91 C4...relatively new to me...

The weather here has gotten summery (85-90 F) and I notice that the car has started pinging a fair bit. I run 92+ octane... aftermarket chip due to a L/F (previous owner)

The only other change is that I had to go from headers/no cat to the full stock system to pass emissions... I also changed the oil in the process.. but i can't see how that relates...

Could the pinging be from the more restrictive exhaust? Or does the chip need to be adjusted? Or do I need to just run at higher revs? Pinging is usually in 2nd/3rd gear below 2500RPM

 

The first thing you need to do is swap your aftermarket chip for the original and see if that fixes your problem! And if you have the opportunity you should also drive around with a Bosch Hammer and watch for knock sensor activity. The regular octane fuel available at gas stations on most of the west coast does not support advancing the timing a whole lot beyond stock. The easyist way to check this is with a Bosch hammer but most don't.

 

You will likely find your knock sensor is bad. Not cheap to fix unless you are brave enough to do it yourself. My knock sensor is bad and I get pinging with 92 octane but if I run a mix of 101 octane and 92 octane I get zero pinging regardless of temp.

 

Are you using an aftermarket chip or the original EPROM? If your knock sensor has failed (there are no moving parts so it is likely to be the connection to the knock sensor that has failed and not the sensor itself...) and the CEL is illuminated the ECU will automatically retard the ignition timing by 6 degrees. So if the engine is still pinging with 92 octane and you're running the stock chip there is probably something else that is causing your problem. With the factory ignition timing and a healthy engine there should be zero knock sensor activity.

 

Did you check the alternator belt? When my belt went bad during a drive to work, i knew it had happened by a slight loss of power and pinging under load. Good luck.

 

Sounds like the chip. I've heard numerous accounts of modified chips making the engine ping. The compression ratio on these engine is relatively low, so I would not ever expect to hear pinging on these engines.

If you decide that you're not going to change the chip or timing, then I would also pull a plug to make sure it is the correct model number and heat range. After you pull the plug, if you notice that you have a great deal of carbon buildup, I would run a can of BG44k through your tank and see if that makes a difference.

 

I have the aftermarket chip. I also know the knock sensor is bad from code dump during service. I am just lucky to live right next to race track so I have easy access to race gas. Spendy, but my girl luvs to drink it. Very noticable difference between only 92 octane and probably what is more like 96 to 98 with mixing 101.

 

You should also check your distributor belt. When mine broke, the car pinged very easily.

Edit: Even after I dumped in a few gallons of 110 octane gas on top of the normal 92 octane.

 

not only check the belt as Rob suggests but also check that the belt hasn't jumped a tooth. there are small markings just before the tabs on the distributor housing which help you check the timing refer to -pg 428 of Adrians book.

Hope this helps
Bill
90C2

 

Funny that you mention pinging....I've also noticed mine do it recently under load. I bought an aftermarket chip for it last summer....and I know it wasn't doing it before. I thought that maybe it was just cheap high-octane gas I was buying....

Maybe I should go back to the stock chip...

 

I noticed slight pinging in mine as well over the last few weeks here in Portland with the warmer temps. Stock chip and exhaust. It is not too often, just occasional under load. I better check the distributer belts as well.