Jaguar Repair: XJ6 idles fine, dies in gear, air flow meter, gm unit

Question
Hi Howard,

I have an 87 XJ6-probably about 150Kmiles- that starts, idles and drives fine for about a minute, then the engine will stammer and die in gear.

I got about a half mile from home the other morning when this first started. I was going about 40mph when it sounded like my engine died.  I coasted to the side of the road.  Re-started it...it sounded fine.  I put it in gear and it quickly died.

If the engine is warm/hot it barely moves the car in gear or sputters to a stop. It seems to idle and rev fine in Park or Neutral.

I had my son put it in gear while I pushed in on the MAF valve with a screwdriver and the car started moving again.  I'm assuming I've got a bad sensor somewhere.  I cleaned the MAF, but it didn't help.
Any ideas where to look next?

(I know my fuel filter & pump, cap/rotor, plugs and wires are all good... and fairly new. ) I haven't checked the coil.  My next thought was to take off the throttle body and clean the TPS.  Good idea?

Thank you very much in advance!
Dave


Answer
Hi Dave,
This car has the Bosch "L" jetronic injection system and there are some tests that need to be done before you can condemn any part. Fuel pressure is critical so you need to know what the fuel pressure is at the time of failure. It needs to be about 32 PSI and when you apply a heavy load it needs to go to about 42 PSI. Did you try switching tanks when this problem started?
Your problem does sound like a fuel problem. The throttle position switch is just a full throttle switch and not in play with your problem. Even though a air flow meter can fail like that it usually stays failed and does not come and go. When you opened the door in the air flow meter you triggered the fuel pump but you still don't know what the pressure is.
The ignition can go until it heats up and get weak so you can test it with a timing light when it is failing. The module is a GM unit inside the box on the front of the intake manifold. The pick-up in the distributor is just a coil type and can be checked with an ohm meter. Air gap is about .015". When the engine is running wiggle the wires from the distributor to the module as they often break that lead.
Howard