ML 320 CDI - Crank Non-Start

[V12cat]

I'm no expert on these particular engines but have had my fair share of experience and trouble with bigger mercs. OM422's, OM502LA's (in profile pic) as well as numerous other makes.

How is the high pressure pump output (rail pressure) being measured? Actual gauge or via the rail pressure sensor (B4/6) in diagnostics?

I'd suggest someone doesn't know what they are doing. @avantgardeauto has already laid out what should be done and in what order. IF the pump is ok then something is letting the pressure go. There's only the relief valve and injectors left isn't there? Have the injectors been tested as suggested?
My money would be on one of them. Should be easy enough to test.

But 3 pumps and a crank sensor sounds like they don't know what they're doing to me. Surely Star would have cleared the sensor?

 

[DuncanPoundcake]

I'd suggest someone doesn't know what they are doing. @avantgardeauto has already laid out what should be done and in what order. IF the pump is ok then something is letting the pressure go. There's only the relief valve and injectors left isn't there? Have the injectors been tested as suggested?
My money would be on one of them. Should be easy enough to test.

But 3 pumps and a crank sensor sounds like they don't know what they're doing to me. Surely Star would have cleared the sensor?

As I said, that has all been done and the injectors have been tested. Star is not throwing up codes and the relief valve is brand new.

It's a specialist Mercedes garage and tech working on the car is ex-dealership with 20 years experience working exclusively on Mercedes, so, all things considered, he does know what he is doing but I'll pass it on.

 

[SteveFromAvantgarde]

If you have 4 bar at the HPP that confirms the delivery pressure.

Why fit 3 HPPs?! If 2 dont work (the original and the replacement) it cant be the HPP.

To my knowledge there is no ECU cut out for the HPP, its done via rail pressure monitoring (the sensors on the end of the rail). You can test those with Xentry very easily and the fact the ECU monitors the current rail pressure (EG it can see its delivery pressure) that would tell me electrically, everything is spot on.

So I would say you have a mechanical issue on what connects to the HPP.

 

[DuncanPoundcake]

If you have 4 bar at the HPP that confirms the delivery pressure.

Why fit 3 HPPs?! If 2 dont work (the original and the replacement) it cant be the HPP.

To my knowledge there is no ECU cut out for the HPP, its done via rail pressure monitoring (the sensors on the end of the rail). You can test those with Xentry very easily and the fact the ECU monitors the current rail pressure (EG it can see its delivery pressure) that would tell me electrically, everything is spot on.

So I would say you have a mechanical issue on what connects to the HPP.

Yes. the camshaft.

 

[V12cat]

[....]

So I would say you have a mechanical issue on what connects to the HPP.

I had a quick look on WIS. Not very easy to see but it looks like the HPP has a gear keyed onto its shaft, and that meshes with the inlet camshaft drive gear. If so, trouble with the pump gear would be obvious on the pump (unless the key has been forgotten) and cam drive gear damage would be pretty catastrophic.

 

[DuncanPoundcake]

I had a quick look on WIS. Not very easy to see but it looks like the HPP has a gear keyed onto its shaft, and that meshes with the inlet camshaft drive gear. If so, trouble with the pump gear would be obvious on the pump (unless the key has been forgotten) and cam drive gear damage would be pretty catastrophic.

Hey. Thanks for the reply. You will have to excuse my ignorance here but 'keyed' on?

From what I can see in pictures, is the cam has a black dome type device which the pump gear fits into. Can this fail?

 

[V12cat]

OK. As I said at the at the start I'm no expert on this particular engine but from the pump position seen here, 1 o'clock from the crank pulley, it can't be driven directly from the end of the cam. The mounting hole is too low in the head. So the pump is gear driven off the cam shaft.


Cut into the pump shaft is a slot. Cut into the gear and the correctional weight (behind the gear) is also a slot. A piece of metal called a key sits in both and makes sure the all turn together. I'd be amazed if this isn't fitted but if it isn't the gear could spin without the pump. I guess it is also possible the gear and the weight could be interchanged (if they are separate) which would mean the gears wouldn't mesh and the pump wouldn't turn but that would also be pretty surprising for an MB tech.

Just trying to put options on the table as something is obviously very wrong somewhere. Someone with actual experience of this engine may know better. Maybe I've got the wrong engine completely!!!

Both scenarios are pretty unlikely IMHO and I'd still say the pressure is escaping via the relief valve or an injector. Simply because getting this pump drive wrong seems so unlikely.

Interesting problem, although annoying for you obviously!!

 

[DuncanPoundcake]

View attachment 152228

OK. As I said at the at the start I'm no expert on this particular engine but from the pump position seen here, 1 o'clock from the crank pulley, it can't be driven directly from the end of the cam. The mounting hole is too low in the head. So the pump is gear driven off the cam shaft.
View attachment 152229

Cut into the pump shaft is a slot. Cut into the gear and the correctional weight (behind the gear) is also a slot. A piece of metal called a key sits in both and makes sure the all turn together. I'd be amazed if this isn't fitted but if it isn't the gear could spin without the pump. I guess it is also possible the gear and the weight could be interchanged (if they are separate) which would mean the gears wouldn't mesh and the pump wouldn't turn but that would also be pretty surprising for an MB tech.

Just trying to put options on the table as something is obviously very wrong somewhere. Someone with actual experience of this engine may know better. Maybe I've got the wrong engine completely!!!

Both scenarios are pretty unlikely IMHO and I'd still say the pressure is escaping via the relief valve or an injector. Simply because getting this pump drive wrong seems so unlikely.

Interesting problem, although annoying for you obviously!!

Lol. Interesting certainly.

 

[DuncanPoundcake]

Lol. Interesting certainly. So from what, I can understand the gear at the rear side of the pump fits into the black 'shroud' - for use of another term - which should spin the pump gear. If the internals of the shroud are worn, maybe it is slipping?

 

[V12cat]

Isn't that the rear end of a camshaft? The pump is on the front.

 

[DuncanPoundcake]

Isn't that the rear end of a camshaft? The pump is on the front.

The rear end has the large toothed gear on the end for the chain? Only the RH side cam has this black 'shroud' on one end.

 

[V12cat]

The rear end has the large toothed gear on the end for the chain? Only the RH side cam has this black 'shroud' on one end.

The chain is at the front surely?

 

[DuncanPoundcake]

You are of course, extremely correct on that!

 

[V12cat]

You are of course, extremely correct on that!

The timing chain drives the exhaust cams and the balance shaft. Inlet cams are gear driven off the exhaust cams. Fuel pump is driven off the LH (passenger side) bank inlet cam gear from what I can see.

 

[DuncanPoundcake]

The timing chain drives the exhaust cams and the balance shaft. Inlet cams are gear driven off the exhaust cams. Fuel pump is driven off the LH bank inlet cam gear from what I can see.

It depends which way you look at the pump. Standing in front of the car, the fuel pump attaches to the nearside/right cam.

Every other options has been ruled out. All the suggestions in this thread, done. The cam shaft is the only option left.

 

[V12cat]

It depends which way you look at the pump. Standing in front of the car, the fuel pump attaches to the nearside/right cam.

Every other options has been ruled out. All the suggestions in this thread, done. The cam shaft is the only option left.

You ALWAYS hand car parts as if sitting in the drivers seat looking forwards. I know exactly where the pump fits I've posted a picture showing it!

If the cam gear is knackered there will be a LOT more damage than just a gear! It would be obvious turning the engine over and you said you had viewed the drive gear turning earlier.

 

[DuncanPoundcake]

You ALWAYS hand car parts as if sitting in the drivers seat looking forwards. I know exactly where the pump fits I've posted a picture showing it!

If the cam gear is knackered there will be a LOT more damage than just a gear! It would be obvious turning the engine over and you said you had viewed the drive gear turning earlier

Jesus man calm down. I didn't say you didn't know where the pump was. I'm looking at the front ok.

Thanks for your help.

 

[geoffus]

Jesus man calm down. I didn't say you didn't know where the pump was. I'm looking at the front ok.

Thanks for your help.

That should help your cause no end.

 

[V12cat]

Jesus man calm down. I didn't say you didn't know where the pump was. I'm looking at the front ok.

Thanks for your help.

I'm calm. It's not my money. Good luck and let us know what it turns out to be.