DLB_Adelaide

Summary:
Takes two crank cycles to fire-up the engine. Battery voltage low at 12.5V. Engine fuse box (F58) relay H slot (not the relay itself), pin85 and pin86 shorted. Need to diagnose why circuit is shorting.

Here goes.
I have this long crank problem for a couple of weeks now. The vehicle would always fire-up on the second crank. There are a few indicators to why this is but I wanted to focus on the obvious ones first. Long story short, opened the rear, battery, prefuse, and engine fuses boxes to notices anything unusual. I have my multimeter handy and went through the fuses. When I reached the engine fuse box and noticed F58 relay D and F58 relay H were hotter than usual. I hooked up my multimeter and my relay diagnostic tool, I did not noticed anything unusual with relay D yet but I did notice that relay H pin85 and pin86 were shorted together. Also, at the end of this thread will be a similar repair to the F58 circuit board by another user in this forum. Off for the night, ran out of time to go deeper in the diagnostic.











Added bonus, other part of the wiring diagram
Unknown about this one is wire 87 does not exist in the previous wiring diagram (MAA).


Here below is a F58 circuit board fix by strok Similar thread with a resolved action

Max Blast

I think it might be starting in the wrong end here but the proper method to do a parasitic draw on a Mercedes 164 is to allow the car to fall asleep. And if it doesn’t fall asleep, find which door is still reporting an open condition.

It was a great YouTube video out there a couple years back by a Danish mechanic who did this on an ML and it’s almost always the tailgate.

so you can’t do a current draw without telling the car that it needs to go to sleep so at least confirm that you did that by simulating all doors closed by pressing in the door sensors. With the car not asleep it will have current passing through certain terminals, and that could be a red herring in your search..

DLB_Adelaide

Thank you for sharing your thoughts on my diagnosis. I have posted here on another thread my adventure in opening the rear tailgate, other thread here. Indeed, the tailgate was pooling water. After a few months after I did the tailgate inspection, my tailgate lock actuator failed and I replaced with an aftermarket device. I always practice proper plug connector closures by applying dielectric grease wherever I touch a plug/receptacle. When I hooked up the clamp meter yesterday, the lowest current draw I have observed was about 90mA.

Another update to my first crank cycle this morning, the GL320 fired up on the first go and did not require a second crank cycle. The changes I made since my inspection yesterday were a couple:
a. Removed trailer module (can be found in rear compartment)
b. Removed rear compartment fuse box (F4) fuse number 20-23, cant remember which ones. I believe I reinstated F4f23 because this controlled the RF key receiver.
c. Removed F4 fuse number 41 or 42? Can't remember exactly which one. I will update once I look at the F4 area again.
d. Replaced camshaft hall sensor (B6/1) with an aftermarket (Hella brand) sensor. I believe the original one was not faulty but was throwing DTC into the system because of the low voltage.

I will update this post once I have another go at diagnosis?? Which can be the next no-work holiday.

DennisG01

Just to clarify (I have the same engine as you), what do you mean by crank cycles or second crank?

-- By two crank cycles, do you mean that it cranks and cranks and cranks and then stops... then you have to press the start button again?
-- What do you mean by "the vehicle would always start on the second crank"? That sounds a lot like the first statement? Or do you mean, it starts in "two puffs" - as in puff-puff-start? I know, puff is not exactly scientific but it's a different word than crank to help avoid confusion.

12.5 is quite low. Is that measured at the battery or the dash display?

Have you fully charged and load tested your battery? How old is it?

Is your glow system working properly and are all of the glow plugs good?

My engine has always (8 or 9 years now) taken a longer time than expected to start - even in warm weather.

I'll post a video of it starting for comparison.

DLB_Adelaide

Hello Dennis, I would explain the crank procedure now. I have a key ignition on my GL320 compared to your push-start ignition.
1. Turn the key to Position 3 where all accessories are on. Leave in this mode for 5 seconds to give the fuel pump a chance to prime the fuel pressure and glow plugs to warm up the cylinders.
2. Turn the key to Position 4 where the engine attempts to ignite. Leave in position 4 for 5 seconds, approximately. I consider this to be one crank cycle. The engine might turn about 3 turns, approximately. I keep saying approximately since I dont really count and do this by feel.
3. Return the key to Position 1 where all systems are to be turned OFF. Leave in this position for 5 seconds.
4. End of crank cycle. Repeat step 1 for second crank cycle.

I don't wait for the system to halt the crank procedure. No point in waiting for a crank cycle to finish since I am confident the engine cannot start. Fuel pressure drop and Cold Cranking Amps (CCA) has droppped. I give a chance to the "tired" systems to have a rest and reset the procedure. My GL320 was built 2007 with majority of the large components being factory parts and have not been replaced since.

By the second crank cycle, the engine would always fire-up. I can't explain this scientifically but if I have to give a guess, this would be the combustion cylinders having been "warmed" from the previous crank cycle. Mind you, I live in Australia and temperatures here do not get cold. I would also like to mention that I have a problem with Glow plug #3 (RHS rear-most). This is in my list of must-fix items. Once I fix this glow plug issue, I am confident I put less strain on the ignition system. Unfortunately, money and time are limited. This is why I can manage to fix one issue every 3 months.

The voltage was measured straight from the battery. I opened up the battery compartment under the RHS front seat. I agree the voltage is low, this is because of the parasitic voltage drain which I have only noticed the past few days. The battery is less than 2-years and it is my fault that the battery has degraded this quick. I have not fully charged the battery but I am planning to buy a battery management device to save the battery while I sitll can.

DennisG01

Thanks for the extra clarification - that helps.

Just out of curiosity, I can remove the push-button and use my key - put I only have to briefly turn it to position 3 and then let go - the engine will crank by itself just like pushing a button. In your case, it sounds like you turn your key and hold it in position 3?

3 turns in 4 to 5 seconds is definitely quite low. Low cranking speed, coupled with (at least?) one bad glow plug will definitely cause your issue. But you know that already!

Try fully charging the battery over night and see how that changes things.

Was the 90mA draw AFTER the car "went to sleep"?

Relay H... I'm not at my car right now to look at my owners manual... is that for the airmatic?

DLB_Adelaide

I dont "hold" my key on position 3 but to be more specific, I turn they key to position 3 and leave it there since there is a detent. Position 4 would have a spring mechanism that you would need to HOLD the position and returns to position 3 when released. I would assume the vehicle wasn't full "sleep yet" since I was not aware of this until Max brought it up. I will be having a look again next time.

Relay H is for terminal 15 which "metaphorically" will power up multiple control units. Same as terminal 30 and terminal 87. Here below is the circuit diagram again. You can see here just what t15, t30, and t87 enables in just this F58 fuse box ALONE, among many other control units. The Airmatic relay (or one of them) is in this same circuit diagram as Relay G. Have a look at my first post and the F58 fuse box relays are introduced. Relay G circuit also seen below, labelled as kG or with full name of F58kG.




I have included below a diagnostic guide on how to test the receptacles and what values to expect. Take for example, MR3.3 which activates relay H (kH) and MR3.1 which feeds the Airmatic relay (kG). This is only page 1 and there are a few other pages.

DLB_Adelaide

The battery maintainer arrived today. I will try to fully charge the battery this weekend and continue with the diagnosis.