i have a s4 TII. i noticed sometimes when cruising at around 2k-3k rpms in like 15" of vac i get a really lean condition. jumps from 14A/f to sometimes 17A/F! then a sec or two later it goes away and A/F drops back down to normal. i dont know why its doing it. any thoughts?
fuel filter was changed bout 3 or 4 months ago (only use 93 octance)
have a fd fuel pump
have tried 3 different ecus and the samething
replaced TPS still the same
i have a crane cam high on leading coil (maybe has something to do with it?)
removed emissions but keep twin scroll (" ")

 

Is your 02 sensor connected? I'm betting it isn't and if you reconnect it you won't see those high figures again.

 

Yes I have a connected narrowband sensor also. Bosh replaced on may

 

Seems if the 02 was connected and you were cruising, then the ECU would go into closed loop and pull those 15afr figures down to the 14.7 afr area.

I've no idea why then your afr go that lean. SAFC leaned out too much?

 

no safc. no fuel mangment at this time, it goes up high 16's or low 17's sometimes for a sec or 2.

 

Is it during slight downhills, or where very very little throttle is needed? because there is a spot where it cuts fuel to the rear rotor. This may cause a very lean reading?

 

Just a thought, have you done the fuel pump mod? try checking the voltage to the pump at low rpms it could be that your not getting enough voltage to the pump. Our cars are old and so is everything in them ( wires included :b). I had this problem twise before first time was a bad fuel pump, second time was a wrong setting on my SAFC II.

 

Its not during downhills its on like normal streets. Ya I might have to check the voltage to the pump, I didn't do the rewire mod yet.
Its under very little throttle though....

 

My TII does the exact same thing. Only thing I haven't tested or replaced is the AFM. To the best of my knowledge the rear rotor has fuel cut at the rev limiter.

 

ya me either but its not even near readline hehe.
wat else have you tried?

 

Bah I think you're worried about nothing.

 

If you're under vacuum going lean is OK.

 

It's likely a misfire. Check the condition of your plugs/wires.

Don't worry about it though...Only an issue under boost.

 

Not worried, just curious on what is causing a situation that previously wasn't there. Mine is enough to cause surging in some cases.

xboxthug13b,
I have checked plugs, wires, TPS (cleared it up a little), and Vacuum leaks.

 

So a misfire would cause the A/F to jump up? Lean under vac is good but not when it jumps up suddenly and goes back down!
I have replaced plugs aaron cake but not wires yet, ill be doing that next.
If I remeber correctly (gotta recheck) narrow band would read full rich I think.

 

A misfire will cause a momentary lean reading.

 

o interesting! also my car has been running terrible rich i think. i dont beat on the car and im getting 170 miles to a tank with stock primarys...

 

Attached is a jpg of a Palm connected to a Zeitronix wideband.

The car is in fifth gear and the 02 sensor is connected up.

In the left hand display it shows AFR. Just under the AFR you see two figures. One is the high and one is the lowest afr while cruising and the 02 in closed loop.

Make of it what you will.

 

Mines reaches 17s

 

I still wonder if your 02 sensor is functional or not. Sorry, no offense meant.

 

Its a bosch put in new on may. Maybe I can find some old rtek datalogs for u to see?

 

If you have a RTEK 2.0, then if you go to the Diagnostic page, it will show if you have a failed 02 sensor. I know that because I did that on my car the other day just to check it out with your figures and sure enough it showd the 02 not connected.

Bad workmanship on yours trulys part. Done did pull that wire flat intwo sometime. When? Got me.

That said, I had a problem with my other car with high afr during steady state driving. So I found if I went to the fuel bars and added fuel to the MINUS boost figures (like minus 2, minus 4, minus 6) for the first three bars, then that high afr at steady rpm went south.

 

i HAD rtek 2.0 and it didnt say that, was doing it tonight at around 3,500rpms. not boosting dont know why.

 

here are some old datalogs

 

and now sometimes when i floor it the car bogs and then takes off, also my 3800 transistion isnt smooth at all (maybe because of bigger secondarys?) i have reground the grounds, cleaned ground on batter, starter and the one by strut tower.