2.5 Diesel hard starting hot or cold

Hi all. Just wanted to ask you very knowledgeable people for your advice with a starting problem. I have an early 4 door classic with the M51 diesel fitted. I have been having starting problems hot or cold. It takes about 10 seconds for it to fire. I have changed all six glowplugs and fitted a non-return valve between the injector pump and the filter as I noticed that the fuel was draining back to the tank after a short while. It has a very rare manual injector pump which I am assuming has been tweeked as their is a large Iveco intercooler fitted and throws out loads of black smoke when accelerating. Does turning up the pump cause starting issues or could the electric fuel pump which I believe is the original pump for petrol not have enough delivery pressure to back up the injector pump for starting. Once it starts, it runs fine with no hesitation or lumpiness?

Thanks all.

Pics of M51 in Classic please!

Bladerunner919 said:

Pics of M51 in Classic please!

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I've only got it a couple of weeks and have been going around it mechanically just trying to sort these issues. It needs a bit of welding but that's for another day. I love the M51 and those that say they are gutless are way off the mark. Standard tune is pretty poor alright but this thing with mechanical pump goes like stink and has loads of torque. I will try and get a pic up in the next couple of days as I away at the moment....

not sure about m51, what engine is it ?,ayway a diesel is a diesel, you said the electric pump, usually a diesel engine has its own lift pump, but it does sound like a fuel problem, as its when its hot or cold, take off the diesel feed pipe to the pump and turn on the ignition to see if any fuel is being pumped up by the electric pump, if so could be an injector pump problem or worse bad compression

peter8315 said:

not sure about m51, what engine is it ?,ayway a diesel is a diesel, you said the electric pump, usually a diesel engine has its own lift pump, but it does sound like a fuel problem, as its when its hot or cold, take off the diesel feed pipe to the pump and turn on the ignition to see if any fuel is being pumped up by the electric pump, if so could be an injector pump problem or worse bad compression

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Thanks for the reply. I have fuel coming to the injector pump as I had fitted a non-return valve the other day because fuel was flowing back to the tank and the pipe between the injector pump and filter was empty. This has sorted the problem of fuel draining away. I would have thought that compression problems would be piston rings or valves and would show up as lots of blue smoke no?....

landyboots said:

Thanks for the reply. I have fuel coming to the injector pump as I had fitted a non-return valve the other day because fuel was flowing back to the tank and the pipe between the injector pump and filter was empty. This has sorted the problem of fuel draining away. I would have thought that compression problems would be piston rings or valves and would show up as lots of blue smoke no?....

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Forgot to say that the M51, as fitted to the P38's, has no lift pump afaik and uses and electric pump from the tank, that's why I was asking if the original electric pump for the 3.5 V8 carb engine which this vehicle has, would have the same operating pressure as the P38 electric pump which is in the tank.

i think you have got to narrow it down then to the injector pump,

The injector bleed off pipes are often the cause of fuel drain back may still be letting air in or diesel out, worth checking them, a few people have had starting issues from them.

brianp38dse said:

The injector bleed off pipes are often the cause of fuel drain back may still be letting air in or diesel out, worth checking them, a few people have had starting issues from them.

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And the pipe from the filter to the FIP has been known to go porous.

I had similar problems on P38. After testing glowplugs I read that timing chain wear does necessitate adjusting the FIP. I moved the FIP twice. (towards the block) Once a little bit, then a bit more without obvious improvement in starting. Note: many on here commented that moving of the FIP should be very precise and requires the use of a jig, however it worked for me. If you have access to nanocom diagnostics you can check the modulation percentage which I think should be close to 50%.
This led me to work on the starter.
On dismantling it, there was no obvious wear so before bringing to the reconditioners I decided to give the armature and inside the coil a sanding and try it.

RESULT: different car!! engine turns over much easier. Starts Hot or cold ok.

Low cranking speed is a common cause of poor starting on a diesel.

Especially on hot engine.

N2O said:

Especially on hot engine.

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Even on a hot engine.

It's funny situation, because properly adjusted cold M51 Enigne will start with half a turn of crankshaft even with almost flat battery - gearbox fault will probably show up, but it starts!
Hot starting becomes a problem when real kick from starter is needed.

N2O said:

It's funny situation, because properly adjusted cold M51 Enigne will start with half a turn of crankshaft even with almost flat battery - gearbox fault will probably show up, but it starts!
Hot starting becomes a problem when real kick from starter is needed.

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No difference hot or cold on mine

Thanks for all the brilliant info there guys, some very interesting stuff. I did think it was cranking over a bit slowly so I fitted a second battery to see if spinning it up quicker would make a difference....It didn't. It just reduced the starting time to about 5 seconds of cranking so, next step would logically be injector pump timing adjustment as some of you stated, the timing chain does stretch over a period of time and could be the problem here......

Thanks again everyone for your input.

landyboots said:

Thanks for all the brilliant info there guys, some very interesting stuff. I did think it was cranking over a bit slowly so I fitted a second battery to see if spinning it up quicker would make a difference....It didn't. It just reduced the starting time to about 5 seconds of cranking so, next step would logically be injector pump timing adjustment as some of you stated, the timing chain does stretch over a period of time and could be the problem here......

Thanks again everyone for your input.

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If it's a mechanical pump it needs to be set to about 1.54 mm lift and not to what is stated in RAVE for the M51 EDC system.

wammers said:

If it's a mechanical pump it needs to be set to about 1.54 mm lift and not to what is stated in RAVE for the M51 EDC system.

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It is a mechanical pump so I will have to look at that in the proper parameters as you say Wammers.....What would be the simplest way to do this?....

Thanks.

landyboots said:

It is a mechanical pump so I will have to look at that in the proper parameters as you say Wammers.....What would be the simplest way to do this?....

Thanks.

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You need an engine locking pin a timing adaptor for pump and a DTI. There is a guide to how to do timing in RAVE, follow it, but i would use 1.50 mm or so lift on cam instead of 0.90 mm quoted for the EDC pump. The mechanical pumps are usually set at 1.54 mm lift. But that is not on this engine. Never seen a M51 with a mechanical pump. So it's a case of suck it and see.