I just bought a 96 XJ that doesn't run. The guy I got it from had a new fuel pump put in so I went straight to spark. Long story short, after a new CPS and coil, I noticed the fuel pump relay was clicking, the injectors were making noise like they were pulsing and the fuel pump was priming on and off.. No start. I pulled the fuel pump relay and it fired right up but died within a few seconds because the fuel pump was not on. I plugged the relay back in and lost spark. So basically, I either have spark or fuel. Has anyone dealt with this before?

 

I just researched the FSM to see if I could help shed some light. But as I suspected, there isn't a whole lot that connects those 2 systems. When I say two systems, I am primarily talking about your Automatic Shutdown Relay (ASD) and your Fuel Pump Relay. The ASD provides power to the ignition coil and the fuel injector pulse drivers. The fuel pump relay provides power to the fuel pump module/motor.

The only obvious circuit that the 2 relays have in common is the battery positive that comes from the ignition switch when in the run or start position(s). The ignition switch provides battery positive to the control (or coil) side both of the relays. The computer (PCM) provides the ground to the control (or coil) side of both relays, via 2 separate PCM cavities/wires.

So they are fairly separate when it comes to fuel and spark. So the first thing that comes to mind is to pull the tabs on the PDC and take a look underneath to ensure it hasn't become a corroded mess that is allowing circuits to interconnect in ways that they shouldn't. The next idea would be that for some reason the system voltage isn't strong enough to run both the fuel pump and ignition system at once. So when you pull one of the relays you get the other system to work, but when you try to have both relays in the fuel pump or injectors are dragging the system down (I would suspect the fuel pump over injectors of course).

Have you monitored battery/system voltage during startup to see if there are any strange drops?

 

I have not monitored battery/system voltage yet. I will get back to it in the morning when it's a bit warmer. Thank you for your response.