Backfire between shifts

[SBDSM]

I was wondering if anybody could give me any pointers as to why our cars would backfire between 1-2 and 2-3 shifts with the following information:
-It doesn't happen all the time, just once in a while
-HK$ is vented back to intake
-Zero boost leaks
-I don't think it's the injectors because it happens with both the stock injectors and new 750's

Hmm, if you need any other information I'll gladly provide it. I just really need to figure this out because I need to pass emissions and I think this is the problem (the thing I'm failing is high HC's).


Thanks guys

 

[Defiant]

Possibly an exhaust leak, such as a cracked header, O2 housing, or pipe flange gasket blown.

 

[SBDSM]

Originally posted by Defiant
Possibly an exhaust leak, such as a cracked header, O2 housing, or pipe flange gasket blown.

All right I'll check that out. Before I did check that, but just did a quick visual inspection looking for huge cracks and making sure all bolts were torqued down correctly....
What's the best way to check for exhaust leaks? What I heard before was with the car on, have a friend cover the exhaust with a piece of plywood REALLY quick, like less than a second, while you are under the hood looking for an exhaust leak. I'm kind of scared to do this though. Does anybody else have a good technique for looking for not so obvious exhaust leaks?

 

[Defiant]

Get 4' of vacuum hose, hold one end to your ear and start going over the system with the other. When you find a leak, it'll sound like an F-14 going over. Do it with the idle around 2K.

 

[SBDSM]

Originally posted by Defiant
Get 4' of vacuum hose, hold one end to your ear and start going over the system with the other. When you find a leak, it'll sound like an F-14 going over. Do it with the idle around 2K.

Cool thanks. I do that for those hard to find intake leaks

 

[Defiant]

If you have a compressor, you can also plug the intake and give the tailpipe about 15-20psi, and listen.