Backfire thru the tail pipe

alsz71 · November 17, 2001

This started about a week ago with the truck at work, as you drive under very light lengine load around 2000RPM the truck starts to backfire through the tailpipe and stumble as though the timing is way off. The boss figured it was the cats and had them removed using a bypass harness for the second set of O2 sensors(they apparently fool the computer into thinking that the cats are still there) after doing this I took the truck for a drive and was very impressed with the increase in power....however , the backfireing problem was still there. He seems to want to go after the muffler now but I'm thinking that he's just wasting his efforts on (exhaust)pipe dreams and guesses. I tend to think that the problem is either something as simple as a plugged fuel filter or a engine sensor specifically the TPS thats gone haywire. THe truck didn't set a code and thats what has me puzzled though. Any thoughts or inputs ??

kctrading · November 17, 2001

1st it's best to do a back pressure check before and after the cats...a lot easier than replacing parts!

Here's a good tester for $35!

http://www.mytoolstore.com/toolaid/diagn04.html

Also I would find someone (like me) who has a scanner and check all your sensor readings...esp a lazy front 02 sensor...also make sure your wires and plugs are not breaking down and arching....you can check for arching by getting a spray bottle with water and spray the plugs/boots and wires...the water lowers the res. and will cause a arch if there is a problem...also your computer will store history misfiring and you can check that as well if you get a scanner hooked up.

Ken

http://www.kctrading.net/sierra/