M51 (non) Running Issue

Hi all, I have the M51 diesel in a BMW 325TDS (sorry) which has issues.

The engine will start but only for a few seconds, after cranking it chops about between 600-700rpm then jumps up nearer 1000rpm and dies (with a knock), with some light density smoke from the exhaust.

The above symptoms are with the inlet manifold disconnected, which I beleive would discount the turbo (?), there is some oil in the EGR/inlet which I cleaned previously. Also the FIP has been backed off by moving the top sections to reduce fuel quantity which has the effect of stopping it firing at all (back to normal position now).

This started immediately after I had the water pump, thermostat, coolant, aux belt and tensioner replaced, apparently it smoked out a workshop . Since then it's had a compression test which was OK (~400psi on 4-5-6 and just under on 1-2-3), injectors 2 & 3 visually checked OK and glow plugs checked OK. Previously I've replaced the upper two injection pump / FIP seals and all leak off pipes successfully with a good few hundred miles since. Also it's had oil and filters changed a couple thousand miles ago. The MAF sensor recently failed with 'hesitant' symptoms, relieved by running without it, I've since replaced it with a used non-OEM part which has run OK for a few hundred miles. I also suspect the car has been chipped as it was supplied with a microchip in a plastic box.

At present, I think the FIP is the initial candidate (been quoted £170 to test it and £575 for a repair/exchange unit if faulty from Merlin Diesel) however I plan (on Sunday in daylight, hopefully not in the rain) to try bleeding any air out of the fuel lines and disconnecting sensors to see if it has any effect (this would be preferable solution!). I would appreciate any advice you may have regards further tests or suggestions on what might be at fault. In other respects the car is pretty sound, would be a shame to lose it.

Many thanks in advance, Regards, Alex.

Most of the doozel boys are in bed, Wammers maybe around mind you!!

Hope you get it resolved.

If I'm reading your post correctly, the car was running fine when you dropped it off for some work to be done and once the work was done it's not running fine? If that's the case, just hand it back to whoever did the work and tell them to call you when they've fixed whatever they broke.

Bladerunner919 said:

If I'm reading your post correctly, the car was running fine when you dropped it off for some work to be done and once the work was done it's not running fine? If that's the case, just hand it back to whoever did the work and tell them to call you when they've fixed whatever they broke.

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Thanks for your reply, the work was done by a friend (mechanic), who I have reason to trust. If only it was that simple a solution

Who has been playing with the FIP? Sounds like someone has been without knowing what they are doing. How do you know the top sections are back in the same position? If the bottom section isn't then that will affect the tickover. How do you check injectors by looking at them? Think you should have a word with your mate to sort it. :welcome2:

Backing off the injection pump as you say (moving top away from engine) will not reduce fuel quantity it will retard timing. If centre section of pump has been off an not put back correctly that will effect fuel quantity. People should not play with things unless they know what they are doing. Obviously someone does not. If it was running fine before it went into the garage take it back and get them to sort out whatever they have done wrong. The MAF sensor gives info for EGR operation. The hesitance will have been the EGR being open at the wrong time due to the faulty MAF signals confusing the ECU.

tomcat59alan said:

Who has been playing with the FIP? Sounds like someone has been without knowing what they are doing. How do you know the top sections are back in the same position? If the bottom section isn't then that will affect the tickover. How do you check injectors by looking at them? Think you should have a word with your mate to sort it. :welcome2:

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Thanks for your reply. I know the FIP is where it should be (or very close) as I marked it when replacing seals, it's close enough that my experience of adjusting it previously suggests it should run reasonably smoothly. This was not touched during the replacement of water pump etc.

I do find it very odd that it has developed an issue in this way, e.g. After replacing water pump etc. What I am trying to avoid is assuming that I can't trust my friend and that he deliberately or inadvertently adjusted the pump, try to readjust it and fail, deeming it broken, whilst there is something else which is at fault.

Regards, Alex.

Is the fuel coming through to the FIP in sufficient quantity, have you checked the fuel filter?

Datatek said:

Is the fuel coming through to the FIP in sufficient quantity, have you checked the fuel filter?

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Thanks for your reply, I'll add this to my list of checks. I have also noticed the fuel filter does not have the water spill off at the bottom.

Regards, Alex.

AJB2494 said:

Thanks for your reply, I'll add this to my list of checks. I have also noticed the fuel filter does not have the water spill off at the bottom.

Regards, Alex.

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Condensation and bacterial growth in diesel can be a problem at this time of year and would tie in with the smoke after repair.

AJB2494 said:

Thanks for your reply. I know the FIP is where it should be (or very close) as I marked it when replacing seals, it's close enough that my experience of adjusting it previously suggests it should run reasonably smoothly. This was not touched during the replacement of water pump etc.

I do find it very odd that it has developed an issue in this way, e.g. After replacing water pump etc. What I am trying to avoid is assuming that I can't trust my friend and that he deliberately or inadvertently adjusted the pump, try to readjust it and fail, deeming it broken, whilst there is something else which is at fault.

Regards, Alex.

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Does it accelerate? When you put the top of the pump back on did you make sure that lug engaged with the hole in that little square thing? Sorry for the imprecise language. I cannot remember what they were called; I'm just going from what I saw.

Mine was a total bar-steward when the seals were done, not doubt because my pump is a little tired. Although it went back where it was it became apparent that it was not happy. Subsequent testing revealed that as the bolts were tightened by up it was making a big difference to how it ran. Eventually in desperation we got a piece of wood and with the engine running (!!!) we EVER SO SLIGHTLY tapped it forward or back until it ran nicely, tightened a little, did the same again, and so on until all torqued up correctly. By eye you couldn't see anything different. Tiny, tiny movements. Overdo it and it goes onto max revs and you're in a world of pain.

Grrrrrr said:

Does it accelerate? When you put the top of the pump back on did you make sure that lug engaged with the hole in that little square thing? Sorry for the imprecise language. I cannot remember what they were called; I'm just going from what I saw.

Mine was a total bar-steward when the seals were done, not doubt because my pump is a little tired. Although it went back where it was it became apparent that it was not happy. Subsequent testing revealed that as the bolts were tightened by up it was making a big difference to how it ran. Eventually in desperation we got a piece of wood and with the engine running (!!!) we EVER SO SLIGHTLY tapped it forward or back until it ran nicely, tightened a little, did the same again, and so on until all torqued up correctly. By eye you couldn't see anything different. Tiny, tiny movements. Overdo it and it goes onto max revs and you're in a world of pain.

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Quantity sleeve old boy, quantity sleeve. Near enough is not good enough. From what he says, looks he has retarded the pump to close the delivery valve at TDC to make up for centre section being in the wrong place. Not the way to go about it. People should not play with things they do not understand.

wammers said:

Quantity sleeve old boy, quantity sleeve. Near enough is not good enough. From what he says, looks he has retarded the pump to close the delivery valve at TDC to make up for centre section being in the wrong place. Not the way to go about it. People should not play with things they do not understand.

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Thanks for your reply. It's done 1,000 miles since seals were replaced.

As far as I am aware, I haven't retarded the pump as I don't know how other than move the centre section as described.

Regards, Alex.

AJB2494 said:

Thanks for your reply. It's done 1,000 miles since seals were replaced.

As far as I am aware, I haven't retarded the pump as I don't know how other than move the centre section as described.

Regards, Alex.

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OK i misunderstood your first post. Centre section if removed must be set to give a rock steady 750 rpm at idle hot. Is the EGR valve stuck open?

wammers said:

OK i misunderstood your first post. Centre section if removed must be set to give a rock steady 750 rpm at idle hot. Is the EGR valve stuck open?

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I'm not sure how close to 750rpm it was as the tachometer doesn't have many graduations ( only 500 and 1000, and 0-500 is a smaller increment) but the car has run fine. The EGR is closed when I look into it, manifold is off and this issue persists.

I took the fuel filter off just now and the diesel that came out of it looked OK, although I poured it into a black container in the dark with only torches. When I refilled it (with fresh diesel) I noticed some black particles exit as it filled up and overflowed slightly, they seemed to disperse easily and there wasn't a significant amount. Looking into the centre of the filter the bottom looked slightly green/algae looking but it wasn't that astounding.

Regards, Alex.

AJB2494 said:

I'm not sure how close to 750rpm it was as the tachometer doesn't have many graduations ( only 500 and 1000, and 0-500 is a smaller increment) but the car has run fine. The EGR is closed when I look into it, manifold is off and this issue persists.

I took the fuel filter off just now and the diesel that came out of it looked OK, although I poured it into a black container in the dark with only torches. When I refilled it (with fresh diesel) I noticed some black particles exit as it filled up and overflowed slightly, they seemed to disperse easily and there wasn't a significant amount. Looking into the centre of the filter the bottom looked slightly green/algae looking but it wasn't that astounding.

Regards, Alex.

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Half way between 500 and a 1000 would be 750. If you have crap in the diesel that could be part of your problem. Make sure you have clean fresh fuel going into the injection pump. Maybe you should find someone with diagnostics. As a matter of interest your mate has not turned the engine backwards for any reason has he?

wammers said:

Half way between 500 and a 1000 would be 750. If you have crap in the diesel that could be part of your problem. Make sure you have clean fresh fuel going into the injection pump. Maybe you should find someone with diagnostics. As a matter of interest your mate has not turned the engine backwards for any reason has he?

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I google diesel bacteria and I'm sure the debris which exited the filter was just that, although unknown if this is the cause of the issue or was present anyway. Regards turning the engine backwards, I can find out, what would this mean?

Regards, Alex.

AJB2494 said:

I google diesel bacteria and I'm sure the debris which exited the filter was just that, although unknown if this is the cause of the issue or was present anyway. Regards turning the engine backwards, I can find out, what would this mean?

Regards, Alex.

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Possible chain jumped a tooth or two. Never ever turn a M 51 diesel backwards other than a few thou to get the timing pin in.

wammers said:

Possible chain jumped a tooth or two. Never ever turn a M 51 diesel backwards other than a few thou to get the timing pin in.

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The aux belt was changed, which runs over the crank pulley, is it possible to turn the engine from the pulley when fitting the belt? E.g. By hand?

Regards, Alex.

AJB2494 said:

The aux belt was changed, which runs over the crank pulley, is it possible to turn the engine from the pulley when fitting the belt? E.g. By hand?

Regards, Alex.

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He didn't turn the crank pulley by hand unless his name is Popeye. No need to turn anything changing belt.