I picked up an 88 V12 XJS recently and am slowly getting it going after it had been sitting for years.

I am a little bit stumped right now as I can walk out to it at anytime in the day and it will start right up (quickest and easiest of any car I've owned.) However after turning it off I'm unable to restart it without severe struggles an hour or so.

New parts that have been installed are
Fuel pump
Fuel filter
Both fuel pressure regulators
Distributor cap
As well as various rubber lines in the engine bay

I am fighting a bit of a low idle which I am expecting is just some vacuum lines that I'm replacing as I come across them. First start after a while it will idle at around 500 rpm but when I get it started after struggling it will only idle at 1-200.

Just wondering if anyone had an idea of what to attack next as I don't have much experience with the V12s.

 

If its a marelli car your crank sensors may be faulty, I'd also ensure that all the throttle components are set properly with the right butterfly gap etc.

That should be done anyway. I suggest finding the Kirby Palm book and absorbing that.

 

The coolant temperature sensor can cause problems too.

 

Ok, so it starts up fine the first time. Have you tried starting it, just letting it run for a minute or so, then shutting it down and starting it again? Will it start then.

Just trying to figure out if this is engine temperature related or something else.

When you try and start it again, does the starter sound like it's getting full power, or does it seem like its just not getting any gas?

FYI, the return fuel regulator is worthless. You can toss it and feel no ill effects.

Thanks,

John
1987 XJ-S V12

 

If by the "return fuel regulator" you mean the one on B bank that the return line connects to, IT MOST CERTAINLY IS NOT. The OP's car will never start if he removes it!
OP
Have you tried adjusting the tickover? 500 rpm cold seems too low, and 1 to 200 warm is far too low. Search AAV to find aout about this subject.
IF you floor the throttle when warm, will it start?

 

Yes I have tried starting it letting it run for a minute or so and restarting. That is where the issue, with the subsequent starts.

With the second attempt at starting the starter does sound strong. There will be points where it sounds like it wants to start, but it just doesn't catch. Although if I hit the gas pedal at those moments after four or five times it will go, but it doesn't seem to like it much.

I did try to adjust to tickover a bit. I think I went about a full turn either direction but it didn't really seem to do too much. I'm not sure how sensitive it is so it's possible I didn't go far enough. Or is it possible that the valve could be bad and part of my problems.

I am not getting a coolant temp indication inside on the gauge. It remains pegged at the bottom. Am going to look into that this coming week.

The longest I've had the motor running is four or five minutes at a time it does this whether it runs for one or five so I don't believe its temperature related.

 

You won't get a temperature indication for a few minutes anyway.
As far as I can recall there are 2 temperature sensors, one for the gauge and one that feeds the ECU; this is the one that causes problems and is located on the top of the water jacket, near the return line fuel pressure regulator.

 

Anti siphon valve in line with fuel filter in back. Might be stuck from old fuel, as you have renewed everything else. Just a thought.

 

The temp gauge takes several minutes to register. As Steve said, the gauge sender is on the RHS (A bank) thermostat casting, just one gree wire on it.
The ECU temp gauge is on the opposite side, as Steve said, and it has an injector-type plug. It is worth renewing this sender anyway, as if flaky the car will not start, and it just could be part of your problem.
Open up the tickover adjuster several more turns!
Greg

 

I replaced everything that you have already done and she still would not start after shutdown. .....I had gone one step further than you have.....I had already installed an after market Crank Shat Position Sensor.
The Forum guys suggested finding an OE CPS.....I found one at Jag Bits and installed it......Problem solved for me
Good Luck
Don

 

Just a quick update since it's been a little while.

After doing a lot of research on the crankshaft position sensor it appears that my car does not have one since it has Lucas ignition.

I did change out the coolant temp sensor on the LH side of the engine this morning and that seems to have resolved the issue.

The car has started right up each time I have turned the key today.

I greatly appreciate all of the suggestions and help fixing this issue.

 

Result!