Jaguar Repair: 84 XJ6 loss of power, vacuum leaks, vacuum gauge

Question
I purchased an XJ6 from an individual and only traveled about 30 miles before I lost power. It was still running, but at low RPM and had no HP. I pulled over to find the entire length of the exhaust smoking and decided to pull the car. After 20 miles of pulling, I was able to start and drive the car another 10 miles before it lost power again, but this time, no smoke. I pulled it the rest of the way home (150 miles total)and found several vacuum lines either disconnected or rotted, etc and replaced those and have now driven it another 30 miles with no problems (yet). Is it possible for the vacuum leaks to have caused the condition I noted before, or is there perhaps something else lurking? I also thought I had a poor idle due to coolant temp sensor, but it idles now at 900 RPM (or so) and if I unplug the sensor, it dies immediately. Should I still replace?

Answer
Hi Michael,
It sounds like  you have several issues. It also sounds like the car has not been driven in a long time. With so many issues you need to start from scratch and do some testing as I would have to do if you brought the car to me in a dealership.

The first two tests require a compression gauge and a vacuum gauge with a long hose attached.
First and most important is to run a compression test (throttle open) and let me know the readings. Then set the timing to specs. 17 degrees as I remember but check that.
Next is a intake manifold vacuum test at idle, at 2000 RPM and take the car down the street under acceleration and read the vacuum as you go. (this is where you need the long hose, place the vacuum gauge under a wiper arm so you can see it driving) Again let me know the readings.

Don't replace anything unless you tested it to be bad as unless you have deep pockets you will run out of money before you run out of parts to replace. (Temp sensor does not control idle, the idle is controlled by the Aux air Valve but can be affected by the over run valve if it is sticking) The injection temp sensor controls fuel mixture through the engine coolant temp range.

I found out from working in several Jaguar dealerships over the years that symptoms may give you an idea of what section a problem is in, but other than to indicate something is wrong, symptoms are mostly useless information. Testing is the only method to locate a problem.

The injection system is a Bosch "L" Jetronic system which only requires a volt/ohm meter, a 12v test light and a "Noid" light (A Noid light is an inexpensive test light available at most auto parts stores) Get the Bosch / Lucas light as there are several different ones.

After you have done the first preliminary tests let me know the results and I will cover the next step.

Howard