Lean at specific RPM only (1500 rpm)

[itzl0l]

...tune myself with prp....

I am getting a lean spot ONLY at 1500 rpms...back to normal by 1700.

Happens regardless of gear, speed, MAF count, or load (though slightly higher loads make it worse.)

Happens in OL or CL (stft tries to correct).

Happens when the car is hot or cold.

In OL the maf xfer is pretty well dialed in ...i see mid 14's as expected while cruising unless my rpm's are at 1500 ...then its lean @ around 16. Under slightly higher loads (.60) going up a hill for example it will stumble and go very lean (18+).

LWFM is dialed in via histagrams. (no help)

EGR currently disabled as well. (no change).

I cant find anything in the tune that would account for this as evrything is spot on in all other regards. Even if its a mechanical issue I cant think of anything that would cause such a specific issue at specific rpm.

Any Ideas?

Car is:
03 Cobra (amz2)
Whipple
60 lb inj
stock pumps w/ bap

thx guys!

 

[01yellercobra]

What are the STFTs showing at that point?

 

[itzl0l]

What are the STFTs showing at that point?

tries to correct for a lean condition. Problem is the lean condition doesnt happen at any specific maf count.

1500 rpm = lean, no matter what the maf counts are. No matter what the timing is either

I have played with injector slopes, I've played with timing, I've played with dashpot/isc duty cycles ect ect...to no success. I cant think of any reason for it to be lean at a specific RPM.

and on the flip side....i dont know of any way to increasing fueling per rpm

 

[itzl0l]

Bump.

What else could cause a lean spike at a specific RPM low load. I think it may actually be mechanical in nature. I couldnt find any vacuum leaks (and I think it would be lean over a wide range, not just 1500 rpm)

It does this in OL and CL (stft tries to correct). I've played with everything in the tune I can think of. Injector slopes, LWFM, timing, ISC, dashpot. ALWAYS lean at 1500. Hot or cold...any gear. Low load.

Is there anyway in the tune (amz2 03 cobra) to add fuel at a specific RPM?

What types of mechanical issues could cause this? COP, cam/crank pos sensor? ...ive changed plugs, several times. ...ive even tried a dif MAF and intake.

03 cobra
stock pumps w/ bap
60# inj
2600 maf

 

[antcjr]

Bump.

What else could cause a lean spike at a specific RPM low load. I think it may actually be mechanical in nature. I couldnt find any vacuum leaks (and I think it would be lean over a wide range, not just 1500 rpm)

It does this in OL and CL (stft tries to correct). I've played with everything in the tune I can think of. Injector slopes, LWFM, timing, ISC, dashpot. ALWAYS lean at 1500. Hot or cold...any gear. Low load.

Is there anyway in the tune (amz2 03 cobra) to add fuel at a specific RPM?

What types of mechanical issues could cause this? COP, cam/crank pos sensor? ...ive changed plugs, several times. ...ive even tried a dif MAF and intake.

03 cobra
stock pumps w/ bap
60# inj
2600 maf

Any luck with this? I have the same problem.

 

[kb1982]

Bump.

What else could cause a lean spike at a specific RPM low load. I think it may actually be mechanical in nature. I couldnt find any vacuum leaks (and I think it would be lean over a wide range, not just 1500 rpm)

It does this in OL and CL (stft tries to correct). I've played with everything in the tune I can think of. Injector slopes, LWFM, timing, ISC, dashpot. ALWAYS lean at 1500. Hot or cold...any gear. Low load.

Is there anyway in the tune (amz2 03 cobra) to add fuel at a specific RPM?

What types of mechanical issues could cause this? COP, cam/crank pos sensor? ...ive changed plugs, several times. ...ive even tried a dif MAF and intake.

03 cobra
stock pumps w/ bap
60# inj
2600 maf

Have you used a smoke machine to check for vacuum leaks? Low load at that rpm would still be pulling quite a bit of vacuum, more so than at idle. Do you notice any kind of bucking at that rpm while cruising? When the rpms come down near that rpm while driving, does the car feel as it surges forward? If so, unmetered air is coming in from somewhere creating the lean spike.

 

[cj428mach]

What kind of Throttlebody do you have? The issue could be a lean tip in issue if you have a monster monoblade.

 

[Skud]

I had a similar issue, but mine was at 2700RPM. It would start at 2500RPM, peak at 2700 and then be back to normal by 3000. No matter what as RPMs crossed 2700 it would go lean. Eventually, it was determined to be the injectors. I assume it was the transition between slopes.

Riley