when wanting to speed up, does it downshift properly
Thread Starter
Member
Joined: Sep 2017
Posts: 173
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From: UK
Mercedes R320L CDI 4MATIC 2007
when wanting to speed up, does it downshift properly
My car has got 642 engine CDI, 2007, gerabos 7g tronic 722.9
When the car is moving, and i want to speed up, i start accelerating and it does not downshift properly, i have to kick it harder, a couple of times, then it downshifts.
Also, on cold start it cranks the engine for too long before the engine starts up. The fuel pressure builds up i guess. The fuel system does not maintain the residual pressure. Not sure where that prassure is failing to be maintained.
I tried to switch ignition on and leave it for 30 seconds, the pump at the tank prebuilds the pressure in that time. Then the cold start is ok, no long cranking before it starts up.
I have read some old thread in this forum, that problem with the downshift and long cranking are related. Possibly cause of the fuel pressure is not maintained properly?
Any advises are appreciated.
When the car is moving, and i want to speed up, i start accelerating and it does not downshift properly, i have to kick it harder, a couple of times, then it downshifts.
Also, on cold start it cranks the engine for too long before the engine starts up. The fuel pressure builds up i guess. The fuel system does not maintain the residual pressure. Not sure where that prassure is failing to be maintained.
I tried to switch ignition on and leave it for 30 seconds, the pump at the tank prebuilds the pressure in that time. Then the cold start is ok, no long cranking before it starts up.
I have read some old thread in this forum, that problem with the downshift and long cranking are related. Possibly cause of the fuel pressure is not maintained properly?
Any advises are appreciated.
Thread Starter
Member
Joined: Sep 2017
Posts: 173
Likes: 25
From: UK
Mercedes R320L CDI 4MATIC 2007
I did not include ML model, cause my car is nor ML, it is R class, but the engine and the gearbox is shared units. I am expecting the users of ML mercs possibly faced similar problems and could advise me what could be the reason?
My merc is R320 CDI, OM642, gear box 722.9, year 2007.
Sorry to post my thread in the ML section, i hope to have more chances to receive an answer to my problem.
Best regards,
V.R.
My merc is R320 CDI, OM642, gear box 722.9, year 2007.
Sorry to post my thread in the ML section, i hope to have more chances to receive an answer to my problem.
Best regards,
V.R.
Thread Starter
Member
Joined: Sep 2017
Posts: 173
Likes: 25
From: UK
Mercedes R320L CDI 4MATIC 2007
On my car filter there is no threaded connection. I did replace the filter, thought it could be clogged. It did not make any difference. So that can be excluded.
Thank you for your post and the attachment. Appreciated.
In addition to my post at the top i will add that the scan does not give any errors, which does not help..
Thank you for your post and the attachment. Appreciated.
In addition to my post at the top i will add that the scan does not give any errors, which does not help..
Thread Starter
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Joined: Sep 2017
Posts: 173
Likes: 25
From: UK
Mercedes R320L CDI 4MATIC 2007
Some time ago, when that problem appeared, I did check the fuel pressure of the fuel low pressure line. When testing, with engine running idle, the pressure was building up up to 4.5 bar, which as computer said, was ok. If i remember right when i stop the engine, the pressure did go down quite quickly. Doesn't it have to be maintained at same or similar level?
If it is not maintaining the pressure and it should, will it be the pump at the fuel tank?
Thanks for your reply.
If it is not maintaining the pressure and it should, will it be the pump at the fuel tank?
Thanks for your reply.
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Thread Starter
Member
Joined: Sep 2017
Posts: 173
Likes: 25
From: UK
Mercedes R320L CDI 4MATIC 2007
so, i checked the high fuel pressure line pressure, when engine running idle, then when engine stops, how much it drops down.
I used the OBD bluetooth adapter which gets plugged into the port in the car, gives live data on the app on my phone. I would think it is reliable enough (unless the pressure sensor would be faulty?).
The logged data below for the high pressure line in the rail:
- when the engine is running idle - 284 bar
- when engine stopped - the pressure goes down from 284 bar to 6 bar in matter of seconds
- ignition switched on (the fuel pump in the fuel tank starts building the pressure in low pressure line for 30 seconds) - the pressure in the rail goes up to 11 bar
- ignition on, past these 30 seconds the pump stops building pressure - the pressure in the rail goes down to 6 bar again
I did not check the pressure when the car stays off for longer yet. Will do that tomorrow morning. I am guessing the rail loses pressure to barely anything (will see tomorrow morning), cause the engine is cranking for a good while till it starts. With the figures noted above the engine starts up ok.
To my understanding, the pressure in the rail should be maintained to certain level for the car to be started and till the pump builds the pressure in the low fuel line?
What keeps the pressure in the high pressure line? Fuel pump itself? Pressure control valve (Y74)? Quantity control valve (Y94)?
If that would be any of the injectors faulty, if the pressure drops that quick, the car would be smoking? But when the car starts up, there is no smoke.
I used the OBD bluetooth adapter which gets plugged into the port in the car, gives live data on the app on my phone. I would think it is reliable enough (unless the pressure sensor would be faulty?).
The logged data below for the high pressure line in the rail:
- when the engine is running idle - 284 bar
- when engine stopped - the pressure goes down from 284 bar to 6 bar in matter of seconds
- ignition switched on (the fuel pump in the fuel tank starts building the pressure in low pressure line for 30 seconds) - the pressure in the rail goes up to 11 bar
- ignition on, past these 30 seconds the pump stops building pressure - the pressure in the rail goes down to 6 bar again
I did not check the pressure when the car stays off for longer yet. Will do that tomorrow morning. I am guessing the rail loses pressure to barely anything (will see tomorrow morning), cause the engine is cranking for a good while till it starts. With the figures noted above the engine starts up ok.
To my understanding, the pressure in the rail should be maintained to certain level for the car to be started and till the pump builds the pressure in the low fuel line?
What keeps the pressure in the high pressure line? Fuel pump itself? Pressure control valve (Y74)? Quantity control valve (Y94)?
If that would be any of the injectors faulty, if the pressure drops that quick, the car would be smoking? But when the car starts up, there is no smoke.
Last edited by virgisr; May 27, 2019 at 05:13 AM.
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2002 ML 320 & 2006 ML500
If the fuel pressure drops quickly after shutdown, then it is usually the fuel pump. If it drops at a slower pace, then usually it is the injector/s.
You make the call as I am not a diesel enthusiast.
You make the call as I am not a diesel enthusiast.
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From: UK
Mercedes R320L CDI 4MATIC 2007
Hi, thanks for your reply. I would think its the pump. i will keep digging, want to make sure first before replacing it.
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2010 GL350 BLUETEC, 2013 E350 Sport
Thread Starter
Member
Joined: Sep 2017
Posts: 173
Likes: 25
From: UK
Mercedes R320L CDI 4MATIC 2007
nope. The problem is still there. Replaced the pump, no change. Replaced LH rail with pressure regulator, no change. The injector leak off test showed me two of them are up to 3 times over than the rest of the injectors. There is a plan to replace these. But still did not get to that. Some time this year probably..
