QuestionQUESTION: My 87 XJ-6 starts fine and runs great with warm engine. However, upon cold start it runs horrible for about 10 mins. In gear car will not get above 1200 RPM (manual gear box). Have to shift up to fifth gear to get to a max top speed of approx 45 m/h.
Letting it run stationary with cold engine gives a lot of condensated oil from exhaust pipes, which disappears after engine gets warmer.
Feels like it doesn't get the right fuel mixture during first 10 minutes. What is the most logical cause of this?
ANSWER: Hi Gilbert,
The coolant temp sensor has control of a necessary rich mixture when the engine is cold. The cold start injector is only active during start up. An Aux Air Valve controls RPM for the first few minutes after start up but has no control over mixture.
To confirm that it is a lack of fuel (lean mixture) when cold you can attempt to hold the throttle open a little more than it wants to run cold (1200 RPM as you indicate) and spray some kind of fuel into the intake like WD-40 or such. If the RPM picks up then it is a lean condition and you should look at the coolant temp sensor (second from the rear on the coolant rail)If you don't have the specs, let me know and I will look them up for you.
The smoke out the tail pipe may be important or not. The color of the smoke is an indication of what it is. Blue smoke is oil, black smoke is fuel and white smoke is either coolant or brake fluid. If the OAT is cold, white smoke can be just water vapor from the air and when the exhaust system gets warmed up that usually stops. Coolant smoke usually has it's own distinct smell as does brake fluid which usually burns the eyes.
Howard
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QUESTION: Thanks Howard.
The coolant liquid warning light goes on an off all the time, yet there is enough coolant in the reservoire and pressure of it seems fine (clearly under pressure: if you take the cap off you hear the air escaping). Can this be of influence? Car doens't overheat at all.
Some is white, but only when engine and exhaust are cold. The smoke does contain a lot of 'liquid', oil I think. which is clearly visible at the pavement where exhaust pipe is aimed at. Again, this only is the case when engine is cold.
AnswerThe coolant warning light you are talking about is just a coolant level indicator in the front of the reservoir and has nothing to do with the injection system or running.
Unless you are loosing coolant your white smoke is probably nothing more than water condensation in the exhaust.
Run the test I told you about with a spray fuel of any kind and then test the coolant temp sensor with an ohm meter at different temperatures like cold, warm and hot. Then let me know what the readings were.
Howard
