Poor Vito W639 starting.

[VitoVanMan]

My Vito W639 very poor start up.
When starting, it cranks for a couple of seconds and then ignites at 700 rpm and climbs to 900 rpm and idling is very rough.
When driving away there is no hint of a misfire? After driving about six miles, with the engine up to normal running temperature, stopped engine and then the engine started straight away and straight to 900 rpm and no rough idling.
Have checked for air leaks and non found, fuel pressure delivery is normal.
New injectors were fitted by a main dealer three years ago and only 25,000 miles covered.
Has anyone experienced this type of scenario?

 

[MinionBob]

I cant quite remember how this all goes together so please do not take as verbatim, but on the OM651 there are two valves that together control fuelling, Y74 and Y94 I think they are called. However, one of the valves, cant remember which has a large influence at startup. I would be looking down this route and looking at fuel pressures/delivery cold vs warm for both valves.

Y74 bolts onto the side of the fuel rail. I think the rail is sold as one but the valves can be obtained off Ebay.

 

[VitoVanMan]

Hi Bob,
Thanks for the information. I have been doing some more investigations with the slow starting. I spoke with the main dealership and after a couple of hours in their workshop they pointed the finger at " Injector bleed on starting " and said they needed to have the injectors sent away for testing.... at this point I pulled the van out. They did say, there was a three second delay before full fuel pressure was achieved which would account for the prolonged cranking and slow engine speed before full idling speed achieved.
Since this episode, I have established that normal starting returns when the engine is warm, even after just three miles, its starting perfectly.
So like you say, it's a cold start issue probably attributed to Y74 and Y94 . So I will conduct some scanner data streaming on these valves. Then i just need to know the position of each said valve on the fuel rail. I have an OM 646 engine so it should be a similar set up to the OM 651 I guess.

 

[VitoVanMan]

Hi Bob,
It has become self evident that the starting issue is a function of temperature.
Poor starting from cold, whether it was overnight or a prolonged stop, eg. six hours, was enough for the engine to cool down and give a poor juddering start.
When driving for ten minutes, stopping and restarting, after filling up with diesel, so almost an instant restart, the van started perfectly. Again after a journey of two hundred miles, it would start up perfectly again.
So back to the scanner and data streaming for a cold start condition, it will itemize all the components required for starting. Both valves Y74 and Y94 performed perfectly.... then I noticed the coolant temperature was reading 85 degrees C from the initial start up and remained between 84.6 to 86 all through the warming up process????
On initial scan checking, there were no electrical faults on the engine diagnosis, so this problem had not been high-lighted, so it appears the sensor was sending a temperature albeit a permanently high value.
So having this permanent high value, the ECU would assume high temperature and not initiate a cold start, hence the stuttering, struggling cold start. Once normal engine running temperature was reached, normal starting was resumed with no stuttering.
I have ordered a new coolant sensor from Mercedes....I always use original equipment sensors as I and my collgue have gone down the cheaper versions only to have hours of grief and cost going down this avenue...lesson learned!!!!
So fitting the new sensor the weekend weather permitting, and will report back.

 

[MinionBob]

Just to satisfy curiosity, does the dash temp show 85degress when cold? Either way sound like you are on the right track.

 

[VitoVanMan]

Hi Bob, Mercedes Benz in their wisdom did not fit a coolant temperature gauge on my Vito W639....only the out side ambient temperature gauge, located under the bumper.
On the start up from cold programme on my scanner, the cold start temperature is 85.6 C.

 

[M80]

They did,
scroll to the overall mileage page, and then select up or down, can't remember which but you can see the temp on a rising bar.

 

[curious]

They did,
scroll to the overall mileage page, and then select up or down, can't remember which but you can see the temp on a rising bar.

On a pre-facelift?

 

[M80]

Yep

 

[M80]

In my manual, admittedly for the facelift, it's page 194.
It's been a few years since I've had a pre facelift, but sure I found it the same way.

 

[curious]

Ah, needs the steering wheel buttons (which mine doesn't have). Mine's got the single window display (rather than the double window display).

 

[VitoVanMan]

Hi Martin, thanks for the info.. When you talk of scrolling up and down, are you referring to the controls on the steering wheel?

 

[VitoVanMan]

As mine is an early 2005 W639 vehicle it doesn't possess such technical buttons !!!!

 

[VitoVanMan]

Hi Bob, thanks for pointing me in the right direction.
I connected the new senor to check the temperature and it read 18.6 C. on the scanner. So cranked the engine and perfect instantaneous start.....now that was the easy part.
When it came to fitting the sensor ,that was a different story. It became apparent the old sensor was totally seized and given the nature of how delicate these sensors are, it soon destroyed itself. I should have expected this, given I have never had to touch this sensor in the past and my vehicle is over 18 years old with 700,000 miles on the clock.
So I have invested in a new thermostat housing from ebay, which incidentally comes with a new sensor and clip. So will be fitting this in a few days once it arrives. So if you need to fit one of these sensors and your vehicle is fairly old expect to have the thermostat assembly to hand just in case.
I noticed a few Youtube videos on how to fit these sensors....(i) the one which just slides out with your fingers or (ii) the sprinter guy with the seized destroyed sensor with only the thermocouple wires to grip.

 

[curious]

over 18 years old with 700,000 miles on the clock.

!

 

[VitoVanMan]

Yes, registered in 2005....and I was a long distance courier in a former life.

 

[MinionBob]

I think you get the award for highest mileage on the forum...possibly ever! Can anyone beat it?!

 

[VitoVanMan]

I certainly hold the record at my local MOT station.....

 

[VitoVanMan]

Fitted the new Coolant Temperature Sensor and the temperature reading was 18.6C. Started up the van and instantaneous start.....thanks for all your help, Bob.

 

[curious]

Fitted the new Coolant Temperature Sensor and the temperature reading was 18.6C. Started up the van and instantaneous start.....thanks for all your help, Bob.

Onward to the next 700,000