Hey guys, its been a while. my 97 expy is starting to ping under a load. it sounds like a bad timing type of ping. i know the timining is not adjustable (that i know of) any ideas?

 

It could be due to carbon build-up, a bad EGR valve, bad gas, or a bad knock sensor.

 

I haven't had a chance to put a scanner on it yet, what should I look for? It is throwing a code for a bad cat, could that have anything to do with it?

 

Yes, a bad cat can throw the air/fuel system out of whack and cause pinging.

 

is there a way to remove carbon without pulling the heads?

 

Yes but it's a slow process that has to be done over a long period of time by using fuel cleaners or by installing a vapor bottle.

 

. what about running seafoam through the vacuum line every so often? ill have the code reader on it later tonight. ill post up what i find. thanks

 

i only pulled 1 code. 0420-catalyst system efficiency below limit,bank one. help me out, where to begin?

 

Check into either a bad cat or a bad downstream O2 sensor on the passenger side.

 

Will do. I have a feeling it is the cat because it threw a code for that a while back, but it was after she filled up with ethanol. That code never came back and was the first code we had in months. Should I just throw an 02 sensor in it and see what happens?

 

IMO, it's less expensive than changing the cat.

 

I had the same problem and posted some things I did maybe it will help. The thread name is Expedition 1997 strange sound getting worse