I am curious as to whether anyone has had to replace their fuel pump module and if so what the symptoms were that led to replacing it.

My car is a 2006 XK8 convertible. I parked the car running perfectly and several weeks later it cranks but won't fire. I feel a little dumb that I was 99% sure the fuel pump had failed. However, I have a new pump installed and nothing. A lot of money thrown at a problem that was an incorrect diagnosis.

I've confirmed power to the fuel pump module and that the harness ground is good per electrical guide. I've confirmed continuity of the wiring from the fuel pump module connector to the connector at the connector at the top of the tank. I've also confirmed continuity of the pins top and bottom of the connector at the fuel tank that the pump plugs into and the harness connects to.

I've also inspected the ECM area up front and the harness front to rear. No damage, no mice, just perfect.

I've also sprayed a bit of starting fluid into the throttle body and the car fires so I know it is a fueling issue.

Curiously, the fuel gauge does not register either with the new pump and from what I can tell from electrical diagrams it is separate from the fuel pump module wiring. I find it hard to believe that both a new pump and the reostat on the float are inoperable out of the box on a new assembly.

I have a friend coming to help me see if power is leaving the fuel pump module to the tank connector when cranking. I don't have a way to test the ECM input into the fuel pump module.

​​​​​I really am a bit stumped and don't want to throw money at parts again without some kind of certainty. I'm just frustrated that it has been made so difficult to diagnose. A summer of top down driving lost🙁

Sorry for the long diatribe. Any insight would be welcomed.

 

Have you tried to reset the immobilizer?

 

Good thought but it is not an immobilizer issue. If the immobilizer were tripped the car would not crank at all. I literally parked a perfectly running car with a full tank of fuel and a few weeks later it no longer started. It was during a very hot stretch of weather so after confirming the pump was not coming on and I had no fuel pressure I changed the pump. Basically the diagnosis you would make on any other normal car on the planet. This was before I truly understood the wicked web of electronics to make a Jaguar run which I've had to dive deep into because I spent big dollars on a pump to no avail.

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Do you mean the inertia switch? Definitely worth checking if that has tripped as it will stop the fuel pump running.

The next thiing to check is that the control signal from the ECM is reaching the Fuel Pump Module - this is a pulse width modulated signal, so as ever this is where one of those cheap multimeter/oscilloscopes comes in very handy.

For those of us with 4.0 cars, the pump is either on or off, 12v or nothing, so easy to check. 4.2 owners have the more complicated pump, but at least you get slightly better fuel economy to compensate for the extra expense.

 

Yes, I should have said inertia switch.

 

Immobilizer/inertia, I knew what you meant so all good. I ruled that out long ago as, if tripped, it would prevent multiple systems from working, not just the fuel pump.

Talking with folks in my local Jag Club to see if anyone has an oscilloscope to check the signal.

Finally, you are correct the 4.2 is much better on fuel. Mine doesn't burn any at all🤪 (If I don't laugh I'd be crying at this point.)

 

Thanks to all who responded. After our local Jags and Java this morning one of our club members who is quite good with electrical came over ready to go to battle. (He is "The Fixer" here on the forum.) I showed him everything I had verified and then we began. One important note is that I had decided to perform the 8.5" hole in the rear deck modification of my convertible rather than pulling the tank when I originally changed the pump. Thank God I did as if I hadn't we would have never solved this. It allowed us to pull the vapor recovery top plate and the new pump a couple times during diagnosis. Had I pulled and reinstalled the tank we would have had no access and been dead in the water. It also allowed me to easily siphon some fuel out of the top of the tank so I could put my hand in and out of the tank.

First we verified various inputs and outputs at points on the harness itself per the electrical guide. All checked okay as I had thought. We then did some tests on the old pump. The pump itself was indeed bad. we momentarily put voltage to it and it struggled so we knew it was bad. I had no fuel showing on the gauge with the new pump so we pulled the vapor recovery plate and plugged the old pump into the connector, turned the key on and manually moved the old float and sure enough my dash showed as if there was fuel. A test of the new pump harness confirmed there was an issue so we decided to pull the new pump out of the tank. Not fun but only possible because I had made the access hole in the rear deck.

I got the new pump out, which I had bought on Rock Auto. It was from a reputable well known company so I figured it would be okay. It was also half the cost of a Jag pump but still $600.00. Once the pump was out we discovered on inspection that it had a wire broken on the rheostat for the float. After ample time for the gas and fumes to dissapate we soldered the wire, plugged it in to the harness and voilla it showed on the dash when manually moving the float. We also quickly put some voltage to the pump itself and it purred which confused me as I had it in the car and it would not build pressure. But now all seemed good so I reinstalled the pump.

We plugged the scanner in, turned the key on, the pump made noise but no fuel pressure......what. Had I bought a pump that ran but didn't build pressure and had a broken float gauge? I stuck my arm into the tank and pulled the fuel line off the tank connector (a magic trick of arm bending) and had my friend turn the key on....it ran but nothing out of the pump. Again thank God I had drilled the access hole as out came the pump again.

We had the pump on the ground and we were inspecting it when my friend suddenly said "Wait a minute, it can't be" We put the new and old pump next to each other and sure enough the factory had wired the new pump backwards. (it indeed has a + & - on it and the schematic shows that it matters.) It was running backwards! We got a teminal tool, changed the wires around, reinstalled the pump, and shazam 60psi and a car that was running and showed fuel level !!! I can't tell you how estactic I was. The car had been sitting in my garage since August.

So I had bought a pump that out of the box had a broken wire on the float and the pump wired backwards. If I had done the job by pulling the tank we would have never been able to do any of the tests we performed, I would have been totally baffled, and would have never been able to determine any of this in an afternoon. I still have to take the slug I cut out of the deck and make a cover out of it to put back in the deck hole, put all the bits and pieces back in the car including the rear seats, and button it all up. I have a couple codes but that is to be expected and hopefully they will clear up as I run it for a few days and check it on the scanner.

Many many thanks to "The Fixer" who was such a valuable helper and more importantly a good friend in spending his day to help. I never would have figured this out alone, nor stayed on task as we performed each test. Having two people definitely was essential. Many thanks to those who responded here trying to help.

And most importantly, Check your parts! Don't assume they were built correctly. I will be sending a note to both Rock Auto and the manufacturer of the pump telling them of the insanity they put me through. I'm also very fortunate that none of the electical modules don't seem harmed by the pump being wired backwards.

Hopefully going to take it straight to the gas station tomorrow and take it on a quick run with no more issues! A good day overall!

 

That is a really tough one to spot - brand new pump that will run, just not properly as it's backwards.

Well done for persevering.

 

Thank you. I was totally confused as all my electrical checks indicated nothing was wrong with the wiring. A fresh set of eyes on the problem was key, especially someone very knowledgeable in electrical.

That and having created the access hole when I first did the job. I can't imagine having had to pull the tank a second or third time. Some may cringe at the thought but once I make the cover plate and put it back together no one but me will know.

I don't regret doing it now!

 

Well done....

 

Are there any online instructions for cutting the 8.5 inch hole for convertible fuel pump access?
Like in exactly where to cut the hole. I can remember a video showing someone cutting the hole in wrong place. UGLY.

Thanks

Jack

 

Jack, I bought a 8.5 inch hole saw on Amazon and rented a HD 1/2" right angle drill to cut my hole. It takes some torque to turn an 8 inch hole saw. You can see in my pic that it jumped on me once, but I was very careful not to drill into the vapor recovery plate so I probably relaxed for a second and the saw jumped on me. (Damn near broke my thumb when it did) I removed the back seat completely and there is also a cross bar that once out gives you just enough room to work. I then removed the covering for the tank in the trunk so I could see the pump. There are some vent holes in the deck. I think they are still taped up in my picture as I didn't want chips to fly into the trunk and pump area. I used those vent holes as a point of reference to roughly measure to the center of the pump assembly and then transferred those measurements inside onto the deck. I drilled a very small pilot hole to verify I was where I wanted to be before using the hole saw. One other thing I did was to shorten the drill bit that came with the hole saw before I started. It is dang close and I didn't want to damage the pump while drilling. Finally I covered the pump in the trunk with a tinfoil tray I made to catch anything that fell while drilling. It does make a mess on the deck that had to be carefully vacuumed.

In the end it was measure ten times and drill once. It gives you access but I will tell you it still isn't a fun job. I had a full tank of fuel when the car died so once I got the vapor recovery plate off it was very easy to use a HF siphon pump to get the fuel out from the top of the tank. I don't know about older models but 2003 up has that type of pump and check valves in the fill tube so you can't just shove a hose down it to siphon the fuel off.

The pump is locked on a tang in the bottom of the tank and the connector hose from the pump to the exit of the tank is at the front of the tank. Removing that hose and the pump takes a bunch of arm twisting. That part would be easier with the tank out but I was able to do it and in this case it saved me as we removed the pump two more times as we tried to figure out what was going on. I would have been livid if I had to remove the tank a second and third time to solve what happened here.

Once I clean up the slug and make a cover plate out of it I will try to remember to post another picture.

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Thanks jluvzcarz, I hope I never have to do this job but if I do, I have a right angle nibbler where you drill a small hole and insert the nibbler and follow the cut line. I think that might work as it doesn't need but very little room underneath. The scary part for me is working in open gasoline inside the car with a steel rachet and socket to get pump unattached.
Thanks very much for taking time for detailed instructions. Very clever, well done.

Jack

 

Jack, a nibbler may work. I have one too and decided against it ultimately. The deck has a sound deadening material adhered to it that is about 1/8th thick. It is not really removable. I was afraid it would clog up a nibbler.

As far as removing the pump, the only mechanical jobs are disconnecting the hoses on the vapor recovery plate and the lock ring. Once you have access to the tank, and have siphoned the fuel off, the pump and the hose are removed by hand. You just squeeze the hose connector to release it and the pump is turned by hand to release it off the bottom of the tank. You are doing this from inside the car so you do have to wrangle your arms in very tight angles but obviously it's doable. Having the new pump to look at gives you a visual of what you are trying to do. Anytime I was not working in the tank I had another tinfoil cover I made to cover the hole so no debris fell in. Vapor was not a huge issue overall.

 

The sound deadening material would probably be a problem with nibbler.

Jack

 

I know some people don't like these kind of hacks to make jobs easier, but cutting a hole in the parcel shelf is on my winter to do list. The coupe has a hole, so why not add one to the convertible?

 

Removing the tank has a lot of parts and pieces that have to come out including disconnecting the line under the car which is a job in itself. More potential to break or screw something up in my opinion. I could be wrong but I don't ever see these XKs as ever being high dollar value cars so cutting a hole didn't upset me at all. To each his own though.

 

I think the plastic parts and electronics will be the killer of the wonderful cars. I'm too old to wait for them, or at least my 2005 to be old enough to not have to be inspected which is 30 yrs. old at which point you could strip them out and install a chevy engine with a carburetor. If the thought of that don't make you sick you are younger than me.(72) in a few weeks.
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I am fortunate to live nearby Motorcars in CT where Jaguars are the speciality. Dean the owner, who is well known in the business, has told us before that the modern 4.2 cars are harder to find parts for than the 4.0 models because they are fairly reliable. My 06 Victory Edition XK8 convertible will always stay stock have its 4.2 in it. That said, and I'm just a bit younger than you, and if I found an old 4.0 coupe with a bad motor I would consider putting a fuel injected LS in it if I could also find an old Grantley Design body kit for it. I think it would be a fun one off.

I'll keep it the way it is thank you. (Especially now that it runs again!)

But would LS and body kit one of these for something different.

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What's the fuel pump part number so we can avoid this in future