HELP!! 2004 Cobra going Lean @ WOT

[2k2MustangGT]

I have been having a hard time figuring out this issue with my 2004 cobra. Car has a 2.3 whipple. 60 lb injectors, stock pumps and a BAP. I bought the car with the fuel upgrades and they all have been on there since 08.

Had the car tuned by Henson performance in AL.(he has since closed the door and isn't willing to help at all) Ran great for about two weeks. But I don't drive it much (bc I pulled the trans to rebuild) and the weather was warm then. About a month ago it's started to break up in the top of 3 and 4th gear. Data logged it yesterday and it's going lean there.. 12.3-12.5 AFR and spiked to 12.8 at one point. Duty cycle at 100% and from what I see the fuel pressure doesn't drop. When it was tuned the duty cycle was fine and safe.

He says on the dyno he set The base fuel pressure was set at 50 psi and saw the minimum of 49.5 on the log. As far as a/f’s he targeted (11.4) and saw the leanest of (11.6997).

Swapped in known good coils packs, Checked and changed plugs (.026), has a new fuel filter and tested the BAP it shows 17v so its fine.

I have a data log if anyone wants to check it out....

Why did the duty cycle increase so much??

Why is it going lean all of a sudden nothing has changed?

Only thing I can think of is clogged injectors?

 

[Bdubbs]

Did you datalog log fuel pressure drop across injectors? You might have a weak fuel pump or a bad one. Or maybe a hose on one of them popped off? Any engine codes?

 

[2k2MustangGT]

Only code I get is 02 and I think one was a heater circuit. But the 02 dont control WOT on these cars. Other then that no code.

I did log fuel pressure drop across the injectors. They were identical to what the rail sensor saw. min-34psi- average 55psi- and 63.9psi max. I dont know what those valves should be.

But if i had a bad or weak pump or leak the pressure should drop when the duty cycle goes up right? In theory..

 

[Bdubbs]

Correct, I would assume pressure would drop a lot. I'm just throwing ideas out there. A weak alternator can cause a lean issue as well.

 

[2k2MustangGT]

Oh i appreciate it bro! It has a PA alternator and the min voltage is logged was 13.1 which is more than enough from what i understand.. 13.5v most almost the entire log.

 

[Savage_SVT]

I just had a similar issue with mine, at 5k RPM it would feel like I hit the revlimiter. Turned out my alternator was only putting out 10 amps. I know you have an upgraded alternator, but its possible that it could be failing. You want 13.5-14 volts, did it drop off at higher RPM when the pumps were at full duty cycle?

 

[2k2MustangGT]

Thanks for the reply! I did look at that also. It is 13.5-14v the entire time

 

[lowflyn]

I'm glad we aren't the only ones stumped on this Ivan. This is Brad BTW.

We logged my car directly after his and tried to compare results on a car with no issues to see if anything jumped out to us.

 

[cj428mach]

Does it have a PPRV delete? I'd lean toward a blown hose or something in the tank.

Fuel pressure should remain at whatever base pressure was setup at when going WOT which in this case is 50 psi. The only time it should change is during quick transitions in and out of WOT but the pressure should catch back up to the base pressure almost instantly.

 

[Wicked46]

Do you have your original tune file?

 

[2k2MustangGT]

No PPRV delete. I was thinking cut hose also... But the fuel pressure does not fall off at all! Stays strong.. Thats why im stumped lol

Wicked46 Yes the tuner sent me the tunes in the email thank god.

I actually emailed Eric Brooks from Brooks speed today to see what he thinks. It maybe a bad tune... IDK at this point. All the hard parts look and check out ok.