92 xj6 sovereign with 150k miles

A few weeks ago I tried to start the car and while it turned over it wouldn’t start. The limp mode light, abs, and brake lights all came on. After reading up, fixed the abs/brake with new accumulator ball. Went through the limp mode “checklist” and everything passed. I’m getting spark but did notice the fuel pump wasn’t coming on and the fuel rail had little to no fuel in it after being primed.

I have 12v at the relay but not at the connector in the trunk ahead of the fuel pump. I replaced the fuel pump relay with another relay and still 0v at the connector in the trunk. When I jump out the fuel pump relay, I have 12v at said connector. I tried leaving the original fuel pump relay in place and replacing the o2 relay and still no voltage in the trunk. This was the o2 relay in the Front passengers footwell. Then I applied 12v from an independent source to the fuel pump side of the connector in the trunk and it did not come on. I’m thinking the wiring to the fuel pump (with the diode) may be bad and/or the fuel pump itself but I’m not sure why I’m not getting 12v into the trunk through the relay. I have the key turned to the “on” or second position when testing for voltage. Also, I have had the battery on a trickle charge to keep it up and avoid problems with low voltage from it causing problems.

any thoughts would be appreciated.

thanks

 

Hi dtrain,

Just a couple of quick thoughts: first, the ECM will only power the fuel pump relay for a few seconds when the key is turned to position II (ON) without cranking the engine to prime the fuel rail but not run the pump continuously before the engine starts. Once the ECM detects engine rotation via the CPS, it provides continuous power to the pump relay.

You can also measure the resistance across the wires to the pump at the relay socket to see if you have very low or very high resistance. On our '93 the diode or capacitor in the noise reduction circuit near the pump connector burned and prevented the pump from running. The '92 schematics show that you have only a "suppression resistor" across the wires to your pump, but you may find that you have more.

If you don't have the schematics, you can download them here:

Jaguar XJ40 Electrical Guide 1991-1992

Cheers,

Don

 

Thanks Don


I’ll look over the wiring diagram. Any reason the pump wouldn’t run with 12v applied directly to it other than it needs to be replaced? If I remember right, the resistance was very low across the wires leading to the pump.

 

There's some issues with the connection between the pump and plastic the flange on top of the tank, can't remember details but try an archive search for "evaporative flange".

May help if that's your problem ...on my own car, the pump had failed and had to be replaced.

Larry

 

At this point, I have determined that the fuel pump is not functioning. It is relatively new so I feel as though there is a good chance the problem is the electrical connection at the evaporator flange. Can this be checked without removing the tank?

If not, can someone direct me to the procedure for removing the tank? I did a search and found some general references but nothing with more detail. I also have about 1/2+ tank of gas that would need to be removed as well. Anyone have a good way to remove the gas without getting a bath?

Thanks

 

Hi dtrain,

You can bypass the fuel pump relay by forming a large paperclip into a U and using it to jump terminals 30 and 87 in the fuel pump relay socket. If the fuel pump doesn't run, try measuring for battery voltage at the evaporative flange electrical connector while jumping the relay socket.

If you still have no voltage at the connector, there could be a break in the wire between the relay and the pump. To test, set your meter to its lowest ohms setting and measure for continuity (near 0 ohms resistance) between the terminal for the Blue wire with Red tracer line at the evaporative flange connector and terminal 87 in the fuel pump relay socket. Then test for continuity between the terminal for the black wire at the flange connector and a good ground, such as the battery negative cable.

Another possibility is that the suppression resistor may have bridged, causing a lower resistance path for current to travel, bypassing the pump. The suppression resistor is spliced into the harness near the connector at the evaporative flange, and probably covered with heavy heat shrink tubing. The symbol for this resistor is the zig-zag line with the backward S across it that is shown wired in parallel with the pump in the 1991 schematic below (I don't have a 1992 specific schematic on this computer). To test for a bridged resistor, check for continuity between the two terminals in the connector at the evaporative flange.


I believe your 1992 probably has the resistor, but if it has the 1993 setup, in place of the resistor it has a zener diode and capacitor wired across the harness near the evaporative flange connector. On our 1993, either the diode or capacitor overheated and bridged, causing a short that starved the fuel pump of current. Here's the 1993-94 setup:




If your '92 has the '93 setup, there is an additional electrical connector between the fuel pump relay and the evaporative flange connector. This additional connector is on the bulkhead forward of/behind the battery. On our '93, this connector once burned and opened up, breaking the electrical connection to the fuel pump, causing a sudden cranks-no-start condition.

Please keep us informed!

Cheers,

Don

 

Since I didn't have a garage to work in, I took the car to a local mechanic and he replaced the fuel pump and resister. Car has run well for about a month and then I started smelling gas. I had just filled up the tank and when I got back, parked and came back later, I could smell the gas inside the cabin but even more in the trunk. I pulled everything apart and found a little bit of gas in several areas. I wiped everything down and had my wife start the car, move forward/backward but couldn't see a leak anywhere. I left it for a day or two and came back to find more gas along the tank and the shelf it sits on as well as the wiring/supply/return gas lines.
Here's the crazy part:
The connector for the fuel pump was wet so I moved it and tucked it under the insulation on the top of the tank to keep it out of the way. when I returned to check the trunk, there was gas "coming from the connector..."
I pulled it around and checked it but couldn't see any gas on the lines from the fuel pump to the connection (maybe 6" or so of wire), the connector was wet with gas and the wires after the connector were also wet.
Is it possible that it leaked from the fuel pump and ran down the wires to the connector where it built up and began running down the tank? Then the 6" of wire coming from the pump to the connector just dried out while the rest remained wet?

The first pic is where the connector was initially tucked under/along the gas line. Next two pics show where I moved the connector and now there's gas on the connector and down along the gas tank where it was stationed.

 

It is common for the insulation pad on top of the tank to become saturated with fuel. Is it possible fuel was dripping from the pad into the connector?

Cheers,

Don

 

I'll check the pad. Originally the wiring ran along the vapor line and up to the pump (not near the insulation) and there was gas on it. I moved it and tucked it under the insulation to avoid more gas getting on the connector thinking it may be coming from the flange at the top of the tank but the connector was saturated again when left under the insulation.

 

I was able to check everything today. No gas on the insulation.

Here's my thought: Can the gas be exiting the tank in the wires themselves? I'm wondering if it can be making it's way through capillary action inside the insulation. I don't know how the wires are attached once they are inside the tank so I can't say if they make contact with the gas in the tank when it's full. Any thoughts?

 

That is certainly possible, at least theoretically. The wires connect to the fuel pump motor, which is submerged in fuel, so the wires could wick fuel up into the connector.

 

While I agree in theory about the wicking idea, I think it is more likely that the leak is from a damaged or loose locking ring at the flange or the vent hose is loose, split etc.

Larry