help - 90 xj fuel pump turns into total electrical disaster

As I was heading home from vacation the fuel pump on my 90 XJ went out. I had it replaced by the local shop in Weston WV, where it left me stranded. The new pump came on, but the injectors would not spray. They hooked up a used computer, and the injectors began to spray, but now the engine only runs with the key turned over. If you let up on the key, it dies. I've already bought $200 worth of electrical parts and these guys aren't any closer to getting it fixed than they were when I broke down a week ago.

Any idea on where to look for problem? Is there something tied into the fuel pump circuit that may have gone out with it? Is it a common occurence to have computer problems when a Cherokee fuel pump dies? Thanks in advance.

Check for a ballast resistor on or close to the firewall. It's a white ceramic thingy with 2 wires attached to it. The pump circuitry bypasses it when the key is in the "start" position, but then runs thru it in the "run" position. You can bypass it to see if you've got fuel to see if it's the culprit.
HTH,
Jeff

Check the fuel pump relay also. It is bypassed in start.

Like Jeff said, you can short around the resistor. It is mounted on the drivers side fender and has two push on lug terminals. It will not hurt to drive home with the resistor shorted. It mainly helps make the pump quieter.

you mean jumped not shorted right?

massxj said:

you mean jumped not shorted right?

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He means jumped (by-passed).

Eagle said:

He means jumped (by-passed).

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You're both right. Bypassing a resistor is "shorting" it. If the entire circuit consists of more than one resistance it is not entirely short circuited, but it is "shorter" than it was.

Matthew Currie said:

You're both right. Bypassing a resistor is "shorting" it. If the entire circuit consists of more than one resistance it is not entirely short circuited, but it is "shorter" than it was.

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I was going to write that they're the same, but I decided someone somewhere would interpret that to mean they should ground the wire leading to or from the ballast resistor, and I didn't want to be responsible for causing that to happen.