Funky A/F ratio problem-HELP!
Thread Starter
Melting Slicks
Joined: Jul 2004
Posts: 2,826
Likes: 39
From: Central NJ
St. Jude Donor '05-'06-'08-'10
Funky A/F ratio problem-HELP!
My car has been tuned and retuned both with traditional and speed density and continues to have unexplainable periods of crazy A/F ratio changes. It generally occurs after a cold start within the first few miles of driving. No one has been able to figure it out. The car just suddenly goes to like 18:1 for a few seconds, then returns to normal. There are also some problems with it switching to closed loop. O2's are new and functioning properly. No other obvious problems. The car has all the "bolt ons" and a G5x3 cam. (no head or intake work). I'm considering a new PCM, but wanted to see if anyone ever saw this problem. 
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
Thats weird...I just installed my AEM wideband (yesterday evening) and noticed pretty much the same thing. On a cold start it went to ~18:1 for ~10-20 seconds. Don't have much useful information since I have not started to tune it with the wideband.
Instructor
Joined: Sep 2005
Posts: 170
Likes: 1
From: Newcastle OK
If you have a tuning program at your disposal, I would start with checking this table in your calibration:
B3605 Commanded Fuel when in Open Loop
There might be a weird spike or something in there.
HTH,
Brent
B3605 Commanded Fuel when in Open Loop
There might be a weird spike or something in there.
HTH,
Brent
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
Holy crap! I didn't know that table existed. I just got my wide band and am getting ready to re-do my VE and MAF tables. This would have thrown me off big time as I will force open loop to tune. I don't see any sort of weird spike in that graph in my tune or the stock tune althought there is a small bump in the 104-122 degree range. I need to go through and set that table to all 1's, a least for anything over 170 degrees.
Once I get the wide band tapped into my HPTuners via the AC pressure switch I will do a cold startup log and see if a weird AFR is being commanded.
Once I get the wide band tapped into my HPTuners via the AC pressure switch I will do a cold startup log and see if a weird AFR is being commanded.
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Instructor
Joined: Mar 2000
Posts: 230
Likes: 0
From: Brandon, SD
Mine does the same thing. Cold start, WBO2 reads 14.7+/-, then in about 20 seconds, closes the loop and reads 17, 18 19 sometimes lean. After driving for a minute or so, back to normal at 14.7+/-.
Thanks brentg454, I will look into B3605 Commanded Fuel when in Open Loop. Does this table have a temperature dependent on it. I also have a hot starting issue in the summer, where the car stumbles to a start - only when engine hot and temperature outside hot (over 80 outside).
Robi
Thanks brentg454, I will look into B3605 Commanded Fuel when in Open Loop. Does this table have a temperature dependent on it. I also have a hot starting issue in the summer, where the car stumbles to a start - only when engine hot and temperature outside hot (over 80 outside).
Robi
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I your fuel pressure at cold start NORMAL?? Could be that you are being leaned out because your fuel pressure isnt high enough at cold start. Just something to think about and maybe check just for grins. Do you have any codes???
I also agree about the AIR Pump. That runs at start up for a few seconds.!!
BC
I also agree about the AIR Pump. That runs at start up for a few seconds.!!
BC
Instructor
Joined: Sep 2005
Posts: 170
Likes: 1
From: Newcastle OK
[QUOTE][I also agree about the AIR Pump. That runs at start up for a few seconds.!!/QUOTE]
Right on fellas, that sounds like a likely culprit. Try to turn it off (B0201 or use the bi-directional controls) and see if that makes a difference.
Robi, the B3605 table does in fact reference the coolant temperature. You might also check out your closed loop enable temperature (B4205).
Good luck,
Brent
Right on fellas, that sounds like a likely culprit. Try to turn it off (B0201 or use the bi-directional controls) and see if that makes a difference.
Robi, the B3605 table does in fact reference the coolant temperature. You might also check out your closed loop enable temperature (B4205).
Good luck,
Brent
Instructor
Joined: Mar 2000
Posts: 230
Likes: 0
From: Brandon, SD
Thanks brentg454!!! Will check it out.
BTW, my FP is always above 50 - I always insert key, turn to on but not start, watch the gauges come to steady state, then start the car. I have heard that doing this also helps with letting all the computer crap do its thing and not get interupted - and this is good. I don't think its FP, but thanks for the suggestion.
BTW, my FP is always above 50 - I always insert key, turn to on but not start, watch the gauges come to steady state, then start the car. I have heard that doing this also helps with letting all the computer crap do its thing and not get interupted - and this is good. I don't think its FP, but thanks for the suggestion.
Racer
Joined: Jul 2006
Posts: 447
Likes: 0
From: San Jose Ca
Originally Posted by 5 Liter Eater
I confirmed it's the AIR pump. I commanded the air pump off after a cold start when my AFR was ~18:1 and it instantly went back to stoich. 
Originally Posted by muncie21
I believe the air pump goes on in an attempt to heat up your O2s faster.
