hi all
i bought an 84 xj6 about a year ago and she was running like a dream up till a week ago.i was driving back home when she suddenly missfired and came to a stop. i tried to start her again but she just turned over not firing.now she starts but miss fires then stops. when she runs theres bluish smoke. the spark plugs are sooted and soot at the tail pipe. can anyone give me some idea whats going on? compression on all 6 cylinders are at 200 psi

 

Sounds like the fuel mixture has gone rich. Here are some conversation starters:


XJ6 Series - EFI Rich Mixture


Cheers
DD

 

in my experience with my '84 there will always be some black soot stain at the tailpipes, what is not normal is the blue smoke and misfire. If the car has been sitting, something has become stuck, I dare say it is the AFM flap but Doug will guide you.

 

Check coil connections and all ignition components for loose connections. I had coil get warm and loosened wires and would run great until warm then die. Let cool and would do same all over again.

 

cheers doug very much appreciated

 

the ignition side of things are ok as its all new.theres a good spark, fuel pressure is ok.i put a new thermo time switch on and still she runs rough and smokes.good compression on all cylinders. Airflow meter is ok. any more suggestions?

 

How do the spark plugs look? Wet and black? Dry and black? Oily?

Cheers
DD

 

how about cap and rotor? running in the dark will show if there is any misfiring on outside of cap or wires. just a thought.

 

the plugs are black and sooty the cap and rotor arm are new. i looked to see if there is a plug to see if a computer could be pluged into it but couldnt find one. i guess there isnt one on the early jags

 

Which suggests over-fueling/rich mixture



Right!

Cheers
DD

 

What reading did you get?





How did you determine this?



1) Check the connector and wires at the coolant temp sensor.

2) Test the coolant temp sensor itself with an ohm meter. OR....use a paper clip to jump the terminals inside the connector, bypassing the sensor reading.

Any change?

Cheers
DD

 

i checked the wires and connector theyre ok. i put a tester on the wire and it has power.
i tried with a paper clip. the engine just turned, didnt fire. i put the connector back on and it fired up but was running the same, rough then dying out.

 

We *might* be closing in on something.

The engine should run with the paper clip jumping the coolant sensor terminals. Jumping the terminals simply fakes out the computer a bit, giving it a constant 'fully warmed up' reading....eliminating the chance of a 'cold enrichment' signal.

When you says the wire 'has power', do you mean 12 volt "+" ? If so, something is amiss. The coolant temp sensor is a grounded circuit.....it sends a varying ground signal to the ECU. If you have "+" voltage on either of the wires, something is haywire

Cheers
DD

 

I have to say all that has been said so far does not appear to address the "blueish smoke" symptom. It is the suddenness of the symptom appearing that makes me think it is not a simple duff sensor problem. Blue smoke to me is always excessive oil in the combustion chamber, Or am I wrong ?

 

You are absolutely right! I believe they are trying to figure out why there is excess, doesnt always mean internal damage. I had a 66 chevy once that had a faulty NEW plug in it so it didn't fire right and slowly didn't fire at all. That was not a fun challenge since I knew I just put that plug in. Gotta love A.C. Delco quality control.

 

No, not wrong at all, but an engine can burn quite a bit of oil and emit quite a bit of blue smoke.....all while running sweet as a nut !

The 'black and sooty' spark plugs, however, suggests too much fuel....which might account for the misfire and running problems described.

Cheers
DD

 

when i put a tester on the sensor wire it didnt come live until i turned the engine over.
i used a tester with a light put one end on as an earh and put the other on the sensor wires. the oil level isnt going down so as you say doug its got to be running rich.

 

doesn't the AFM control the air fuel mixture?

 

i took the vacuum pipe of the manifold that goes to a sensor on the fuel rail then to the fuel pressure regulator, she started rough but when i covered the pipe she ran better and didnt smoke as much.does that mean it could be the fuel pressure regulator is naff ???

 

also the fuel pump is running all the time is that normal?