94 XJ12 with 83k miles won't start when it's hot

Tiny
JAKE_GUMM
  • MEMBER
  • 1994 JAGUAR
My mechanic accidently made the car back fire into the manifold when reving the motor to check to see if the belts had quit sqealing after replacement. Since then it won't start when it's hot. They've had me replace the cap & rotor which didn't have any black or cracks in it, found a small vaccumme hose on the left side that was under the MAF sensor.

When it's cool in the morning its fine but by mid afternoon it won't start hardly, it will cough, shudder, back fire a little and die. I've found it will eventually start if I keep pumping the pedal like I do on my old farm truck and it will fire up and blow smoke out the back that has a strong gas odor to it. Once it's started it runs fine, idles fine it's just restarting it I go through the same process. What should I look at doing next? The VCM is giving fuel fail 13 for the MAP sensor and on this car it's apparently 2000$ as it's attached to the ECU for the entire injection system made just that way for just that car just that year. I'm trying to find another solution before plunking down that kind of cash on it and finding out that it was something else.

Thank you in advance!

Jake
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Sunday, August 12th, 2007 AT 7:21 AM

4 Replies

Tiny
RON MAYFIELD
  • MEMBER
Try finding a used MAP Sensor online or at a Salvage Yard instead of buying a new one. It should only cost around $25. So what if it does not work, if it does you just saved $1575! If you have fuel injection, I am surprised that you can pump the gas and start the car! There are no accelerator pumps on fuel injection. Backfiring through the carbs, if you have them, is another issue, but I would have your air/fuel mixture checked to see if you are within limits.
A well equipped garage should have an exhaust analyzer to determine if you are ok. In my experience, a backfire usually does not cause any harm, just means something is not right with the engine but it could be fuel, ignition or a timing problem.
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Thursday, October 18th, 2007 AT 3:45 PM
Tiny
JACK42
  • MEMBER
Dont forget to check the fuel pressure regulator for a blown diaphram
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Thursday, October 18th, 2007 AT 6:16 PM
Tiny
JAKE_GUMM
  • MEMBER
Actually it I found the problem after all. On the XJ6 and the XJ12's both there are relays under the hood up by the dash. If they are the light blue ones moisture can get into them and allow them to corrode. Apparently on the XJ12 the one plugged into the yellow connection is for both the O2 sensor heaters & the fuel pump. Replacing it with a black new sealed relay corrected the problem.
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Thursday, October 18th, 2007 AT 7:09 PM
Tiny
JACK42
  • MEMBER
Great find
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Friday, October 19th, 2007 AT 7:51 AM

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