I’m dumbfounded as to why this is happening! I’ll try to include as much info as possible.

The Car:

-1999 WS6 convertible 4200lb race weight (yes 4200lbs is correct)
-QMP single T76 Q-trim Turbo Tuner Kit with a HKS Waste-gate & Racing Blow-Off Valve.
-Forged/Studded standard bore/stroke 346 CID short-block with 8.8:1 compression & TEA stage II LS1heads.
-226/0.551”in 222/0.558”ex Comp XER cam, LS6 intake with catch-can PCV
-Stock fuel pressure regulator is removed from tank, CAS boost referenced fuel pressure regulator in place of the return line T, Stock Fuel lines for Feed & Return, ARE/Racetronix Dual Walbro in-tank 255 lph fuel pumps (second pump activated @ 8psi of boost via boost management system), Speed Inc Billet Fuel Rails, Seimens 57lb(@43 psi) Hi-Z injectors. (base fuel pressure set @60 psi).
-SMC alcohol injection kit activated @ 8psi of boost via boost management system (pump turned up 100%) using 100% methanol with the nozzle approx 8” in front of throttle-body.
-Turbo-Smart e-boost Electronic Boost Management System.
-Open cut-out approx 36” from turbo on down-pipe.
-LS1 Edit, Innovative Wide-Band O2 sensor & EFI-Live used for tuning.

The Problem:

At the track on Friday night with the e-boost controller set for 14lbs of boost. The car ran great in 1st-3rd gears with a steady 10.5:1-11.0:1 AFR all the way to 6400rpm with minimal Knock Retard, injectors maintained a steady 74% duty cycle and fuel pressure was steady @ approx 74 psi. In 4th gear everything was OK until about 5500rpm, at which time the injector duty cycle began to fall from 74% to a low of 50% @6200rpm (where I crossed the traps). The injector pulse width fell from 16ms @ 5500rpm to 10ms @ 6200rpm. The fall in the injector duty cycle caused a correlating increase in AFR from 10.6:1 @ 5500rpm to 14.8:1 @ 6200rpm. The PCM pulled 10 degrees of timing by 6200rpm obviously due to the detonation from it going so lean. Why the motor didn’t go KA-BOOM I still don’t know!!! The fuel pressure was steady throughout 4th @ 74psi and did not fall and I am positive both fuel pumps were on.

I added fuel @ 5600rpm & 6000rpm using LS1 edit and attempted another pass. It affected 1st-3rd gears where the AFR dropped from a steady 10.6:1 to 9.3:1 beginning @ 5600 rpm. The added fuel had NO EFFECT in 4th gear, the injector pulse/duty cycle began falling again at approx 5400 rpm and the AFR rose up to 14.8:1 @ 6200rpm.

The MAFS is MAXXED OUT @ 511.99 (12,000 Hz) in every gear by 5000 rpm.

Here’s pics of the EFI-Live Log and the AFR, boost, fuel pressure log from the 1st pass that this problem occurred on.

Can somebody please tell me what is happening and how to fix it?

 

maybe it is topping out the MAF

 

What do you mean by "topping out the MAF"?

The MAFS is Maxxed out at 5000rpm in every gear but its only going lean in 4th gear. I tried adding fuel with the PE/RPM table but it had no effect in 4th gear.

 

I mean the MAF is running off its scale so that the PCM can no longer use its readings to calculate fuel.

 

It is running off its scale! Its running off its scale in 1st-4th gear but only going lean in 4th above 5500rpm.

 

what do you have for a VE table?

 

I have the stock 1999 VE table.

The only things I have changed with LS1 edit are.

1. IFR table at 6.16 for 57lb injectors which gives me a -2 LTFT
2. Lowered timing
3. Lowered the PE/RPM table to achieve approx 11.1AFR at 100% throttle.
4. Extended the MAF to 511.99 at 11750Hz
5. Changed MAF fail freq to 14336
6. Turned off a bunch of emission codes
7. Turn fans on earlier for 160 deg thermostat

 

Does your stock 99 VE table flatline above ~4800rpms?

I have seen a couple of FI tunes where they take the flatline from 4800 up and increase it by say 25% for all the MAP rows that are in boost (say MAP 70-105). Not sure if this would help your situation.

 

Deezel,
I think you may be on to something. The VE table flatlines starting @5200rpm right about where I start to have the problem. Heres an excel copy of my VE table.
What units are MAP in?

 

Personally, I think with both pumps in-tank and stock lines, you are out of fuel volume in the higher RPM's and more load (3rd gear). Even though you technically have more than adequate fuel pressure. In fact, I think if you were to tune the car without the 1:1 hooked up (i.e. 62psi constant), it would probably be fine even with stock lines.

Just a guess....

 

welll try the ve thing.. but i dont see how that rocky of a p.e. table can lend itself to a smooth 11.1 but if it works leave it i guess.

 

Another thing to consider is that you have changed your MAF table in the upper range, and this may be affecting your fueling there.

Here is a comparison of the stock and boosted VE tables I mentioned. These were used with stock MAF table and increased PE.