87 XJ 4.0L Fuel Pump Electrical

[anyoceans]

Rig refused to start. During the trouble shotting process I turned off the A/C Blower to reduce noise so I could hear if the fuel pump was cycling on for the start. With the blower off the XJ fired and drove fine until I turned on fan, then it stalled. with the fan off it ran fine then died completely a week later. Fuel pump runs if voltage is supplied direct. Relays seem to be good, I switched them with new and I can hear and feel them cycle for the start. no voltage getting to pos wire at fuel pump.

I understand there is no balast resistor in the 87 but that wouldnt apply to a failed start according to some of the replys on other threads.

rig will start and run if I send voltage direct to the pump.

new to some of the tec terms abbrevations, pls use long version in reply, thanks

[Digger87xj]

sounds to me like a ground issue.


Look at the ground strap that attches to the firewall near the brake booster...the bolt that is there tends to corrode and then the body looses ground.


remove the bolt, clean it, the strap eyelet and the firewall, and replace it.

Then, make a ground strap from the batt - post to the fender for redundancy.

[anyoceans]

Not the ground, checked and cleaned it anyway, it looked good. Lights etc. are bright, blower works fine so ground is sufficent. No power getting to fuel pump positive wire, relays are clicking on then off like they should but no pwr even when they cycle on for the start to pressure the system

[Eagle]

An 87 could have a ballast resistor. I believe it was made standard midway through the 87 model year, and it was also retrofitted to some vehicles as a TSB.

If you are certain that the relay is good, the next step would be to get an assistant. Unplug the connector back by the fuel pump, hook up a test light to the fuel pump feed wire and ground the light, then have your assistant turn on the key. You should see 12 volts (or 9 volts if you have a ballast resistor.

Now have your assistant turn the key to the START position. You should still see 12 volts (but in this position it'll be 12 volts regardless of whether or not you ahve a ballast resistor).

If you're not getting power back there, either the relay isn't good or you have a wiring problem.

If you have 12 volts in the START position but no power in the ON position, look for a ballast resistor and check it for continuity.

[Digger87xj]

okay... check the fusable links at the starter relay, and also there is a flat 5 way connector in the same area that has the f/p feed wire in it.. i have seen those corrode.


are you also sure that the f/p relay is good?

[anyoceans]

getting voltage through all 5 fusable links, no voltage at pump at any time. The forward two relays cycle on and off when the key is turned on.

Cant find any ballast resistor but that only comes into play once the engine is running right?

sent pwr direct to the fuel pump and the engine fired and ran until disconnected the 12v jumper attached to the pos feed wire to pump.

Wire is pink with black stripe but I cant find that wire in or near the relays.

did not see a flat five wire plug, got a six wire.

[Eagle]

If there is a ballast resistor, it is in the circuit when the key is in the ON (or RUN) position. When you turn the key to START, the start circuit by-passes the relay. That's why I suggested that you test for voltage with the key in both positions. When you say there is no voltage at any time -- did you test with someone holding the key turned to START?

[anyoceans]

Voltage is actually 0.017VDC in start and run positions. Switched the meter top read 1000's of a volt and received that reading.

I swapped relays and also put in a new one, next step will be to have them tested to see if they are ok, even the new one.