car is falling flat on its face at like 3500-4k. - Page 5

justinschmidt1 · 06-22-2009, 06:51 PM

So the car is still running like this yet I have no idea whats going on.

Maybe I have an intake manifold leak or something?

Had the car on the dyno to see if we could figure anything out.

Car went extremely rich, pegged it at 10.0 so it was going far lower than 10.0 A/F I would imagine

Its nothing with the fuel system.

Seems like its load related, gauge will read like 3-4-5 psi or so, but wont go anywhere and just bucks and dies at like 3500

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mustangman281 · 06-22-2009, 07:25 PM

Do you have a vacuum/boost gauge in the car? If so at idle a vacuum leak reads steady 5in hg on the vacuum gauge. You may have a boost leak. Is your car draw thru or blow thru?

justinschmidt1 · 06-22-2009, 09:13 PM

Quote:

Originally Posted by mustangman281

Do you have a vacuum/boost gauge in the car? If so at idle a vacuum leak reads steady 5in hg on the vacuum gauge. You may have a boost leak. Is your car draw thru or blow thru?

Its blow through.

It reads normal vacuum, like 20

mustangman281 · 06-22-2009, 09:30 PM

Then you don't have a vacuum leak.

mustangman281 · 06-22-2009, 09:31 PM

If you were missfiring you a/f would go lean not rich.

mustangman281 · 06-22-2009, 09:33 PM

The only other things I can think of is belt slip or MAF.

justinschmidt1 · 06-22-2009, 10:42 PM

Quote:

Originally Posted by mustangman281

The only other things I can think of is belt slip or MAF.

I dont think its belt slip...Its like sputtering and dying...

I doubt it would be fine one day, then the next the belt would be slipping so much it cant make any boost.

I dont know at this point..

I dont know how it could be the MAF cause its reading the incoming air, I datalogged it.

Smokin04 · 06-23-2009, 03:43 AM

Ok bro, I can tell you what it isn't.

Not an intake leak. Car would idle crappy and sputter and want to die at all rpm. Not to mention back fire REALLY loud upon decel.

Not a fuel filter....especially if you're hitting 10.0.

Not a COP or connection. Again it would run really crappy and at all RPM not just above 3500. And it would throw a code.

When you pulled your plugs, they should've been black if your AF was 10.0. That makes me wonder if your wideband is working properly.

I initially thought pegged MAF, but since you said you just had it tuned 3 weeks ago...

It's most likely a blown FRPS (Fuel rail Pressure Sensor). Happens all the time on boosted mod motors. They're about 80 bucks from ford and most high HP guys carry a spare in the car because it happens often. A way to tell is if you smell fuel when you pop the hood after it happens. With no way to judge how much fuel pressure the rails are seeing, the PCM spikes pressure to save the motor. FP is also based on load. Another way is look at your STFT (short term fuel trims)...if they are unusual than it's the FRPS. Normal STFT is -25% to +25%...it should bounce around between the two...rarely if ever sitting on one number.

Smokin04 · 06-23-2009, 03:49 AM

double post sry.

mustangman281 · 06-23-2009, 10:16 AM

I forgot about the frps. That was one of the reasons I ditched the crappy stock returnless system. Datalog your fuel pressure.