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LTFT and FPDC

1K views 2 replies 3 participants last post by  40th GT 
#1 ·
Built forged 4.6 with trickflow heads and bullet cams
Vortech v2 with downsized to 2.62 pulley; equipped with an 8 rib serpentine belt
60# injectors
Dual ford gt pumps with BAP, FPDMs, and wire upgrade
Large FMIC with Air to water cooling set up.


So in a previous post I was having an issue with belt slippage and now that I moved from a 6 to 8 rib set up the car runs like a dream. So...time to mess with stuff. I dyno run it before and it dropped 450 rwhp and 440 ft lb torque. After 5k RPMs it runs a little lean. I am guessing I need to retune now that I got my belt slip fixed. I did some datalogging and wanted to pick yalls mind.

My LTFTs show a 1.06 and 1.11 on bank 1 and 2 respectively. My FPDCs never peak past 24%, is my fuel set up that efficient???? If my FPDCs are not even peaking past 25% then I could assume that the computer can make up for the .06 and .11 difference effectively and allow me to postpone a dynotune session until the fall?


Also another question, ever since this engine build I have done two dyno session and each time my results where fairly low for the almost 18+ PSI the supercharger is pushing. The confusion is that everything looks fairly well on the charts besides we are now running a little lean due to the fixed belt slip. A few weeks ago I checked my tire pressure...it wasn't a couple PSI low...it was 8 PSI!!!! I promptly aired the tires but this had me wondering if this would have skewed my dyno results.

Thanks for your time guys! Appreciate your responses.
 
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#2 ·
I believe on our PCMs when datalogging (At least with SCT) the fpdc will read from .0-.5 and you multiple that value by 2 to get actual FPDC %. Were the numbers .24 which would mean 48%?

I'm wondering is only one pump is working at full capacity. Have you tested voltage at both pumps? Are you running dual FPDMs? OR a single? Triple check everything in the tank, connections, lines, etc...That's a good setup and should not have a problem supplying the fuel needed.

Have you checked PSI with a manual guage during the dyno runs? Wondering if pressure is falling off due to a pump issue...

Is this still a returnless setup?
 
#3 ·
An LTFT of 1.06 is perfectly normal, and I would even say 1.11 is within acceptable range. A variation of .20 away from 1.0 is within the correction range of the PCM. With that said, LTFTs are measured with stock narrowband o2 sensors and is just a diagnostics tool for idle and part throttle driving. For safe WOT AFR you need to get a wideband gauge and see how far you are from the target AFR set by your tuner.
As for FPDC, some duty cycle PIDs give you a two digit decimal and you have to multiply the figure by 2, then 100 to get the percentage. So if you saw .24 your actual percentage may have been 48%. Your fuel system should be good to 650-700whp so it would make sense for your duty cycles to be low. With such low duty cycles it's safe to rule out the fuel system as the cause of a lean condition. But you can't say it's actually lean until air-fuel ratio has been verified with a wideband.
 
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