Hi all, completely new here so my apologies for requesting help straight away, but it is actually the main reason for signing up. For the last 6 months I have been trying to get my xj12 running again, after hibernation for about 2 years. I think I have read the entire internet, and screwed in and out every part of my jag but without any luck.
Here is what’s happening, when cold engine will run (only idle) for a couple of seconds and then stall. Starting it requires me to turn the throttle half way, it takes a while but than it starts but won’t rev above 1000RPM. turning the throttle any further does really make a difference. There has been one occurrence where after holding the throtle at 50%, it all of a sudden picked up and rev’'d up, after that it stalled and I was back where I started from.
I have measured all temperature sensors (at the ECU) and these are all within range, both when engine cold and hot. Replaced the maps sensor, the old one did not hold vacuum very well this one does, coil-resistance is within margin. (all resistance measured at the ECU btw, to make sure it not a wiring problem).The hall sensors work ok as well, tested this by using a magnet and I can hear the injectors clicking (which btw, I’ve cleaned and tested). Drained the fuel, replaced the fuel filter, added new fuel. Measured the fuel pressure, perfect 2.0bars, swapped the ECU, still same behaviour. Sparkplug are rather black but completely dry, so that would indicate a rich mixture, but can that prevent the engine from running? It’s not soaked? Plugs spark like there’s no tomorrow…
After cleaning the auxilary air valve, and checking this was working by holding it in warm and cold water, out of curiosity I tried starting with the air-tubes (the ones that lead to the manifolds) disconnected, so sucking air completely freely. The V12 started and ran perfectly smooth at idle +/-600RPM, after a couple of minutes the started climbing up to 750/800RPM and stabilized there. So idle was fine, but the second I touch the throttle it dies. Reconnected the tubes, started, idled for maybe 1 seconds and died again, disconnected the tubes, perfect idle. I removed the air filters (left the housing open), but this resulted in nothing. It really wants the breathe completely free.
I just don’t understand what the problem can be, looking at the sparkplug, and the fact that giving it a lot of extra air allows it to run (or at least idle), i tent to saying that it’s running too rich, but what could cause this? I though the only factors that influence the mixture are the temp sensors and the MAP sensor and these seem to be ok? To be on the safe side I disconnected the cold start injectors but this didn’t make any difference either.
Does anybody here have any clue what can be wrong, or what else I should/could check?
This is a cross post from jaguarforums.com, I’ve been helped by Grant Francis a lot, but unfortunately all his help still didn’t lead to a running engine so I’m hoping to find a bigger “audience” and more opinions here.
the link to the other post: https://www.jaguarforums.com/forum/xj6-xj12-series-i-ii-iii-16/xj12-sii-not-running-climbing-walls-222539/