I’m new to this forum, but I’m sure I’m in the right place for assistance. So here’s the deal. Bought a 89 Cherokee. Had it trailered to my house. Put a new battery in it and it started up. Ran a little rough but was due to old gas and had been sitting up for a few months. Changed oil, added new gas, changed fuel filter. Alternator was bad so changed it. Ran fine and drove it to nearby shop to do other work to it. Put all new master cylinder, calipers, rear cylinders, brakes, front axle u-joints, differential and transfer case fluids. Now it won’t run. It’ll start and run for 3-5 seconds and then dies. If you try giving it gas, it’ll backfire and then won’t fire up at all. Looked at the spark plugs and they have gas on them. Have to leave it for an hour or so to let the gas clear out before it’ll start again. But will not continue running. I plan on changing plug wires, distributor cap and rotor, and crank position sensor. Am I missing something?

 

The symptoms you describe can be caused by a faulty fuel pump ballast resistor. It is a whiteish ceramic bar on the inside of the left fender, outboard of the air filter box. There are two wires plugged into the side of it. If you take a jumper wire across the two conductors, the resistor will be bypassed. Don't touch anything else with the jumper wire, it will be carrying 12 volts. If your XJ starts and stays running with the jumper in place, that is your problem.

 

X2 on checking and bypassing the ballast resistor. It can stay bypassed if that's the problem. It was added to reduce the voltage to the fuel pump when you're not cranking or at wide open throttle, to address complaints about the pump being noisy.

The connections at the ballast resistor are also a great place to measure voltage, as one side comes from the starter relay and the other goes to the fuel pump. The resistor is around 1.2 ohms as I recall. You should have 12-volts on the wire coming from the starter relay, and around 7-9 volts on the other side going to the pump.

 

That did the trick. Thanks guys!!