[SVTorDeath]

I recently purchased an all stock 1998 Mustang Cobra with 50,000 miles. My problem is at around 4,000 RPM to redline it hesitates, bucks and has little power/acceleration. It idles smoothly and throws no check engine codes. Below 4,000 RPM/normal driving it drives great and seems to have advertised power. In addition it takes 2-4 turns of the key to start the engine.

I changed the fuel filter and ran some Seafoam cleaner through it. That helped a little with the hesitation but both problems still plague. I hooked up a fuel pressure guage and when turning the key to run position fuel pressure spikes to 10 PSI and quickly drops to zero. While driving it stays between 30-40 PSI throughout 1000-6000 RPM range. Do these sound like problems that could be solved with a new fuel pump?

Thanks, Mark.

[markwondi]

Your problem lies in the IMRC's in the intake manifold. They open the secondary valves (B heads have two intake ports). They require frequent cleaning, hence why the seafoam helped release some of the carbon deposits in them. Your fuel pressure is perfectly fine.

The IMRC's open at 3250 rpm. They are closed below this RPM to create turbulence and low end torque. Above this RPM they open to flow into a shorter runner to help high RPM power.

[SVTorDeath]

Sounds logical the seafoam helping the hesitation. The previous owner was an older gentleman probably not prone to high RPM driving habits.

As far as the hard starting issues it takes up to 4 key on and off cycling to build up enough fuel pressure on the rail to start the car. The fuel pressure guage reading off the rail reads 10 PSI and falls to 0 about 2 seconds after turning the key to run and not starting the car. Would it be the fuel pump bleeding pressure back into the tank?