Fuel issue. Help please!

[knimmerrichter]

Hey guys,

Im having an issue with my 03 cobra and I believe its fuel related. I had my car tuned about a month ago with a pump gas and a race gas tune. I ran race gas for about two more weeks and then I switched back to pump gas changing the tune at the same time. The car ran fine on the dyno with a fuel pump duty cycle of 85%. Right when I switched the tunes to my pump gas tune and made a pull I had a real bad hiccup at 4500 rpm, and the a/f spikes. I went back and datalogged another pull and noticed my fuel pump duty cycle was jumping from upper 70% to 100% then correcting itself again and dropping back down. The car has a bap with wire upgrade, pumps from a low mile cobra, pprv delete, 60 lb injectors. The engine mods are 2.76 upper, stieg stage 5 ported blower, 4 lb lower, jlt intake, and magnaflow exhaust. It made 500/550 on race gas. Any help is appreciated.

 

[me32]

How is the alternator ouput?

 

[bubblehead93]

Fps?

 

[knimmerrichter]

it was dropping into the 12s so I replaced with a 160a alternator and its doing the same thing not dropping below 13.3v Forgot to mention that thanks.

 

[knimmerrichter]

frps is brand new.

 

[TRBO VNM]

I can confirm there is no difference in the tunes aside from timing and the race gas tune has 2 cells with a little fuel added.

That hiccup imo will still be there if you put race gas back in since the tunes are identical aside from what I mentioned. I think it is just coincidence. I am leaning more towards coils for the hiccup, but you still have the pumps pegging issue. Only other thing that can be checked is the pprv delete, but if that was an issue you would see the FPDC high at idle as well.

 

[Rich'sTRsvt]

Fuel filter?

 

[me32]

it was dropping into the 12s so I replaced with a 160a alternator and its doing the same thing not dropping below 13.3v Forgot to mention that thanks.

Is it possible a bad batch of fuel? Also check replace fuel filter. Donesnt take much for those to get clogged on the cobras. Are you data logging at all when it does this?

 

[knimmerrichter]

The fuel filter has less than 500 miles on it. It is done the same thing through two different batches of fuel. And yes we did datalog a few pulls

 

[TRBO VNM]

Have you tried coils yet? I have a used set coming. We can try on yours as well if you don't get with Colby or Dan.

 

[decipha]

what does the fuel pressure do while the pump dc is jumping?