You are here:

Jaguar Repair/1984 XJ6 starter stuck?



So last we spoke I had a stuck starter and got my new one in and it started immediately - then died. Then would not start for anything. I had suspected for some time I had injector problems and I sent mine off to an outfit that promises to clean and flow test them. They came back today, having had one replaced outright due to being stuck open, a few had insufficient flow on initial testing, and a couple were found to be stuck closed. I don't know how my Jaguar was running at all! Now, it still will not start. It will if I spray starting fluid while my assistant turns the key, and it will actually run as long as I'm spraying. As soon as I stop, it dies. I have a fuel pressure gauge inline and it was reading nearly 40 psi, and now after several hours of not trying, I see it has fallen to about 20 psi. I'm thinking I don't have a signal to the injectors - that is all I can think at this point. I haven't had this problem before. Please help me with the appropriate test for this. I pulled #1 & #2 injectors from the intake earlier and observed a small mist from each as my assistant cycled the starter, but not what I would expect. could it be that the signal is weak, not opening them enough, considering I have plenty of fuel pressure at the fuel rail? I'm baffled by this one. The car was starting, albeit after a few tries, and running and driveable before the starter thing...

ANSWER: Hi Michael,

The injection system on your car is a Bosch "L" Jetronic system. It should have about 32 PSI on the fuel rail with manifold vacuum applied to the pressure regulator. But with no vacuum (when not running or at full throttle running) it should have about 42 PSI on the fuel rail.
If you only have 20 PSI at the fuel rail in a "T" connector, either the regulator is dumping too much fuel back to the tank or you have a pump or filter problem. It will not run without the correct fuel pressure so it is no use looking at other things until proper fuel pressure is achieved.

Here are some tests. connect a "T" in the fuel line just before the fuel rail with a pressure gauge on the "T" and so fuel can go through the rail to all of the injectors and to the regulator. Now, turn the ignition key to "ON" (not start)and put a screwdriver or anything in the front of the air flow meter to hold the door (flap) open a little. You should hear the fuel running through the rail and to the regulator and back to the fuel tank (which ever you have selected). You must see about 42 PSI on your gauge.

If you have less then 42 PSI follow the return line from the regulator around the front of the cylinder head to the AC compressor and you will see the fuel enters a can on the "Low" pressure AC line. Then it exits the can and goes to the rear of the car. After it exits the can it should be a flex line in that area. Use a fuel line clamp tool or just put two pieces of rubber hose on the points of a pair of needle nose pliers to clamp the return line while you watch the fuel pressure. DON'T leave it clamped off !!! just clamp it off momentarily to see if you can raise the fuel pressure by the clamping. If you can raise the fuel pressure above 42 PSI in a quick clamping, then you have proved that the regulator has failed.

If you can't raise the pressure above 42 PSI by any amount of clamping then you have either a fuel pump problem or possibly a stopped up fuel filter in the wheel well next to the pump. Or an empty tank and it is drawing air.

The starting of the engine is done by the "Cold Start Valve" only and that is not controlled by the ECU. It is powered by the "Start" position of the ignition key but the valve (injector) is grounded by the "Thermo Time Switch" in the coolant rail over the intake manifold. It is usually the large unit in the most forward position on the rail. It too is powered by the "Start" position of the Key so if the coolant is cold it grounds the injector which then sprays fuel into the intake manifold about in the center. If however the engine does not start and you try to start it several times the electric heater in the Thermo Time Switch disconnects the ground and stops the injector from flooding the engine.

Your test of starting fluid into the intake proves that the ignition system and the engine are probably ok. First get the fuel pressure correct and then test the cold start valve.

It is good that you have had your injectors cleaned and serviced but that is normally the last item to be tested. You must have 42 PSI first.

Let me know.


[an error occurred while processing this directive]---------- FOLLOW-UP ----------


Sorry if I somehow confused you with all of that, but I do have a good strong 42 psi on my gauge installed inline with the key on, and opening the flap in the MAF. Now, I have to admit my cold start injector is broken and was I guess no issue when starting before as maybe the leaky injector was providing start up fuel, but if I am spraying starting fluid in and it will start and run off that, and fuel pressure at the rail is strong, should it not keep running off of the regular injectors? Fuel pressure is not an issue. When I said it was 20 psi, that is now, gauge still installed, 5 hours since last start attempt. If I turn the key on and open the flap in the MAF, it shoots right back up to 42, but will not start. Is it crucial that the cold start injector be in place, as in is there no other way to start this engine and keep it running? It would seem to me that spraying starting fluid in, in excess actually of the 11 second cold start injector interval, would get it running.

ANSWER: Ok, I see, you are past that and you are correct that the starting fluid will take the place of the cold start valve. But rarely will the main injectors enable the engine to start mainly because there is not sufficient air entering the air flow meter to open the flap enough to supply enough fuel for starting. A leaking injector will still not supply enough due to it being only in one port. If you had several leaking it might.

But it looks like you are past the first parts of the tests and now need to see why the injectors are not supplying sufficient fuel to run. Now you need a NOID light. One for Bosch / Lucas. Most auto parts stores have them and they are not expensive.

The ECU needs to see a few things to start to do something. First it needs several powers and several grounds and it most of all needs to see the ignition pulse signal. (a single 14 ga wire that runs over the top of the intake manifold with a single Lucas bullet connector usually located about at the #3/4 cylinder intake position.)

The most complicated part on the Ser III Jags is the ECU but oddly enough the ECU is the only part on the car that is very rare to fail. But signals to and from it do often fail. You need to get a NOID light and test the "End Result" (NOID light flash) when spinning the engine.
An alternative is to get a mechanic's stethoscope and listen at each injector as the engine is spun over to hear the injectors "Click" as they operate.

Here is how the system operates, the ECU receives a pulse from the ignition to start grounding the injectors. They are powered by a resistor pack mounted on the right fender well.

Each injector opens two times per cylinder firing but not necessarily while the intake valve is open. (probably why the Ser III Jags are noted for carbon build up on the intake valves)

The main control of mixture is the air flow meter which controls the pulse duration of the injectors measured in milliseconds. The coolant temp sensor is also a major controller of pulse duration (mixture). Air temp sensor in the airflow meter is a minor control as is the O-2 sensor in the exhaust. The throttle position sensor (Bosch) is empty except for a full throttle switch to lengthen pulse duration at full throttle. The Aux air unit is just to supply extra air for cold starting. The vacuum controlled pressure regulator acts as a accelerator pump in a carburetor supplying extra fuel when the throttle is opened dropping manifold pressure. The range is about 32 PSI with vacuum and 42 PSI when vacuum is lost due to an open throttle or at start up.

I think your next tests are, listen for injector "Click" then put a NOID light on each injector plug and spin the engine over each time to confirm every injector is receiving pulse.

One more odd thing about the Ser III Jag is the battery. Many Series III Jags will not start using a standard battery even a new one. The Ser III needs a "Deep Charge" or Diesel battery. Even an aged deep charge battery will fail to start the ser III Jag. Even though it spins the engine over fast and shows ignition. There is a simple test. Connect a known good battery in parallel like you are jump starting a car with a dead battery even if the battery is fully charged. If that makes the car start then all you need is a new deep charge battery.

Often a deep charge battery that fails to start a ser III Jag will work in any other brand car for several years more.

Let me know,

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


I had tried the battery test already and that was no change. I did get a noid light tonight though and I have a very weak, orange pulse at every injector. I tried to save some time by searching you responses to others, but could not find a case quite like this. What do I need to look at next if I have a weak signal at the injectors?

If you see a pulse with a Noid light the next test is to check if it is operating the injectors. This is easy to do with a mechanic's stethoscope and just listen to them as you spin the engine. Injectors are nothing but solenoids and they "Click" as they operate. Be sure to check all of them because they are each powered by their own resistor in the resistor pack. (mounted on the right front inner fender well low and up toward the front below the air filter.) If you hear them clicking then they are operating and that is all they are suppose to do. Each time they "Click" they open and if you have 42 PSI of fuel pressure they are spraying fuel.

The ECU grounds the injectors for only a short time measured in milliseconds and the power to the injectors is less then 12 volts as it is coming from the resistor pack.

The XJ-6 has another problem and that is that the Bosch injection system sprays two times per cylinder firing and not necessarily when the intake valves are open. When the engine is hot this causes a problem as the fuel sprayed on the intake valves tends to coke up the intake valves. This "Coke" gets very large on the under side of the valves and acts like a sponge and the fuel sprayed on this is soaked into the coked up valve and the only fuel that gets into the combustion chamber is droplets of fuel which don't ignite.

The only way to check this is to remove the injectors and the injector sleeves and use a small light to look into the hole at the valve stems.

If you have 42 PSI pressure and the injectors are "clicking" there is one more test you can run and that is to feed a dry gas into the intake like Propane or Butane and try to get it to run on that.

The earlier BMW's that also used the Bosch "L"-Jetronic had so much trouble with this that the factory supplied a cleaning system to their dealers that they had to remove the intake manifold and rotate the engine to close an intake valve and they blasted the carbon with crushed walnut shell to clean the carbon off and then vacuum the dust and carbon out of that port and then proceed to the next port that same way. The reason they had to use walnut shell is that any of the normal sand blasting material could get into a valve guide and cause a valve to stick thus destroying the engine when tried to start.

I had a tiny light bulb I soldered to a stiff pair of wires and I could insert that into the injector hole and see if the valves were badly coked up. In the dealership we never tried to walnut blast the carbon. We just removed the head and did a valve job.

Let me know,


Jaguar Repair

All Answers

Answers by Expert:

Ask Experts


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.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

©2017 All rights reserved.

[an error occurred while processing this directive]