98 Mustang GT Not Starting

It would be very handy to know what the fuel pressure is at the rail.

Check the fuel regulator intake vacuum referene line. Is it connected and leak free? Disconnect and check for liquid gas. If found, the regulator is bad.

Has an aftermarket fuel pump been installed?

Frankly, this problem could have multiple causes. Including:

• vacuum leak. This should be considered the front runner. Don't cut corners here!
• dirty MAF. Clean only with products designed for the job
• Fuel pressure leak down or incorrect fuel pressure.
• weak ignition
• weak battery or dirty battery cables
• bad IAC.
• poor compression, poor vacuum, or other base engine problem.
• bad fuel pump speed relay (long shot)

Before diving in and changing any more parts, perform these tests and post the results.

Make sure the battey and charging system is in tip top shape. Don't under estimate the importance of this item. Today's cars can not run without a strong battery and charging system.

Hold the throttle half way open during cranking. Does this improve starting?

Push the trottle all the way to the floor during cranking. Does this improve starting?

Disconnect the electrical sensor to the MAF. Does this improve starting?

Measure the fuel pressure. Start the car and let it idle. Disconnect the vacuum reference line. The fuel pressure should jump to 40 PSI. Reconnect the vacuum reference line. Fuel pressure should drop to about 30 PSI. Turn the motor off and let is set of 1 full minute. Does the fuel pressure drop by more than 5 PSI?

The 98 MY Mustangs uses a return based fuel system. Part of the design includes a relay that makes a crude attempt to vary the fuel pump's output. This relay selects between low speed and high speed mode.

The relay uses a ballast resistor to reduce the voltage to the fuel pump during periods of low demand. This makes the fuel pump run slower thus reducding the amount of retuned fuel and fuel heating.

The fuel pump speed relay is located in the passenger's kick panel near the PCM. Inspect for signs of overheating or water damage.

Based upon the test results will determine which way to go.

Just with through something similar with mine. No start condition. Could not hear pump prime. Replaced the relay module - no effect. Replaced in tank pump - bingo. That was it.

I got the one from Autozone, ~$119. Turns out it is a Walbro pump. Car runs great now.