe spec is 6*BTDC. My '90 is at 8* with no issues, but I like a little more advance. I check mine with engine cold(closed loop) before the computer takes over. You will need a timing light. Also try a different gas station. All premium gas is not the same. You might also try an octane fortifier but not till checking all the obvious things.

The above demonstrates a misunderstanding of how the L98 spark timing works. After start-up, once the engine is running, even in closed loop, the computer controls spark timing. The procedure discussed, ie: set "base timing" with the engine running in closed loop, is not correct. You set base timing by disconnecting the "timing connector". Also, "base timing" is not the same as "initial advance" on a non-computer engine. With L98s the spark timing is determined by the calibration in the ECM, not by base timing, so when you set the base timing to 8°, you're not getting two more degrees of total advance. You only get the total advance which is in the calibration. All you'd done is decrease the amount of spark timing change the computer makes. That is, if you add 2° base timing, the computer will add 2° less spark to get to its calibrated spark value.

As for octane boosters, most of them are not capable of any useful increase in octane and the ones that are will damage your engine over the long term. Bottom line: don't use them.

 

[David Parker]

pinging

The service engine light comes on and then is off the next time I start it

 

[kpic]

Go here: L98 timing procedure - just want to make sure... - Corvette Forum

Post #4 and click the link.

 

[kpic]

David,
I hope it works for you.

 

[DonB]

There are a number of reasons why the engine may ping.

Combustion chamber deposits
Poor fuel
Knock sensing not working properly

...are a few.

Is the check engine light on?



The above demonstrates a misunderstanding of how the L98 spark timing works. After start-up, once the engine is running, even in closed loop, the computer controls spark timing. The procedure discussed, ie: set "base timing" with the engine running in closed loop, is not correct. You set base timing by disconnecting the "timing connector". Also, "base timing" is not the same as "initial advance" on a non-computer engine. With L98s the spark timing is determined by the calibration in the ECM, not by base timing, so when you set the base timing to 8°, you're not getting two more degrees of total advance. You only get the total advance which is in the calibration. All you'd done is decrease the amount of spark timing change the computer makes. That is, if you add 2° base timing, the computer will add 2° less spark to get to its calibrated spark value.

As for octane boosters, most of them are not capable of any useful increase in octane and the ones that are will damage your engine over the long term. Bottom line: don't use them.

Hib, thanks for pointing out my shortcommings understanding the L98 system. I guess I'll have to dive deeper into my service manual. I just did a total rebuild of my '90 350 L98 and she runs real strong. I must have "lucked out." Most of my overhauls had points or electronic ignition, quite a few years ago. This is my first Vette. My 60 year old fling. I bought it in March with a bad engine. I am humbled to be in the company of such experts