A neighbor who has never owned a Jaguar or anything like it but always wanted a convertible just bought a pair of non-running 1990 XJS V12's. One is a 5.3 Convertible and the other is a coupe. The coupe has no drive-train or seats but looks to be a good body with lots of other parts left on it.

The convertible will not start but the man he bought them from said it did when he bought it a few years ago, then a weeks or so after he got it he was going to take a friend for a ride and I forgot the exact story but either it did not start at all that morning, or did but then died, and has not ran again since. That was 2+ years ago. He later got the coupe to get the ECU and some other small parts out of to try swapping.

So now my neighbor has them both. He has the coupe body for sale (cheap if anyone wants one) and he's trying to start the V12 and we need some ideas from those more familiar with this generation of the 5.3...

Here is what we know or have tried;

It's got new plugs
Looks like the plug wires are also new
Distributor cap and rotor look new
Looks like the previous owner put in a new Crankshaft Sensor
Two ECU's have been tried
Pulled plug wire and it's getting a good spark
Has pressure at the fuel rail when cranking
I said maybe there is fuel but the injectors are not firing so we plugged my noid light into one and it did flash while cranking.
So then we actually removed one injector and when the engine is cranked it sprays fuel.
Removed the oil fill cap and can see the timing chain turning inside.
At least two cylinders have decent compression, really hard to test them all but two should be enough to make it caught or backfire or something.

So now we are stumped...

Since it's getting fire, and it is getting fuel, why is it not doing anything at all? ... I mean no coughing, no backfires, no nothing. Even if it was way out of time you would think it would at least backfire or do something.


Anyone have any suggestions what to try next?

 

The 90 XKS has Marelli ignition. It has two crank "sensors". One gives the Marelli ECU the voltage for timing (front one), and the other gives engine speed for fueling (rear one). If either of these are faulty, the car simply won't start. A Marelli car may have great spark and not fire due to either being bad. I don't say it is absolutely required, but my starting point with a unknown engine is always a complete compression test. The V12 Jag engine is known for dropping valve seats. You can pt a lot of time, energy, and money into it to get it running, only to find that it skips horribly due to a dropped valve seat. The compression check is essentially free if you have a compression tester. From there, I would pull BOTH coil wires from the distributor, and put them near ground and then turn the engine over. It needs to have good spark from BOTH wires. They both should fire for as long as you crank the engine. I spent many hours getting my 89 Marelli car running. What didn't make sense, is that it had good fire on both coils, but only for 3-6 seconds, and then the B bank would drop out. Turned out to be a bad rear "sensor". I put "sensor" in italics due to the fact that they are not really sensors. They are a magnetic pulse generator. They send a AC signal to the Marelli ECU. The Marelli ECU then uses that signal to fire the engine at correct timing intervals, as well as send a signal to the Lucas ECU for injector duration. They DO NOT signal each other. If one bank doesn't fire, and the engine is hot enough to continue running when one bank drops out, the Lucas ECU will continue to send fuel to the engine without it having spark. The large amount of unburned fuel ignites in the exhaust system, and then you have the infamous "Marelli meltdown". Don't be afraid of it however. Once running, if maintained properly, it will seldom if ever let you down.

 

Thanks, and we didn't find the rear one (and it's not shown on charts I found online) but will look for it.

Will it not even backfire at all (after a lot of cranking) if this is the problem? That's what's odd to me, not even attempting to backfire or even cough when we know it's getting fuel into the cylinders and fire into the same cylinders. With every car I have ever tinkered with before (though never had one of these specific models, had earlier and later) even an out of time engine will eventually backfire a cylinder or something when you have both fuel and fire and compression on a cylinder.

 

https://uk.images.search.yahoo.com/s...g&action=click

 

I know when I bought my non-running 89, it too, would not pop, backfire, or anything. Occasionally it would sound like a engine way out of time. It never popped or backfired. But one I identified the problem, it came to life almost immediately.
I'll go a step further. It has been shown that you can measure the ohms of resistance across the terminals as a indication of one being bad or not. In my case, I found that wasn't the case. My new one measured almost exactly the same amount of resistance.
As I have stated on here many times, these "sensors" have a magnet in their core. A magnet breaks down with heat. They both are subject to a lot of heat. Especially the rear one. It even has its own little heat shield since it is right next to the exhaust. One more thing you can check with a feeler gauge. The distance from the teeth on the flywheel to the face of the "sensor" The specs say .045. I say get it as close to .020 as you can. They are a service item, and need replacing periodically anyway.

 

One thing to consider given the above is that previous owner might not be telling the whole truth. It sounds like quite a bit of new parts and work might have been done, and it's impossible to know if it was done because it wouldn't start or perhaps might be the root cause of why it doesn't start.

IOW, you might want to double check that previous work. For instance are the plug wires going to the right places, etc.

Don't take for granted that prior work was done correctly.

 

Oh we're not taking anything for granted, and the parts actually LOOK new. But we didn't know at the time (and didnt make it down there today) that where was a second crank sensor at the back.

 

That is a very good point especially it being a marelli ignition car and its unique plug lead order. It would not be the first one set up by a local mechanic with plug wires in the wrong order at the distributor.
This is not directly relevant but I acquired a '76 some years ago that somebody had been trying to get started and the ignition timing was a full 180 degrees out at the distributor.

 

Hi , I am wondering wether or not that you pumped old fuel into the fuel lines .Old fuel will turn into an oily liquid that does not seem to want to burn, you may want to remove the fuel hose after the filter ( also remove the coil wire ) and turn the engine over until the fuel runs clear. Disconnect a fuel line on the opposite bank and blow compressed air through until no fuel remains fit new filter and reconnect lines and coil lead . you may have to crack a fuel line to bleed out any air . It may take awhile as stale fuel could still be in the injector lines and ultimately you may need to remove these and clean them. Another quick test is to remove one or both air filters and spray a starting fluid into the air intakes , you will need another person to turn the engine over and keep the accelerator pedal full open , if the engine fires even a little you know it is probably a fuel problem. Hope this helps ..John