A/F ratio lean

[rattle_snake]

I have noticed that my AFR has gone up (lean) over time. Tune/combo hasn't changed in years. I have a wideband gauge and keep an eye on it as much as possible. I tried a full pull thru 2nd gear today and the AFR starts in the 11's as expected but goes up as RPM increase. I shut it down as quick as possible, was climbing to 13 around 5k rpm. Planning to take a datalog with the usuals including fuel pressure, FPDC, ect. for at least the lower rpm range.

Car has a pre-FPDM BAP, stock pumps & injectors, 2.8 upper. I had plugs out and check gap about 1k miles ago. Fuel filter has <10k on it. Last data log was a few months back and was lean. Battery was shot, and after replacing battery AFR was more or less back to expected. Re-calibrated wideband sensor when trans was out about a year ago.

What else can I look at? Pull the MAF and inspect? Anything else?

 

[01yellercobra]

Check your voltage under WOT. I had a weak alternator that would drop voltage on the top end. Swapped it with a high amp alternator and it stayed over 13.5 all the way to red line.

 

[rattle_snake]

I have taken 4 data logs at different times and looked through them. I cleaned the air filter and MAF. Car still pulls strong, without gauge I wouldn't know its dangerously lean. Battery voltage is weak, as low as 11.0V on one log. Usually when alt or bat is low car runs weak.
Fuel pressure seems all over (33-45), but I looked at the logs from 2 years ago before and after the current tune and they are about the same. The top end is lean, also (sometimes) where bat voltage is low. Fuel pump DC is as expected.

As any terminator owner should, I have a spare alternator to swap in and retest. Battery is new. Charging system wiring has the 'big 3' and has no corrosion.

 

[MalcolmV8]

Battery voltage is weak, as low as 11.0V on one log.

Fix this first or you may be chasing your tail in circles.

 

[Brutal Metal]

buy a new alternator cause 11 volts at WOT is gonna surely effect your fuel flow..

 

[rattle_snake]

Agreed low voltage is an issue and will try alternator #2 first and report back

....but the fuel pumps are on a voltage regulator (BAP) and it doesn't care what battery voltage is. As long as there is enough current the BAP's duty cycle will compensate to get 17V output.

As many know the FPUMP_ACT_VOLTS' in a datalog is not that at all, and is a calculated value. There is no analog feedback wire out of FPDM to ECU A/D.

Thinking of wiring the 2nd analog input channel of the SCT to the BAP output (with voltage attenuator as 17V is too high for SCT input) and see what is really happening.

 

[MalcolmV8]

There's more than just a BAP needing voltage. Injectors comes to mind. Also just because a BAP can take 13.6 volts and make 17 doesn't mean it can take 11 volts and make 17. Like I said earlier you'll be chasing your tail with voltage issues. Fix that first so you have a solid foundation to work from and go from there.

 

[rattle_snake]

There's more than just a BAP needing voltage. Injectors comes to mind. Also just because a BAP can take 13.6 volts and make 17 doesn't mean it can take 11 volts and make 17. Like I said earlier you'll be chasing your tail with voltage issues. Fix that first so you have a solid foundation to work from and go from there.

Thanks for the feedback, didn't think about the injector coils (or ignition coils). as Vbat drops they need more and more current to energize... I certainly hope the BAP can regulate and deliver 100% of it's rated output (30A for the '40A' version) down to 11V, if it can't it's a terrible design for it's application.

I installed a fresh alternator last night, didn't log but A/F gauge seems to report as-expected values.

 

[rattle_snake]

Took logs of a few pulls, and things look better.

Note on this pull the AFR is somewhat inversely correlated to battery voltage, as it goes below ~13V:

But this pull 60 seconds later it doesn't, as bat voltage stays higher....

 

[Nukem1040]

What alternator did you go with? This might fix my exact problem I'm chasing right now. Car has slight spuddering from 2500rpm to 3500rpm under boost. Car was hardly ran for the last few years and put away in the winter. I have topic going on, http://www.svtperformance.com/forums/showthread.php?1069708-Spark-plug-gap-with-pulleys if you want to look at my problems.

 

[rattle_snake]

What alternator did you go with? This might fix my exact problem I'm chasing right now. Car has slight spuddering from 2500rpm to 3500rpm under boost. Car was hardly ran for the last few years and put away in the winter. I have topic going on, http://www.svtperformance.com/forums/showthread.php?1069708-Spark-plug-gap-with-pulleys if you want to look at my problems.

I had the factory ford unit rebuilt locally. Low voltage may be your issue and it is a good idea to check it. If you don't have a tuner with logging capability, a $20 Bluetooth ODB adapter can be used as well.

 

[Nukem1040]

Great! Thank you. Didn't know they made these. I'll pick one up at sears. I checked my voltage before and after starting and works as it should. I didn't check it while raising the RPM. I'll do that this week.