QuestionQUESTION: Hi, Howard sounds like you are very knowlegeable about Jag series 3 so Here's my dilema. Have a 84 Jaguar series 3 4.2L that likes to run well only after you put a new fuel filter on it for a few times then goes back to idle rough dying after you put it in gear. I thought there was rust, dirt in fuel tank so I have drained it. fuel was dirty, wanted to take the pickup filter off and put a new one in but I can't figure how to get it out of the tank. Another thing about this car is that when you open gas cap it has alot of pressure release. Is this normal?? Thanks in advance for answering the questions. Hope that you can help.
ANSWER: Hi Cliff,
Look at the drain plugs to see if the small drain plug is inserted in a large plug like some of the older Jags. If it is, then you should be able to access the screens by removing that larger plug that holds the drain plug. I have never pulled a Ser III tank and I don't have anything in any of my manuals that tells me. However, you could just drain the tanks and remove the large hoses from the tank switching valve in the trunk and blow air back into each tank. Then rince the tank with a little fresh gas.
As for the pressure in the tanks, that is normal and is about 3 PSI which I felt was too high so I removed the pressure valve (plastic valve in the vent line next to the charcoal canister behind the right front head light)and I drilled a hole in the body and removed the spring and replaced it with a weaker spring and I now have about 1.5 PSI on my Ser III. I didn't feel the 1.5 PSI less on the tanks would put undue stress on the fuel pump because as you eliminate the 3 PSI on the fuel you make the pump work harder to keep the 32 to 42 PSI necessary to operate the injection system.
Howard
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QUESTION: Hi, Howard. I need some help getting the jag to at least run. I did all the cleaning of the fuel lines and tanks. Then put new gas in the tank. and a new fuel filter. It turns over strong and has plenty of good spark. It will not even hint at starting. Just turns over and over. So what is my next move and how do I go about doing the checks that have to be made in order to get it going. Thanks, Cliff
ANSWER: Cliff, If it does not fire up at all now you need to see which is missing of the three items necessary to run, Compression, fire & fuel with conditions on each.
It is unlikely compression as you said it ran ok just recently.
So you need to look at Fire and Fuel. You claim it has good spark so to check to see for sure it is fuel just spray starting fluid into the intake when spinning the engine over. If it fires off but only runs as long as you are spraying then for sure it is fuel.
but if it does not fire off and run as long as you keep spraying fluid into the intake then it is something else.
At that point you need to do the first thing for a Series III and that is to connect up a known good battery as a jumper battery as though you were jump starting a car with a dead battery. If it starts then, purchase a "Deep Charge Battery" (Diesel Battery)
If that don't start it, do a manifold vacuum test. (throttle closed) If you have little to no vacuum or the vacuum decreases as the engine spins loosen the front CAT from the exhaust manifold about a good 1/4 inch and try to start it. If still no start run a compression test on all 6 cylinder (throttle open)
Physics say an engine has to run with compression (sufficient compression), fire (Good blue spark at about the correct time for each cylinder) and fuel (a combustible fuel available to each combustion chamber)
No 4 stroke engine can fail to run with those three items.
Let me know,
Howard
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QUESTION: Hi Howard, My Jaguar is running again!! I read a previously wrote answer from you and dedided to check the fuel pump circuit. Key on, hold air butterfly flap open, and you could hear relay #1 open but could not hear the pump switch on and the fuel run up through the lines. SO, I replaced relay #1 and wala the pump ran and the fuel came right up the fuel rail turned the key and it fired right up. But, when you put in gear it wants to die still. So am asking for yet some more of your excellent advice. What can I start to check now that it is running but not the way it should. Thanks Howard your Jag expertise is much appreciated and I feel as though you were there all the way through it!! also I did ask her last night if she could tell me what was wrong and maybe she did just that..am looking forward to your reply. Cliff
AnswerIf it runs but dies when you put it in gear you need to check idle speed and if it is too low set it up a little. If it will not pull the car even if you do get off idle check timing and fuel pressure (32 PSI running and about 42 PSI not running or with vacuum removed from pressure reg.
You may need to start from scratch with a compression test, timing set and fuel pressure test. Also test for exhaust back pressure. (no more than 1 1/2 PSI at speed.
If it is over 70 K miles and has never had the intake valves cleaned it could have coked up valves. Sometimes this can be seen by removing the spark plugs and turn the engine over until that cylinder has the intake valve open then take a small light and look into the plug hole at the under side of the intake valve.
The symptom of cutting off when put in gear narrows the problem down to only a thousand things. It just tells you you need to do some testing.
Howard
