S320 kickdown leads to CEL, intermittent rough idle
Thread Starter
Newbie
Joined: May 2022
Posts: 13
Likes: 2
C209 CLK 200
S320 kickdown leads to CEL, intermittent rough idle
Hello,
I have a facelift w220 s320. The car sometimes runs a little rough on idle (happens intermittently e.g. at stop lights) and especially on some cold starts, the car shakes like a lada diesel truck. When my foot is on the gas, cruising, the car is absolutely butter smooth.
Every time I kickdown (say we are in gear 5 cruising and I suddenly need to overtake), the car abruptly downshifts, cel comes on, starts shaking like crazy and I need to turn it off and on again to continue driving. If I gently apply throttle so that the car downshifts one gear at a time, this doesn't happen. Also the car doesn't have any problem revving out to it's redline as long as a downshift isn't involved.
For reference, the car has been converted to LPG a few months now. The car was previously misfiring due to a faulty cable in the fusebox which has been replaced. I have a feeling this issue is again due to the poor LPG installation or some kind of short in the fusebox.
Any ideas? I will also buy an OBD scanner so I can read the codes next time a CEL comes on.
I have a facelift w220 s320. The car sometimes runs a little rough on idle (happens intermittently e.g. at stop lights) and especially on some cold starts, the car shakes like a lada diesel truck. When my foot is on the gas, cruising, the car is absolutely butter smooth.
Every time I kickdown (say we are in gear 5 cruising and I suddenly need to overtake), the car abruptly downshifts, cel comes on, starts shaking like crazy and I need to turn it off and on again to continue driving. If I gently apply throttle so that the car downshifts one gear at a time, this doesn't happen. Also the car doesn't have any problem revving out to it's redline as long as a downshift isn't involved.
For reference, the car has been converted to LPG a few months now. The car was previously misfiring due to a faulty cable in the fusebox which has been replaced. I have a feeling this issue is again due to the poor LPG installation or some kind of short in the fusebox.
Any ideas? I will also buy an OBD scanner so I can read the codes next time a CEL comes on.
Super Member
Joined: May 2021
Posts: 554
Likes: 150
From: Netherlands
CL 600 '00 5.8L V12
A kickdown instructs the ECU to open the injectors@100%. Whenever there isn't enough pressure in the fuel rails, your car will misfire due to a sudden drop in fuel rail pressure, be it LPG, be it gas.
Whenever you gently increase the throttle input, the fuel rail pressure has time to 'restore' and won't suddenly drop down big time.
How is the LPG installation installed? Before or after the fuel pump and filter?
Whenever you gently increase the throttle input, the fuel rail pressure has time to 'restore' and won't suddenly drop down big time.
How is the LPG installation installed? Before or after the fuel pump and filter?
Super Member
Joined: May 2021
Posts: 554
Likes: 150
From: Netherlands
CL 600 '00 5.8L V12
Check the fuel pressure. Does the car take longer to start than it usually did?
(I don't have any knowledge about LPG systems, just thinking out loud here)
I think that there should be a check-valve between the LPG and fuel rail, otherwise fuel might be forced into the system if the LPG pressure is low enough.
(I don't have any knowledge about LPG systems, just thinking out loud here)
I think that there should be a check-valve between the LPG and fuel rail, otherwise fuel might be forced into the system if the LPG pressure is low enough.
Thread Starter
Newbie
Joined: May 2022
Posts: 13
Likes: 2
C209 CLK 200
The car does indeed take longer to start than before. Would the low fuel pressure explain the rough idle and cold starts? I am in the process of finding out the exact LPG system the car has (I know it's a "dual" injection system, it injects both LPG and regular gas). This issue is giving me a massive headache and these fools that installed it (supposedly reputable...) have no idea what the hell they have caused.
Super Member
Joined: May 2021
Posts: 554
Likes: 150
From: Netherlands
CL 600 '00 5.8L V12
Super Member
Joined: May 2021
Posts: 554
Likes: 150
From: Netherlands
CL 600 '00 5.8L V12
If you leave the LPG tank empty, the system should just be disabled right?
I would do that first actually, then you can get the car running like it should. After that you can add LPG back into the mix
I would do that first actually, then you can get the car running like it should. After that you can add LPG back into the mix
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Thread Starter
Newbie
Joined: May 2022
Posts: 13
Likes: 2
C209 CLK 200
Car has fuel pump issues currently and is still misfiring without CEL. Idle shaking issue is somewhat fixed through ECU tune (raised fuel pressure at idle). Thanks for the help Mr. Tim and I will come back with further updates when I have the time.
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