Dead fuel pump?

Hello all.
It’s been a long time since I’ve been on here. My 1991 XJ-S convertible has sat in storage for almost 10 years with some of the engine disassembled.
My son really wants to ride in it, so I replaced the TPS (set to .34V), did the linkage setup procedure, removed all the old gas, and buttoned everything up. It started after a few tries. Idles a little rough, but revs decent. (Needs to be driven and clear out the dust.) Might be intermittent miss on A bank. Vacuum low at 12. Fuel pressure was low at 32. Let it run for about 30 minutes.
Next day I replaced the 10 year old battery. Now the fuel pump won’t come on. Inertia cut-off switch is in the non-red retracted position. Brown wire spade connectors are tight. Fuel pump relay has 12V between pin 30 and pin 87, but jumper between the 2 does not turn it on. (Incidentally, I used the fuel pump to pump out the old gas by removing the line to the rail.)

Odd that the pump would “die” after changing the battery. Feels electrical. Is there also a fuse to the brown wiring that goes from the relay to the battery? Can the ECU disable the pump even if the relay has a direct jumper? Any other thoughts?

Tony Evans

Easiest thing to do is to connect the pump directly to a 12v source and see if it works.

Note that if you have ever used ethanol mixed fuel and then the pump sat for a long time, the o-rings inside will have shrunk and the pump might be leaking internally, externally or both.

Hit it w a rubber mallet several times it may free it up. Do it while key is in 2nd position. Has worked for me in the past.

…and check the fuse as it should be blown first if pump seized :wink:

Yep, I think the relay w the red stripe if I recall

So there is a fuse for the fuel pump relay?
Where is it? In the trunk near the battery?


I don’t think there is a fuse for the fuel pump, just the relay.
When I jumper pins 30 and 87, I get 12V at the fuel pump connectors. I used my battery charger to apply 12V directly to the fuel pump and it buzzed but did not pump fuel (0 on the pressure gauge).
Looks like a bad fuel pump. I’ll replace it and see what happens.


According to the S57 Electrical Guide for my wife’s 1990 XJ-S convertible there are no fuses for the fuel pump. It is powered by the battery through the relays. Your 1991 is probably the same.
Try reversing the leads from your battery jumper to the fuel pump momentarily to drive the fuel pump backwards. I have freed up a few fuel pumps this way when they got jammed. Sometimes I had to swap the leads back and forth several times to get the fuel pump to run again. The fuel pump can get temporarily jammed from debris and reversing the leads back and forth has freed up fuel pumps for me. If this does work for you be sure to investigate further of why the fuel pump jammed. It could be from fuel tank debris and require cleaning out the fuel tank or sump tank, and/or replacing the strainer in the sump.


Isn’t there an inline fuse at the power tap from the battery cable? This is my feeble memory at work 18 years after I sold my XJ-S.

Buzzed? Did it sound like a motor spinning, or just windings humming? Could you have had it hooked up backwards? What’s the amp rating on your battery charger? It might not have enough ooomph to run a fuel pump.

I think it’s just the windings. Not the usual pump sound when it’s moving gas. I have an in-line fuel pressure gauge under the hood. No movement on the needle. The charger puts out 10amps, higher than pumps usually draw, so no lack of “oomph”.
Same as Paul suggested, I had actually reversed the charger leads to see if the pump was seized and might break loose. No go.
If the new one works, I’ll dissect the old one and see if there is crud inside. Hope not. Not excited to do the tank/sump cleaning thing.

Mine was jammed with what appeared to be a small bit of cellophane. No way it would have made it through the pickup screen in the surge tank. I guess it was probably stuck to something when the car was assembled.

You really don’t need to clean the tank/sump. Just remove and toss the pickup screen, and install an inline filter between pickup and pump inlet. Then the tank/sump will clean itself as you drive!

Now THAT idea I like. I’ll clean/fix anything I have to, but filters have the exact purpose of picking up crap we can’t prevent.
In my field, there are vascular filters we implant in people because a clot is sometimes unlikely to prevent.
I already ordered the new pump and a new fuel filter, but I’m also going to do that small mod.


You don’t have to clean the sump however it may clog filter again relatively quickly if it looks like mine did in attached pic. I took another sump tank out of my other xjs and it was even worse. I made a blog post about it on my foreverxjs site.