Jaguar Repair/test


I don't think that u received this email yesterday. I sent it before I sent the one telling u that I had to do the compression test over. So here goes.
Ran over last night to do test. Compression was 120. Then did fire and ignition test. Very little spark all hair line ,orange.
I noticed that when I crank engine over no spark till I back off on key a little. I have noticed this before, that my car does not start when I turn the key all the way, but when I back off the key a little starts up right away. Does this sound right?
Seems like I have no spark when turning the key all the way.
I am going to test it today with my meter when the cars is cranking over and see it I have power to the coil at that time or only when I let up on the key.

ANSWER: Hi Mike,

It sounds like you may have found your problem but to be sure run an additional test. You will need a volt meter for this test. Write down the reults of this set of tests.

Put the voltmeter across the battery terminals and note battery voltage. Now hit the starter and read battery voltage while the starter is engaged. Now put the volt meter on the (+) terminal of the coil and turn the Key to IGN (run not start) note voltage, then hit the starter and read the volage of the coil (+). Leave the voltmeter on the coil and remove the White w/Red tracer wire from the starter relay. (larger metal relay on the firewall just behind the intake cam of the head) Turn the key all the way to start and read the volt meter and then back off a little on the key like you were doing to get it to start each time reading the volt meter.
Leave the volt meter on the (+) side of the coil and take a known good extra battery and connect it to the car battery as though you are "Jumping Off" a car with a dead battery. Hit the starter and read the volt meter on the coil wire and compare that to the other test of the coil voltage in the "Start" position.

If you have lost voltage at the coil while all the way to the "Start" position of the key but still do have the starter motor operating then you have a ignition switch going bad. Thus you need to replace the electrical part of the ignition switch.

Also if you noted a low voltage at the coil (+) when in the "Start" position with just your car battery but noted a higher voltage at the coil (+) when the jumper battery was applied then you may need a new "Deep Cycle" battery for your car even though the existing battery spins the engine quit fast.

The series 3 XJ-6 had an odd thing that it would get hard starting with a standard battery or a deep charge battery that was aged. A battery that quits operating a Ser 3 XJ-6 can often be used in other brand cars for years to come. The jumper battery is the test for that problem. This may be the cause of the weak spark you are having along with your ignition switch problem.

Let me know,


---------- FOLLOW-UP ----------

QUESTION: Hello Mr. Howard
 Again thank u  for all the help
First when should I put back on the white /red from the starter relay, and I no exactly the wire, and were it is at.
Second I ran all the test today, compression, from bulk head to front 125 , 125, 130, 130, 135, 135.
Fire, ignition I put the car in a dark garage today to make sure that I could see the spark better. and a friend help me and when we ran the test he said that I had good spark.
Third I ran the car till I thought it was hot enough not to start, turned it off and then went to start it again, and it STARTED, so I ran it a little longer, turned it off again , went to start it and it STARTED again , ran it some more , turned it off , went to start it and again it STARTED. I am lost.
I also ran the fuel test and had 3lb.
I am so lost, I just don't understand.
I put new plugs in on Tuesday, drove the car 6 miles turned it off and did not start. Drove back home 6 miles , it did seem to run a little better, on the way home. I went  to  a jag show on  Saturday,  when I would get to a stop lite it would want to stall, one time it did and I sat for 45 minutes, waiting for it to start. I was very hot out Saturday 92% .AT the show I was talking to a jag. mechanic
about my car having these problems, told him that I had fooled around with my cards, and turned one screw on each carb and he looked  at it  turned the screw on the carb. and told me to put the new plug I did .Could that have any reason why it would keep running today?

Well like I said  I am very confused!!!
 Please tell me what u think about the test, I ran.
I will ran all the new test tomorrow and let u know the results.
AGAIN thank u for all the help
PLease one more thing. I did the test on the oil sender, on my gauge and  on the sender the wire is  white/brown tracer, I did not have any power at the oil sender, I did it with the wire on and off. I then took my 12v test lite to make sure that I had power on the green wire that runs from the voltage stabilizer to the gauge and had power, I also checked the white/brown wire on the gauge to see if it had power and it did not , and I did not think that it should. Were does it get its power from? and what is the next test I should run. I also tried to buy a  universal hydraulic oil gauge and have not yet been able to find one. Please  tell me the next step on the oil gauge sender and how or were to get power to it.

ANSWER: The sending unit should only have one wire and the test is to turn on the key and test the Green wire for power as you have already done then remove the wire off of the sending unit and with the key on ground the sending unit wire just for a few seconds while someone watches the gauge. If you can get the gauge needle to deflect by removing the wire and then grounding the wire the gauge and the wiring are probably ok and it is the sending unit that is bad.

The car not starting at times is always difficult to locate because the test must be done while the car is in it's failed mode. When I had a car that would not start only on ocassons I had to put a timing light on the coil wire not #1 like when setting the timing and then I taped the trigger down on the timing light and ran the wires out from under the hood and placed it under a wiper arm so I could monitor the flash of the timing light. Then when it would not start I could see if it was caused by ignition or not. if it had ignition I would spray starting fluid into the intake to see if it would then start and if it did, I know it is a fuel problem not an ignition problem.

Since it is only not starting at times you have to catch it when it is not starting to test ignition and fuel. It is no use testing while it is starting ok.

let me know.


---------- FOLLOW-UP ----------

QUESTION: Howard, I am not sure what u mean with the KEY on ground the sending unit wire just a few seconds

When you turn the key "ON" you power the green wire to the voltage stabilizer and since the wire on the sending unit varies the ground to the gauge, when you remove the wire it makes the gauge needle deflect all the way and then when you ground the wire the needle will deflect all the way the opposit direction. This tells you that the gauge is reacting to you when you "Open" the circuit and when you "Close" the circuit (ground the wire) it makes the gauge needle go all the way in the opposit direction. It does not tell you if the gauge is calibrated and reading the correct amount but it does tell you that from the wire on the sending unit to the car battery everything is doing something.

The sending unit is just a variable resistor that changes the amount of ground by the amount of oil pressure that is applied. By removing the wire and then grounding the wire you are testing each extream. (Open circuit and Closed circuit)


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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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Import Car magazine

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