ML270 struggling to start

[tttonyyy]

So here's where I'm at:

It has on-and-off taken a fair bit of cranking to get started, this is intermittent and getting worse.

I replaced all the fuel pipes with fresh ones and fresh clamps. There is no evidence of air bubbles in the clear pipes between the low pressure lift pump and the high pressure pump.

I've just replaced the high pressure pump with a reconned one that's been tested - and now it's worse than ever.

No fault codes appearing - though there were historic ones for:
P1187-001 Rail PRessure monitoring: The maximum pressure has been exceeded
P1197-032 Rail pressure monitoring: Control variation below 1500/min (rpm)

I have cleared these and they have not recurred after multiple starts now.

If I disconnect the fuel tank and feed fuel from a raised funnel directly into the fuel heater before the filter, it is then much easier to start.

So I am currently suspecting the low pressure lift pump - has anyone experienced the symptoms of this failing?

Once it has started it runs fine, no stalling.

 

[mersum1es]

once again: measure injector tank line leaks.

Can you see live data and rail pressure during cranking?

Which one this engine is, OM612 or OM647?

 

[M80]

Many 2.7 CDI's didn't have a lift pump, did the ML?

 

[supernoodle]

2003 ML 270 no-start. Need some help guys.

200K on motor. No issues. Suddenly failure to start. Recovered to workshop. Nothing showing on scanner. Mechanic can get started by priming the mechanical low pressure fuel pump but, after stopping, won't start again. Fuel half full. Do these pumps fail - they are a geared thing. Is there...

forums.mercedesclub.org.uk

Your funnel test does imply the pre supply pump is struggling as on the vid or the line from filter back to tank is causing an issue.

 

[mattkh]

Once it has started it runs fine, no stalling.

Does it have the little mechanical fuel pump (as in a oil pump) worked by the camshaft..?

 

[mersum1es]

Thats why I asked, OM647 has pump in tank and different hp pump (with quantity control valve which can cause problems too), OM612 ha mechnnical lift pump on cam. But leaky injectors apply both models...

 

[supernoodle]

OP stated

There is no evidence of air bubbles in the clear pipes between the low pressure lift pump and the high pressure pump

That implies cam driven pre supply to me.

 

[tttonyyy]

OM612 with cam driven gear lift pump before the main high pressure pump. I can't monitor the rail pressure, unfortunately.

Took it for a spin this evening to get it hot, and when it came back it would immediately struggle to restart the moment the engine was stopped without a lot of cranking.

I've just swapped the recon high pressure pump back out for the original one and it's starting much better again, not perfect but back how it was. Sounds like the recon pump isn't working as it should, though the company insist they tested it before it went out the door (cold, presumably...)

 

[M80]

You might try the free Torque app on an Android.
That is fed from an EML327 via BT for about £5.
An 03 might be too early but later models can see rail pressure this way.

 

[tttonyyy]

You might try the free Torque app on an Android.
That is fed from an EML327 via BT for about £5.
An 03 might be too early but later models can see rail pressure this way.

Yes it's too early, no EOBD. I have a iCarsoft MB V2.0 that does most stuff including transmission, but unfortunately there does not appear to be any live data from the ECU.

 

[mattkh]

OM612 with cam driven gear lift pump before the main high pressure pump.

I would suspect the seal on the cover of this gear lift pump, given the age of the engine (rather than the mileage).

 

[tttonyyy]

Lift pump swapped. Mag coupling to camshaft - clever - no snapping shafts if it jams.

All primed up and running. The old pump did seem to have a decent suck when turned by hand, but that was with liquid in it - when dry I could blow backwards through it which doesn't seem ideal. Didn't try that with the replacement one.

No evidence of the body seal failing, though without putting it on a vacuum pump or airline it might not be obvious.

Now I just wait and see if it runs any better after standing, and then wonder what to do about the recon high pressure pump that didn't work very well.

 

[mersum1es]

aux pump fails very rarely...

 

[tttonyyy]

Well, you're not wrong, swapping it out didn't make any difference.

However, I have found my air leak. It's getting in at the pressure test point that tees off on the line between the LP and HP pumps.

That test point looks like it's a simple syringe arrangement; Mercedes must have a special tool that clamps over it with a spring pushing against it to measure the pressure from the LP pump without opening the fuel system. You can feel the LP pump push back at you when you push it in.

Clever, except on mine it's letting air in and that's bubbling up to the LP pump and draining fuel back to the tank. That explains why a raised container of fuel as a feed was easy to start, and why it runs fine when it's started.

The duff reconditioned HP pump was a red herring just to waste more of my time finding this.

Looks like it's fixable with a knife and £1.42 compression end stop from Screwfix...

 

[Steve@Avantgarde]

Blimy this thread takes me back a few years! I have replaced a few lift pumps on these engines. Thre pressure from memory should be around 2.5-3 bar on delivery. It uses a venturi swirl system (which starts in the fuel tank) to drive the fuel around the system, which is why, if you get air in the system, the venturi collapses and fuel runs backwards to the tank.

If you have had rail pressure monitoring codes then its very possible that the delivery pressure cannot keep up with the high pressure demand, if that drops below 160bar then the engine will (a) not start or (b) if its running, will cut out.

Lift pumps used to be fairly cheap, it might be worth just putting one on and do make sure all the plastic pipes and their seals are in good order, its also worth replacing them if they are more than 5 years old as ive had some leak air around the formed joints.

WIth these older engines, as we used to discover years ago when they were a common car through the workshops, was to over repair them and guarantee the system rather than replacing bits and bobs for those to repair days, weeks or months later.

 

[tttonyyy]

Still grumpy about starting. Symptoms are different now the air leak has been cured.

Hot: lots of cranking, eventually struggles to life
Cold: starts immediately

I've just swapped out the crank position sensor and the cam position sensors. Might be too early to tell but a test start wasn't perfect. Will see how it goes.

Next will have to be injector leak-off testing, it's really the only thing left aside from the fuel pressure regulator. I've got some spare injectors for it sitting around somewhere.

I don't think I've ever replaced so many fuel system parts on any vehicle I've owned...

 

[Flyinspanner]

If it starts perfectly when cold…

what comes into play for a hot start? A temp sensor controlling the amount of fuel?

 

[mersum1es]

Now it sounds crank or cam shaft sensor.

 

[stumo]

The fuel is thinner viscosity when its hot, so a badly leaking-off injector can start to show up when hot, but fine when cold.

Cam and crank sensors you can spray some knid of aerosol freeze spray on the sensor when hot to see if it then starts like it does when the engine is cold.

 

[tttonyyy]

Drove it to the Netherlands and back - runs a treat when it's going. But, the hot start issue remains despite new crank and cam position sensors. Leak off next when I get some time.