QuestionQUESTION: Howard, 85 xj6 starts up fine but press on accelerator and black smoke comes out and car is ovefueling. Replaced water temp sensor and water temp sending unit with jaguar parts. If I let the vehicle warm up at about 80 to 90 degrees celsius according to the gage you can here the engine change modes and become very smooth and runs like a cat. Will run great all day except when cold in the morning.
ANSWER: Hi Jeff,
You are on the right track as far as it being too rich as black smoke is only from a over rich fuel mixture.
The injection temp sensor is a major influence on mixture but there are others. Fuel pressure and the length of time that the cold start valve is open.
First check to see that the fuel hose on the cold start valve is not so hard as to crack if you pinch it closed with a pair of needle nose pliers. If you can pinch it closed then start the engine cold as you usually do and have someone pinch the hose to the cold start valve closed and note if the engine stops running rich. If that corrects it, test the cold start valve and the thermo-time switch. (large one most forward on the coolant rail)
If that don't correct it, put a "T" in the fuel line at the fuel rail and test fuel pressure when cold running. (should be about 32 PSI running and about 42 PSI with the vacuum hose removed from the regulator.
The air temp sensor in the air flow meter is only a minor influence on mixture.
Let me know the results of the tests
Howard
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QUESTION: Thanks for your advice Howard, you have helped me with this coach before with great results as usual. I been really busy with work but it looks like a can look at it this weekend. I will let you know what it was when I find it. I will tell you that I can get it to go when its cold but I have to barely push on the accelerator, and when its cold it has a bad hesitation. Also my fuel mileage is about 9mpg and I usually get better than that. I live up hill from work about 3 miles away can get it to work but if I have to go up any kind of grade, it loses power and black smoke pours out the tailpipes. But when it reaches about 80 degrees the engine just starts to purr. Thanks again I will be in touch.
Jeff
AnswerJeff, there is another possibility and that is that you need to run a compression test.
When a cylinder does not fire for what ever reason the injection system keeps injecting fuel and that could also be the reason for the excess fuel. This would not be noted as black smoke on an older car with no CATs but on a car with two cats in a row like your car that excess fuel can ignite in the CATs and not burn completely thus the black smoke. (Just a thought that should be eliminated by a compression test.)
If it were a primary ignition failure there would not be a injection pulse so no extra fuel but a intermittent failure of the secondary there would be injection thus possible extra fuel.
I toss this out because you can't leave stones unturned when looking for a problem.
Howard
