Hi All,

I'm a new (and proud) XJS owner . The car will run just fine, pull strong, purr smooth, everything great.... And then, intermittently, and with no noticeable pattern, die. I lose power steering of course, and have to coast to the nearest safe stopping location. I generally can't restart the car for about 3-4 attempts over the next 5-7 minutes. Then, with a mild amount of sputter on another attempt, it will fire up, and I'll be back on my way with no apparent problem.

Sometimes it will happen at idle, sometimes going 25 around the block, and sometimes going 45 down the state highway. Sometimes it happens after driving for a minute, and sometimes 20 minutes. Generally happens about once a day or every other day. My wife is scared to drive the car, because she doesn't want to be stuck in the middle of the road for several minutes... So I need to fix it.

I left it with a local "all british imports" auto shop down the street just to see if it was an easy fix. Several days later, I'm told they are 90% sure it is the ignition system, but that they couldn't get it to stall more than once for all the times they drove it so are not sure, and I opted not to have them replace the whole ignition system till I considered other options.

I'm hoping for advice from those who have had this problem, starting with the simplest (even if not likeliest) issues. I'm mildly mechanically minded... But feel extremely intimidated by the engine compartment in the XJS haha. I'd love to try to do a lot of my own work, but would rather start with simpler try's first. I've been pouring through Kirby's book since I purchased it, but want some specific thoughts.

Advice?

 

The two times I had problems vaguely similar to this:


1) 1983 XJS: 6CU went bad - replaced with a 16CU from a 1987 XJS. No problems since. If you can find a decent price on a 16CU, it might be worth picking one up as a backup even if that isn't the problem. They are easy to swap as a test to see if the problem persists.


2) 1986 XJS: Rotor in distributor was warped, and continued to warp more and more over time.

 

Welcome to the forum, these are great cars, but you have to reconcile yourself to carefully re-doing lots of things that will have been neglected before you have it reliable. Do not be too scared of the engine bay, it looks terrifying at first, but is no more complicated than any other injection engine, just a bit more cramped !
It is either ignition or fuel that's for sure! I would start by eliminating fuel, which is in principle straightforward.The fuel system from the tank to the fuel rail should be cleaned and any replaceable parts replaced. This is time consuming but not expensive and there is no reason you cannot do it yourself. Your symptoms are consistent with fuel starvation caused by the system not being able to keep up, then after a few minutes recovering. This is a diagram of the main tank and pipes.

This is a diagram of the sump tank which is fed from the main tank:

I suggest you proceed as follows, unless you know for certain all this has been recently done.
Remove the battery
Undo the metal cover below the battery
This reveals the sump tank
Under the sump tank under the boot floor is a rubber bung, under this is the drain plug. Drain the entire system from this plug, main and sump tank.
Undo the locking ring on the sump tank exit spout and remove the spout with its filter. Renew the filter and clean out the tank.
If the feed pipe to the sump tank from the main tank is soft or even old looking, renew it, it can collapse internally unseen.
Check the pipe from the sump tank to the pump is also strong and not soft, renew it is you are not sure.
Behind the spare wheel is the filter, renew it, being careful to ensure the filter goes in the correct way
While the main filter is off, in the engine bay disconnect the fuel line before the A bank fuel regulator (The one on the US passenger side). Blow compressed air through the fuel line at the filter end to the engine bay to clean out the line. Ensure the air flows through this line freely. The line goes under the car and can get pinched by idiot mechanics.
Ensure the tank venting system works properly, as if blocked this can cause fuel starvation; this is rather a complex system, so many people just install a modern two way tank vent valve and vent it to air. The tank vet system is part nos. 26, 27, 28 29 in the first diagram.
Now reconnect the pipes etc, refuel the tank, and with a friend to help, before you reconnect the fuel regulator in the engine bay, hot wire the pump feed and ensure the pump produces a really strong fuel feed at the engine. If not, the pump may be getting tired. But clean the pump earths (grounds) that you will find on the RHS of the boot tunnel under the carpet to be sure before you renew it.
If all well, that leaves only the B bank (US driver's side) fuel pressure regulator that could be getting tired, but this is not consistent with your symptoms.
If all this is OK, then you know the fuel supply is good. So try it out.


If the problem persists, do not despair, the ignition system is not too complex on your model. So this post is not too long to take in, I suggest that you post again when you have eliminated fuel. But in the meantime, as long as your garage has renewed, dizzy cap, rotor, HT leads and plugs, that is a good start. Also the ignition amplifier (the black box about a pack of cigarette size on the B bank inlet manifold top at the firewall end) is a very possible culprit. But I suggest fix for sure one system at a time.
You have hours of fun ahead! Good luck
Greg

 

I would also start with the ' swirl pot ' pickup filter as described above

this manifests its self as loosing power, stalling out and can also make the fuel pump whine a bit louder due to working harder,

this is a free fix as well providing you don't need to replace anything else while your there

BB

 

Hi there Your car looks like it just came out of the showroom , stunning , thanks for the pic. I have just spent 30 minutes typing a reply and the PC did a blip and wiped it all out Grrr so this is the short version for now , even though all the previous posts are valid ( good advice from Dcarr ) here are my thoughts , firstly I have to let you know that my XJS is a 78 which I have owned for 36 years I am the only person that has worked on it .Start your engine shake all the wiring you can see , if the car stops you know what to do . Check all connections to sensors including the connector itself to make sure they are sound ,the coolant temp sensor which is just above the thermos housing on RH bank will stop the car from running as will the manifold pressure sensor located in the front rh corner of the engine bay perhaps a loose or corroded connection there could cause intermittent stopping. I have also heard of wiring breaking down within the insulation although I have never found that on my car (hence the need to shake the wiring ) I am sure someone will let me know if the components on your model differ .So hopefully you find this a simple place to start. Before I go , I do not mean this in a smart **** way but it is worth getting a shop manual so you can at least identify and locate the parts especially if the simple things do not fix the problem and you start getting more technical advice from the members , that's reminded me of something else , hang on , yes coming dear , now where was I oh yea If you do a search for repairing the Ignition amp there is a post by Grant Francis , who has been referred to as the " XJS Prophet " which is something I would not disagree with , showing how to fix them . Got to go , think I will be going straight to sleep tonight !!!

 

All very good advice. Just one small point, on your model there is no manifold pressure sensor.
Greg

 

John is spot on.

The HE differs in that:

Manifold pressure sensor is INSIDE the ECU.
Coolant Temp Sensor is on the backside of the LH thermostat housing, and is a well known engine killer, as is the plug, the wires INSIDE that plug, and at a point about 6" from that sensor up the loom, at a splice point.
Infamous shielded wire from the IGN amp TO pin #18 of the ECU.
The fiddling with the loom/s as John has said will quickly identify wiring and or connector issues. Sometimes this "fiddle factor" fixes the issues, and can last an hour or two, or many years.

 

Greg,
Can you explain, or point me to a post which explains how to install the two way tank valve? I'd like to make my system less complex.
Thanks.
Jon

 

Jon
This is the sort of thing:
Mocal In Line Fuel Tank Breather Valve | Demon Tweeks
Summit Racing and most USA places will have them. You need a two way one, that allows pressure to escape and vacuum to be relieved. You can even get ones that automatically shut off if the car is overturned: https://www.merlinmotorsport.co.uk/p...-tails-m-trl88
The OEM venting is via a condensing canister on the RHS above the fuel tank corner, no. 27 in this diagram:

All you need to do is connect one of the three pipes coming from the main tank to a pipe that vents outside the car, or to pipe no 28 directly, bypassing the cannister etc. BUT your pipe 28 may well go to a complicated charcoal cannister in the engine bay region, so honestly connecting it to the drainage pipe in the RHS boot gutter is easier and far simpler. You just need a Y connector and you are done. It is important to make sure the pipe from the tank points upwards and the valve is installed above the tank so only vapour goes into the valve. You can just strap it to the (now superfluous condenser), then loop the pipe downwards to the drain pipe. Check that the drain goes out through the tunnel side at the bottom and that it is clear. Block up the other two tank exit pipes that went to part 27. A bolt stuffed down their ends with a worm clip to hold it in place works fine.
Greg

 

Thanks Greg, just what I needed.

Jon

 

Occasional stall can be caused by so many things. In any critter.
The diagnostic paths can be daunting. But, not so much, if one
splits them into two. Fuel or ignition.


I've no clue as to why the shop is dead set on ignition. But,
I understand. I like to start with ignition. Simple place to begin.
Jump 12v to the + post on the coil. Drive the car, stay close to home for easier retrieval. Fixed? Work back along the wires to the ignition switch. The switch itself can be the issue. Age and a heavy key ring.
Been there!!! Changing it fixed a lot of stuff.


Great help here from guys that really knw these cars.


That car is surely a beauty... Well worth a lot of effort to make reliable.


Carl

 

Yes indeed ?


Cheers
DD