Jaguar Repair: 76 jag xj6, diesel battery, logic probe

Question
QUESTION: no negitive signal from ecm to injector. ecm is putting out a positive signal when the key is on.

ANSWER: Hi Bob,
I take it you mean an "86" XJ-6?
The ECU grounds the injectors when it sees an engine speed signal (Ignition pulse) and it must have a ground and a power supply to the ECU too. All of the other input signals are to change pulse duration to control mixture.
Howard

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

QUESTION: howard, when cranking engine, the spark is weak. what do you sugest? we can run the car on staring fluid.

ANSWER: Hi Bob,
I have never seen an engine that would run on starting fluid that would not run on gasoline. But your engine can't run on gasoline because you said there is no injection pulse.

You need to go to the ECU plug and confirm that you do have an ignition pulse signal at the ECU. If you don't have a diagram of the injection system go to my web site and copy the one I have there.
http://mg-tri-jag.net/XJ-6InJect1.jpg  for half of the system and change the ending to,
XJ-6InJect2.jpg for the other half.

Confirm that you have "Engine Speed" signal (ignition pulse) at the ECU plug when spinning the engine over and confirm that you have power and ground at the ECU and it would be good to confirm power on the "Start" signal wire too.

Also confirm that you have a "Deep Charge" battery (diesel battery) as the XJ-6 is noted for not starting with a standard battery, even though it may spin over fast.

Howard

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

QUESTION: howard with the test light i have pos power to the speed signal when cranking i still have pos blinking but not changing to neg my test light has a green and red led i do have alldata to print out whatever i need im just stumped on this problem if you are able and willing to leave a number i can call thank you for all your help bob gilley

Answer
Hi Bob,

So you have a Logic Probe with the red and green LED? That is good and it will not interrupt the signal. However, I am concerned that you only have a pulsing red light at the speed signal as that is the white w/black tracer wire on the coil and has to go to ground to operate the coil.
Try your test light on the coil itself to see if you get the same signal. The ignition coil can not operate unless it is receiving a grounding pulse from the igniter (GM inside the box on the front of the intake manifold)
I have a Logic Probe and I will try it on my coil to see if I get a red/green pulse and I will let you know on that later.

Did you confirm the ECU grounds (Pins 5,16,17,35) and the ECU power supply pin 10? And pin 4 for power when in the start position? This needs to be tested at the ECU plug and don't need the car to run.

You didn't tell me if you had a deep charge battery. The series III Jag had a problem trying to start on a conventional battery, even a new one. But I found a method to test if the battery was the problem. When I was a hot line answerman for Beck Arnley I had a customer near Atlanta that had a series III car with a new battery that would not start and I could not convince him to get a diesel battery for it because it spun very fast with the new battery. So I got him to connect a known good jumper battery up to the car as though he was jump starting a car with a dead battery and try it and it fired up right away. So he finally got a diesel battery for it. So this is a stone that you must not leave unturned. Even the diesel batteries quit starting the car as they age and need a new battery and we found that the old diesel battery could be used in other brand cars for several more years after they come out of a series III.

I do this answering questions as a hobby now as I have time and don't work by phone. If I am of any help I can do it in this program just a well as voice.

let me know about the battery and the other tests. I have two Series III cars and I will check them with a Logic probe to see if I get just a flashing red or and alt red/green flash and let you know.
Howard