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Old October 10th, 2020, 11:27
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8Mud 8Mud is offline
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Join Date: Sep 2003
Location: Central Germany
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Re: 1991 XJ SE - Crank no start problems

Originally Posted by TricolorXJ View Post
Thank you both for the replies,

I have not tried hotwiring it, I don't think I have the tools or the know how to do that. I'm sure there are plenty of how-tos around the internet. Not sure what you mean by "Bad connector". Do you mean the male/female power connectors that are near the fuel pump?

I will be trying to bang on the tank haha, a neighbor suggested doing that.

But as I mentioned previously, the power not getting to the pump is concerning. 8Mud, can you clarify a few things, I'm new to XJ's and car mechanics:

Is ASD the Auto Shutdown Relay? Where is the Ballast Relay located? In the relay box in the engine bay? Still haven't been able to find the fuse to the fuel pump itself.

I'll be checking the power to the ballast resistor but what does "A quick check for both the fuel crank and fuel run relay" entail?

Sorry for the 10 million questions, thanks again!

Some additional info: The 1991 XJ is a 6 cylinder 4.0, and 4x4.
I'm not real familiar with the 91 and don't have a schematic handy so some of this is guesswork.
The ASD relay is the auto shut down relay, the ECU (engine control unit/computer) gets a pulse signal from the CPS (crank position sensor) as the motor turns over and closes the fuel pump relay when the engine fires up. The ECU closes the Ballast relay (in the PDC power distribution center just behind the battery). during cranking, this bypasses the ballast resistor and gives full power to the pump to compensate for the power drain needed to run the starter motor. Under normal running the power from fuel pump relay to the pump goes through the ballast resistor which cuts down the voltage a bit. I hope my explanation is clear.
The ballast resistor is located on the inside of the drivers side fender well on most models, not sure for the 91. A white ceramic block maybe two inches long. There should be power there during both cranking and running. You can bridge or jumper the ballast resistor, it is largely useless anyway, it was installed to quiet the feul pump some for sissy drivers.
You have spark so the CPS is likely good, when bad you will have no spark or fuel, the ASD relay won't close. You have spark so the ASD relay is likely good, it also supplies power to the ignition coil.
The harness for the fuel pump and other stuff runs down the drivers side under the inside door sill. That harness has many connectors along it's length any one of which can be corroded, loose or have a poor contact inside a connector that can generate enough heat to discolor or partially melt the plastic connector (happened to me). The connector that melted on one of my XJ's was the one just before the rear fender well, but there are others just as vulerable to failure.

I have no idea where the fuel pump fuse is on the 91 on some later models it was the "2" fuse. But most years the PDC fuse layout changed most every year. There should be a fuse and relay diagram in the cover for the PDC. Or in the owners manual.
Sorry about typos, spilled coffee in my keyboard, makes typing interesting.

No problem with the questions, I just hope my explanations make sense. XJ acronyms and part names can be confussing, expecially because some have evolved over the years. I still use ECU (Engine control unit) the new name is PCM (powertrain control module). I learned automotive electrical on main battle tanks in the military, enough wiring in one tank to build a fleet of XJ's . I've been working on XJ's since 87. Things that seem common to me might be greek to you.
If you have a wiring problem this can turn into a real can of worms, can be labor intensive and may take hours (or days). I always found it to be challenging and interesting, some people get frustrated.
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