Starting Issue:
Our 1991 XJS starts inconsistently. Sometimes on a couple of tries, sometimes 20+. Starter is good, ignition is good. Any thoughts? Also the location of the neutral safety switch on a 1991 XJS.

 

What do you mean starts inconsistently? Does it crank or not?

 

Yes, it starts. But it may take a dozen times before there's a connection and it fires up. Drive fine after that. Thanks...

 

When it has trouble starting, has it been sitting? Or can you drive 20 minutes, turn it off, try to start it immediately, and have it not want to start?

I know my car looses fuel pressure if its been parked for a few days or longer.

 

I read this, and went away, now after much liquid intake, mainly coffee, I have a suggestion or 2 and some questions.

FIRSTLY
Welcome to the Forums.
Please visit the New Members Area and do an Intro, it keeps the powers to be happy, HA.

I am OLD and being from Downunder, terminology can be misread.

I am ASSUMING that the beast fails to engage the starter every time you turn the key to Pos#3 (Start position), then after a few, sometimes many attempts, it makes contact, the starter engages, the engine rotates (CRANKS), then fires up, and you are happy?????

If this is the case, I suggest that the Ignition Switch Electrical Section is waaaaay overdue for a service. By that I mean remove it from the Ignition Lock Assembly, open it up, clean all the dried up grease, and polish the contacts. This has revived dozens of my Jags over the years.

The neutral Start Safety Switch MAY be the culprit, but they usually go AWOL, and do not became intermittent, they work or they do not. I dont know where it is on the 91, but the earlier cars had it at the front of the gearlever, under the top cover.

IF, my assumption in regard the CRANK, versus START, is wrong, and the engine rotates every time you go to Pos#3, and it takes many attempts to get it to fire up and actually run on its own (AKA START), there may be other issues, and being a Marelli car, quite possible.

The attached PDF may be of assistance.

Keep us informed please.

 

Does the car only do this when fully cold (e.g. stood overnight)? Once it's fired/run for a couple of minutes, does it then start OK? I have a 1989 Marelli car which shows similar symptoms. Fuel pressure is fine, ignition/spark is fine. The one thing that has made a difference is 'adjusting' the AAV. If you remove the LHS/B Bank air filter box and, from cold partially block the AAV inlet pipe (ahead of the throttle body opening) - I'd suggest a leather gloved hand: you don't want anything getting sucked in, even if it's unlikely to clear the valve, it will be a pain to remove, plus the air is pulled in hard so your hand will get real cold, real quick. With the pipe largely blocked, have someone turn the engine over. In my case, it fires much, much more quickly. Given that you can't replicate this in day to day operation, the classic Jaguar-trained mechanic approach is to cut off a piece of broom handle and drill a hole in it of the appropriate diameter to restrict but not overly restrict the flow.

If this works, it suggests your AAV isn't right, even if it does bring the idle down to spec when hot, it's too open when cold. New ones are hard to find and expensive but if you search here you will find a rebuilder (John John) who is widely respected. You will either need his rebuild kit or to send him your AAV to repair. Right now, I'm too mean to spring AU$400 on a NOS valve and I like driving my car (once it starts!) so I'm sticking with the DIY restrictor!

Of course, this may not be your problem (it doesn't solve the problem for me 100% of the time - so keen to hear other suggestions) but it's a quick and easy check!