QuestionI have recently aquired the above vehicle. It runs very well but has become hard to start when warm and does not want to idle well at all. Have changed plugs, wires, O2 sensor. Do you know what it may be?
AnswerHi Darwin,
Before I start any such diagnosis I would want to know what a compression test shows. You have not stated your mechanical abilities. It does not take much if you have no mechanics background. A compression gauge is not expensive and if you can change plugs, you can do a compression test. E-mail me if you have not done it before and I will walk you through it. Also tell me how many miles on this engine?
Always use a "No Throttle" starting. Pumping the throttle does absolutely nothing as there is no accelerator pump.
The two items, "not idle well" and "hard starting" may or may not be related, so I would work on the not starting when hot first. There are a few things you can check first that only require a test light and a spray can of either starting fluid or something like WD-40.
The first test should be to determine if it is getting too much fuel or not enough. When hot have someone try to start the car while you spray several shots of spray into the intake horn. If it starts right away, it of course is a "Lack of fuel"
A "lack of fuel" can be caused by several things. The most common is that the engine when shut down transmits extra heat to the coolant and the temp sensor for the ECU then leans out the mixture (injector open time) and the hot coolant also has disconnected the "Thermal Time Switch" which prevents the "Cold Start Injector" operation. All of this is usually not a problem unless something else is wrong (low compression on one or more cylinders)
I don't know how much you know of this system so I will try to go along in detail. The injection system is a Bosch "L" jetronic system. When the engine is cold it uses a "Cold Start injector" in place of a choke. It is a small injector mounted straight up in about the center of the lower portion of the manifold. This is obviously working or it wouldn't cold start. However, if it is working during a hot start it will apply too much fuel to start. This is controlled by the "Thermal Time Switch" (the largest sw. in the coolant rail across the top of the intake manifold) (usually mounted toward the front)
One more important item, if the mileage is high and the car has been using low grade fuel the Series 3 Jag is noted for carbon build up on the intake valves which act like a sponge and absorb the already not much fuel of a hot restart. If everything else fails to correct this can be checked by the removal of an injector and it's plastic receptacle then insert a light probe into the hole to view the underside of an intake valve. If large chunky carbon is present you should call around to find a shop that has the walnut shell blaster equipment. The process was used on BMWs as they had the same problem. You have to remove the intake manifold and they close a valve and blast the carbon out with walnut shells.
My E-mail address is hmfinc@bellsouth.net
Let me know.
HMF
