matt_90lx

i have a 1990 mustang lx with a efi 5.0 with an AOD trans. I drove the car everyday and then parked it and it sat for about a year. i went back to crank the car(with a new battery) and i turn the key on and all i hear is relays clicking(fuel pump relay under driver seat and relay on inner passenger side fender, maybe WOT relay?) So, the fuel pump is running constantly, the relays are clicking constantly, and the coil is shooting a spark each time the relay clicks.. I have replaced: the ignition switch, the pip sensor, the tfi module tested good, new battery, new coil. I have checked the inertia switch and its fine. I am completely stumped as to what could cause this. It ran fine when it was parked. Please help before i go spend more money on a new ECM. Any help would be very much appreciated. thank you

88 orangepeel notch

lol, disregard my reply in the New Members section.

Have you swapped relays with known good ones. Letting a car sit for a year allows corrosion and other laws of nature to really cause havoc on electrical systems. Sounds like you have a bad ground or short somewhere now that you'll have to track down.

The spark at the coil, could be just a bad wire (coil to cap).

ALMOST STOCK

The fuel pump relay contacts are stuck together or the Tan/Lt Green wire has shorted to ground. In extreme ghetto cases, the pump relay may have been bypassed. Remove the fuel pump relay from its socket. Then disconnect the computer and use an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.

Prior to replacing the computer, check the computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness

If all of the checks have worked OK to this point, then the computer is bad. The computers are very reliable and not prone to failure unless there has been significant electrical trauma to the car. Things like lightning strikes and putting the battery in backwards or connecting jumper cables backwards are about the only thing that kills the computer.

matt_90lx

Thanks, i will try this when i go to my shop tomorrow. I was assuming it was the ecm only because it is affecting my fuel system and my spark.. like i said every time the relays click, the coil fires. I mean how else would these two parts be connected? And also there is a relay on the passenger side inner fender, any idea what this is? its clicking also. i will check the relay like you said above and post what i find out tomorrow. thanks for the help.

matt_90lx

ok so i have replaced the fuel pump relay with a known good one, still the same thing. i turn the key on and click, click, click.. any more suggestions on what i could try?

88 orangepeel notch

Have you done what ALMOST STOCK suggested ? There's ways to test everything before wasting money on just replacing good parts.

Also, he brought up a good idea. Check the grounds, ALL grounds. I went through some similar problems on my car a couple years ago and it took me weeks of testing, probing, hair pulling, wrench throwing, to finally find a bad ground on the battery cable to block connection. Cleaned that up and she's been perfect ever since.