88 will start but won't run, no fuel pump prime noise with key on.

Hi guys having a bit of trouble with my 88.

It will start after a bit of cranking (it's been sitting for a while last ran a couple months ago) but it won't keep running. As soon as I let the key back from the start position to the run position it dies. Also the pump doesn't prime when you first turn the key on like it should. It seems to be running when it's in the crank/start position because otherwise it wouldn't keep starting over and over. I've started it around 10 times so it's obviously running when in the start position I figure.

I check the contacts on the ballast resistor and tried a spare and bypassing it with a wire and it still won't stay running or prime the pump.

I thought it bypassed the resistor when it was in the crank position but I could just be assuming things?


I'm going to get out there with the multimeter today but I thought some of you guys might have some ideas?

It sounds like the B+ latch relay is functioning, but the fuel pump relay has failed. Try swapping another relay (other than the B+ latch relay) for the fuel pump relay and see if it primes & runs.

What do you mean by the B+ relay?

We are thinking its the starter relay (the main relay with all the alternator and battery connections). When we shorted from the power terminal to the ballast resistor terminal the pump fired up. After that it also would also prime normal and started and ran. We are thinking that relay was sticking or not making good contact on that ballast resistor contact.

I'm thinking of changing it out for a new one just to be sure.

Spanky414 said:

What do you mean by the B+ relay?

We are thinking its the starter relay (the main relay with all the alternator and battery connections). When we shorted from the power terminal to the ballast resistor terminal the pump fired up. After that it also would also prime normal and started and ran. We are thinking that relay was sticking or not making good contact on that ballast resistor contact.

I'm thinking of changing it out for a new one just to be sure.

Click to expand...

1. Not the starter relay.

2. As suggested, swap the fuel pump relay.

There are three or four relays located on the right (passenger's) side fenderwell, and the starter relay/PDC.

When you first turn the key to ON the fuel pump relay energizes and primes the fuel pump for a second or two.

When you turn the key to START the fuel pump relay does SQUAT--power is sent to the fuel pump from the STARTER RELAY during CRANKING. If the engine will start when cranking but dies when you return the key to ON the fuel pump relay is the first suspect, followed by the ignition switch.

Key ON, engine running from IDLE to WOT the fuel pump relay powers the fuel pump.

Key ON, engine at WOT the o2 heater relay powers the fuel pump.

Listen to Shorty--he has spoken wisely.

Cool, great info.

Can you guys tell me what shorty means by the B+ relay though?

I have some other relays I can swap in for the pump relay but like I said it seems to have resolved it self and it primes and starts and runs now.

I do want to make sure it's reliable and doesn't mess up again though so I can change the fuel pump relay. I'm just wondering if there is anything else I should look at too. That's why I thought of the starter relay.

Also at what times does it use the ballast resistor? I thought it was only once it was running or something like that?

I had it die on me years ago and it would start but not run and again I couldn't hear the pump prime. So I changed the ballast resistor with a spare and it started and ran fine from then on. So is the ballast resistor bypassed when in crank mode? Via that starter relay route?

Thanks again guys, I want to get this sucker somewhat reliable for my wife to use for work.

The B+ relay powers the ECU for a bit after engine shut down so it can set the IAC for the next start up.

PaulJ said:

The B+ relay powers the ECU for a bit after engine shut down so it can set the IAC for the next start up.

Click to expand...

Yes, and more.

B + Latch Relay--controls BATTERY + to the engine management system. It receives power from the ignition switch, and the relay is energized by the ECU when the key is first turned to ON. After a couple seconds if no crank sensor signal is received the ECU will de-energize the relay. The same is done with the fuel pump relay. Without the B + Latch relay there would be no power to the ICM/coil. The ECU keeps the B + Latch Relay energized for 3-5 seconds after the ignition is switched off so that the ECU can position the IAC for next start up.

That is a simplistic view of things. On later model XJs its called the ASD Relay.

Sorry guys, when I was asking what the B+ relay I meant which relay in the engine bay was it? I've never heard any of the books refer to a B+ relay?

Also thanks for all the help and info, I knew some of it from the renix fuel injection book but you're filling in the blanks.

joe_peters said:

1. Not the starter relay.

2. As suggested, swap the fuel pump relay.

There are three or four relays located on the right (passenger's) side fenderwell, and the starter relay/PDC.

When you first turn the key to ON the fuel pump relay energizes and primes the fuel pump for a second or two.

When you turn the key to START the fuel pump relay does SQUAT--power is sent to the fuel pump from the STARTER RELAY during CRANKING. If the engine will start when cranking but dies when you return the key to ON the fuel pump relay is the first suspect, followed by the ignition switch.

Key ON, engine running from IDLE to WOT the fuel pump relay powers the fuel pump.

Key ON, engine at WOT the o2 heater relay powers the fuel pump.

Listen to Shorty--he has spoken wisely.

Click to expand...

Does it work the same way in 96' XJ? .Some time ago It started to splash petrol under the clamp on fuel filter outlet. Changing and tightening the clamp didn't help. Now the pump doesn't even prime. Jeep runs only on LPG.