O2 Sensor Issue, Popping/Backfiring
 

I installed a GHL CAT bypass pipe along with a new O2 sensor on my '85 911. Actually it was a O2 sensor that was Bosch 13913 from a Ford that they said was compatible. I've been running with a Borla 1in and 4out for some time now. The GHL is new.

http://forums.pelicanparts.com/showthread.php?s=&threadid=307164&perpage=20&highl ight=ford%20o&pagenumber=2

Ok, so with the O2 sensor hooked up I get LOTS of very noticeable popping and a couple times a VERY loud pop that actually shoots flames. You can see them after dark. That was actually kinda cool. Anyways, if I disconnect the O2 sensor everything smooths out and there is very little popping sounds.

I would assume a little bit of popping while decelerating or downshifting would be normal but not that much. The car almost feels out of time.

Should I try another one or get the OEM part or disconnect it all together?

Any thought's or ideas would be greatly appreciated.....

Double check your gaskets for proper sealing. These aftermarket units need some massaging to fit well. I just installed a DEC and had to do a little tweaking on the flanges to get them to sit flat on the header pipe flanges. I cinched those pretty good before negotiating the cat onto the muffler. If those gaskets are leaking, you will get popping. Since the car ran fine before, it has to be this or the O2 sensor. I used the same ford sensor and it's fine. I'd wager on the gaskets leaking. If you take the cat back off, you will see where it leaked. Best to correct this and then install another new set if that is, in fact, the problem.

Listen to me, I've had a 3.2 for 40 days and I'm giving advice. ;)

Yes, exhaust leaks near the O2 sensor can increase the oxygen content of the exhaust and fool the DME into leaning out the mixture, hence the pops. Check it carefully. You can do this while running (to begin with) by carefully passing your hand over the flanges to feel for gases escaping. Good luck,

ianc

Edit: I would say to check for leaks both hot and cold...

Ok, tomorrow I'll check for leaks and report back.... Thanks guys!

Decel Valve
 

I have an '83 w/CIS so this may not apply but...

I installed a cat bypass pipe and a home modified dual out muffler. I had some high idle issues and found that my Decel Valve was sticking. I have disconnected the vacuum line to the valve which has fixed the high idle problem but have found that my car pops on deceleration (while in gear).

For consideration,

Good luck, Gordo

No decel valve on DME cars, but thanks for chipping in Gordo,

ianc

Well I started the car and felt for leaking but didn't feel anything. So I just tightened down all the flange bolts just in case. Believe it or not it made a difference. Not completely fixed but it doesn't pop hardly at all now. Only when I downshift with lots of RPMs, but I would think that's normal for my set up. Correct?