Engine Ran 5 seconds then quit

Recently my well running XJR (X308) engine quit! One morning I cranked it, ran for about 5 seconds then it shut down. The motor will crank over fine but will not start. While cranking Tac needle comes off the peg so I don’t suspect a Crank Sensor failure. What I suspect is a Camshaft sensor failure. It’s an AJ26 motor so where is the cam sensor and how to replace it? Any and all suggestions/help would be most appreciated.


Do you have fuel pressure? Any codes?

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fuel pumps are an issue on these.
But an XJR has 2. One happens to be used for starting and the other running so its a little unlikely ?
Both run over ~4000RPM

Cam sensor is at the bulkhead end. And I think the throttle body requires removal to change it.

My guess “wash down” causing lack of compression, is a feature of the early X308! Remove all spark plugs and squirt a little oil into each cylinder.
Or floor the accelerator WOT and crank for 30 or so seconds, there is a risk of backfire blowing the airbox but it is the easier option.

Neil is on too something but…
How many miles on the engine
What year
Washing was a BIG problem but so was chains, tensioners and pumps.
OBD2 What codes.
goood luck.

Here more info:
Original 1999 (AJ26) motor overheated due to a heater hose routing design flaw by Jaguar (approx 23,000 miles). Also, the temp gauge is nothing but a visual “Idiot light”, designed to stay centered UNTIL coolant temp is at the boiling point. Then it will immediately go to full HOT. Jaguar was having too many complaints and modified the computer to act this way. There is another “enthusiast” that sells a module to convert the gauge back to an “actual reading gauge”. That’s for another discussion.

Replacement motor from a 2000 XJR with 31,000 original miles - rear end accident. Had to convert that motor (AJ27) back to an AJ26 version (that was fun). While building up all timing components were changed/upgraded. Also found one valve required adjustment. The original transmission was re-installed and functioned normally. Afterwards the car has driven normally for about 10,000 miles except for a fuel pumps issue.

A couple of years ago the car became hard to restart. Finally had to have it towed home. Diagnosis: Failure of BOTH fuel pumps. Replaced along with new filters. Could not believe BOTH pumps failed with less than 30,000 miles operationally. Installed top-of-the-line BOSCH pumps. Solved starting/re-starting issue.

Several weeks ago I went to start the car. It started, ran for about 4 to 5 seconds, then shut down. Subsequent starting tries unsuccessful. Checked fuel rail pressure with gauge. OK - pumps working.

Cranking over the motor the tachometer needle comes off the peg. I am taking that as an indication the Crank Position sensor is functioning. Have not replaced it.

The only other likely component that would cause the non-start problem I deduced is the Cam Reluctor Sensor. Have not replaced it as I’m not sure how to remove it.

I have an OBDII hand-held reader and it’s showing no codes or Check Engine light malfunction.

My main question is: I know the Reluctor sensor is on the left rear head. How best to remove/replace it?
I also have not tested to see if there is spark or electric pulse to the coil(s).
When working properly this car is a joy to drive. It doesn’t really start breathing until about 80 MPH! New Michelin tires solved the Pirelli P-Zero flat spot issues. Can’t believe Jaguar ever put Pirelli’s on that car; they pure crap IMHO. I’m sure others will disagree!!!

At 70 I’m getting slower and slower working on my Jags. So, if anyone can help with instructions on how to remove the cam sensor I may be able to make progress and get this wonderful car back on the road. Oh yes, New battery installed a month ago!

Removed/Installed all by myself. Yes, it can be done. Just worried about hoist holding the weight!!!

Old motor coming out. Heads overheated/dropped 2 valves. Motor replaced.

Stay Well and Happy Trails,


Good point Joyey, but if the engine spins freely and almost silently (not pumping) try the oil in the bores.
I don’t recall many if any any failures for the CPS other than it being installed incorrectly causing prolonged cranking as the ECM sort out TDC.

If we flatbed and get to a dealer it’s a lot cheaper than cranking the key if the tensioner or chains popped😀

Coming to this thread late, but my car is a 1999 xj8 sovreign 4l x308 aj27 engine, Same problem, stalled when idling after start up. Refused to restart after all attempts for a flooded engine.Turned out to be contaminated petrol with water. The night before had torrential rain, car parked outside. The petrol filler reservoir was full of water, the drain hole blocked with leaves. Water had made it through to the tank. Solved by draining petrol tank, refilled with fresh petrol, dry fuel additive plus injector cleaner and new fuel filter. Boom…runs like a dream.

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Hi John,

Water in the tank… Something I haven’t considered but will further investigate this week. Thanks for the tip.

Happy Trails,


In a message dated 11/1/2023 3:59:27 PM Eastern Daylight Time, noreply@jag-lovers.com writes:

If it starts for 5 seconds most likely the fuel pump has failed. Theres 2 on the XJR. At startup both run and the second then stops and is used at high speed. This means the first pump has failed, which is why it runs for 5 seconds. you can jump the 2nd fuel pump in the fuse box in the boot (trunk) to see if this fixs the problem. i.e run of the second one

Hi Simon,

Thank you for the fuel pump advice. About 20,000 miles ago I had BOTH fuel pumps replaced. Will continue to investigate! Just love these computer controlled cars!!! Give me 12 cylinders, 4 carbs any day!!!

Happy Trails,


In a message dated 1/18/2024 10:12:02 AM Eastern Standard Time, noreply@jag-lovers.com writes: