Boost-a-pump messing with fuel pump PID on 06 Mustang GT?

[bradyzq]

Hi All,

I've got a KB blower-equipped 06 GT at the shop here.

I inputted the correct injector data as per Ford Racing site and elsewhere on HP Tuners. And the MAF curve is pretty well dialed in too.

The car runs quite well on the dyno, but AFR oscillates around the commanded value by + or - 5%, and I see that the commanded pump duty cycle (and therefore voltage) seems to move very slowly while over and undershooting its target 39 psi pressure drop across the injectors.

Can the boost-a-pump's presence require the fuel pump's PID control to be tweaked?

Or shouldn't it make any difference?

Thanks!

[Fox95]

i think your looking in the wrong place but more info is needed.

is your afr varying at wot? at cruise?

if at cruise is it the stft's that are varying 5%. are long terms disabled?

I feel as though you may not have the MAF "dialed in" pretty well.

here's a quick rundown of how to dial in the maf:

force open loop
disable lont term
disable coast fuel cut
disable cat temp
set your entire commanded fuel map to 14.7

make sure your logging maf volts and can visibly see the maf voltage while the car is running on the dyno.

from the tune file you are using write down all the maf voltage break points in the maf curve on a sheet of paper.

with the dyno in a steady state mode where its holding the vehicle speed and won't let it change no matter how much throttle you give it, move your foot down with the accelerator pedal to one specific maf voltage you wrote down and write down your real AFR(what the wideband is reading) next to that maf voltage number

then go through as many voltage points of the maf curve that you wrote down as you can get in 4th gear and 3rd gear and record all the differences in actual afr to the 14.7 commanded in the fuel table.

make the appropriate corrections to the maf curve from the differences you recorded. (ex. lets say at 1.8 volts your reading on the wideband 12.4 afr, so that's .84 differnce from your commanded 14.7, go to 1.8 volts in the maf curve and multiply the #/hr value that is right next to 1.8v by .84 and that will remove 16% of fuel getting you back to 14.7)

once you've done this, then reset your commanded fuel map back to it's original values and the reset of the changes. and your fueling should be very accurate.

if you want to car to be perfect, then repeat the steady state process but with the maf failed so that the car is running soley on the LWFM table, once the LWFM tables are dialed in re enable the maf and the car will "predict" fuel needs much better because the the LWFM table is the first lookup then the maf.

once all this is done your car should be no more than +/- 5% on short term fuel trims when driving around with the long terms disabled.

also make sure you have fans big enough to keep the car cool when doing this method, it may take 2 or three tries to get it absolutely perfect, but once you get the feel for it, you'll do it this method everytime and wont ever use someone elses maf curve again. a load control dyno is necessary as well, but you knew that....

[bradyzq]

Thanks for the reply.

You have described exactly what I have been doing!

Except that this is a blower car so for the high flow end of things, I used .79 EQ ratio (which is actually lambda, not like GM in HPT) instead of 1.

The varying AFRs were at WOT (no fuel trims).

BTW, my AFRs are within 5% of where I want them and of commanded. What I found odd was that the fuel pressure (drop) didn't stay around 39psi during pulls.

[Fox95]

which fuel pumps? I'd run dual ford super car pumps or dual focus svt pumps depending upon what power your making and will make.

if your running a stock pump, that's most likely the issue.

yes, also forgot above that wot commanded fuel should be set accordingly for blower/turbo/na...etc....

[twinturbo]

Actually, he should be running the GT500 fuel system, in it's entirety. The BAP on the stock pump, which he is doing, is good for another 30% of fuel over stock.

To the original OP: Are you using the hobbs 4# switch, like you are supposed to? If so, no issue, but if you are running it wot voltage all the time, you will need to modify your fuel pump base voltage table accordingly. Part throttle surging and driveability issues will occur with a lot more volume, and the stock FP voltage tables.


To the last reply: You are thinking about the older single tank systems.