Hey guys, so I tried to swap out my fuel pump tonight. The car would buck and feel like it was running out of gas at times and the pump was making a lot of noise, so I changed it and even with the new pump the car acts like the fuel pump relay has been pulled. It starts for a split second, then dies. Putting the old pump back in did not improve the situation. I tried adding a redundant ground test wire to the orange wire to see if it could be a fuel pump grounding issue. No dice. My XJS is my daily driver and I need it to get to work, so I'm pretty desperate. where should I check next?

 

V12 or I6?

If V12, do you have any fuel pressure on the rail? How are the pressure regulators?

 

sorry, '83 V12. How do I check pressure on the rail and how should I know if a regulator failed?

 

You must check carefully through the fuel system from the tank to the engine. As follows (half a day's work, max)

1. Check if gravity feed from main tank to sump tank is running freely
2. undo sump outlet spigot and see if the filter therein is blocked
3. if all good, test that the line from sump to pump is not soft or collapsed and runs freely to the pump. It goes in a U shape and can get trapped closed at the U
4. if all good, fix a tube to the pump outlet and check the pump REALLY shoots the fuel out
5. then change the filter behind the spare wheel and ensure the new one is installed the correct way round
6. Before attaching the filter to the fuel line disconnect the fuel line in the engine bay before the A bank regulator and blow it though with compressed air.
7. Then install the filter and test that fuel REALLY shoots out of the disconnected fuel line in the engine bay
8. If all good, try the car
9. If problem is still there it is the FPR, the B bank one is the one that matters, change it for a new one and I advise bypass the A bank one completely. If you do not want to do this, change both.

My guess is that it is a pre-pump blockage if the pump is making a noise. Good luck
Greg

 

Thanks so much! I guess first thing in the morning I'll be pulling the fuel sock and inspecting it.

 

Since you have replaced the pump and it is worse, I would be looking at the +ve and -ve terminals of the NEW pump and ensure that you have the correct wires on the correct terminals.

Some pumps have the "large" terminal as the +ve (and normal in my opinion), some have that terminal size as the -ve. Just take your time and go back to where you started, and make sure all is proper.

I have got them aarse about once, and it really did test my patience, and when I found it, it has STUCK in the grey matter forever.

The rest of the system SHOULD be sorted 100%, but if that pump is running backwards, that will be your problem at the "right now".

 

I tried swapping the old pump back in last night and no luck, I'm assuming I didn't screw them up on that. The thing is, I've gone through the rest of the system recently. now that I think about it little to no fuel came out of the pump feed line when I changed them, I just assumed I'd done a good job of clamping it, but it's worth further investigation.

 

Definitely the gravity feed line. The sump tank is dry. Any recommendations on clearing the blockage?

 

Get a new line and fit it using decent pipe clips. The inside has collapsed, most likely. It is half inch from memory, and is not under pressure so normal fuel line of decent quality will do it.
Greg

 

Also remove the fuel cap, just in case the tank venting system is AWOL. Most unlikely at this point, just a suggestion.

When that hose is OFF the bent pipe, blow back into the main tank. There may be crud built up at the outlet fitting of the main tank.

WATCH OUT FOR FUEL RUSH WHEN DOING THIS HOSE.

That hose is 1/2" ID.

 

Already tried the tank venting, but thanks. So, it's just a 1/2" rubber hose and hose clamps? Guess I've gotta find a syphon for the gas too...

 

OK,

Make sure that hose is fuel rated. Any hose supplier should have it on the roll.

Had one here years ago when the guy "kind of" did the right thing, and replaced that hose with heater hose, and being water/coolant rated, it swelled up and became porous, and the inner lining dissolved, and made a black "mud pie" that got into some wierd places.

 

Should I just hacksaw off the original hose fittings?

 

Thats what I do, but usally with the whole assembly on the bench.

Cut through the swaged sleeves CAREFULLY, then peel them back (fingers beware those ends are SHARP), and then when the hose etc is removed there will be barb ends present to take the new hose with new clamps.

Doable insitu, but one spark from that blade with fuel present, NAH, NOT nice.