Dear all,
I hope all are well and may you be in a good mood to join me in the joy of solving one of those truly Jaguaresque type of problems.

Some background first: The car (85 XJ-S HE) ran fine, normal just a few weeks ago. Then it started giving me some trouble starting quickly and sometimes it would start, idle for 30 sec then stall. The no start problem progressively got worse where it would not idle, but if I got her fired and revved it to 3k rpm, after a few minutes she would settle in normally and work fine for the rest of the day. Next morning she wouldn’t start no matter what. I had to get a new battery as the old one gave up the ghost from all of the repeated cranking and recharging.
In the process of diagnosing this and that I finally got her running again today. She fires right up, idles normally for about 15-20 sec, then she runs rough progressively getting worse until stalling. I can repeat this test all I want. Starts right up, idles perfect for 15 sec then rough, rougher stall. Arrgg!
Here’s an overview of what I have replaced and/or tested:
Distributor pick-up leads tests at 3.2 ohms both at the distributor and at the ign amp connector. I have spark to the distributor and I have ground switching when cranking. I replaced the GM HEI module in the ign amp with a known (tested) good new unit. Although the old one also works the same way (thinking this was not an issue)
The EFI shielded cable from the amp tested fine at 6.8k ohm resistance (amp side) and I checked continuity of the shielded wire all the way to the big connector on the ECU (tested good with very low resistance). I also tested the wire for short to ground and found none.
I replaced my potentiometer a few years back with a Hall-effect sensor and it sits at 0.32v with the ignition on. The voltage changes smoothly when cycling through the range.
On the Fuel side, I can smell the gas getting there, the pump primes on start-up, I hear the injectors clicking and can force the injectors to click by blipping the throttle. I also jumped the fuel pump relay to keep it going to see if that was the issue, but she does the same thing, idles fine for 15 sec then runs rough, rougher, stalls.
I tested the resistance of the coolant temp sensor and found 2.2k ohms which for 75 deg F should be spot on. I checked the voltage to the coolant sensor connector and here I found ~0 V on one side and ~5V on the other side. This is a bit odd as Kirby’s book says this should be about 0v on one side and 2.5V on the other. Not sure if this is an issue or not, but it makes no difference whether the coolant temp is plugged into the sender or whether I bridge the connector, the stalling problem still exists.
I’m stuck, I have spark, fuel, running but not staying running. What sends the” continue to run damnit” signal back to the ECU? What else should I be looking for? Any help would be greatly appreciated.

 

OK, you appear NEW, and having fun already, WELCOME.

Based on the fact it has run fine until now, I will keep that in mind as best I can, as I list the culprits I have found over the years.

The 5v at one wire of the CTS is correct.

That shielded wire IS the "keep running" signal to the ECU. It basically informs the ECU that there is ignition pulse present, and that in turns keeps the injector circuit "alive' and the fuel pump circuit "alive".

The following is going to sound BORING, but I am old and a tad grumpy haha, but systematic diagnosis on a V12 is the only way to sort it.

Bridging the fuel pump relay sorts the fuel pump area kind of. I would get someone to have their head in the boot (trunk/whatever) and listen to the fuel pump, and note any alterations to the "buzz" as the engine goes hissy. I have had a few where the pump just gets lazy within a few seconds of operation, and one person is flat out hearing it.

The fuel filter is on my list, even if it is new, is it blocked.

The small filter INSIDE the sump tank (under the battery), is also on my list. While you at that, check for crud in that small tank, which will indicate the main tank is rusting on the inside. Also check that 1/2" hose that runs from the main tank to the sump tank, they block up inside the main tank with said rust and stuff. Obviously CARE HERE as fuel will be spilt.

The vac line TO the ECU. The section inside the boot that wanders around that sump tank and attaches to the ECU is a known issue, as in it splits. The ECU supplies more fuel with less vac, and vice versa, so the integrity of that line is paramount.

The fuel pressure regulator/s have ruptured and the vac hose is sucking raw fuel into the engine.

The ECU itself. Yours being an '85 may have what is called a 6CU unit, and they were known for issues with the fuel pump control circuit, and the EFI control circuit/s. Swapping to the later ('86 on) 16CU sorts many, many issues with these engines. It is a plug and play swap.

Loss of ign 12V due to a dirty ignition switch electrical section is also common.

That shielded wire. The thin centre core wire is the culprit. I have found them broken/degraded/all sorts, anywhere in the length from the ign amp to the RH side of the engine bay. Mainly near the oil switches/TPS area is my common finds. That wire takes a beating when 6A/6B spark plugs are changed. That inner wire should have perfect continuity to pin #18 of the ECU. If it don't, it wont run at all, or well. Also note that the shielding is generally only earthed at one end, usually the ECU. I have deleted that shielded wire in the engine bay of all mine, and most others in our group, no issues with any of them. Simply used a 3mm wire and soldered to the small inner wire in the good section outside the engine bay in the RH wheel arch rear aperture, making sure the shielding is well clear of the soldered joint, some heat shrink seals it sweet.

There may be more, surely will be, but that will keep you occupied for about 3 hours.

 

Grant,
Thanks for the welcome. I am new to this forum but have had the XJ-S for 15 years or so. The name is Bill Fernandez, I have conrtributed to Kirby's book and co-developed the TKO 5-speed kit with Shafi Keisler many moons ago, so you will find me on Jag lovers as well.

Excellent suggestions, I will occupy myself with the fuel system, filters and small tank as I have not checked either of these in years. My ECU is already the 16CU unit, and I have Roger Bywater's remapped chip in it.

With respect to the sheilded wire, when I checked continitity to the ECU main plug it showed solid continuity with very little resistance, so I hope that is working well, but always open to improvements.

Also thanks for CTS confirmation, that was throwing me for a loop. Well off to the parts store to get a new fuel filter. I'll keep posting what I find or fail to find

Regards,
Bill

 

Been tied up with other tasks for a few days, but finally managed to drain the fuel and check out the pick-up. My fuel (about 7 gals) drained clean of any noticeable sediment. After removal of the surge tank and pick-up I did drain out about a table spoon of crud out of the tank but otherwise it was clean and fairly rust free.
The pick-up screen on the other hand seems original or at least original "old" style. I'm shocked by the design of this filter in how fine the screen is allowing it to be easily clogged. I must be blessed by a very clean fuel system because I have not done a prior clean out of the surge tank in 15 years of my ownership.

Well now it's my turn, the pick-up screen was 75% clogged and I assume that the remaining sediment that I pulled out caused my cut-out problem. Have some new parts on the way so I'll just focus on some tidying up and painting in the area until I can reassemble and hopefully start the beast,

Thanks for your help. I'll post results and some pics of the pick-up screen soon.

 

Update upon additional research I found that my clogged pickup screen was indeed the upgraded Jaguar part # CBC5649. Apparently the PO had addressed this issue before me. So in hindsight, although this screen is a recommended upgrade for the earlier design, it too is prone to failure from sediment blockage.

The key problem is the design of the filter (screen) media. It's just too fine, it makes pantyhose look like fishing net by comparison, it is that small. As such it is likely to clog like mine was by a very fine silt/sediment that was dust sized. I had less than a tablespoon of crud on the surge tank, but the fine sediment had progressively clogged the screen.

In any event the recommended route in Kirby's book of removing the screen and adding an external filter is the most appropriate way to address this inherent design flaw.

I will be installing a 100 micron replaceable filter/canister and locating it in the surge tank area with easy access for future cleaning.

 

Well everything is back together and she still wont start.
Checked for fuel at the inlet regulator and found pressure,
check on the return side of the rail and there was very
little fuel going through the rail. I then tested for
pressure on the outlet prt of the inlet fuel pressure
regulator and nada, just a hint of fuel.

I removed the pressure regulator and tested it separately.
It holds vacuum, there are no signs of diaphragm failure. I
hooked up the air compressor and it held closed to 45psi and
then popped open above that. Releasing pressure showed that
it closed off again at 45psi. Applying vacuum to the
diaphragm reduced these pressures by 5psi, so it seems that
the reg is fine.

I'm staring to feel that although the pump is running and
moving fuel it is not building up enough pressure to pop
open the inlet fuel regulator to feed the rail.

Has anyone else experience a weak pump and similar issues?
I'm going to try to find a salvage pump for testing tomorrow
but would appreciate your thoughts.

Thanks,
Bill

 

Do you have a fuel pressure gauge? If so, testing the pressure might be easier than finding a salvage pump. The pump should produce about 75-100psi.

Not sure if I quite understand your regulator test but, in any case, the inlet regulator can be removed entirely with no ill results if you wanted to experiment.

Cheers
DD

 

If there is hardly any fuel coming through the regulator, and if the regulator is OK, then it has to be either poor pump pressure or poor fuel feed through the system. Have you changed the fuel filter behind the spare wheel? Even if you have, could be a bad one.

Have you blown through the pipework from fuel filter outlet pipe to regulator input with compresssed air? Might be worth doing. Alternatively, with a flexible extension on the regulator feed pipe going into a fuel can, run the pump and see what the flow looks like (needs care obviously!).

As Doug says, you could just bypass the inlet side regulator and see what happens, but a definitive pressure reading would be sensible, the thing will run on lower than spec fuel pressure, but might damage the engine at high loads and WOT.

 

Doug,
Thanks for the psi range. I'm embarrassed to say that I have yet to replace my broken high-pressure fuel gauge so I'll have to get one to get definitive readings.

As to the regulator test my objective was to check for seizure; where the diaphragm can be fine but the valve assembly is frozen. My understanding is that most regs will not flow fuel unless a minimum pressure is available from the pump. By connecting it tho my air compressor I could slowly raise the psi to see where the regulator popped open with or without a vacuum signal applied.

I'll check the pressure and go from there, may even bypass the inlest side permanently and install a underhood pressure gauge in the same location as the inlet reg.

Also Thanks Greg, will get some readings and post results. I did cleanout the surge tank, removed the pick-up screen and installed a new 100 micron external pre-pump filter as well as a new fuel filter. I'll blow out the lines from the filter to the inlet and see if that frees up anything (great suggestion).
Bill

 

OK so the challenge today is to blow through the lines. Yesterday upon checking again, I noticed that the fuel pressure at the reg inlet side is now weak. I did manage to find a salvage pump cheap to use while I await my pressure gauge to arrive. Well the same thing ocurred, pump humms along but little pressure getting to the engine bay, so the only thing left is the line from the pump to the reg, there must be some obstruction there.

I'm going to blow through the lines engine side to pump to see if an obstruction is found, I'm just baffled as to how this could have happened? As mentioned earlier I found little sediment in the surge tank, the main fuel filter was not obstructed, cut it open to verify and it was very clean, replaced with new,

Not sure but metal flaking or rust possibly in the hard lines to the engine bay, will report back with anything found. This is just getting to be a PIA.

Thanks to all for their suggestions!

 

You are nearly there then. Once the diagnosis is done, the fixing is the easy part!

The pressure line is in three parts:

1. Flexible hose from filter to corner of the boot (trunk)
2. Via a brass 90° fitting that goes through a grommet into a pipe which is part solid and part flexible, these are swaged together. It goes over the top of the axle and joins just forward of the axle via a compression fitting to:
3. A long solid pipe that runs along the US passenger sside and up into the engine bay, where you see it join the engine bay flexible.

So if it comes to it, you can separate these parts and find the bit which is the problem.



But first, try the pump flow test without the filter. I had a Range Rover once and spent months trying to fix a fuel flow problem only to find the new Bosch filter was the problem all along!


Greg

 

As Greg said.

Look at the long pipe on the RH side, under the car. I have had some with this pipe crushed. Questioning the owners, reveals that he/she had tyres fitted recently, and those clowns jacked the car without using the jacking points. Also have had some with the LH side return line with crush damage, preventing return fuel flow and a rich running engine mmmm..

Inside the engine bay, just forward of where that supply pipe enters, SOME markets have a valve/reducer in the flexible line, stepping down from 10mm to 8mm, and they are well documented as a PITA, and I have removed many over the years, and simply used an EFI plastic reducer with NO ill effects.

 

Well one would think that this problem was conquered but not in my
case. Fuel pump is working fine as far as I can tell, there is
fuel under pressure on the outlet side of the outlet regulator, so
the rail is seeing at least 43.5psi.

Upon starting the car she kinda runs OK but seems to sputter a bit
and the idle fluctuates but only by a couple hundred rpm from say
650-850 or so. I did open and clean out the AAV last night but the
plunger looked fine, was in the lowest position cold so the opening
to the air cleaner was free and clear and since this issue is
happening with a cold engine I don't think that is the issue.

All injectors are firing although without pulling them I cannot
attest to their spray patterns. I have good spark to the
distributor.

When I try to blip the throttle, it bogs initially and then revves
up OK not perfect but it dosent struggle much to rev up.

I'll check the TPS again but it was spot on during intial diagnosis
so having not touched the area, I cant imagine anything changed
there.

Any ideas of where else to look? My tool supplier sent me a note
saying that the pressure test gauge set is on back-order so I'll
have to test without one, but since fuel is making it through the
regulators (with the vac lines disconnected) it is producing at
least 43.5 psi to pop open both inlet and outlet regs.

Ideas?

 

Without getting picky, I am confused a tad, and that is not hard to do.

"I have pressure on teh outlet side of the outlet reg........".

This is the hose going to the tank. It will have fuel in it, drain back fuel, but it should not be under any significant pressure, maybe 2 - 3 psi. It is return fuel, high flow generally, but almost no pressure.

Try running another hose from the LH reg to a container on the ground, run the engine, see if anything changes, that will quickly eliminate that return piping etc from the thoughts.

A Tassie car I was assisting had pressure in that line, and it tuned out to be collapsed fuel line above the rear cradle, and damage from jacking to the LH under car pipe, just near teh LH front jacking point. Once sorted all the oddities went away, and that was 3 years ago, and he has not emailed for quite some time.

 

[QUOTE=Grant Francis;672854]Without getting picky, I am confused a tad, and that is not hard to do.

"I have pressure on teh outlet side of the outlet reg........".

My apologies Grant, I should have said that I have good flow on the outlet side. I had done as you suggested and run a hose to an eternal can and it has great flow. The line from there to the main tank is also clear and free.

I started her up this moving from cold and she would idle rough as mentioned earlier with a slight ~200rpm oscillation. Shut her down
and went through the following checks and adjustments:

Checked TPS ignition on, 0.36v. Moves smoothly through 90 deg range hitting 4.5v at WOT.

Since I had noticed that the throttle linkage on bank A was a little loose, I went through the process outlined in the Book on throttle plate-rod adjustment. Found that bank A was indeed off with the throttle plate completely closed at idle, although the balance pipe should theoretically
compensate for this. Either way she's adjusted correctly, and both throttle butterfly s move 2mm from TPS idle/stop.

Screwed in the AAV adjustment bolt as the idle had raised slightly from the linkage adjustment. This seemingly has eliminated some of the throttle lag noticed earlier.

Although she was sounding much better now, after running for
about 7-10 min with an odd miss, almost like a missed heartbeat, not like a misfire just and odd sec where it seems as if everything stops for a second and then resumes; she stalls. So I'm back to the start, run, stall scenario,
although now, the engine temp is warm/normal, and the run length is longer than my original experience, she now runs 3-4min before stalling.

Warm start up in now becoming an issue, rather than reaching through the window and turning the key, I have to get in and goose the pedal quite a bit with several attempts to get her started. revvs fine throughout, settles at idle for 3-4 min and dies.

I checked the coolant temp sensor and its showing 0.28 ohms warm which seems correct. The leads to the coolant temp sensor read 5.36v to one side and 0.03v to the other. This is a little confusing I'm not sure if the 5v side is supposed to drop to ~0.95v as stated in the Book?

If so, any ideas of what would cause this reading?
Thanks,
Bill

 

Well after chasing down so many possibilities, I decided to take a look at the distributor pick-up, advance and general state of the distributor. Everything checked out fine with the exception of the distributor cap. The center coil lead "button" on the underside was gone, the plastic sleeve was itself burned and damaged. So the spark was arching a decent distance, at least 1/4 in or more to the rotor.

Luckily,I had a spare Lucas cap and rotor and upon replacing she smoothed right out and ran perfect. Surprised to have seen so much wear to the underside center post of the cap. All of the contact points are like new, and the rotor looks in great shape except for the top contact point. They were replaced 12k miles ago.

Thanks to all for your help,
Bill

 

AHA, that makes 10 carbon brush failures in 6 years, sound like a quality control issue.

I use a GM brush and spring, $6 last time I needed one.

Glad its sorted.

 

I read your post regarding your weak fuel pressure problem and noticed your mention of a hall effect sensor in place of your TPS.
Your quote. VV
"I replaced my potentiometer a few years back with a Hall-effect sensor and it sits at 0.32v with the ignition on. The voltage changes smoothly when cycling through the range."
May I ask where you got that from and is it used in connection with a Digital Potentiometer? I have an '85 as well and my TPS is shot. I was going to design my own with a programmable shaft encoder, but your hall effect post caught my attention.

 

Kirby Palms book explains the Hall effect sensor, and since it uses no contacting wipers, it shouldn't wear out. There are also helpful links to where to procure one and set it up.

 

Agreed, the Book has details on where to source the hall effect sensor. Very reliable mines been trouble free for 15 years