Jaguar Repair: 1984 SeriesIII Federal wont drive when warm, mate brad, u bolt

Question
Hi Howard, Back again with my hiccuping Jag, Thanks for your earlier help. I finally got the car started by getting the injectors serviced, system flushed & disconnecting the LHS tank temporarily as it was rusted bad. So, we got the car going, it even drives quite nice.....until it reaches operating temp. Then it stalls, coughs, farts and back fires on hills then you have to limp home idling all the way, the car refusing to rev. The temp remains stable and there is no obvious smoke at rear. When you pull over it idles roughly and will continue to do so until you turn the key off. Restart it idles smooth, but a bit high, around 1300rpm but as soon as you accellerate it farts and dies again. The over revving seems to be caused mostly by the clamp on the kickdown cable fouling as when you blip the throttle it drops back to around 750rpm. (kickdown cable is on list to do, just want it to actually Run first,lol)I had it over to the Exhaust place and they tightened up a muffler U bolt and checked the rest of the system including the Cat and said it was OK. The guy's a mate of mine so I'm guessing my problem doesn't lie there. I have had experiences before where coils can overheat and cause drama's so just been for a test drive, it went fine until op temp then the drama's started so having taken a spray bottle of water I cooled the coil and tried to drive - no change so I guess that rules out the coil. When we got the car going we put a brand new fuel pump in, just so it was done but this issue remained so I've put the original pump, which tested OK pressurewise back in to save the new one. Any idea's Howard?
Thanks mate, Brad.

Answer
Hi Brad,

My guess is that the injectors needed work because of the rust in the fuel had got past the fuel filter and may still be a problem.

When you have a running problem you MUST be able to see fire (spark) and Fuel. Did you run a compression test? This tells if the engine is ok.

A coil is easy to test. Just connect up a timing light to the coil wire (not a plug wire) and tape the trigger down and place the light under a wiper arm and drive the car to get the poor running condition. Watch the flash of the light as you drive the car. If it is a bright sunny day and the light is hard to see, tape a piece of cardboard over the windshield so you can see the flash of the timing light. Any misfire in the coil will show up as "Blinks" in the steady flash of the light. Without a scope, this is a good test of the secondary of the ignition system. After running this test move the pick up over to plug wires one at a time to see if a miss can be noted. If no blink is noted you can forget ignition as the cause. Cooling a coil with water does not rule out a coil.

You can't see the injection without a test stand set up to test injectors but you can see fuel supply to the system at the time of failure. Connect a "T" in the fuel line just before the fuel rail and connect a long high pressure hose to the "T" and run the hose out to a pressure gauge (I found a 0 to 100 PSI gauge in industrial supply dirt cheap) and put the gauge under a wiper arm facing in so you can monitor fuel pressure while driving (be sure to put hose clamps at each connection) Pressure should be about 32 PSI running and about 42 at open throttle settings.

I don't want to question your friends advice that the CATs were ok but end result is amount of exhaust back pressure at idle and at high RPM. How mush back pressure did it have?

Symptoms are ONLY useful to tell you something is wrong. Other than that they are useless. Testing is the ONLY method to find a problem.
Howard