CLS 2010 3.0 V6 Diesel slow to start.

[dan90210]

Very quickly.

During a cold start it takes maybe 5 to 7 turns of the engine to start.

Once started and warm she starts instantly.

Faults codes show a historic exhaust sensor before the CAT.

Would it be that or something else? Glow plugs maybe. Home fix or.....?

Many thanks

 

[sl500amgsport]

Maybe the plugs are not teaching temp in time, sounds like my lawnmower but that is fuel starvation...

If it starts OK once warm, could be temp sensor.

Sent from my SM-G988B using Tapatalk

 

[Wighty]

Very quickly.

During a cold start it takes maybe 5 to 7 turns of the engine to start.

Once started and warm she starts instantly.

Faults codes show a historic exhaust sensor before the CAT.

Would it be that or something else? Glow plugs maybe. Home fix or.....?

Many thanks

What age is your battery , there is a date stamp on the terminal normally . If it’s 10 years old , change it
Other than that glow plug relay (if it’s original change it ) and glow plugs .
Of course it may be other things …check for fault codes ?

 

[dan90210]

Battery and relays sound like a good place to start, making sure the plugs have a good feed makes sense.

The only historic fault code is the exhaust sensor before the cat. That's been cleared down and hasn't returned.

 

[onefortheroad]

Battery and relays sound like a good place to start, making sure the plugs have a good feed makes sense.

The only historic fault code is the exhaust sensor before the cat. That's been cleared down and hasn't returned.

Before doing all that , try 3 ignition cycles with a 10 second wait in between. Do you get alot of white smoke when it starts now on a morning??

These engines are prone to fuel pressure loss , overnight .

I changed all 6 plugs and the relay for nothing , problem still existed.

 

[Doug1234]

Check the glow relay and plugs , engine is the om642 in this jeep… the air filter setup is different but every thing else is same as yours so just copy the procedure

Starter motor may be tired and slow , you need 200rpm before ecu fires injectors

 

[VitoVanMan]

You seem to have the same symptoms , I had on my Vito.
Checked for faults on my scanner, and no electrical faults, apparently.
Used the data stream Cold Start program looking at fuel rail valves Y74 and Y94, which appeared ok, and then noticed coolant temperature sensor reading 84.6 C. after a couple of cold starts. Obviously an engine doesn't reach this temperature after a couple of turns of the engine.
Purchase a new sensor and hey presto instant start.
The sensor was giving a temperate reading albeit an incorrect value and hence no fault code on the scanner health check.
My van doesn't have an engine temperature gauge on the dash,as Mercedes in their wisdom omitted to install one.
If you have a temperature gauge on your dash , it may be showing in excess of 80 C.. If so it is fooling the ECU into thing the engine is already warm.

 

[dan90210]

Before doing all that , try 3 ignition cycles with a 10 second wait in between. Do you get alot of white smoke when it starts now on a morning??

These engines are prone to fuel pressure loss , overnight .

I changed all 6 plugs and the relay for nothing , problem still existed.

No smoke at all, ever. It runs really clean. No smoke smell either.

 

[dan90210]

You seem to have the same symptoms , I had on my Vito.
Checked for faults on my scanner, and no electrical faults, apparently.
Used the data stream Cold Start program looking at fuel rail valves Y74 and Y94, which appeared ok, and then noticed coolant temperature sensor reading 84.6 C. after a couple of cold starts. Obviously an engine doesn't reach this temperature after a couple of turns of the engine.
Purchase a new sensor and hey presto instant start.
The sensor was giving a temperate reading albeit an incorrect value and hence no fault code on the scanner health check.
My van doesn't have an engine temperature gauge on the dash,as Mercedes in their wisdom omitted to install one.
If you have a temperature gauge on your dash , it may be showing in excess of 80 C.. If so it is fooling the ECU into thing the engine is already warm.

Ah now this sounds spot on. The temp gauge increases really quickly.

 

[VitoVanMan]

The temperature gauge is permanently set at 85 C. This is a faulty sensor. No sensor is -29 C. and a functioning sensor is ambient engine temperature before starting about 10 C. in my case.

 

[VitoVanMan]

Do you have a temperature gauge on your dashboard? And it instantly rises to 85 C.?

 

[onefortheroad]

No smoke at all, ever. It runs really clean. No smoke smell either.

Dpf model ?

 

[VitoVanMan]

Ah now this sounds spot on. The temp gauge increases really quickly.

Looks like the same fault. I am guessing your vehicle is over ten years old.
I looked on line and had this faulty sensor confirmed by a YouTube posting. However the next step was to fit a new sensor....again online you can remove the sensor from the thermostat housing quite easily by hand, don't be fooled....not on a eighteen year old engine having travelled 700,000 miles. I ended up having to fit a new thermostat housing, which was no bad thing as they come complete with a new sensor and securing clip, on removing the housing, expect to shear off at least one of the three bolt heads...I managed two out of three......so being left with short studs...you either need a local enginer stud extractor expert to remove short studs or invest in female extractors.
So hopefully your bolts a not corroded in like mine. The bolts being M6 bolts don't take much torque to snap the heads off.
Hope this helps.

 

[dan90210]

Looks like the same fault. I am guessing your vehicle is over ten years old.
I looked on line and had this faulty sensor confirmed by a YouTube posting. However the next step was to fit a new sensor....again online you can remove the sensor from the thermostat housing quite easily by hand, don't be fooled....not on a eighteen year old engine having travelled 700,000 miles. I ended up having to fit a new thermostat housing, which was no bad thing as they come complete with a new sensor and securing clip, on removing the housing, expect to shear off at least one of the three bolt heads...I managed two out of three......so being left with short studs...you either need a local enginer stud extractor expert to remove short studs or invest in female extractors.
So hopefully your bolts a not corroded in like mine. The bolts being M6 bolts don't take much torque to snap the heads off.
Hope this helps.

I guess next question is. Where is it located on the block? I'll give the threads a good soak over the next couple of weeks and try to swap it out.

 

[VitoVanMan]

My Vito is an OM646 engine and the thermstat housing is located on the cylinder head of the top hose off the radiator.

 

[VitoVanMan]

Not being familiar with the Mercedes V-6 engine , I went on-line to find the position of the coolant temperature sensor.
It is not located in the thermostat housing like the OM646 engine.
It appears its mid-way along the right hand ( passenger-side) cylinder head and is held in by a retaining clip.
You can find its location in your workshop manual for confirmation.
So hopefully as its not in the thermostat housing, which is situated at the front of the engine, and being mid engine its not exposed to the elements as in my case.
So once you have located the offending article, you can apply copious amounts of WD-40,( other penetrating oil sprays are available), this will help ease extraction.
Also before you buy a new sensor you could disconnect the sensor lead, check to see no movement on the temperature gauge and if you start the vehicle it should start straight away, as the false temperature reading, with no sensor will be - 29 C. the ECU will think the car is in Siberia....

 

[VitoVanMan]

Just some advice when you come to buy the sensor.
I bought mine from a main dealer for several reasons.
Main Dealer. On-line.
(i) Price £15 + VAT £17.66 + Postage.
(ii) Warranty. 2 years. No refund if installed. 30 day return unused.
(ii) Application. Guaranteed. May not function. Sets off other fault codes.

Myself and other motor repair colleagues have experienced troubles after fitting spurious Chinese parts, so prefer to pay the extra for piece of mind.

 

[VitoVanMan]

You may want to search on this site the following forum from September 2021.
This describes the location of the sensor on an OM642 engine, which I believe you are running, and has tips on what to do and expect.
Try " Coolant temp sensor location 2012 3.0 L CDI "