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1989 Xjs convertible fuel pump runs with ignition off
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!
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'
I have just completed an engine swap with a lower mileage V12 and a complete drivetrain restoration. I am wondering will the shielded wire cause this problem? The shielded wire on the amp looks terrible and has be soldered on.
Thanks for the help!
Dean
That could be your problem right there, so well worth taking another look at the Shielded Wire and see what happens
The shielded wire appears to be intact. Is there anything else that could cause this? Possibly the ignition switch? I think I caused some confusion but when I pull the main pump relay (not the striped one) the pump will not operate.
Thanks!!
What can cause this pump to run without the ignition on?
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
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.
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?
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...
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...
Hi
I have since replaced the fuel pump and the problem is still there. The car will run fine but when I shut the ignition off the pump makes a clicking noise and surges. I pulled both to main and fuel pump relay and it will not quit. Could this problem be a bad ECU? Whatever it is, it’s bypassing both relays in the trunk and continuing to run the fuel pump.
Thanks for the help!
Dean
Hi
I have since replaced the fuel pump and the problem is still there. The car will run fine but when I shut the ignition off the pump makes a clicking noise and surges. I pulled both to main and fuel pump relay and it will not quit. Could this problem be a bad ECU? Whatever it is, it’s bypassing both relays in the trunk and continuing to run the fuel pump.
Thanks for the help!
Dean
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.
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.
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.
Hello all,
I traced the wire and it was correct to the wiring diagram. After replacing all relays with the correct relays and no luck, I just put the ground on a switch and it worked. When I drive the car I just turn the switch on and vice versa. It can also double as an antitheft device!
Thank you all for your help with my car!
Dean
[left]
Hello all,
I traced the wire and it was correct to the wiring diagram. After replacing all relays with the correct relays and no luck, I just put the ground on a switch
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.