XJ6 & XJ12 Series I, II & III 1968-1992

engine cutting out - V12 Vanden Plas

 
  #1  
Old 07-22-2016, 06:26 PM
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Default engine cutting out - V12 Vanden Plas

Well, having just resolved my fast idle issue, I am on to the next problem, and I should say that I also had this problem before with the fast idle, so I do not believe there is any connection between the problems.
So, the problem: Basically, the car can be running nicely, and all of a sudden it will start to buck and jerk i.e. engine cut out, and then cut back in again, etc etc. This can go on for some time, and it is erratic i.e. does not do it all the time. When you hit the accelerator, the car does take off without hesitation. It is almost like she is running out of fuel, and then she gets a bit, runs out again, and then gets a bit more. And that's when underway. When stopped, or going very slow, she at times stalls now that I have slowed the idle to around 750 rpm. The previous owner told me about the problem, but he had no idea what was causing it.
So, what do you think.....might it be fuel related, ignition/wiring, other????
I should also tell you that I am running on 1 tank now as when I did the IRS last winter, I found that I had a leaky tank. Took it out of service and isolated it from the system. Also had to replace the fuel return lines and vapor lines adjacent to the IRS, which were rusted and leaking.
Any and all thoughts and suggestions will be appreciated.
Regards,
Wayne
 
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Old 07-23-2016, 05:28 AM
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Wayne, the list is longish, but my thoughts in some sort of order:

Fuel pump earth circuit, controlled by the ECU, and IS the Orange wire in the fuel pump relay socket. I would splice a wire into that Orange wire, and attach the other end to a GOOD earth. This will remove the ECU from fuel pump control, and the fuel pump will run ALL the time the ignition is ON.

The TPS is out of range, and/or set inncorrectly.

The RH fuel pressure regulator is sticking, so remove it and attach the supply fuel hose direct to the rail.

Spark plugs are incorrectly gapped. 0.025" is what the HE needs. Too wide a gap and low end RPM is crap, high end is usually OK.

Ignition awitch electrical section is getting hissy, age again.

The AAV is not closing 100%, and this AAV MUST close at engine normal temp, or unstable idle, and to some degree lower rpm will suffer.

Throttle discs AND the rods that work them are out of whack. The infamous bushes in the horizontal rods at the bracket at the rear of each inlet manifold can do this.

The vac hose AT the balance pipe connector is cracked/split. The other end of that hose AT the ECU is split. That hose/pipe combination is full off oily crud (common), so disconnect at both ends, and blow it out with a blast of compressed air. I put the ECU end in a jar (the black crap in that line will stain the boot carpet, and blow thru from the engine end, even adding some "solvent type" degreaser in that line just to be sure.

Fuel pump is dying, age is now against it. Fuel filter is clogged. These 2 are maybe not an issue as you claim it goes like stink when trod on.

I will stop at that for now.
 

Last edited by Grant Francis; 07-23-2016 at 05:34 AM.
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  #3  
Old 07-23-2016, 06:36 AM
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Thank you Grant for the list! Lots of items to check! I will get at this in the next few days, and will post an update.
Regards,
Wayne
 
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  #4  
Old 07-23-2016, 08:05 AM
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Originally Posted by Wayne'sJaguar View Post
So, what do you think.....might it be fuel related, ignition/wiring, other????


Yes

Grant gave you plenty of ideas. I just wanted to mention that one of them, the RH fuel pressure regulator failing, happened to me and did indeed give a symptom similar to what you're experiencing

Cheers
DD
 

Last edited by Doug; 07-23-2016 at 10:08 AM. Reason: sp
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  #5  
Old 07-26-2016, 02:37 PM
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Grant, thanks again for the list of potential causes of this problem. I have a few more questions:
1) Re the fuel pump relay, orange wire, if this resolves the problem, I guess the ECU is faulty. Correct? After the test, should I leave the orange wire connected to ground or change it back to the original wiring set-up? The fuel pump runs all the time anyway when the engine runs, so maybe it is ok to leave the orange wire connected to ground?
2) Dumb question, but what is the "TPS"? Temperature pressure sensor? And where is it located?
3) RH Press Regulator: Interesting that Doug had problems with this as well. Am I correct to assume that it cannot be serviced? Just bypass, as you have suggested, or buy a new one? Is it ok to have the direct connection with no press regulator on the right side? Any value to run a pressure test on the fuel rail?
4) Vacuum hose at balance pipe connector: can you give me some help to find this at the engine end; the ECU end looks clean, although I have not pulled the line yet; looks like I need to remove the ECU to get the vacuum line off.
5) I am ordering a new fuel filter, just to eliminate that one from the list.
Thanks again Grant and Doug. Look forward to any input/suggestions.
Wayne
 
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Old 07-26-2016, 10:10 PM
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Originally Posted by Wayne'sJaguar View Post
Grant, thanks again for the list of potential causes of this problem. I have a few more questions:
1) Re the fuel pump relay, orange wire, if this resolves the problem, I guess the ECU is faulty. Correct? After the test, should I leave the orange wire connected to ground or change it back to the original wiring set-up? The fuel pump runs all the time anyway when the engine runs, so maybe it is ok to leave the orange wire connected to ground?
2) Dumb question, but what is the "TPS"? Temperature pressure sensor? And where is it located?
3) RH Press Regulator: Interesting that Doug had problems with this as well. Am I correct to assume that it cannot be serviced? Just bypass, as you have suggested, or buy a new one? Is it ok to have the direct connection with no press regulator on the right side? Any value to run a pressure test on the fuel rail?
4) Vacuum hose at balance pipe connector: can you give me some help to find this at the engine end; the ECU end looks clean, although I have not pulled the line yet; looks like I need to remove the ECU to get the vacuum line off.
5) I am ordering a new fuel filter, just to eliminate that one from the list.
Thanks again Grant and Doug. Look forward to any input/suggestions.
Wayne
Aussie OLD age assumptions, sorry mate.

1) Your choice, if it fixes the issue. The car will not give a hoot. Only concern, and it is purely on your head, is that the timer/cut out feature from the ECU, of that pump circuit is lost. The enertia switch sswitch will sill the circuit if tripped. Sooooo, in the event of a prang, and the engine is stalled, the pump will continue to pump fuel. Not a concern for some owners, major concern for others. Mine ran for years with that earth in place, until I stole a later 16CU ECU, and all sweet again.

2) TPS = Throttle Position Sensor. It is located UNDER the central capstan at the rear of the engine. Under the alloy "wheel" that the throttle cable wraps around.

3) RH FPR is only a Pulse Damper. The actual Pressure is controlled by the LH FPR. Removal will do NO harm. Mine has been missing for 17 years. I look at it as less wieght, more speed, haha. A fuel pressure test will never do any harm, ever. Messy to do on the V12, but doable.

4) The engine end is dead centre of the largish balance pipe that runs across the rear of the engine. Feel on the underside of that pipe, in the centre, and there is is. This is messy to remove from the ECU, agreed, and simply undoing the 2 X 11mm nuts and sliiding the ECU out is simpler all round.

5) Smart move. Carefully cut the old one in half when done, and what you find inside will tell a very detailed story of the condition of the 2 fuel tanks, etc.
 

Last edited by Grant Francis; 07-26-2016 at 10:13 PM.
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  #7  
Old 07-28-2016, 07:40 AM
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Thanks again for the clarifications and added information on possible solutions to resolve this issue.
Well, yesterday as I was getting back to working the issue, I happened to notice a 4 wire bundle that was fried! It was located adjacent to the ignition amplifier, which I had noticed to run rather hot. Anyway, I traced the wires to the coolant temp sensor and the air temp sensor. The wires were fried to the point that the insulation was gone, so, 4 wires that likely were shorting to each other. So, I am wondering if this is part of my problem, as signals from the sensors to the ECU would possibly be all screwed up. I did a temp repair to the wires and took the car for a short drive. Seemed to work ok so I am hopeful that this is the issue. I will take her for a longer drive today and see if the engine cuts out or if she drives smoothly. Thoughts?
 
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  #8  
Old 07-28-2016, 07:54 AM
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Good find.

Any wire from a sensor to the ECU that does not have a clean path will reek havoc.
 
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  #9  
Old 08-13-2016, 07:25 AM
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Although I still have yet to work a few of Grant's suggestions, I have a few ignition related questions as well.
1) Yesterday, after reading another post that seemed relevant, I did the "constant energy ignition" checklist. Looks like the coil is suspect, as I have 0.19 volts from negative coil post to ground. (+ve post of coil to ground =12.19 volts). Key is "on" in both cases. With wire from amplifier to negative coil post, taken off, voltage = 0.21 volts.
So, the question: Does it sound like the coil is a problem? If so, I am confused as to why the car runs so well most of the time, and just seems to take the "cutting-out fits" erratically. I have not been able to see any pattern as to when, or why, these fits happen. The engine at those times simply acts like the fuel, or fire, have been cut off momentarily, and thus the bucking and jerking, on/off, behavior.
2) The car has an auxillary coil mounted above the rad. I took the above readings from the main coil. Is this correct. What is the function of the aux. coil?
3) I was suspicious of the ignition amplifier, after reading one of Doug's posts, specifically pointing to ignition module "AC Delco D 1906". My amplifier runs very hot; yesterday, I read 125 C. Is this to be expected.
As always, any and all feedback will be appreciated.
Regards,
Wayne
 
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Old 08-13-2016, 07:55 AM
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#1 and #3 combined. That temp is way too high. I suspect a dud coil or 2. Mark, and remove ALL wires from the main coil. Set the meter to OHMS, and probe the +ve and -ve terminals. I would expect 1.2ohms or close. Then check the AUX coil. It should be the same.

When the 2 coils are attached +ve to +ve and -ve to -ve the reading should be somewhere around 0.6ohms. Much higher than that and the amp/module will overheat and eventually die.

Without getting too technical, that 2nd coil is to lower the charge time for HT spark at the high end of the rev range of the V12. Cars with one of the coils not working usually have issues over 3500rpm.

Inside that ign amp is a condensor, tucked in one corner, and attached to one of the +ve terminals of the module. REMOVE it and throw it away. They "leak" to earth and reek havoc. Mine has been missing for nearly 20 years, no issues at all.The snap (thanks to Greg in France) attached shows it at the bottom of the picture with an arrow pointing at it and a RED C.

engine cutting out - V12 Vanden Plas-amp-inside.jpg
 

Last edited by Grant Francis; 08-13-2016 at 07:57 AM.
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Old 08-13-2016, 09:52 AM
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The condenser in that location is a mere RF noise suppressor. Might or might not sense a bit of static in the radio. Or so, I understand...


Carl
 
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  #12  
Old 08-14-2016, 05:00 PM
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Did checks, per your last note, Grant. Resistance between +ve and -ve posts on the main coil is at 1.1 ohms; for auxillary coil, same resistance at 1.1 ohms. With connection of both coils, I get 0.8 ohms. So, contrary to my previous checks, I am now thinking that the coils are ok. Thoughts?
Went back and did the "constant energy ignition" checklist again. This time I get 11.72 volts and both +ve and -ve terminals to ground, on the main coil. The battery was at 12.18 volts. So, again, perhaps coil is OK. Went on to check line from distributor pick-up to amplifier.........this time I had an open circuit! I believe this suggests a bad pick-up?
Oh yes, I disconnected the condenser in the ignition amplifier, as you had suggested.
Any additional thoughts?
Regards,
Wayne
 
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Old 08-15-2016, 03:49 AM
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OK, well done.

That issue with the wires from the distributor to the amp is getting common.

They have a habit of breaking INSIDE that rubber bung where they travel thru the distributor casing.

I have replaced 3 of them so far. I simply fit new wires as required, and fill that hole with RTV, and get on with driving it.

Coil readings are just fine for me.
 
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Old 08-15-2016, 08:38 AM
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I am baffled as to why the car runs so well, most of the time, if the problem is this wiring between the pick-up and the amp. Or, maybe it won't work so well now, until I get the wires fixed up? What do you think?
Perhaps the wire(s) were cracked and just breaking contact from time to time, and thus the cutting out sensation of the engine, like an interruption in fuel supply?
 
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Old 08-16-2016, 09:08 AM
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True. The in and out wires in distributors in a lot of cars going way back have been an issue. Short at timers and at times not. Devilish diagnostic issue .


As Grans suggests, swap in new wires. Does a lot in so many places.


Or, merely tow it around with that old Ferguson!!!


My son rescued an old Case of similar vintage. Tugs stuff around their
Sierra home.


Carl
 
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Old 08-16-2016, 07:50 PM
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We call that wring issue "The Fiddle Factor", and thanks to Doug for that one.

Mostly "fiddling" with a bunch of wires, and away we go, for minutes, hours, even years, then it stops again.

Jaguar V12, GOTTA LUV EM.
 
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