I have a 1997 XK8 with an LPG conversion. When starting on petrol (which it does even with LPG selected), it is fine when cold but difficult when warm, it churns over and over before eventually stumbling into life and climbing to tickover revs. If left to cool for an hour after a run it is a little difficult to start, if left for 2 hours it is then very difficult to start. Hot weather makes matters worse. Cold starting is fine and so is hot starting, immediately after a run it restarts with ease, it is just when the car is neither hot nor cold that the problem arises. There are no warning lights and my MaxiScan MS509 shows no fault codes.

Any help with identifying the problem will be gratefully received.

Alan Kempster
JEC Member 46506

 

Probably better asking on LPG forums as well as it may be LPG related? there aren't many XK8 converted although it cant be much different from an XJ or S Type conversion.
But at first look I would be thinking it is a sensor issue possibly engine coolant temperature either Jag or LPG.

 

Is it still difficult to start with the LPG button 'off! (Ie forced into using petrol?). I can't help wondering if there is something wrong with the automatic switchover, making the engine attempt to start on LPG. You might be able to identify this by running the LPG completely out. Do this be running it out, then when it beeps at you, reselect LPG with the button, and be very light on the throttle until it beeps at you again. If you do this a few times, until you can't get it to switch over at all, you can be pretty confident you're fully back to gas only.

If it now behaves then it suggests that the gas changeover system might be at fault. My previous XKR I modified to LPG, and had a few problems with gas flow - quickly and permanently sorted. I am not an expert on the system, though. I had mine done at Gaspower in Exeter. They are closed now, but if you pm me I can firmly recommend a competent guy (used to work at Gaspower). He works part-time on this, and it would mean a trip right up to Cardiff; you might like to discuss it with him on the phone. If interested, pm me and I'll forward his phone number.

 

I know nothing of LPG conversions, and I would suspect the problem arises from the conversion, but outside of this in the petrol world I would also suspect a sensor. I had a non Jaguar car a few years back and it had an intermittent non start problem when warm, and would only crank and crank. Once cool enough it would fire right up. It ended up being the cam shaft postion sensor going out. Replaced it and no problems after that.

 

Just remembered had warm start problem on a Merc, which was solved by Cam sensor swap?
But it could be one of many things you really need to get some live data to help ifit aint setting codes, which could mean it is an LPG issue. Take it to an LPG specialist and have them do a service and possibly check the tuning map?