Hi all
I would need some tips how / where to start to find the problem with my XJ12 -76 (electronic fuel injection)

Problem 1. Today
Drove 5min today and the car started to run really bad. Wouldnt rev and lost power. with full throttle it would spit a bit and then rev up. I got it towed home while running engine in idle (Ran quite rough in idle and stinks fuel). Spark plugs loooked ok when I came home.

Problem 2: two weeks ago
I drove 20min -> stopped 30min with closed hood -> When starting again the car ran really bad and wouldnt rev. After cooling down it ran fine home. Vapor lock syndrome?

Other info:
I newly have 95 Octane in the tank. In the winter I had 98.
Bot cases ambient temp around 20degC.
I first started using the car November last year so Have not really tested it much until now but it always ran fine.
Oil pressure and water temp always ok.

My best guess so far is something with the fuel system. Temp or vacuum sensor broken? Mybe not enough fuel pressure? But why would it run fine for 5 minutes?

Grateful for any tips where to start

br
Marcus

 

"Newly have 95 octane" Did you just recently pump fuel and it started this? You know where I'm going... Not uncommon at all.

 

It's possible that the coolant temp sender is failing. The car will run ok when cold because it needs the extra enrichment, but needs less and less as it warms up. If you can measure the resistance of the sender at various temperatures (such as in a pan of water on the stove) and see what it does.\

It's a standard bosch sender, there are tables of the resistance vs temperature either here or in Jag-Lovers somewhere.

 

I had an open circuit coolant temp sensor in an XJ6 I had years ago and it did exactly what your car is doing. I fixed the broken wire which fixed the problem but a dodgy sensor could give you the same symptoms.

It would be worth checking the CTS and all the connectors.

If you google ‘Jaguar CTS test’ you will get some good info on how to test your CTS.

Cheers,
Jeff.

 

Fuel smell can mean the injector loom is shorting out and wildly overfuelling, which also gives some of your symptoms. Check if the loom insulation is cracking up.

 

Couple of things to assist us ,PLEASE.

Location?, the use of HOOD tilts to USA, C temp and 95/98 fuel, dunno.

Is it still fitted with the D Jetronic EFI system?
Is it still fitted with the Opus Ignition system ??, if YES, here, where is the Opus Amp. Factory fitmant was in the V, in front of dizzy, and proved problematic and even fatal, especially after 10 or 15 minutes, when it got heated up in that V location. Relocation was a "thing" back in the day, by complaint only.
EFI loom, YES.
CTS and its wiring, YES.
MAP sensor vac hose, and then the electric plug on the side of that sucker.
Trigger board inside the dizzy, for the EFI system, oh boy, then the magnet in the heel of the rotor, old age is at that now.
"Plugs look OK", that has me heading for Ignition, and Opus issues. As these things soot up plugs without any help from us, and they will NOT burn them clean, if they overfuel at all.

The list goes on, as do the nightmares of these beast when I was much younger. 100's of hours spent on them.

Fill in the blanks, help us to help you.

 

I would still check fuel for water contamination first, it's happened to me several times over the years. Pumped it right in there from the gas station.

 

Hi again
Thanks for all the tips. I finally have some time to start searching for problems.

Started it up now and got it out of the garage. Still runs rough and unwilling to rev so problem doesnt occur only with warm engine.

More info:
- My location: Switzerland.
- The injection parts are all original as far as I know. Placed on top of the radiator.
- Vacuum sensor was just repaired by Dr D-Jetronic in Germany so that shouldnt be the issue
- I have just last year renewed all isolation tape on the cable harnesses, I dont think I have a short circuit there.
- Temp sensors not tested.

I think the easisest next step is to drain the tank and try some new fuel. I can put it into my -76 Volvo. It will run on anything

will keep posting