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Eric, Automotive Repair Shop Manager
Category: Jaguar
Satisfied Customers: 31909
Experience:  Automotive Repair Shop Manager, Technician/JA Mentor
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I have 2 Jaguars. 1991 & 1992 xj6 w/4.0 automatics. The 91

Customer Question

I have 2 Jaguars. 1991 & 1992 xj6 w/4.0 automatics. The 91 is a daily driver to work. Any way the 91 didn't start one day, but did for 3 seconds. Went to restart and got nothing. No spark at coil, plugs, and nothing at injectors. After reading changed out the crank position sensor (taking it from the 92 Jaguar). Well it started, "ya". Drove it 4 blocks, then the dash gauges went crazy, door locks went down, dome lights came on, windshield "wiper intermiten" came on. The car wanted to die, but reving it kept it going. In a*****it did this 4 times and then recovering. Does it more at idling and lower RPMs. Rebooted the ECU by removing Neg., turning the switch on then touching Neg. to the Positive for 30minutes. With no results. Now don't trust taking it from the house. Have changed out/traded from the 92 since it has never had an electrical problem. But problem still existed after trading out. Coil, Coil Amplifier,ECU, Micro processor, relay for the CPU, P.I. circuit, & instrument Pack Memory. I have changed these items out singly and have put the old 91crank position module back into the 92 and the 92 has started with no problems. I have checked battery neg. at the firewall & starter, Pos. at the firewall insulater. It seems it takes a little longer before the gauges go wild now, but think now changing the crank position sensor could have been a coincidence. Was thinking it could be ignition in the running position because of the flickering of the gauges. But that wouldn"t answer the 1st problem of not starting, "car would have started in the start position, then acted up in the running position". Live in Oregon, no rust on ECU or Micro Prosesor.
Submitted: 1 year ago.
Category: Jaguar
Expert:  Eric replied 1 year ago.


I am sorry that you have not been helped yet. I just came online and saw your question.

A couple of things come to mind - charging system issue, loose/corroded body ground. I need the vin number to pull the schematics for all these circuits to see if there is a shared ground on them as well as any other common denominator

Customer: replied 1 year ago.
To add to more information, pushing the VCM (on board diagnosis) only shows PRO (what ever that means). Was reading nothing would show wrong on VCM if crankcase position sensor was ever wrong because that is like shutting of the ignition key.
The 1991 Jaguar xj6 vin# ***** I have owned and drove the 91 Jag now for 6 yrs. In that time I have loaned the car out and twice it has just stopped on them. I show up to help and it has started right up. No figure. Would sound like ECU was going. But same reaction when 92 Jag ECU was changed out.
Expert:  Eric replied 1 year ago.


Ok, let me pull schematics and see what I can find

Customer: replied 1 year ago.
Have not got any answer back in 3 days. Eric said He was going look at schematics to see if Starting System was related in some way to Gauges going bazerk, Door locks going down, and Intermiten wiper coming on. Found out there is a rotary switch in the back of Ignition key lock. Could this be shorting out while going down the road and same for Starting system?
Expert:  Eric replied 1 year ago.


I am very sorry. For some reason your question disappeared off my list.

That switch is the ignition switch which feeds power to all these systems. I have looked at the schematics and this is the most likely cause of the issues.

Customer: replied 1 year ago.
Changed out the ignition, same thing happends. Gauges going wild, door locks down, intermitten wiper comes on. Also notice the clock if set to say 1:00 will flip to 2:00 when done cranking engine. When I put 91 Jag items into 92 Jag, that one still starts with ECU, Microproccessor, Coil Amplifier, Crankshaft Position sensor, all the Relays under dash of ECU, Battery, and now Ignition Lock Switch. I got down and dirty under vehicle, tightend every ground body to engine, double checked Starter Pos. nut, took out battery box and checked under the base where Positive cables go into interior where hooks to Fuse box and then to ECU, etc.Now have gone back to basics. Engine won't start. Even though everything goes wild. I have spark & gas. Assume the Crankshaft position sensor works (because ECU won't turn these things on without movement from Crankshaft sensor).Have also took out every fuse in vehicle that does not relate to starting, to see if engine starts. Dash, door lock logic, etc. Engine does not start and I smell gas. At this point of so much cranking, the spark plugs could be gas soaked. How one thing can get so deep!
Expert:  Eric replied 1 year ago.


Hmmm, I am a bit stumped. I am going to opt out and have other experts take a look and see if they have any ideas on this one

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