Dyno showing fuel too rich

[Armytanker]

Well I had my car Dyno'ed and the results were 346WHP and 364WTQ at 6psi(100 degree's in shop),But the slip shows a sudden spike in fuel around 3000 RPM's at WOT and it goes off the scale and doesn't return close to normal until around 5000 RPM's,The guys there said its killing my horsepower,duh.The motor is just a stock Cobra 5.0 With the FMU and the T-rex booster,They couldn't really give me any advice on how to correct this problem but I did hear some other's talking about the FMU being a problem for them as well and they sugested getting rid of the FMU in favor for 42psi injectors,I was wondering if this would be too much for the stock set up? Also I'm planing on getting a set of AFR's and a Trickflow Intake and Stage II cam package in the future....

Any thoughts?:shrug:

 

[cobra4v]

It sounds like you Fmu ratio might be to high. Cobras uses 24lb injectors and the FMU ratio should be 8.1. What is your fuel pressure at full boost? You should get rid of the FMU and install 42lb injectors and have it dyno-tune. Good luck

 

[Armytanker]

Originally posted by cobra4v
It sounds like you Fmu ratio might be to high. Cobras uses 24lb injectors and the FMU ratio should be 8.1. What is your fuel pressure at full boost? You should get rid of the FMU and install 42lb injectors and have it dyno-tune. Good luck

The fuel pressure spikes to 80-90 psi at full boost,But I'll defently be switching the out FMU for 42lb Injectors very soon,What size MAF sensor sould I run? Thanks for the reponse :thumbsup:

 

[cobra4v]

Your fuel pressure is to high due to the fmu. I run a Pro M 75 and BBK 75 throttle body. The most important part is a good tuner.

 

[2000blackone]

FMU's are not the way to go. I'm so glad Ford switched to the new system in 99. Bigger injectors and a good tune bro. :thumbsup:

 

[Armytanker]

Yeah thats what I've been hearing lately,Thanks for the reponses and good luck with everybodys Stangs

 

[cobra331]

How they work

A Fuel Management unit is actually a diaphram. What happens is it senses boost through the vaccum lines and this boost pushes down a rubber disc inside the Unit. he more boost, the more it's pushed. It blocks off teh return fuel line going back to the tank. This raises fuel pressure. There are different ratios of FMU's. If the disc is too big, it'll block too much fuel, hence your problem with too much fuel pressure. I can't believe the guys at your shop don't know that. I would go somewhere else....FAST!!!

 

[Armytanker]

Well Its the only shop I found so far here in central Texas so far,I really need to find a ford specialist