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,
1985 XJS HE (manual conversion)
1994 Daimler Double Six (XJ81)