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2.5TD wont stop with ignition key turned to off.


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Doing some work on my mates 2.5 TD 90. Noticed that the fuel shut off solenoid was leaking diesel, took it out, changed the o-ring put it back. Vehicle started, solenoid still leaking, but i see its leaking from the top. turn ignition key to off, engine keeps running. So i pull off the wire on the solenoid, engine dies.

I restart the engine then turn the key to off. Same thing happens. so i pull off the wire again and it stops again.

I ordered a new solenoid and fitted it, it made no difference, engine still runs on.

I did ground the terminal on the solenoid and there was a spark. After this the engine would turn off on the key twice but then after this went back to not turning off again.

Any ideas?

Thanks.

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Thankyou Blue Spanner, thats very helpfull. Gives me something to look into tomorrow.

Resistor behind speedo cluster, in a fuse holder, potentially faulty. Alternatively a fault with the Alternator, backfeeding a small voltage to the solenoid.

Thanks again.

Love this forum.

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Hiya

I had this same problem on my last truck, turned out to be the ignition barrel, replaced that and all was fine.

From what I can remember on inspection of the barrel there are three ball bearings in a plastic channel, they had set themselves free with wear on the plastic causing them to be live all the time.

You really need to sort this, mine was at a local garage parked on the main road and it kept trying to start itself, (I had a battery isolator key that was off!) if it had been in gear it would have lurched down the road.

Paul

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Maybe not the same, but I recently installed a new trailer plug (harness) on my 200tdi. And since I was tired I did some mistakes in the plug, the result was that she refused to shut down when I turned the key, unless I turned of the headlights. So maybe a electrical error that lets the power continue around... Everything else worked fine so it took a while for me to figure it out. Good luck

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If the solenoid stays open with the key off, but closes when you remove the wire from the solenoid, then the wire is obviously providing power when it shouldn't. It has to be either a fault in the switch, the way the switch has been connected up or a short circuit with the solenoid wire from a permanent live. If you have recently replaced the ignition switch, then I'd start by looking at your connections there, followed by testing the switch outputs with the key in different positions to see if it is behaving correctly.

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So after further investigation, if i start the engine but do not touch the acc pedal (the battery light is on) i can turn off the engine with the key every time. Under this circumstance terminal 3 on the ignition switch (white wire with black tracer) reads 0 volts.

If i rev the engine so that the battery light goes off, then after this i canot turn off the engine with the key. At this point terminal 3 on the ignition switch (white wire with black tracer) reads around 8 volts. I dont6 understand why.

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That sounds like the alternator is feeding the solenoid circuit and holding the solenoid open. I wonder if an issue with the diode rectifier in the alternator could cause an issue like this. I don't have circuit diagrams to hand to check.

What has changed since everything was working fine? Are you sure the ignition wiring is 100% correct from when the switch was changed?

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Sounds likely - the diode pack should be connected to the ign live circuits in the fuse box, so that with the key on but engine not running, current will flow through the charge warning light from the battery, earthing through the alternator, but when the alternator is providing charge, it should cancel the battery's 14V (the voltage being received by the battery directly from the alternator main windings). If the alternator diode pack is allowing excessive voltage back to the light, it could be earthing in reverse through the solenoid, holding it open.

Alternatively, it could be a short on the ign switch. Try disconnecting the battery warning light circuit from the alternator (the thin wire) - if the engine behaves normally having revved it up, then you know it's the alternator. If it continues to run with the key off, it's the ign switch.

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Thankyou Snagger and LandymanLuke.

I cant say i understand your theory, but thats because your explanation is beyond my comprehension of auto electrics. What i can say, is that tomorrow i will try to disconnect the thin wire from the alternator and then try starting the engine, revving it, and then try turning it off on the key.

When you say thin wire at the Alternator, are you refering to the Brown with yellow tracer? I remember seeing that one whilst, staring at the alternator with bemusement.

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That sounds like the alternator is feeding the solenoid circuit and holding the solenoid open. I wonder if an issue with the diode rectifier in the alternator could cause an issue like this. I don't have circuit diagrams to hand to check.

What has changed since everything was working fine? Are you sure the ignition wiring is 100% correct from when the switch was changed?

Everything was working fine until i removed the old solenoid due to a fuel leak. After that moment, the not turning off fault occurred, and then further investigations showed small voltage (2v) at the white wire on the solenoid with the engine running and key off.

I then, changed the ignition barrel and switch because of a seperate fault, to do with glow plug position being worn on the old switch. The new ignition switch rectified the glow plug problem but the solenoid fault was just the same with the new switch, which makes me think this fault is not to do with the switch.

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Ive been researching this problem searching through past posts. There is talk of a resistor somewhere behind the speedo cluster housed in a fuse holder, which is there to stop backfeeding voltage from the alternator, somehow to the fuel shut off solenoid circuit. I have loooked and looked and looked again, but cannot see anything like it on this 90 (1989 2.5 TD).

Did it really exist from the factory? Or is it an add on that some owners have fitted?

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Also, the white wire with black tracer on the ignition switch, that supplies 12v to the solenoid, as soon as the ignition key is turned to the first position.

It runs into a clump of white wires that head toward the centre of the dash and dissappears.

The wire at the stop solenoid on my vehicle is pure white with no black tracer.

2 questions:

1/ Is there a break somewhere along this wire, in the form of connector, fuse, or connection at some other part that would explain this change in wire colour?

2/ If the answer to the above is yes there should be a break in the form of a connection, then where is it, and what is it?

Im sorry for all of my questions. I just cant find a credible wiring diagram that i can read, which is colour coded etc. Seen loads of carp ones but no decent ones.

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The resistor does not prevent backfeed of current, it simply limits the current flow into the alternator field windings. However, there is also a diode hidden in the wiring behind the dashboard which does prevent backfeed (if it's working properly). It's a black cylinder about 40mm long and 8mm diameter with a spade connector in each end.

The white and white/black wires are joined at a terminal block behind the dashboard.

I could tell you more but its meaningless without a wiring diagram, so send me a PM with your e-mail address and I'll send you what is probably the closest thing to a correct wiring diagram for your vehicle.

The wiring diagrams for vehicles of this age are truly dreadful and there may not actually be a completely accurate drawing in existence if it's anything like my 90, which was built as a special order 2.5TD after the 200TDI was introduced. So far as I can see the wiring is a hybrid between two different diagrams, and it's even worse now I have put a 300TDi in it!

Nick.

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Thankyou Snagger and LandymanLuke.

I cant say i understand your theory, but thats because your explanation is beyond my comprehension of auto electrics. What i can say, is that tomorrow i will try to disconnect the thin wire from the alternator and then try starting the engine, revving it, and then try turning it off on the key.

When you say thin wire at the Alternator, are you refering to the Brown with yellow tracer? I remember seeing that one whilst, staring at the alternator with bemusement.

The idea here is that the alternator diode pack voltage may be back powering the fuel solenoid, bypassing the ign switch, so disconnecting the diode pack would prove that whether the ign switch and circuit is functioning correctly. If the fault persists with the diode pack disconnected, you know the fault is not with the alternator. And yes, that is the wire you're after.

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The resistor does not prevent backfeed of current, it simply limits the current flow into the alternator field windings. However, there is also a diode hidden in the wiring behind the dashboard which does prevent backfeed (if it's working properly). It's a black cylinder about 40mm long and 8mm diameter with a spade connector in each end.

The white and white/black wires are joined at a terminal block behind the dashboard.

I could tell you more but its meaningless without a wiring diagram, so send me a PM with your e-mail address and I'll send you what is probably the closest thing to a correct wiring diagram for your vehicle.

The wiring diagrams for vehicles of this age are truly dreadful and there may not actually be a completely accurate drawing in existence if it's anything like my 90, which was built as a special order 2.5TD after the 200TDI was introduced. So far as I can see the wiring is a hybrid between two different diagrams, and it's even worse now I have put a 300TDi in it!

Nick.

An interesting difference from SIII wiring (I have a 200Tdi SIII, using the same ign switch, solenoid, starter and heater plug system as a Defender, but the original loom has no diode in the dash or fuse box - the alternator diode pack would not be prevented from back-powering the solenoid through the fuse box, where all the white, fused ignition switched live wires converge, including the wire to the alternator charge warning light. This is not a failure mode I had previously considered, so a mod might be in order.

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Ok im really getting to my wits end here, ive been 2 days on this and im getting nowhere.

I even just tried a work around but it hasnt helped at all.

I unplugged the white with black tracer wire from the ignition switch, ran it to + on a rocker switch. Then ran a short black wire from the terminal marked A on the rocker switch back to the terminal on the ignition switch. There is an earth terminal on the rocker switch as well, so i ran that one to ground.

With the new rocker switch in the on position i turned the ignition key. The lights came on on the instrument panel as usual and also the little red dot on the new rocker switch glowed brightly, fine. Turned the key further and cranked the engine and it started. The battery charge light was illuminated as it normally is on initial tickover. I flicked the rocker switch to cut power to the fuel cut off solenoid and the engine cut out and the oil light came on like it should. Good i thought.

Next, i repeated the process, but this time at idle, i revved the engine to put out the charge light. I flicked the rocker switch and guess what? It stayed running!!!!!

I had to pull the wire off the solenoid to stop it.

One thing i noticed after i switched the rocker to off the second time, unsuccessfully, is that the little illuminated red dot on the rocker switch was dimly illuminated. Which is not right.

Another thing you should know is that this morning, i removed the alternator and took it to a local test center to have it checked out. The guy tested it before my eyes and told me it had no back feed issues at all. He changed the pack which holds the brushes and cleaned up the slip ring and some terminals, but ultimately it has made no difference to the actual problem i have.

In summary the problem is that if the battery charge light is off, i cannot turn off the engine, neither by the ignition key nor by an additional rocker switch in the system. What the hell is going on?!!

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Tried a different version of my work around.

I disconnected the white and black wire from the ignition switch. I ran a new wire from the ignition switch (terminal that the White and black wire lives) to the rocker switch. Then i ran a new wire directly to the solenoid.

Trouble is the battery light and oil light would not come on with ignition on. Engine would start, but the alternator was not charging.

So i cant get around this poxy white and black wire!!

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If i did have a short in the ignition switch then my rocker switch in front of the ignition switch would negate that, which is partly why i installed it. Also this fault occured in the old switch and housing. I changed the switch and housing day before last and this problem still exists. It surely cant be two faulty ignition switches?

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