Hi I have a 93 Jaguar XJ5 Sovereign with 123K miles on board. When I turn on the ignition key, I can hear the starter motor running fine but the engine won't start. I got a new battery installed but the problem persisted. Then I went to Autozone and got the alternator tested, but they told me that the alternator was fine (the test they performed was to measure the voltage as the engine was on in Park at 2000 RPM). The spark plugs are about 3 months-old and are properly gapped (I gapped them myself and installed them according to the Haynes manual specifications). The problem I am describing above came about gradually, i.e. it became harder and harder for me to start the engine and eventually it didn't start at all (even with the new battery installed). I even bought a 600 Amp portable battery but the car still wouldn’t start even with the jumper battery properly connected.
While I was driving, there was no problem at all and the battery voltage indicator on the dashboard would continuously stay at the normal 14.4 V. This would continue until the car would come to a stop (in which case it would stall and die when I pushed the brake). A detail that may be important is that it would die in drive ONLY when I pushed the brake (if I did not push the brake the engine would stay on and rattle smoothly). Also, whenever the brake was pressed as the car came to a halt, the battery voltage meter would go down below the normal 12.5 V. This, to me, indicates a vacuum problem (the car can’t maintain vacuum and so it draws power from the battery when it brakes). However, it does not explain to me why the engine is so difficult (essentially impossible) to turn on.
My questions are


A. Is there indeed a vacuum problem?

B. If there is one, is it independent of the engine cranking problem?
C. How do I solve these problems? In the case of the vacuum, I'd have to inspect the vacuum hoses and such looking for cracks etc., but I'm not sure where to start. Any suggestions?

Thanks a lot in advance Andrei

 

Being a '93, it is an AJ6 engine, and has an "idle control valve", or "stepper motor", depending on the terminology in your part of the world. They assist with extra air to aid starting, and control idle relevant to the load on the engine, such as A/C, brkes, alternator load etc etc. These valves are well known to cake up with carbon, so the engine is hard to start, idles toooo slow, cannot compensate for load etc, just what you got I reckon. Pull it out, clean it, you may be lucky, if not a new one will be needed.

 

there was someone else with a 94 xj6 was having the same problem would crank but not start which is the same problem with my 94 xj6 he went thru changing the fuel pump or relay that wasn't the problem bought a scan and it said it was his crank shaft relay sensor he replaced it and his car is working fine. that may be my problem as well and your's to. but i'm just gonna purchace a scan as well. good luck