barks944

Looking further it seems your getting backfire at 1500 rpm, I don't get that problem. Certainly other than that my car is similar to yours. Asside from the backfire being strange I dont think you have a problem.

beebone

So what about your car setting?
Do u guage the AFR?

beebone

Finally give up to adjust close to 14.7 at idle. I let the AFR stop at 13.2-14 at idle, I can't find the right point to balance the AFR at idle and backfire when off throttle. I think the vacum may have some leaks, but find out later on.
So now, the AFR are:

- idle: 13.2-14.0
- touch of throttle: 13.2
- mid load turbo just spool: 12.5
- heavy load: 12.5-11.5
- off throttle: 14s w/o backfire now

Sounds good?

fbgh2o

I am by no means an expert... but it sounds a bit rich...

beebone

Not a problem, just a talk.
I feel like the pick up is fine, rock solid turbo spool and full boost to the red line, I'm running 23 lbs boost, but the idle T______T

schip43

Do you have an adjustable FPR, it does seem a little rich at idle, so I think that would promote the popping under light low, throttle lift off so it should be coming from the exhuast? Have someone follow behind you at night and see if they see flames?
Sounds cool to me!

beebone

I got no adjustable FPR.
Yes, the pops just under light load, off throttle from the exhaust (I'm sure).
I think its not loud enough to be a flame, just few pops, thats it all.

beebone

I finally found the thread from 930 turbo forum

https://rennlist.com/forums/911-turb...ting-afrs.html

"With the IA fuel head, it is possible to tune the idle to 14.5 AFR (0.2 %CO) and still have enough fuel under boost at redline. Then you can adjust the cold control pressure to richen cold starts. For cold starts, an AFR of around 11 to 12.5 (9.4 to 5.3 %CO) should do the trick depending upon your climate. The mixture will immediately begin leaning out from there as the heating element inside the WUR warms up."

My 89 951 is EU spec, the CO is 1.0-1.5% (w/o cat), compare the US spec with cat, the CO is 0.6%, this is I think the US car has leaner AFR at idle, I guess its 14.7. Thats why mine can't reach 14.7 at idle.
So what is the AFR of CO 1%? It is around 13.2?

schip43

Ok so it is a little rich by US specs. I don't know the CO at idle but maybe someone that's done a smog could tell you. I'd get a 3 bar FPR anyway. Then you could adjust the idle to 14.7 if you want the mileage would be a little better anyway.

But it does look like it's all good!