RR 1995 TD: engine stops but fuel pump doesn't!

Grrrrrr said:

Doh. Got rid of all my leading spaces!

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That is not pin 5. That is pin 1. Pin 5 is the one that goes across. As opposed to the other three that go up and down. Fuel pump is energised in three ways. When glow plugs are lit. When engine is cranked, when engine is running pull down is powered directly by alternator. If it runs when ignition is off and there is no power to pin 5, with relay removed, but runs with relay in, then it has to be relay faulty. If it runs when relay is out it has to be fuse box but can't see that happening. If relay checks out OK and pump runs with it in, one of the diodes may have cooked closing the pull down circuit. Pin 3 power from fuse 39. Pin 5 feed to pump from pin 3 when relay is pulled down, when current is applied through other two pins by any of the aforementioned senarios..

OK, been back out and checked. My mistake on the pin numbers. Pin 1 is permanently live. So, now we know where the issue is. That's really helpful chaps.

So, it could be the fusebox or (in my head) it could be getting power from a faulty ignition switch so I'll take the steering column apart now and see what I can see.

Many many thanks. Hope rekindled ...

Thanks Wammers. Reallly useful. I'll recheck in a bit but it has just started raining (again) so retreated inside for a break.

Only pin 1 permanently live. Looking more and more like a dodgy fuse-box. Odd, I took it out yesterday and it looked clean. All contacts good. No dirt. It could pass as nearly new. I squirted some electrical cleaner on all contacts just to be sure. Didn't make any difference!

Grrrrrr said:

Thanks Wammers. Reallly useful. I'll recheck in a bit but it has just started raining (again) so retreated inside for a break.

Only pin 1 permanently live. Looking more and more like a dodgy fuse-box. Odd, I took it out yesterday and it looked clean. All contacts good. No dirt. It could pass as nearly new. I squirted some electrical cleaner on all contacts just to be sure. Didn't make any difference!

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Right got a little twisted up there. There should be no power to anything with ignition off. With ignition on there should be power to pin 3. That is the one immediately above pin 5. The pin you have power to is pin 1 the other to the right of it obviously pin 2. So as the others said it looks like you maybe needing a fuse box. You may have a duff diode that is feeding back that is the only thing i can think of.

Ah, that is interesting. Well, I have power with the key in my pocket! Just out of interest, could the BECM be waking up and supplying power to the fuse-box?

Just double-checked and with fuse 39 in the pump runs (no key). Taking out the relay kills the pump.

When I was testing yesterday I noticed most relay had pin 3 (opposite 5) as permanently live but not all. Would that be another indication that the fuse box is faulty?

Going to test all fuse box linkages for resistance (connectivity) now ...

Ah. Now that's what I didn't want to see. I took the fusebox out and took the top off. Fuse 39 connects straight through to relay 12 pin 3 permanently. If I put fuse 39 in and nothing else then I have no resistance between the bolt where the +12V comes in and pin 3 on relay 12. Exactly as it should be. Infinite (i.e. no connection) to any of the other pins.

So, looks like fusebox is OK. What does that leave? Brain? Ingnition switch?

Grrrrrr said:

Ah, that is interesting. Well, I have power with the key in my pocket! Just out of interest, could the BECM be waking up and supplying power to the fuse-box?

Just double-checked and with fuse 39 in the pump runs (no key). Taking out the relay kills the pump.

When I was testing yesterday I noticed most relay had pin 3 (opposite 5) as permanently live but not all. Would that be another indication that the fuse box is faulty?

Going to test all fuse box linkages for resistance (connectivity) now ...

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Looking back through the diagrams for earlier models, the pump circuit is the same for all, with the exception that fuse 39 becomes 20 amp on later models instead of the 10 amp used on earlier models. On mine a 99, made in 98, there is no power to pin 3 until ignition is on. There should be no power to pin 1 at all unless one of the scenarios i mentioned earlier is present. There should be power to pin 1. IF glow lamps are lit. IF engine is being cranked. IF engine is running. Current flow through these various circuits is controlled by Zener diodes. If one of those has gone down you may well be getting feedback voltage from one of the three available supplies to pin 1. Possibly the one from the alternator, which according to the specs works by polarity reversal to pull down the relay when the engine is running. Can't be any of the other two feeds as the power for the pump is taken direct from number 6 glow plug to activate pump when glows are lit, and the other is only live when starter relay is engaged. So it leaves just the circuit through the alternator.

That sounds plausible but why would power be coming from the alternator with the key removed?

wammers said:

There should be no power to anything with ignition off. With ignition on there should be power to pin 3.

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According to the circuit diagram I'm looking at PIN3 is constantly live. The feed from FUSE 39 (10A) is designated 30 meaning Battery Volatge supplied constantly.

http://www.landyzone.co.uk/lz/attachment.php?attachmentid=33551&stc=1&d=1342274214

http://www.landyzone.co.uk/lz/attachment.php?attachmentid=33552&stc=1&d=1342274214

This doesn't explain why your PIN 1 is constantly live, but it does tell us why the pump is running with the key out. If the relay is duff, or there is this Diode problem. We need to find out why that Relay 12 is being pulled in no? Because that's what's feeding power to the pump, even with the key out.

MrGorsky said:

According to the circuit diagram I'm looking at PIN3 is constantly live. The feed from FUSE 39 (10A) is designated 30 meaning Bettery Volatge supplied constantly.

http://www.landyzone.co.uk/lz/attachment.php?attachmentid=33551&stc=1&d=1342274214

http://www.landyzone.co.uk/lz/attachment.php?attachmentid=33552&stc=1&d=1342274214

This doesn't explain why your PIN 1 is constantly live, but it does tell us why the pump is running with the key out. If the relay is duff, or there is this Diode problem. We need to find out why that Relay 12 is being pulled in no? Because that's what's feeding power to the pump, even with the key out.

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Yes you are correct pin 3 should be live at all times. Head knackerd job i think.
Can only be a diode faulty i am thinking. What i should have said is no power to anything other than pin 3 with ignition off.

Grrrrrr said:

That sounds plausible but why would power be coming from the alternator with the key removed?

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Because the diode controlling the flow of current is duff allowing current to flow in both directions. There is always power to the alternator from the positive side of the battery. The key only activates the exciter coils. Read the explanation in RAVE of how the pump is powered at various times and with engine running.

Right have had a closer look at diagrams. On the 94 to 98 there are only two diodes. Pump is only powered when glow lamps are lit and engine is running NOT when it is cranked. On 99 and up, three diodes are used to initiate pump when engine is cranked. That is maybe why there are two different fuse boxes. And possibly why fuse 39 was up rated from 10 amps to 20 amps on later models. Maybe this was done to partially sort the hot start problems. A quite interesting find because fitting a S/H box to a post 99 car from a pre 99 car will stop the fuel pump from running whilst cranking. Maybe giving hot starting problems. Check it out in RAVE. Interesting in this case as the supply to pin 1 can only come from two sources. Glow circuit or alternator. As glow circuit cannot be active with ignition off or you would have a seriously flat battery in minutes. It has to be a failed diode on alternator circuit.

Thanks chaps. Latest find:

Fusebox refitted. All relays and fuses present.
Battery connected.
Positive from alternator disconnected.

All works as it should! Pump doesn't pump and all seems correct. So, power is coming back up through the alternator and somehow triggering pin 1.

Cup of tea time!

Where are these Zenden diodes physically within the car? In the alternator? In the fusebox? Ignition?

Grrrrrr said:

Where are these Zenden diodes physically within the car? In the alternator? In the fusebox? Ignition?

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Zener diodes will be on circuit board in fuse box. A few pence each from CPC or the like. It's great when a diagnosis is correct.

Yes, just seen them on Y1-7 in RAVE. I still cannot get my head round why it seems to work with the alternator lead off though. After all, it connects to the battery before the battery goes into the fuse box. So why does it work with the alternator lead off?

Diodes might only be a few pence but the fusebox is made of two boards facing each other with about 20 solid wires connecting it top and bottom along 2 sides - i.e. getting it apart will not be child's play and I might break it trying!

Plus, given my fusebox is different from later models, Fleabay will be a mine-zone.

Still, we think we've sorted it so if that's the case (I'm a little uncertain still!) then we're winning!

Grrrrrr said:

Yes, just seen them on Y1-7 in RAVE. I still cannot get my head round why it seems to work with the alternator lead off though. After all, it connects to the battery before the battery goes into the fuse box. So why does it work with the alternator lead off?

Diodes might only be a few pence but the fusebox is made of two boards facing each other with about 20 solid wires connecting it top and bottom along 2 sides - i.e. getting it apart will not be child's play and I might break it trying!

Plus, given my fusebox is different from later models, Fleabay will be a mine-zone.

Still, we think we've sorted it so if that's the case (I'm a little uncertain still!) then we're winning!

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Depends how good you are with a soldering iron and de-soldering tool. You have disconnected the supply to the alternator that is why there is nothing coming out of it. The wire that feeds pin 1 and BECM from it is colour coded Brown/Yellow and goes to pin 6 on fuse box loom.

You said the newer model has 3 diodes and the fusebox must be slightly different. Any idea if a later fusebox would work in an ealier model?

Grrrrrr said:

You said the newer model has 3 diodes and the fusebox must be slightly different. Any idea if a later fusebox would work in an ealier model?

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From 99 on three diodes. There is one fuse box 94 to 98. One 99 to 2001. One 2001 to 2002. Apart from what i see in the pump circuit don't have a clue what other difference there are. Think you are better sticking to the earlier one.

OK. Will stick to an earlier one. Are there any differences between petrol and diesel other than what's attached to it? They both seem to look the same!