Jaguar Repair: Jag XJ 12 1986, mode compression, starter fluid

Question
When the car starts cold it starts without problems. Once vehicle warms up and is driven for 1/2 hr, it will just quit without stuttering. After about 1/2 hr cool down it will restart and run again until it warms up and quits again. Could this be the fuel pump dying when it gets warm?

Answer
Hi Byron,
While it is true that it could be a fuel pump, it is also true that it can be one or more of a thousand things possible. It is useless to try to guess what it might be. The only method of diagnosis is testing, then replace only what has made it fail.

All engines only require three items to run with conditions on each. Compression , fire and fuel. Unfortunately there are a thousand items that can cause one or more of the three to fail.

It is relatively easy to test which of the three systems has failed thus narrowing the problem. You MUST however, test in the failed mode.

Compression can but usually will not just come and go so you can test in the fire and fuel. Fire is easy to test by just putting a timing light on a plug wire when it is in it's failed mode. Fuel is also not hard to test by just spraying starter fluid into both intake necks when it is in it's failed mode.

Once you have identified which system has failed (fire or fuel) then you can test further. Each MUST be tested in the failed mode. No fire at the plug then put the timing light on the coil wire to eliminate the cape and rotor. If no fire there test for a pulse signal at the negative side of the coil with a volt meter and test for power on the positive side of the coil (if it has the slave coil out front be sure to check for power and pulse there too.

If it was fuel test for fuel pressure at the fuel rail (32 to 42 PSI) if none (in the failed mode) test for power to the fuel pump. If no power get a wiring diagram and start testing relays etc. If that is where the problem is and you don't have a diagram let me know and I will put one up on my web site for you to copy.

In the mean time read my tech tip on starting a dead engine. http://mg-tri-jag.net/tech14.htm
Howard