My car has been sitting for 7 months. Went to drive it for the first time two days ago. Started right up and drove fine. Once or twice I noticed a lack of power (stalling), then it picked up.

1992 5.3L. 55,000 miles.



Diagnosing it, I could not hear the fuel pump running. Pulling the fuel rail line off, there was no fuel pressure.

Disconnected the two wire plug leading to the pump (in the boot). Blue/red and black. Impedance measured 0.6 ohms. I went to jumper it from the battery. Immediate large spark. I have confirmed the black wire has continuity to ground. The blue/red does not.

I should be able to get the pump running by putting 12v to it, correct?

 

Correct, providing other terminal of the pump is also earthed.

 

The power to the pump is being switched on correctly for about 10 seconds, when I measure the connector at the loom side.

But it looks like the pump may have to come out. Last year, I thought I avoided this nightmare when I found a wire to the pump chafing on the panel behind the tank. Looks like I am not so lucky this season.

Here is what I found on the harness connector fascia.

 

Jumpering the pump directly from the battery gives a BIG fat spark. And no pump

 

The pump has had it.

 

Which leads me to my next question. Given the potential for a short and overload in a fuel tank, would it not make sense to fuse the pump?

 

So, last night I removed the fuel tank. Seems at 55,000 someone had been in there before.

I found a Walbro pump. P/N 31655. A0j015. 240192-1.

These cross to a Walbro AOU168 pump. Also a ITP087 kit.

Most stock seems to be only available in the UK. I am stateside.

Anyone that might have a line on a US based source? Summit Performance lists a ship date of September.

 

Well, well, well

The Walbro pump crosses to,a Delphi FE0199 pump.

 

NO idea on the XJS, but both my X300's, In Tank Pump, 1 pump on one car, and 2 pumps on the other had issues MAINLY with the loom that runs from the tank access hole to the pump.

OK, all 3 pumps were iffy, but mate, those looms were shiiit in a big way. Made my own, and that was a looooong time ago, still OK.

Just mentioning to check that loom and the thru connector, wherever it is on the XJS tank.

That plug is sad, and shorting has been going on.

 

Discovered something interesting. The noise suppressor appears to be a zener and a capacitor circuit across the positive and neg lines to the pump. The zener was shorted on mine.

I am convinced more than ever to install an inline fuse

 

Scott
Are you sure that the diode etc stuff you describe is OEM?
Secondly, have you found out why the pump was running when it should not be?

 

Greg,

The zener is stock. It is on my wiring diagram. A zener is used to shunt transient voltages caused by the motor turning off and on.

The pump wasnt turning on when it shouldnt. It wasnt running at all. Given the overheated connector that I showed in the pic, I suspected the pump was drawing too much current. But having removed it, I found that it was working properly, and was drawing just a few amps. That caused me to dig deeper to find a cause of the excessive current draw.

A zener diode goto solution for a parallel transient suppressor. Ford/Jag must have thought it necessary, or else they would not have built it in. But it hidden near the top of the tank. It is coming out to be replaced with a fuse and coil based series suppressor.

The stock setup is nonsense. Also, the ground wire on the harness inside the tank is half the size of the positive wire. Again, makes no sense.