Fuel cut around 5,000 RPM

[KrayzieFox]

After installing the 626 IM and the Turbolife FMIC, I've noticed that my air fuel ratios from 4.5-5.5K RPM are a lot leaner than they used to and should be. I see nice and stable AFRs of 11.0-12.5 up to 4.5K, then after that they slowly climb into the 13's and sometimes even hit a low 14 around 5K RPM. Then after 5.5K RPM they drop back down into the 11's.

I have an automatic turbo P5 and I use a rising rate fuel pressure regulator (RRFPR) to deliver the extra fuel. What I can't seem to understand is why the fuel cut occurs at those RPMs only? The pump shouldn't be maxed out, and neither should the injectors.. as plenty of you MSP guys have the same setup with no problems.

The FPR I use (BEGi RRFPR model 2025) has a rate of gain needle and it is adjusted for the maximum gain, but I still get this lean spot for some reason. Anyone have any idea?

Is it time for bigger injectors?

 

[Wagonbacker9]

I think your best bet would be to get a real tuner... no chance you can get it to add more fuel per lb of boost is there?

 

[KrayzieFox]

My problem with that though is the auto transmission. There's not a whole lot out there that works well for us turbomatic guys. There's been several failed attempts at using the MPI, and a couple guys are currently struggling with the SS AFC. And the Unichip hardly even works properly on the MSP.. so the BEGi FPR is kinda the most effective method as of now cuz it's just so simple.

The FPR has two adjustments. One adjustment is for the onset fuel pressure, which is the pressure when the boost gauge reads 0 and you're entering boost, and the other is the rate at which the fuel pressure rises relative to the airflow/boost increase.

My onset pressure is ~15 psi (which means +15 psi on top of what the stock FPR is doing) and the rate of gain needle is fully closed, which is maximum gain. So there's not a whole lot of adjusting available.

 

[Wagonbacker9]

sounds like you've basically just got your tunability maxed out... has anyone tried an SSAFC on top of the BEGi? maybe the BEGi can keep you close, and you can use the SSAFC to tune out the hole?

sounds like it would be a b****, but other than that, idk...

only other thing that comes to mind is upping the onset pressure and dealing with a rich condition in lower RPMs?

 

[KrayzieFox]

Yea I tried that. I upped the onset to 20, then 30, then 40 and it didn't help at all. I think all I accomplished there was maxing out the fuel pump.

Speaking of which, does anyone know what the maximum output of the stock fuel pump is?

 

[Wagonbacker9]

well, if the AFRs are coming back down up top, I suppose that could be because the turbo is leaving its efficient range... in which case it could be your fuel system that is the weak link... just where in it is anybody's guess without a pressure gauge though.

 

[KrayzieFox]

Well I talked to Prosport today and they're getting their next batch of fuel pressure gauges on Monday, so I should have that sometime next week I hope. My current gauge is a mechanical one and is mounted right on the fuel line itself so I can't see what the pressure reads as I'm boosting.. which really sucks. Having an in cabin gauge will be a huge help in figuring out what exactly is going on.

 

[Wagonbacker9]

can't say as though I'd want a mechanical in-cabin... lol but yeah, knowing fuel pressure is pretty critical for you right now... would at least narrow down the questions you need to ask..

 

[KrayzieFox]

Umm yeah, no fluids in teh cabin. K-tx

I guess I'll wait until I get the gauge hooked up before I pursue this further. I'm just simply stumped at the fact that the AFRs drop back down after 5.5K RPM. Could be the turbo efficiency like you said though..

 

[Wagonbacker9]

thats the only thing that makes sense... do you know what your boost is doing in the entrance and exit to the lean condition?

 

[XoX1de]

if you boost NA usually you maxed out MAF around that rpm range, on my 626 did fuel cut around 4500 5000, because the maf recieved more than 4.8V, I clamped it 4.5V so no more misfore.

 

[KrayzieFox]

5-6 psi.. stock wastegate actuator.

 

[KrayzieFox]

if you boost NA usually you maxed out MAF around that rpm range, on my 626 did fuel cut around 4500 5000, because the maf recieved more than 4.8V, I clamped it 4.5V so no more misfore.

Wait.. what? Can you elaborate on this a bit more please? How is the MSP MAF any different from the NA Protege?

 

[JCell]

Im having a similar issue, where b4 the 626 install i was @ 10.5 all the way to redline, now im at 12.5 AFR

how can u fix the maf issue?

 

[KrayzieFox]

What do you use for fuel management JCell?

 

[Wagonbacker9]

allowing the car to flow more (or cooler) air bumps up the voltage reading from the maf. If you were already near the max (Stock MSPs have been know to hit fuel cut in cold weather, I know mine has)... If the voltage goes over max voltage (5V), you'll fuel cut. a maf clamp will stop the ECU from seeing this volatage, and as long as you're not relying on your ECU to match that added air (metered by MAF) with more fuel (if you're using a FMU, you aren't) this will allow your car to run when normally the ECU would shut it down to protect itself...

just for the record, this should ONLY be done when you KNOW you're getting adiquate fuel delivery. if you are getting a lean condition, do this with EXTREME caution. datalog your fuel pressure, wideband, and ideally boost... make sure there aren't any holes or anything.

 

[JCell]

nothing, still on stock MSP unflashed ECU

no boost controller either, just the atp wastegate

 

[Wagonbacker9]

unfortionately, that issue is fairly common with the 626 intake on the stock MSP ECU. Time for an SSAFC for you for SURE...

 

[KrayzieFox]

12.5 is good though.. that's peak power right there. I wouldn't worry about it JCell.

But I do wanna hear more about this MAF clamp. Where can I get one? How do you hook it up?

 

[Wagonbacker9]

that one I can't tell you, i have no use for one, as I'd basically be asking to blow up my car if I tried. I'm sure someone here knows though. just be careful please. keep a tight eye on the AFRs, especially where you know youre problem zone is.