hard starting, fuel pressure Q&A

joebeemish · Feb 11, 2007

I bought a nice 98 6 cylinder mustang for my daughter. When the car is parked for an an hour or 2, it can be hard to start. I also noticed that it is not an instant starting car. I think the ignition system is OK and the air filter is clean. I connected a fuel pressure guage to the fuel rail and it reads 0 when the car is not running. When I put the ignition to on (not start), the pressure is 0. I then start the car, the pressure stays 0 until the car starts and then it takes about 10 seconds to go to 30 LBS pressure. I hit the pressure relief on the fuel pressure guage, the pressure drops, and the returns quickly to 30 LBS. When I shut off the ignition key, the pressure returns to 0 over 10 seconds.

This stikes me as strange. I have a souped up 95 camaro and the fuel pressure stays at 40 LBS. If I release the fuel pressure on it, the fuel pump charges up the pressure when I put the key in the on position.

Is the Ford design different? The guy before me put an alarm system and remote starter on the car - can this change the way the fuel system works?

Thanks.

Skymarshal · Feb 11, 2007

It sounds like your in-tank pump is dead.

The '98 Mustang had a return fuel system, meaning that fuel was provided by the in-tank pump at full pressure continuously, and the fuel pressure regulator modulated fuel back to the tank to maintain the desired pressure.

With the ignition on 'ON', listen for the pump running in the tank, or put your hand on the tank to see if you can feel the vibration.

sixxer · Feb 11, 2007

I dunno about a 98 but on my 04 it doesn't keep under pressure when the car is off. Being a 98 though it wouldn't hurt to change the filter and check the pump, there might be a small leak in the line somewhere as well.

fiveohwblow · Feb 11, 2007

joebeemish said:
I bought a nice 98 6 cylinder mustang for my daughter. When the car is parked for an an hour or 2, it can be hard to start. I also noticed that it is not an instant starting car. I think the ignition system is OK and the air filter is clean. I connected a fuel pressure guage to the fuel rail and it reads 0 when the car is not running. When I put the ignition to on (not start), the pressure is 0. I then start the car, the pressure stays 0 until the car starts and then it takes about 10 seconds to go to 30 LBS pressure. I hit the pressure relief on the fuel pressure guage, the pressure drops, and the returns quickly to 30 LBS. When I shut off the ignition key, the pressure returns to 0 over 10 seconds.

This stikes me as strange. I have a souped up 95 camaro and the fuel pressure stays at 40 LBS. If I release the fuel pressure on it, the fuel pump charges up the pressure when I put the key in the on position.

Is the Ford design different? The guy before me put an alarm system and remote starter on the car - can this change the way the fuel system works?

Thanks.

I have a return fuel system on both my 91GT and my 98 sixer. The GT's fuel pump you can definitely hear when you turn the key to the first position before starting, the 98 not so much. Either way, I have an installed fuel pressure gauge and it instantly charges, not all the way, but charges when you turn the key. I would check your relay and make sure its grounded well, and then go to replacing both it and the pump if necessary. That should be all you need to do.

joebeemish · Feb 11, 2007

Thanks. How much fuel pressure do you get? How did you install the fuel guage? Do you have a picture of your dash?

fiveohwblow · Feb 12, 2007

joebeemish said:
Thanks. How much fuel pressure do you get? How did you install the fuel guage? Do you have a picture of your dash?

Well I get roughly 40 but I have installed an adjustable fuel pressure regulator. The fuel gauge can either be electric of mechanical, the latter being less trusty. I unfort chose the mechanical. You install the line off the schrader valve on the fuel rails, but the install is much more complex than this and would take a page of writing. As for a pic of the dash I have it for my fox, not my V-6....

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