M51 hot starting issues (don't shoot me ive searched until my eyes bled!)

simon allen · Nov 11, 2019

Hi Guys.
I've got an m51 fitted to my discovery 1. I'm using a mechanical pump from a 524td fitted with the m51's camplate so that the fuelling is the same.

I am getting a hot start issue, in that it won't start (even with easy start) when its been running for even 5 minutes. It will crank and crank but not fire.

When it does run, it runs fine. To Date I have checked:

Injector pump distributor head (known good one fitted from another pump)
Injector pump timing (1.54mm plunger lift at tdc)
static cam chain timing (set to a 4.5mm gap underneath the tool on the cam when the crank is locked at tdc)
new starter and batteries fitted, it cranks real quick.

I'm stuck pretty much. It looks like my last thing to check would be compression. I need to get the right adapter for my compression testing kit.

I tried to send the pump away for testing, but was met with a certain amount of hostility because ive had the thing apart myself. I've build pumps for all my 300tdi landies and a few Peugeots, as well as this m51 and have never had an issue like this before.
Is there anything glaringly obvious that I could have missed?

Thanks in advance,
Simon.

tomcat59alan · Nov 11, 2019

Stretched chains? how many miles has it done.have you checked Rave, from memory the injector pump lift should be around. 90-.95 depending on new or used chains.

Datatek · Nov 11, 2019

tomcat59alan said:
Stretched chains? how many miles has it done.have you checked Rave, from memory the injector pump lift should be around. 90-.95 depending on new or used chains.

He has the earlier mechanical FIP

Datatek · Nov 11, 2019

simon allen said:
Hi Guys.
I've got an m51 fitted to my discovery 1. I'm using a mechanical pump from a 524td fitted with the m51's camplate so that the fuelling is the same.

I am getting a hot start issue, in that it won't start (even with easy start) when its been running for even 5 minutes. It will crank and crank but not fire.

When it does run, it runs fine. To Date I have checked:

Injector pump distributor head (known good one fitted from another pump)
Injector pump timing (1.54mm plunger lift at tdc)
static cam chain timing (set to a 4.5mm gap underneath the tool on the cam when the crank is locked at tdc)
new starter and batteries fitted, it cranks real quick.

I'm stuck pretty much. It looks like my last thing to check would be compression. I need to get the right adapter for my compression testing kit.

I tried to send the pump away for testing, but was met with a certain amount of hostility because ive had the thing apart myself. I've build pumps for all my 300tdi landies and a few Peugeots, as well as this m51 and have never had an issue like this before.
Is there anything glaringly obvious that I could have missed?

Thanks in advance,
Simon.

If it will not fire with Easy Start when hot then it does not sound like it's the FIP.
A compression check would be a good place to start.
Low cranking speed might also be the problem

tomcat59alan · Nov 11, 2019

Datatek said:
He has the earlier mechanical FIP

Ok first time I'm ahead of my time.

Henry_b · Nov 11, 2019

I wouldn't be pumping easy start throughit.

Imo

Datatek · Nov 11, 2019

Henry_b said:
I wouldn't be pumping easy start throughit.

Imo

A mist of Easy Start does no harm, flooding the inlet with the stuff does.

Dopey · Nov 11, 2019

Crack cocaine for cars

simon allen · Nov 12, 2019

I have to confess I don't like the easy start method of getting it going but it certainly does help with diagnostics sometimes, and that's all I use it for.

I don't pump it through there, I give it a light mist as suggested. since the issue has arisen it has been started warm only a few times.
I feel I should add that this problem seemed to happen all of a sudden, the car doesn't get used regular and I took it to one off road event, it was fine, then I took it to one the month after and have had nothing but trouble since.
I'll wait for the compression tester adapter to arrive and report back. I just wondered why it would start cold but not hot, compression normally is lower when cold I believe?

Kev12 · Nov 12, 2019

Do your glowplugs come on for hot start too? Wondering if they are masking a bit of chain stretch when cold. Of course this doesnt explain why it wont fire on easy start

simon allen · Nov 12, 2019

yeah the glow plugs are on an override switch for diagnosis. I am using ngk ones though rather than the beru ones that people seem to like here?

tomcat59alan · Nov 12, 2019

Kev12 said:
Do your glowplugs come on for hot start too? Wondering if they are masking a bit of chain stretch when cold. Of course this doesnt explain why it wont fire on easy start

I've already been corrected that its a mechanical fip so I'm guessing it's cog driven not chains.

simon allen · Nov 12, 2019

its still on the original chains, and they had stretched a bit when I checked the timing. I reset the cam timing to where the 4.5mm spacer fitted underneath the inlet side of the cam fixture, and the injection pump is set properly too. I assumed this would "adjust out" the error caused by stretched chains?

tomcat59alan · Nov 12, 2019

Datatek said:
He has the earlier mechanical FIP

Still has chains, see post#13

Datatek · Nov 12, 2019

tomcat59alan said:
Still has chains, see post#13

I just said it's the earlier mechanical FIP, I said nothing about the drive to it which as it's the M51 engine had to be chains.

tomcat59alan · Nov 12, 2019

Datatek said:
I just said it's the earlier mechanical FIP, I said nothing about the drive to it which as it's the M51 engine had to be chains.

I never said you did.

Saint.V8 · Nov 12, 2019

Excessive injector leak off?

My 530d (M57 common rail) failed to start and I found 2 injectors leaking back excessively enough to fail to build pressure in the rail.....I know the M51 doesn't have a rail, but if the injectors are leaking back they may not be building internal injector pressure enough to open and spray.....

For it to happen on all 6 would be quite a thing...but yer never know!

wammers · Nov 13, 2019

So you have fitted a VE mechanical pump and buggered about with it. Only suggestion i can make not knowing exactly how much you have played with it. Is allow to idle and adjust fuel quantity until you get 1500 RPM. Then lock adjuster off and adjust idle back to 750 RPM. See what you get, if you get smoke at high RPM back fuel off until it just stops or reduces to acceptable levels. Playing with injection pumps unless you really know what you are doing is not a very good idea.

simon allen · Nov 13, 2019

I've not only fitted the pump, but I built it myself. I've had the truck running perfectly for 2 years on the setup I'm on now. It's not my first time building injection pumps, I used to rebuild them in house for the MOD for the 300tdi and 19j engines. Although I haven't got the calibration equipment I used to have access to, I am fully conversant with every adjustment on the pumps and like I say, it has been running immaculately.

simon allen · Nov 13, 2019

Just to confirm my original post, I can start the truck from cold perfectly and it will idle and run fine. It will run until warm, BUT if I shut it off it will not restart even instantly. It just cranks.

M51 hot starting issues (don't shoot me ive searched until my eyes bled!)

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