I know this is a bit of an open ended question but any tips on where to start looking would be appreciated.
I live on a road with a speed limit of 100kph. Often The car has only been running for a minute or so before I take it onto the highway and accelerate to the speed limit. Lately when I do this the car is extremely sluggish and reluctant to accelerate, if the throttle is opened too wide power (or lack there of) will mildly oscillate. There is no smoke visible in the rear view mirror when this happens and once the car has warmed up a bit everything returns to normal.
I recommend that you provide the year, model, and engine (5.3L or 6.0L V12?) Jaguar you are having problems with and include the type of fuel delivery (carbs or EFI) and ignition system. Without that necessary information anyone replying with tips would be taking a shot in the dark.
Sorry Paul, you are right. It is an 1987 XJ12, 5.3 HE running a 16CU ECU.
I have very recently fixed a no crank issue by strapping the positive posts on the firewall but do not imagine that this would contribute to the sluggishness.
Does it start up readily? If not, perhaps the coolant temperature sensor (or the wiring) is faulty and the ECU doesn’t do its job for a cold engine.
You may also want to check your fuel filter. Unlikely, but if the filter is partially clogged, it may not be letting enough fuel.
It does not start with great eagerness but usually does so on the second attempt, this is a lot better since I replaced the ECU with a reconditioned 16CU about a year ago.
I have checked the CTS, it reads 2100 ohms at room temperature (28 C) when cold which is about where it should be with infinite resistance between each pin and earth. With the ignition switch on I also get 5 volts at the connector which loosely tells me that the connection to the ECU is good.
I had thought about the fuel filter and pump but I’d expect that these would be more of a problem when running at highway speeds which is not a problem once warmed up.
I’d assume you’re not getting the enrichment a cold engine requires. If CTS checks out OK then Air temp sensor is another input that influences mix. Is it in range as well?
