XJ81 starting issue

[Starbuck]

Hi Dave,

The specs for the gap are reasonably broad to allow for manufacturing tolerances, but they don't necessarily account for any set of combinations. Generally speaking if a shim is required it is installed at the factory and when you remove the sensor it will be there and will need to be reused. This cannot be guaranteed though depending on the supplier of the replacement sensor.

The front gap can be checked with non-metallic feeler gauges and shimmed if necessary.

The rear is a little more tricky. With the old sensor out of its bore, nudge the crank with a long extension bar and socket on the front pulley bolt until one of the teeth on the flywheel is visible, but close to one side of the bore (this is much easier with two people). I use dial verniers (a depth micrometer is specified) to measure the distance from the mounting surface to the top of the tooth. Record the measurement.

Now measure the height of the new sensor barrel and tooth, from the tip of the tooth to the mounting surface. Subtract this measurement from the first you recorded and it should be within the 0.457mm to 1.067mm specific by Jaguar. If it is less than the 0.457mm you will need to cut a shim from appropriate non-magnetic material that brings the distance within spec. I have never seen one over the 1.067mm, only ever under the 0.457mm and in both cases Jaguar had already fitted a stainless shim.

Good hunting,

Starbuck

[dstary]

Hello again all! It’s been a while since I have been on the site, so I thought I might provide you an update for the last six months of XJ81 motoring.

To summarise my issues, the car would occasionally fail to start (lots of cranking, fuel smell, but no spark), would sometimes start and run horribly roughly for a few seconds before the idle came up, and would sometimes be up and running and then stall (revs just plummeted to 0) a short distance from starting - when that happened, the car would always then fail to start despite lots of cranking, usually only firing into life 5-10mins later, and after that it would never stall later that trip.

The replacement extra air valve (EBC1198) was relatively easy to fit, and seemed to make the car run a little smoother once it was up to an idle, but didn’t cure long cranking while trying to start, or the odd stall.

So off the car went (late last year) to my mechanic to fit the flywheel and crankshaft position sensors (DBC12507 and DBC12508) and temperature switch/sensors. He did fit the position sensors, but didn’t get around to the temperature sensors. The car seemed cured, and was running well for a month or so before twice in a week it stalled while driving, and on another (albeit very hot) day I noticed the temperature gauge started creeping towards the red - the fuse for the cooling fans had blown, and in traffic with the A/C running there was insufficient airflow. They were fine after replacing the fuse. After this happened, I recalled the suggestions here about the passenger side fuse box, so off that went to be resoldered (it is VERY hard to find any for sale!).

The resoldering took a bit longer than I hoped, but while the fuse box was away I had more time to think about what had happened. I had had intermittent issues with two fairly minor things which I decided to live with until I got some time: the auto-dimming rear view mirror only worked sometimes, and the passenger side rear view mirror would not dip down when selecting reverse and toggling the mirror adjustment joystick down. Neither bothered me much, but as it transpires the fuses for those, and the cooling fans, are in fuse box 2 (passenger side for RHD cars). Fuse box came back, and hey presto, the mirrors now worked properly, the cooling fans have come on and off properly, but the car was still taking a bit of time to start, and sure enough, it stalled again in traffic having been running for only five minutes or so. Like the other times, this stall manifests itself with either revs dropping to 0 on coming to a stop, or hesitation at light throttle followed by revs falling to 0, and in either case, then not being able to start straight after.

Now I’m wondering how far I go with this. Do I send it in to my mechanic for weeks of methodical checking of connectors and signals to try and find something spurious? But then I had another think about it... long cranking (obviously when cold), stalling shortly into a drive (5 mins or so), then failing to start for some time, then once started didn’t stall again... it was clearly (again, as suggested here!) related to temperature. So I rummaged through the garage to find those two temperature sensors/switches (DBC12183 and DBC3729), and whacked them in.

Well since then I can report I have had no stall events, and the car fires into life quickly and regularly. So while the crank/flywheel sensors may have been suspect, I now believe that one or both of those temperature sensors was contributing to my stalling, but I clearly had fuse box issues too. For anyone experiencing similar, in order of difficulty I would recommend tackling those temperature sensors first.

All the best,

Dave

[abercanadian]

Happy ending to the story - surprised though that the mirror dips when in reverse - I thought that function was eliminated on the 94's?

(Mine doesn't have it)

Larry

[dstary]

Hi Larry,

I’m not sure how long the mirror dipping was around for, but it’s referred to in my owner’s handbook as being available with the seat memory function.



Dave

[rvdz]

Happy ending to the story - surprised though that the mirror dips when in reverse - I thought that function was eliminated on the 94's?

(Mine doesn't have it)

Larry

Mine is a late '94 car and has the mirror dipping function.

[abercanadian]

Lucky guys!

Although I should add I changed out the mirror on that side (right; LHD car) and installed a 91 model mirror; (had to modify wiring/plugs) however, don't remember ever having it before I swapped mirrors ..maybe only a delete on LHD cars?

Larry

[pimgmx]

Nope: also featured on my early MY 94 (Aug 1993 iirc) LHD Sovereign...

[naki_k]

Hello again all! It’s been a while since I have been on the site, so I thought I might provide you an update for the last six months of XJ81 motoring.

To summarise my issues, the car would occasionally fail to start (lots of cranking, fuel smell, but no spark), would sometimes start and run horribly roughly for a few seconds before the idle came up, and would sometimes be up and running and then stall (revs just plummeted to 0) a short distance from starting - when that happened, the car would always then fail to start despite lots of cranking, usually only firing into life 5-10mins later, and after that it would never stall later that trip.

The replacement extra air valve (EBC1198) was relatively easy to fit, and seemed to make the car run a little smoother once it was up to an idle, but didn’t cure long cranking while trying to start, or the odd stall.

So off the car went (late last year) to my mechanic to fit the flywheel and crankshaft position sensors (DBC12507 and DBC12508) and temperature switch/sensors. He did fit the position sensors, but didn’t get around to the temperature sensors. The car seemed cured, and was running well for a month or so before twice in a week it stalled while driving, and on another (albeit very hot) day I noticed the temperature gauge started creeping towards the red - the fuse for the cooling fans had blown, and in traffic with the A/C running there was insufficient airflow. They were fine after replacing the fuse. After this happened, I recalled the suggestions here about the passenger side fuse box, so off that went to be resoldered (it is VERY hard to find any for sale!).

The resoldering took a bit longer than I hoped, but while the fuse box was away I had more time to think about what had happened. I had had intermittent issues with two fairly minor things which I decided to live with until I got some time: the auto-dimming rear view mirror only worked sometimes, and the passenger side rear view mirror would not dip down when selecting reverse and toggling the mirror adjustment joystick down. Neither bothered me much, but as it transpires the fuses for those, and the cooling fans, are in fuse box 2 (passenger side for RHD cars). Fuse box came back, and hey presto, the mirrors now worked properly, the cooling fans have come on and off properly, but the car was still taking a bit of time to start, and sure enough, it stalled again in traffic having been running for only five minutes or so. Like the other times, this stall manifests itself with either revs dropping to 0 on coming to a stop, or hesitation at light throttle followed by revs falling to 0, and in either case, then not being able to start straight after.

Now I’m wondering how far I go with this. Do I send it in to my mechanic for weeks of methodical checking of connectors and signals to try and find something spurious? But then I had another think about it... long cranking (obviously when cold), stalling shortly into a drive (5 mins or so), then failing to start for some time, then once started didn’t stall again... it was clearly (again, as suggested here!) related to temperature. So I rummaged through the garage to find those two temperature sensors/switches (DBC12183 and DBC3729), and whacked them in.

Well since then I can report I have had no stall events, and the car fires into life quickly and regularly. So while the crank/flywheel sensors may have been suspect, I now believe that one or both of those temperature sensors was contributing to my stalling, but I clearly had fuse box issues too. For anyone experiencing similar, in order of difficulty I would recommend tackling those temperature sensors first.

All the best,

Dave

Nice easy fixes ultimately. So often running issues can be traced back to one of the sensors/ valves. Did nothing show up on the VCM?

The fuseboxes will go or have gone on all battery in boot XJ40 sooner or later. I just did another set yesterday on one of mine.

[dstary]

Often nothing on the VCM when that happened, but sometimes I’d get a fail code. I can’t remember which it was, but at the time it was indicating a mismatch between the crank and fly position sensors. On my last stalls (after those sensors were changed) it never had a code, so I might have had simultaneous issues.

Dave