Hi I got a 1989 Xjs convertible with a fuel pump that runs no matter what. It sounded like the pump failed because the car would not run so I swapped pumps and I hooked the battery up with the ignition off and the new pump burst and started leaking. I pulled the pump relay and it still runs? What can cause this pump to run without the ignition on?
Thanks!

 

Hi Morgan

Please could you provide a few more details....

Have you only just got the Car from a previous owner?

When you say the Pump burst, do you mean the Actual Pump or did it burst one of the Rubber Hoses?

If your Fuel Pump is running all the time, its sounds like the Orange Wire from the Relay is Grounding to earth

Which would By Pass the Relay and cause the Fuel Pump to run Continuously

As such it could be a problem with the ECU or the Infamous White Shielded Wire


The 'Infamous White Shielded Wire' has been known to cause problems
This one is on a 'Marelli'

 

 

Hi Dean

That could be your problem right there, so well worth taking another look at the Shielded Wire and see what happens

 

 

Hi Dean

If you pull the Fuel Pump Relay, the Fuel Pump will not work 'Full Stop' as you have found out

Also inspect the Orange Wire from the Fuel Pump Relay, as if the insulation has been jammed or nicked or broken and it is

shorting to Earth, then the Fuel Pump will run continuously

Can you borrow a Relay from a 'Shop' and try that out, as there is a 'possible' chance it 'may' have a fault

And could be running to ground from the inside

But also be 100% about the 'Shielded White Wire' as if the Fuel Pump was working Ok before the Engine swap, then it is still

very likely to be the cause of the problem

Greg/Grant/Warrjon/Doug. Are the Experts on this (to name but a few) and will hopefully be sliding by to show you how to do

a 'Continuity Test' on this 'Shielded Wire'

 

Let's start with something simple

Pull out the fuel pump relay and main relay and look at the terminal designations. They should have terminals marked 30-85-86-87-87. If the terminals are marked 30-85-86-87-87A then you have the wrong relays. The main relay should also have a diode....look at the little diagram on the side of the case

I haven't fully sussed out the consequences of an incorrect relay but it might cause the problem and is easy to check

Post back if no joy. I'll mull more deeply


Cheers
DD

 

Hi Doug

I might be way off the beam here but since the OP has done an Engine swap, would it be theoretically possible

That if the FPR on 'B' Bank had a Ruptured Diaphragm, then Fuel could flow continuously round and round in Circuit

without the Fuel Pump ever shutting off

Which may explain why the OP was describing the New Fuel Pump as bursting

Nothing more than a 'Shot in the dark' on my part but would that be possible?

 

On all mine, the Ignition ON, activated the Main Relay, which, among other items, activates the Fuel Pump relay, which the Orange wire, as mentioned, is earthed via the ECU.

Pulling the Pump relay stops the pump, goodo.

Doug is correct also, coz that 87a will reek havoc whichever way you look at it.

I suggest pulling the Main relay, Ign OFF, and then replug that relay, and "feel" the click of activation as yo plug it in. If you do "feel" that click, then the Ign circuit is LIVE, even in the OFF position, pointing to an electrical section of the Ign switch that is overdue for service.

If there is NO click as you replug that relay, then there is some other gremlin in the system that is keeping the Pump relay live, AND the ECU timer is not doing what it should.

The shielded wire has nothing to do with the pump working, or not working, until you go to "start" mode, and the engine actually fires up.

A stuck relay contact is also high on my list, so pull the metal cover off, and clean the contacts, CAREFULLY, and spray dry them with p/pack electrical cleaner. This applies to BOTH relays.

 

When the engine is running, the fuel pump is always running. Modern cars have a 'pressure on demand' pump system but the XJ-S didn't.

When you starr the car and let the fuel pump prime, it will run for a couple of seconds - timed by the ECU.

For the pump to run with the ignition off, theRe would have to be some kind of electrical supply to the pump which is not switched via ignition switch. Alternatively it can be a wrong relay, which switches power off when the ignition switch is on...

 

 

I suspect someone has changed some wiring around.

Although....crazy thought here....I one time spoke to an XJ6 owners who thought his fuel pump was making a racket when he shut the ignition off when, in fact, it was his power antenna motor.

Cheers
DD

 

Start at the pump positive lead and trace it to where it is going to. Nothing else for it. That live lead is coming from somewhere. Find out exactly where and let us know. If it is coming from a relay, then removing the relay, or the wires from the relay, will stop it. Then test if the low current side of the relay is always live (ie the low current signal that trips the relay is not stopping when the key is off). Then let us know what you find.

 

 

What switch?


Glad you're sorted out


Cheers
DD

 

There is still something wrong which really, you would be better off finding and fixing. If the live wire goes to the relay as it should per the diagram, and the relay is working as it should, the next question to determine is: "why is the relay low current input always live?". Test the low current wire to the relay; this should be live ONLY when the ignition is on. If it is always live, it would be better to follow the wire further up the system.