ML 320 CDI - Crank Non-Start

[DuncanPoundcake]

Hello all,

Ok so, Cranks but doesn't start:

High Pressure Pump - Replaced
FPR - Replaced
Crank sensor - Replaced

Still not enough pressure at the HP pump to start the car.

I'm running out of options. Is this an ECU issue?

 

[SteveFromAvantgarde]

Have you got fuel delivery pressure from the tank to the HPP?

2 ways of checking that, either with a fuel pressure tester or with a Xentry machine.

Sounds like you're throwing parts at it without actually doing any proper diagnosis. The most expensive and frustration way to fix a car.

 

[mersum1es]

Injectors leaking,,,

Is this W163 or W164? Different fuel system...

What pressure reading you having on crank?

 

[SteveFromAvantgarde]

In his profile it says he drives a ML320CDI....so ill assume its a W164.

Crank pressure is irrelevant as hes already replaced the HPP and its not starting. Fuel delivery pressure from the tank is the first thing to check. It needs 3.8-4.2bar. If you havent got that it wont start in a month of sundays.

I've not seen a 642 not start with worn injectors. They usually misfire and smoke, but always still start.

 

[mersum1es]

Oh yes, W163 was never fitted with 6cyl diesel... my bad.

I assume fuel quantity valve was replaced with hp pump?

How the problems started? What codes are triggered, if any?

 

[DuncanPoundcake]

Have you got fuel delivery pressure from the tank to the HPP?

2 ways of checking that, either with a fuel pressure tester or with a Xentry machine.

Sounds like you're throwing parts at it without actually doing any proper diagnosis. The most expensive and frustration way to fix a car.

There is pressure/fuel but not enough.

 

[DuncanPoundcake]

Have you got fuel delivery pressure from the tank to the HPP?

2 ways of checking that, either with a fuel pressure tester or with a Xentry machine.

Sounds like you're throwing parts at it without actually doing any proper diagnosis. The most expensive and frustration way to fix a car.

The AA came out before Christmas, stuck a scanner on it and told me it was the FPR or HP pump. I replaced it and it didn't start. I have no fuel pressure gauge so I sent it to a specialist MB garage. They tested the fuel pressure and it was very low at the HP pump. So, they replaced it. That didn't solve the problem, so they tried a new crank sensor -as this can cause non-starts, still doesn't start. That's as far as it got.

 

[SteveFromAvantgarde]

I'm not aware of any diagnosis equipment that will condemn a HPP.

I think you need to go all the way back to the start and carry out your diagnosis. Or the garage does.

Do you have delivery pressure from the tank? If yes - move forward. If no - you have an issue with the fuel pumps in the tank.

If yes, what is the rail pressure? It should be above 280bar. If yes - move forward and look at injector leak off. If no - you need to find out why and you'll need to look at the rail pressure monitoring system and see if its giving the correct data.

You're/they are missing something obvious somewhere. All good garages should possess a fuel pressure tester.

 

[DuncanPoundcake]

In his profile it says he drives a ML320CDI....so ill assume its a W164.

Crank pressure is irrelevant as hes already replaced the HPP and its not starting. Fuel delivery pressure from the tank is the first thing to check. It needs 3.8-4.2bar. If you havent got that it wont start in a month of sundays.

I've not seen a 642 not start with worn injectors. They usually misfire and smoke, but always still start.

Yes a 164.

 

[DuncanPoundcake]

I'm not aware of any diagnosis equipment that will condemn a HPP.

I think you need to go all the way back to the start and carry out your diagnosis. Or the garage does.

Do you have delivery pressure from the tank? If yes - move forward. If no - you have an issue with the fuel pumps in the tank.

If yes, what is the rail pressure? It should be above 280bar. If yes - move forward and look at injector leak off. If no - you need to find out why and you'll need to look at the rail pressure monitoring system and see if its giving the correct data.

You're/they are missing something obvious somewhere. All good garages should possess a fuel pressure tester.

I've mentioned the injector leak to them this morning. I was told pressure was good at the fuel filter, so dismissed the tank pump but will mention this also. Thanks.

 

[DuncanPoundcake]

I'm not aware of any diagnosis equipment that will condemn a HPP.

I think you need to go all the way back to the start and carry out your diagnosis. Or the garage does.

Do you have delivery pressure from the tank? If yes - move forward. If no - you have an issue with the fuel pumps in the tank.

If yes, what is the rail pressure? It should be above 280bar. If yes - move forward and look at injector leak off. If no - you need to find out why and you'll need to look at the rail pressure monitoring system and see if its giving the correct data.

You're/they are missing something obvious somewhere. All good garages should possess a fuel pressure tester.

It will turn out to be something really bloody obvious.

 

[SteveFromAvantgarde]

I've mentioned the injector leak to them this morning. I was told pressure was good at the fuel filter, so dismissed the tank pump but will mention this also. Thanks.

Again, what does that mean? Because 2 bar of fuel will pee out everywhere and give the impression of good fuel pressure. But its not enough to power up the HPP into giving good rail pressure. Thats why they need to measure it. A weak delivery pump can still give good pressure but not good enough.

Have you ever released a schroder valve from a tyre at about 30 psi? It blows your hand away. Well you need 3 times that pressure just to ignite the HPP system and why its so critical.

 

[DuncanPoundcake]

Again, what does that mean? Because 2 bar of fuel will pee out everywhere and give the impression of good fuel pressure. But its not enough to power up the HPP into giving good rail pressure. Thats why they need to measure it. A weak delivery pump can still give good pressure but not good enough.

Have you ever released a schroder valve from a tyre at about 30 psi? It blows your hand away. Well you need 3 times that pressure just to ignite the HPP system and why its so critical.

Mate, I'm not an expert on MB, MLs or diesels, High Pressure Fuel pumps or Schroder Valves. I came here for advice and I am just repeating what I know.

 

[SteveFromAvantgarde]

Good job I am

I've tried to give you the best advice based on my experience.

 

[colinallcars]

It will turn out to be something really bloody obvious.

Blocked fuel filter?

 

[DuncanPoundcake]

Good job I am

I've tried to give you the best advice based on my experience.

And it is appreciated.

 

[DuncanPoundcake]

Blocked fuel filter?

Unfortunately not. New one fitted with the HP pump.

 

[DuncanPoundcake]

Hello all,

Ok so, Cranks but doesn't start:

High Pressure Pump - Replaced
FPR - Replaced
Crank sensor - Replaced

Still not enough pressure at the HP pump to start the car.

I'm running out of options. Is this an ECU issue?

#Update:
All fuel pressure and flow rate is correct up until the high pressure fuel pump.
3 HPFP have been fitted. Pressure still at 4 bar, pump is filling but pushing out at 4 bar.
With the fuel pump off, the end of the camshaft gear that drives the HPFP is spinning. All teeth are present and is not loose.
So, thinking is now it is an ECU issue, or less likely, the problem is the camshaft gear where it meets the HPFP..

 

[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?

 

[DuncanPoundcake]

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?

Actual values, without asking, I don't know but I have been told it's low pressure - 4 bar - at the pump in the tank and I am presuming, all the way into the injectors. They have been using Star and a pressure gauge at every point of the fuel system where you can take a pressure reading.