Fuel pressure on 03 cobra fluctuating between 30-40psi

[IMPORTSMOKER]

i just installed a bbk liquid filled fuel press gauge on the fuel rail at the shrader valve on my 03 cobra....but it seems that my fuel pressure is fluctuating and bouncing around between 30 and 40 psi....is this normal?? i think there is something wrong here.....when i dynoed the car a few weeks ago ..it was rich all the way to the top...any suggestions?

 

[Uncle Meat]

As far as being rich all the way up, that's normal for all 03 & 04 Cobra's running the stock factory tune. It's Fords way of playing it safe. As for the bouncing fuel pressure I couldn't tell you.

U.M.

 

[Don 95Vert]

It's probably normal - the PCM attempts to keep pressure drop across the injectors steady, not fuel pressure. If you have a datalogger log that and see what it is, chances are it'll be pretty steady.

It is NOT normal for the car to be rich at idle and part throttle...

 

[Uncle Meat]

It is NOT normal for the car to be rich at idle and part throttle...

Don, he stated when he dyno'ed it was rich all the way to the top. A/F readings from the dyno are measured and recorded at WOT, not at idle or part throttle, so in this instance being rich all the way to the top is inherent in the stock 03/04 Cobra ECM calibrations. You are correct though that at part throttle and idle conditions the ECM should be keeping the A/F ratio at a stoic (14.7).

U.M.

 

[IMPORTSMOKER]

What should the stock fuel press be at idle? and should it be a dead on steady reading? only reason im concerned is that im new to the 4.6, my old 5.0 would be a steady 40psi on the gauge at the same location on the fuel rail....

 

[Dr. Wu 2000]

I have an Autometer fuel pressure gauge and I see around 30psi or so at idle with a bounce here or there....I think a bit of fluctuation is normal, a few psi.