Jaguar Repair: 1985 JAG XJ6 Series 3, vacuum gauge, brain cells

Question
Hello Howard,
My car Starts fine, runs ok cold, but when it warms up a bit it start to bog out and misfire when I accelerate only and worst under a load.  I did your test with the timing light, great compression at all cylinders, good fuel delivery. The test tells me it's a fire problem. I have replaced the thermo time switch, the coolant temp switch, the coil, all spark plugs  and wires, rewired all bad and cracked wires new battery correctly set timing and still............it doesn't run right. PLEASE.....Help me....I am very familiar with this car and I am a good mechanic so if I can just figure this out I can fix it. I am out of money and brain cells:) Please......Help me.....
Thank you, Marie

Answer
Hi Marie,
You said you think it is a fire problem. Did you put the timing light on the coil wire and run the wires out from under the hood and put the light under a wiper arm and tape the trigger down and drive the car and watch the flash of the light?

Is the "misfire" a quick harsh jerk or does the car just kind of mush out of power and run ok at low speeds and low load?

To help the "Out of money" problem quit buying parts until we find the problem part. You are not out of brain cells yet. Sometimes when I feel that way (often) I divide the car into sections and eliminate sections until to narrow the problem to smaller and smaller section and I always find the problem that way. When working in dealerships I had to do that as there were no options that had the words that "can't" in it. (not that I always fixed problems quickly) but ALL had to be fixed. So lets divide the car up a little more.

What were your compression readings? and what fuel pressure did you see? and tell me after the timing light run what you had. And do one more test, put a vacuum gauge on the intake manifold and run the gauge out from under the hood and read it also as you SLOWLY go up to the speed that it misfires at and tell me the vacuum reading. We will find the problem!
Howard