Hello everyone, just trying to get my head around a little issues I am having, I do have a GL350 2010, I have purchased this truck about 3 years ago. Since then I always had a minor inconvenience, but now it seems to get worst. So in the summer the truck will almost all the time start on the first try (99% of the time) as the temperature goes down even to mild cold ( 0-5 celsius) then I have to sometimes hit the starter 2-3 times, Wait 30 minutes and redo, it eventually start (most of the time) I've check for glow plug and glow plug controller, everything is great. The battery has been replaced 2 times within the last 24 months, with sign of getting better each time, and the charging system was checked to make sure everything was good.

Now when I plug in the odb tool, I get the following reading: when starting about 100-135 RPM, and pressure about 2000PSI. Now everywhere I read it said it needed about 200rpm to start correctly. I've even attached a second battery and a boosterpack to make sure there where no missing available current and the speed seems to be topped at 135-150rpm... I've called a Mercedes dealer and ask if with these numbers they tought the starter may be comming a bit weak of something, they told me that start either work or not, but don't get weak overtime. The batt voltage drop is also from 12.6 to 10.2 v when using the battery dedicated. If the batterie is 100% new, it seems for the first winter it actually improve the starting, but as soon as the battery start to slowly get less power the problem comes back.

I've hooked up the battery to an OGM battery tender now 100% of the time when resting in the driveway, this seems to have improved the starting but still slow speed but more constant, typically I get
135-135-135-130-125-115-105-100-100-100-100 and stop. I will post picture of the information from the ECU (Voltage, RPM, and FuelPressure)

As far as I can tell not getting 200rpm seems to be the likely cause of hard start, now charging system is ok, battery is ok, I am left with 2 choices that I can think of:
1 - Poor wire terminal, wire connection, or problem between the battery and the starter.
2 - Started brushes are getting worn out and thus reducing the speed/power of the start.

Is there any easy way to further diagnose the problem? I just want to check before starting to throw part at it for no good reason.

THanks,

 

2000 psi is pretty low. When that can be slightly different between engines, you need closer to 5000 psi for engine to fire.
What scanner do you have? The HT/AP200 are very good bang for a buck. When I had fuel pump failure, I found whole troubleshooting page, who did show me all the parameters involved, showing weak points in red.
I had starters burning some coils and turning slower. Rare failure, but it does happen.

 

I am using the MBII scanner to measure and check for the 3 component I am trying to isolate. So its harder to tell on this one since it did start without any problems as I already started the trunk this morning. On running operation I have my 4400-4800 PSI in the fuel rails. At start as we can not really tell but it did go to about 155rpm starting, dropping voltage from 12.6 to about 9V at the worst, fuel pressure around 2000-2500psi and then ramp up to full start no problem.

Tomorrow morning on the first start I try to get a graph with no sucessful start that will show more of the information I am trying to show here.

 

I bought MBII few years ago and not only it is terrible slow, but it was giving me bogus data on DPF cleaning.
Since I bought HT200, the MBII collects the dust.
Its only advantage is that it works independently from anything, while HT needs android and sometimes needs Internet for license checking.

 

Hi Sorry for the delay it worked correctly yesterday at -22C no problem 1 start, today its about -15 outside I tried about 4 times this morning,

Still I am using the MBII since I only have this at this time, but on a fully charged battery (hoocked up to a battery tender and on the first image its even with a 400amp boost capacitor pak. So in the best world I am not getting 120RPM on the start and below 1600psi.. Typically what I see is when I reach about 130-140rpm and about 1800psi then the engine start, but it I dont get over that 1800psi it seems the injector are not even throwing fuel in the cylinder. Now my understanding is that it should be at least close to 170rpm, I believe with the 70rpm more this would allow more pressure to build and should get a good start!

So my question still remain, if the charging side is working and the battery is getting the expected rating, what can explain the starting going from 100-110 rpm to 135-140 or even higher. I believe the cold is affecting the battery charge, and also the resistance in the engine, I have had no problem once the engine is started, it will start hot as well. Eventually it will start, its just the time it takes to start it will vary. Since I can get a bosh started for around 200$ and that our hourly rate for MB Service for check if 155/hr I am leaning to replacing the starter as a try, then perhaps have a full dealer diagnostic. But right now its very cold outside not really happy to go under the hood at -20!!!

If any other ideas that would be nice.

Thanks!

 

UPDATE: Well it turns out starter do wear out over time, even tho the starter was always turning and trying to start the amount of required power or anything in the process of the old starter was causing some issues. So typically I was getting lower and lower craking RPM (temperature has an effect on the main resistance in the engine and thus slowed even more the RPM in a condition where the RPM are KEY to get to that heat required for ignition of the fuel. So getting from 110RPM to 120 RPM on very cold start = NO start at all, then when temperature warmed up a little I was getting luckier with 140-150 - at that range the truck would usually start after a few seconds, not immediatly but reliably. Now the new started is in the trunk, within less than 1 second the RPM is up to 190RPM, and there is no more and studdering while trying to crank, it just go without any problem from 0-130-191-600-800rpm within less than 2 seconds, I've had the truck for over 3 years (went 2 time back and forth from canada to mexico, and it never started this quick witouht any hesitation. So short story, even if typically stater will go bad and not work at all, over time sometimes they can get weak. (And weaker each year, it still took about 3 years before being unusable!) first year was starting at the second crank attemps, the year after it took a new battery and it work great, then another year where it needed a capacitor booster to start each time, and this year it just wasn't working anymore!!!

Anyhow!!! THanks for the help, and again, if you aren't seeing about 180-200 rpm when starting your diesel! Check battery and charging but if they are good there is possibility your starter has become weak! (Could be the wiring too).
Have a great one!

 

Thanks for this clear explanation. My GL 350 to 2010 has exhibited the exact same symptoms - with low rotation speed around the 120’s - I am able to get it to start if I add a lithium jumper Battery that has 16 V as an output as the extra voltage increases the starter motor rotation speed and starts it straight away.

as you point out a new battery does Help as it increases the CCA and stops the voltage dropping as much on start, therefore allowing for a better rotation speed of the starter and starting it.

however overtime, the CCA decreases and the rotation speed decreases, making it hard to start. Strangely I found if I turn the key on and wait 15 seconds or so it does start better , but overtime that also fails.

this thread, and thank you, has given me enough confidence to try a new starter motor. I’m pretty confident now that the increase rotation speed will get the OM642 going.

 

This is very interesting - thank you, Nface, for taking to post this and show the graphs. I have (I think) the newer version of your scanner - I'm going to see if I can find that graphing function.

My GL320 has always taken, what I believe, a little longer to start - although it hasn't gotten worse in the 8 years I have owned it. It definitely starts harder in the really cold weather - sometimes taking 2 or 3 attempts.

However, doing a couple glow cycles does help as it warms up the combustion chamber more. Dave, this is what you are doing with that "15 seconds". What I do, though, is to push the start button (without foot on the brake) to activate the glow plugs (you'll see the light). I let it go for a few seconds after it goes out, then wait 10 seconds and repeat.

 

This is from my understanding very typical of the OM642. One thing I have noticed is increasing the voltage makes a difference. If I put on an auxiliary battery starter with 14 V, it will generally start without having to glow it. That is it will start directly off the button even in cold conditions.

I did think the issue might be also associated with low rotation speed, as I was adding the extra voltage it was definitely increasing the rotation speed and starting well. I put in a new upgraded starter motor on, (merc upgrade starters from 1.2kw to 1.7kw) .This definitely increased the rotation speed from 120rpm to 200rpm where it should, however starting still remains an issue as soon as it got a little bit cold. As soon as the cylinder chambers are warm enough, either by outside weather or have been around that day there isn’t a issue starting.

The next course of action for me is to potentially put in new glow plugs, and I already have a new OEM glow plug module. This I hope get the engine starting off the button again in all conditions as it would’ve come out of the factory.

There still is that underlying, possible fault, all the systems may have developed over time of not getting just enough voltage. My mechanic indicates there’s lots of X164 that have this cold starting issue and they think it’s to do with the length of cable between the battery and the motor.

it is worth noting that I did put an aftermarket glow plug module in the vehicle about a year ago. I did not change out the globe plugs, however it did start off the button for the first time in a long time. Only lasted a couple of months and then it went back to needing to manual glow the car and pretty much the same why everyone is indicating, giving it up to 15 seconds, and repeating when very cold.

I hope this helps anyone in the same position. it would be interesting whether, this occurs outside of the X164 , that is a design that does not have such long cable length from battery to motor.

 

Good points to bring up, Dave. As a side note to "adding a second battery"... I've done that, too - using a battery jumped directly to the jump post under the hood. I saw no difference in starting ability. HOWEVER, this was still a standard battery. I was adding it for the amp capacity and, quite honestly, expected to see a difference.

I've wondered about the cable length, as well. Maybe it should be a thicker cable?

 

Regarding the extra battery... what I "should" do is run a heavy cable directly to the starter. That should eliminate any guesswork as to whether or not enough volts (or, really, amps) are getting to the starter.

 

Starter motors are DC machines and have brushes and commutators. Yes they wear out, springs go weak, brushes get shorter and the comm gets black. -20 is a real test of any electrical circuit though! Thanks for posting back what you found