Long crank time on Mercedes Benz ML320 Bluetec
I've got a 2008 ML320 diesel with an intermittent long crank, which occurs cold and hot. Occasionally it cranks and cranks for around 12 seconds, while other times it starts in 2-3 seconds.
No trouble codes at all in the CDI.
We've tried the following (or has been recently replaced); fuel filter, battery & alternator, turbo, air filters and crank position sensor. We've swapped used fuel rails (both sides) and high pressure fuel pump. We've had the CDI software updated with the latest software and cleared adaptations. I don't suspect glow plugs as the issue occurs even when hot.
The customer had it at another shop previous to us, and they replaced some of the parts listed.
There is a message displayed on the dash saying “You need a new key”, but the customer states even with another key that he recently got, the same long crank occurs (He hasn't brought me the second key to verify).
Anyone else experienced this issue?
Do you have the ability to check fuel pressure, high and low side? Also check to make sure the injectors are coded.
We did look at pressures, although I can't remember what they were, they were within spec. I'll get the numbers off the injectors and code them in… That was one idea we had considered.
I agree with John. I have seen several where for whatever reason the Injector Coding is incorrect. On both BMW &Benz This of course will cause either starting issues or performance issues. Usually both. I have been trying to find out how the flow rate is getting changed . And Unless someone else has an answer for this problem , at this point I can only assume that another shop or even the…
I've seen on a couple MB diesels now where the CDI just lost the coding on an injector (single, relatively new injector only) both times it did throw a code, but I suppose it's possible to lose it and not throw a code.
I have a question regarding the fuel pressure as well. Did you T in a gauge at the outlet of the fuel filter to the high pressure pump? KOEO you should have around 5 bar. When you turn the key off does the pressure drop immediately or does it hold? Once the car starts you should have around 250 bar which you can read with your scanner, does the high side pressure drop immediately? There is an…
Thanks Bob, I'll look into that. I know we were reading the pressure with the scanner, I don't believe they teed into the line. I'm pretty sure the pressure dropped right away after shutting it off (again using the scanner) which is what led to them replacing the rails. The customer picked the vehicle up to try for a bit, but is bringing it back in later today, I'll revisit the fuel…
Have you done a leak off check on the return side on the injectors 🤔🤔🤔🤔🤔🤔🤔
Do you know if that was an OEM crank sensor that was installed? If not get one from Mercedes. Those ECM's are sensitive and do not work well with a lot of aftermarket sensors. How many miles are on this? Remove the oil cap, look straight down at the piston on the Chain Tensioner. When New, the Chain Tensioner piston extends about 5 to 6mm from the body of the Chain Tensioner. When the piston…
Check injectors return leak. After shut off the engine pressure should drop pretty much immediately. As far as I remember is anywhere between 3-5 sec. This is correct operation.
I think a good explanation of how to check for injector line leak would be nice. I know I would like to know. Both banks feed into a T and then to the supply line for the fuel filter. Are you checking it at the T (before or after) or at the individual injectors?
Most likely you have defective injectors,do leak off test,leak off pressure may be to high,the hotter the engine gets the more the leak off pressure will leak,I am sure once it starts up the vehicle performs well.It can be 1 or all 6 injectors.Pressure is being lost through injector leak off while cranking.Would be nice if you have injectors to swap Or…
Lots of great information and ideas here, thanks guys. The vehicle is back now, and I'm starting to work through these ideas. Now the vehicle doesn't even start. I did the bleed line test, and all except for 1 injector filled the line I connected very quickly, so obviously that's an issue. I peeked down at the timing chain tensioner and its sitting about 9-10mm out, so not quite to the end…
For us we replace the left fuel rail with integrated fuel pressure sensor first.
We unplug the exh backpressure sensor as they get plugged up and car will not start in the parking lot first. Really need codes posted
That's the problem, there literally isn't a single code.
Just try using a little starter fluid and see what it does.
This was SUPER helpful justin, Thanks! I tried searching for it earlier but couldn't access it. I've worked through the entire procedure and found low side pressure and volume to be fine. Fuel quality looks fine. Rail sensor offset is fine. Pressure regulator has no leak. Rail pressure when cranking is half of what is required to start the vehicle, and I've got 5 of 6 injectors that leak a lot…
I know this isnt maybe the the best idea. However because of all the time and money put into this car could you try to pinch off the return and see if it helps your rail pressure at all. At least maybe for a few seconds or so?? Just to prove your point??
I considered doing that, but I know that's a no-no. I did try to give the return line a light squeeze to restrict it a little without blocking it, but I only cranked it briefly to see if it would start (it didn't), I didn't check to see if the pressure rose.
The bolts for the high pressure pump are one time use and need to be replaced anytime they are removed. I believe they have also been improved with a encapsulated Loctite.