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Jaguar Repair/1984 XJ6 not starting



I cannot hear the injectors clicking, but I also don't hear very well. Like I said, the noid pulse was weak and orange. Shouldn't it be a bright white flash? I pulled #1 & #2 injectors and had an assistant turn key while I watched and I had to struggle to see the tiniest amount of fuel coming from each injector. I'll look for the coke on the valves, but this was really an overnight kind of thing and that is what concerns me. I took the car to a small paint shop on a Thursday afternoon and told them that it does take a couple of tries to start sometimes due to the injectors leaking down and the following Monday they said it would not start or do anything. I went by there and found a locked up starter, dead battery, etc., and had it towed back to my shop. Replaced battery, starter, and had injectors refurbished and it has never run since. My concern is what if they hooked up a battery booster backwards? Could that cause damage such as to leave me with a weak injector pulse now?

ANSWER: I can't say if a booster battery connected backwards can damage a ECU or not.

I do have a question though. When you had the injectors out and spun the engine over, did you hold the air flow meter flap open? If not it would be normal to see only a light mist from the injectors as everything is telling the ECU to NOT spray much fuel.

Have you done a compression test? If so, what were the readings? Did you try spraying propane into the intake to see if you could keep it running on propane?

Are you wetting the plugs when it don't start?


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No, I did not have the air flow meter flap open when spinning the engine to answer that question. I did do that test again tonight though and saw a more satisfactory spray from injectors. Also, as you asked, did three cranking attempts, then pulled plugs and they were not wet. While they were out, did compression test and got #1 - 150, #2 - 145, #3 - 135, #4 - 145, #5 - 145, #6 - 135. Now, I also found that I can spray about 20 seconds worth of carb cleaner directly in to the cold start injector hole, then after a few seconds, start it and even affect rpms with pulling the throttle, until it slowly peters out and dies again, sometimes backfiring out the intake. I still have not tried the propane, to be honest - what will that show me?

Is it beginning to sound like the head needs to come off?

I guess That is not the end of the world. I actually did one of those BMW jobs you mention just a couple of years ago. Cleaned the valves on a wire brush wheel on my bench grinder. Removed about 1/16" of buildup from the back side of the valves.

ANSWER: When you have a lot of coked up carbon build up on the intake valves, the carbon stops the spray fuel from entering the engine and it soaks into the carbon and then when fuel continues to spray on the carbon it dribbles off and into the engine as large droplets of fuel and will not ignite. By injecting Propane or Butane, it is a dry gas and can't be absorbed in heavy carbon and is already vaporized so it can ignite. Gasoline will not ignite unless it can vaporize and the chunky carbon prevents that. That is why you have to look at it to see. A 1/16" is not usually enough to cause a Jag a problem. When it gets to a 1/4" or even more it stops it from starting and causes a very rough idle even if it does start.

Your compression readings are not great but it should run. Did you hold the throttle open when running the compression tests?

You don't have enough info yet to warrant pulling the head. If you didn't open the throttle doing the compression test run it again with the throttle open and then pull several injectors and the sleeve they mount in and look at the valves to decide if the head needs to come off.


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The car starts and runs when starting fluid or carb cleaner is sprayed in to the intake, so it seems that running on a dry gas is a redundant step that wouldn't prove anything either way.

Now, you guessed right - I forgot to hold the throttle while testing compression last night so I did that tonight throttle open, and the numbers changed slightly to #1 - 150, #2 - 145, #3 - 130, #4 - 135, #5 - 140, #6 - 135.

Also, pulled injectors and peered in with a tiny bulb I soldered to a wire with a 9v connector at the end and my best line of sight was in to the #6 cylinder with the air filter housing removed. I got a good eye on a valve and had an assistant spin the motor while I was looking and it wasn't shiny and clean, but there wasn't a 1/4" of crud on it, either.

I wasn't in a hurry to pull the head on this, but it is also easy work to get to a good running engine sometimes. Maybe I'll keep after it with the carb cleanrer and get a properly working cold start injector in there and be lucky.

By the way, I have the proper Jaguar manual, as well as the red Haynes book and the only part of top end jobs that generally intimidates me is getting the timing back right. Looks almost idiot proof on these - what is your take?

Michael, clear something up for me. You say it starts and runs when you spray starting fluid into the intake. Did you mean that it will only keep running as long as you keep spraying starter fluid in? Or does it run on it's own after the starting fluid is used to start it?

The carbon on the intake valves needs to be quite large for it to cause hard starting. So I don't believe you have a carbon on the intake valve problem. While it is true that the spray can of starting fluid is similar to propane or butane, it is very difficult to control the volume of starting fluid into the intake to keep an engine running. With a dry gas like propane or butane, you can easily control the volume sprayed into the intake and make an engine run continuously smoothly.

I have spray cans of starting fluid all over my shop and use them often but when an engine needs it to start but will not keep running on it's own I get out the propane to keep it running.

I would not think of pulling the head yet with what you have told me even though you do have a lot of difference in compression on several cylinders. When I find one or more cylinders lower then others like you have (130 vs 150) I run a "Wet" test to separate a valve problem from a ring problem. Squirt about 4 or 5 squirts of engine oil in a plug hole and run a second compression test on each cylinder. The compression (Wet Test) will be higher with oil, but it should not be more then 10% to 15% higher. If it is more then 10 to 15% higher then the first Dry test.  Then that cylinder has a ring problem. If a low cylinder barely reads higher on a "Wet" test then that cylinder has a valve problem. The trouble is you don't know if it is the intake or the exhaust valve.

You might say "what's the difference? the head needs to come off either way. The difference is that a leaking exhaust valve will not make a engine hard to start but an intake will, especially on a ser III Jag. Due to the large can shaped intake manifold close to the head.

A light puffing of pressure into the intake manifold will destroy the vacuum formed by other cylinders and dilute the intake air charge with depleted O-2. Thus preventing the engine from running at low RPM. An example of a different design intake is the old slant 6 Chrysler engine with the funny looking long intake runners. This engine could burn an intake valve badly and only drop that cylinder where a Jag gets a minor leak in an intake and it stops it from running at low RPM completely.

Will the engine run on it's own after starting on starting fluid?


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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

ASE Master Auto with L-1 certification up to 2000

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