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Need Some Help

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Looks like I have fallen into the old trap of doing too many things at once. My car has developed a slight hesitation just as you release the clutch fully and start to accelerate in first and second. The car was running fine until I fitted the new Shelby Fuel rails. At the same time my mechanic also modified the fuel filler breather, as I had been having trouble filling the car and I reloaded the Evolution 91 octane program to compensate the speedo for the 3.73 gears I had fitted previously. When I took the car for a drive after completing these tasks the hesitation (miss) appeared.

I have also noticed the fuel pressure seems to be a little erratic now. The gauge previously sat on 40psi, but now sits on anywhere between 25 psi and 45psi. It doesn't fluctuate just goes to a setting and stays there once you start it, eg.25 psi ans stay there and then next day will go to 38psi and stay there.

I don't believe the fuel filler mod is related to this issue. Given the fuel pressure inconsistencies I am leaning towards something to do with the fuel rails.

I am concerned it may be something to do with the new tune? It is the same tune I was using previously with the dif ratio adjusted. I have reloaded this tune a couple of times and also loaded the 93 octane tune but it's made absolutely no difference to the "miss".

There are no fuel leaks I can see.


Any thoughts or comments greatly appreciated.

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Not sure about the filler breather... I don't know if that would affect your fuel delivery.


Sounds to me like maybe the fuel rails are the culprit.


I'd try installing the old rails and see if that fixes it.

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