Pete L

Question is on A/F ratio I should see on my wide band A/F gauge @ idle and when running. I believe car is running a bit rich

Car - 86 early 5 speed with X pipe and Porken chips (s4 version), 87 s4 FPR, two fuel dampers have no evidence of raw gas or fuel smell and hold vacuum. T2 sensor checks with R value at LH. MAF recently rebuilt by injection labs.

Set idle A/F to 14.5+/- with O2 disconnected. Able to adjust A/F between 12:1 to 15:1 with MAF @ idle.

Reconnected O2 and A/F went from 14. 5 to 13.5:1 +/- ie richer. When driving, seeing 13.5:1 ie rich. Suspect O2 sensor.

Comments and expertise of the list appreciated

KenRudd

I don't have any firm answers for you, but here are some related threads:
https://rennlist.com/forums/928-foru...n-at-idle.html
https://rennlist.com/forums/928-foru...-85-86-us.html
https://rennlist.com/forums/928-foru...lh-system.html

KenRudd

Curious: What kind of gas mileage are you getting?

davek9

What I see on my 85 is cold start up around 13.7, once warm not hot but out of white strip on guage
I see the AFR go to 14.5/.7, crusing it's at 14.7 ( no throttle input).

I'll be installing wide band guage on the 86.5 this Spring, that one has Ken's chips.
sorry this may not be what u needed, the point i wanted to make is you should see a change during warm up
Also I think you meant to say chips are S300 (version 4), I think Ken is working on an S4 set for the 928 S4

Pete L

appreciate the responses. Still stumped

This weekend installed a new O2 sensor, oil change, set MAF to 14.7 on the A/F meter with O2 disconnected and pulled plugs (that were clean and look to me to be running lean, not rich). I checked ohms from MAF at computer after setting idle A/F via meter to 14.6:1 and interestingly was at 390 ohms, the starting point Ken usually recommends

Started car up, showing 13.9 to 14.2 at idle with O2 hooked up, under cruise and gauge continue to show mid 13s and it shows 11.8 to 12:1 when floored

Maybe my A/F guage needs calibrated? I am going to try this later and will post if it clears the mystery

davek9

IMHO, those numbers are a bit rich, hot idle, I see 14.7 - 15.ish
Fuel injectors and reg/ dampener's new/good ?

Edit: I re-read the thread, I see that you have checked the above.