beebone

Hi guys,

I've asked about the AFR to rich at idle beofre. So now, the AFR can reach 14.7 at idle now.

But off throttle in low rpm when it start to show the AFR 15.4 - 14.7 (normally it show "- -" because of off throttle), and I heard few backfire. So is it normal? or I should I adjust the AFM bypass screw a little bit rich?

Here is more info and what I found while driving:
-Idle: AFR 14.7
-light throttle on curising: AFR 14.5-13.9
-50% throttle when turbo spool up: AFR 12.5
-Full throttle and full boost: AFR 11. something
-Off throttle at high rpm: AFR - -, because injector off
-Off throttle at low rpm (under 1500 rpm - idle): AFR shows 15.5 very fast and backfire, then down to 14.7

fast951

Is the backfire from the intake (lean) or from the exhaust (rich)?

beebone

From the exhaust, just only few.

fast951

A backfire from the exhaust means a rich mixture. However, based on your AFRs (15.5:1) it is not rich, but a bit lean. Are you sure the popping is not from the intake side?

schip43

What chips are you running? I have a set of Guru Chips 18 psi that the previous owner reported would run rich off throttle and light flames out the back! Sounds cool but I have the Max chips and no flames!

beebone

Got it. May be adjust the screw a bit rich and see how it goes, thanks!

beebone

ProMax from UK.

beebone

So turn a screw a little ( 1 turn), the ARF when off throttle in low rpm still showing 15 very fast then back to 14.7. I still can hear the pop.

The car is very smooth in crusing and turbo spool, only the pop started when let say 1st gear rev to 3000, then shift to 2nd gear (I think the rpm is around 1500), then off throttle. the AFR guage show "--", then 15 just a show up (few pops coming at the same time), then return to 14.7.
So u guys think is it harmful to the engine?

schip43

Is it rich or lean at WOT? Can you data log?

Hmm,reread your info, it might just be the chip? Your AFR looks OK at WOT, as long as your not lean under load you should be Ok. Maybe someone else has the same chips and give you their observations?

beebone

WOT is around 11.5.
No problem on high rpm and WOT.
The only above problem is only on low rpm and off throttle.

beebone

I tried to adjust the AFM screw rich a bit, everything fine now. Except 1 thing!!!!

When downhill, off throttle at low rpm (e.g. 1100-1500rpm), the AF guage shows 17, 16s, 15s. Then I hear the pops coming out. Any idea?

schip43

It sounds normal to me. I 'd called your chip guys and ask them or maybe try another chip. But as long as your not lean under load you should be ok.

beebone

Yes, its abso. normal under load.

Slight throttle 13.2, more load 12.5, WOT 11s

barks944

Got the same chips as you beebone and my car is very similar. Does backfire now and again. The 944's injection system can be a little slow to respond at times.

Car will run lean off throttle above 2k rpm as the DME shuts of fuel for economy.

beebone

So your car is EU spec w/o cat? Did the problem solve yet?