Hey everyone,

sorry for my English, I try my very best with help....well: My XJR ran perfectly for 500 km on the north side of the Alps, but then suddenly stalled for the first time on the south side—with the check engine light coming on—so we had to load it onto a trailer.

We’re still trying to figure out what’s going on. When the weather was cooler, the car ran for a few hundred more kilometers without any issues. But now that it’s gotten warmer this week, the problem is back:

Most of the time, the engine stalls at low RPM, like when I’m coasting up to a red light. But sometimes it happens while driving, too: suddenly the revs drop from 3000 to 2700 with a jerk, and then it usually catches itself again. You can drive maybe 20 km if you’re willing to put up with 20-30 stutters and restart the car at every stoplight. The weird thing is, it always starts up again right away like nothing happened.

We’re lucky enough to have a WDS at home, but it doesn’t show a single error code. The WDS works great—helped us find faulty lambda sensors and some other issues, and the car has been fully checked through. But right now, no errors are coming up at all. Even a standard scanner that can at least read the engine ECU finds nothing.

Just to be safe, we already replaced the fuel pumps—but that wasn’t it. What’s interesting: the bucking always starts right before the check engine light comes on. Even when idling, you can hear the fuel pump relay clicking in the trunk just before it dies. So the relay is being triggered. We tested the relay itself—it works perfectly. It’s apparently getting the signal from the ECU to cut the fuel supply. After it dies like this, the ECU itself seems to lose power and has to reboot— you can tell because the diagnostics tester normally connects in 2-3 seconds, but after a stall, it takes 14 seconds before it’s back, even though the ignition stays switched on the whole time.

We also checked the ECU relay up front by the right headlight, to see if maybe it was cutting power to the ECU. That seemed fine, too—we swapped it and nothing changed.

So something is cutting the car’s power, especially when it gets warm. It has to be something that doesn’t show up on diagnostics. Anybody got any ideas? Anyone ever had something like this caused by a sensor? Or any other tips or things to check?

Thanks in advance!
dieselflo

 

Change the crank sensor, it’s something that can fail when hot nd is not that expensive to swap.

https://www.sngbarratt.com/English/U...on%20sensor%60

good luck!

 

The crankshaft position sensor is a enable that closes the fuel pump (s) relay

The CKPS can fail in the fuel pump enable aspect of the single CKPS signal being used for other aspects and still be OK like ignition timing and tachometer ( 300 on engine start ) . The CKPS CEL code P0335 rarely shows

A cheap try is to clean the CKPS sensor " face " looking at the target , different than sensor connector cleaning

Some keep a spare CKPS in the trunk from reading

You can directly power the # 1 fuel pump with a jumper wire between sockets 3 and 5 with a blade type medium gauge wire end

There is a secret fuse that is the control power ( the ECU provides a ground ) to close the fuel pump relay ( both in your case ) that has to have the relay in the corner of the fuse box remain closed , you can swap this relay with the left engine bay fuse box relay ( only controls the car horns in the left bay position )

Notice I have circled the large 48 pin BT4 connector above the fuel tank , there should be a tie wrap on it holding the lock bar closed , do not open connector unless you have to as can break the lock bar pins putting it back together and then your up the creek

Off the top of my head the fuel pump relay control power is pin 31 and the ECU provided ground to close relay is pin 16

There is a simple whole power to all points of car test if needed and fortunately the ignition switch ( heart of the electrical distribution system ) can be changed leaving the key barrel in place so no new key needed

 

Thanks a lot for your help! We changed the CKPS yesterday, now the XJR is running without problems. The car did that from time to time, so maybe it is too early to believe in a solution, but i will tell...

best regards from Stuttgart
dieselflo

 

this blows my mind sometimes...

A Jaguar breaks while trying to drive in the Alps.
A post is made
A person in London and Kansas City give advice
Meanwhile my XJ6 is doing similar things (close enough)
Not only is the Jaguar trying to drive in the Alps fixed
Unknown to anyone else - so is mine in Louisiana.

Thank You to the man whose car broke down and made the post
Thank You to London and Kansas City

 

A good CKPS will read about 1300 ohms as a basic meter reading , functional different as requires a scope

I blow a CKPS on car battery hooked up backwards .........................................twice

There was a resent post on the quality / worth the effort different manufactures of this generic part and a flag on one manufacture

 

was thinking maybe replace mine to try and further diagnose. now previously i did replace it but i replaced with a cheapish generic one.
what is one that is good to get and ones that are good to avoid?
i previously chose what was listed here as the $27 option

 

I have exclusively purchased the cheap ones on Amazon with long lasting results. I daily drive my car.

Its possible that it was a dud, but I wouldn't necessarily avoid the cheap ones.

I purchased a Walker branded one, which is a legit brand, by the way. Then I purchased one from A-Premium. I purchased the Walker in 2021, and I don't know why I replaced it, but I did in 2024 with the A-Premium. No issues.

 

well i will swap it out with a 2nd hand spare one and see if any difference before buying anything else.
first time i have heard anyone mention a-premium.
i just purchased a landrover MAF from there recently as ours is not available and this is the same except i had to cut a notch in the pip in the car as the landrover one is mounted upside down.