I have a 2009 GL350 CDI X164 with what appears to be multiple issues causing extended crank on start . It has 170,000 km (105,000 miles) and is having trouble starting cold and hot but less so warm ! I have long absorbed information from this great forum so thought i would put back by making sure the resolution is also posted here, once resolved. It sux when it is not !

At this stage I think i have

1. At least 2 injectors with issues
2. Burned out Starter motor
3. Air in Fuel lines.

Cause the poor starting

Starting when in the morning it talked 10-12 cranks to start. Runs fine and shows no obvious signs of issues once started
If you run it for 10 mins (warm bit not hot) and stop it then it start relatively easily at 4-6 cranks.
Hot starts are a different matter,if you come off the highway and try to start it once stopped, it will not start the first round of cranking, may start the second round of cranking ( immediately after) or usually will start the third round of cranking. Starter seems sluggish. Adding a portable jump starter has the starter rotation speed increasing and the motor starting after 8-10 cranks yet not what you would expect even with extra Amps.

I have been using and following this excellent write up on OM642 Crank no Start as linked to trouble shoot..
https://diag.net/msg/m42gozknibrjhlt701d3th52f5
One area highlight in the trouble shooting session is the rotation speed of the starter motor. My Starter more is only getting me 100-114 rpm as measure via the OBDE port. It mentions 200rpm is normal to build rail pressure to open the injectors and create enough heat and compression. The starter also has just started to make a strange sound so may be on the way out.

The battery is 1 year old and usually sits at 12.6v before the starter engages and goes down to 11v volts under starter motor load. That seems normal. The alternator is good.

You can hear the stange noise at the beginning of the below Leak off test video. sound Goes away when starter disengages, so suspect it is that. Note the bubbles in the leak off tubes. WE checked that tube where sealed on the leak off and they were.

Leak of Test 1
Leak off Test 2

Note the air bubbles !! assume this is not normal and another issue contributing to the poor starting. Any ideas where from ? tank pump, fuel filer, o rings in fuel lines ? High pressure pump.

The leak off result over 2min 10 sec were 1. 5ml

2. 3.5ml

3. 4ml

4. 11ml ( had to stop test)

5. 3.5ml

6. 7ml

Seems 2 and 6 are not going well !! May replace all 6 to be sure as they are original injectors.

The current thinking is with internally leaking injectors and slower rotation crank speed, the engine is not building enough rail pressure quick enough to let the engine start ina timely manner. This may explain the further difficulty when hot as injector leaking more and rotation speed more sluggish, (heat soak ??)


Start RPM of only around 115 and associated rail pressure,


Any thoughts appreciated - on next steps ?? think to check. I have DAS so can gain access to vehicle data. No fault codes are showing !!!

At this stage I have ruled out the Crank Position Sensor as it starts with extra battery power when hot. Usually, CPS is all or nothing when hot.
I have ruled out Glow plugged out Glow plug modules as no fault codes, and has issue starting cold or hot.

Thanks for reading.Any ideas or anything i might have missed to look at.

 

Have you noticed an increase in engine oil level or have done an oil analysis test?

The caution is that extended cranking and leak down might dilute your engine oil to the point where it is mostly black colored diesel and seizes.

 

Fair point and a concern - just recently changed the oil after 8000km/5000 mile and it looked reasonable

The plan now is resolve the issue to reduce this risk
Have just had a fuel pressure test kit arrive today so will test the low pressure system for leaks - I think I am looking for 35psi plus constant and for this to be sustained when key turned off - I.e no leaks in the system

 

You need 58psi minimum post filter and before the injector pump. Ideal level is in the 63-68psi range. Slightly more than that and the cascade overflow valve opens and bleeds off pressure. IF you have any less than 58, I would remove the cascade overflow from the injector pump and make sure the valve isnt stuck.

 

So had a shot at measuring the psi of the low pressure fuel system post filter. The video shows the pressure at 58psi when the pump is actuated. On turn over it drops a little down to 54psi and then 58psi when engine starts.

The pressure drops right off when the pump stops - down to 10psi very quickly ? Is this normal. Wouldn’t the tank pump have a one way check valve that should maintain pressure on key off ?

the other test I did was Volume - looking for airation or lumpiness in fuel delivery - this looked good with litre delivered in about 18sec - spec is looking for at least 500ml in 9secs.

I wonder where too next - leaky injector replacement or trouble shoot low rpm starter ie only getting the motor to 114rpm - 120rpm .Starts when cold However only achieved 100rpm when hot and does not start. Rail only gets to 100bars when the injectors need 120bars to open !!

I do wonder if a couple of leaky injectors can really mess with the rail pressure that much or it it the combination of low rpm start and leaky injector ?? Or something else too !!! 😀

 

My 2007 GL320 always starts after a few too many cranks in the morning but perfectly fine once warmed up.

Don’t have any other GL320 to compare with so assumed it’s an expected behaviour. It does blow a puff of white smoke when it starts just in the morning.