C240 difficult to start when hot
Thread Starter
Senior Member
Joined: Mar 2003
Posts: 448
Likes: 4
From: San Antonio, TX
'11 SL550 - '08 ML350
C240 difficult to start when hot
Hopefully someone can shed some light on this. The car starts fine in the morning. When I get off work and the car has baked in 100 degree heat all day, it won't start unless I turn the key to the on position for 20-30 seconds, then crank it.
I had an issue with it taking longer than normal to start (5-6 seconds versus 2-3) a few months back. I removed and cleand the MAF and it was back to instant starts.
Could this be a fuel filter issue?
I had an issue with it taking longer than normal to start (5-6 seconds versus 2-3) a few months back. I removed and cleand the MAF and it was back to instant starts.
Could this be a fuel filter issue?
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Joined: Mar 2007
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From: VA
THE C350
Fuel Filter could be possilbe or a fuel issue in general. It could take the fuel pump longer to get the fuel preasure up to where it needs to be. No CEL right? if not I would check fuel preasure at startup
Thread Starter
Senior Member
Joined: Mar 2003
Posts: 448
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From: San Antonio, TX
'11 SL550 - '08 ML350
Super Moderator
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
Check fuel pressure at the Schrader valve on the fuel rail connecting the injectors. s/b > 3.8 bar or 55 psi while cranking.
Good luck!
Good luck!
Super Member
Joined: Mar 2007
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From: Phoenix, AZ, USA
2005 C240 4MATIC, 2020 GLC300 4MATIC
I'm calling CPS on this too. Those were the symptoms that led to mine finally failing on me.
Eventually it won't matter how cool the engine is, it will fail and it won't crank over.
Eventually it won't matter how cool the engine is, it will fail and it won't crank over.
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Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
It could well be CPS.
Need air, fuel & spark at the right time to start & run.
Fuel pressure is a quick check to eliminate or confirm that.
Need air, fuel & spark at the right time to start & run.
Fuel pressure is a quick check to eliminate or confirm that.
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Thread Starter
Senior Member
Joined: Mar 2003
Posts: 448
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From: San Antonio, TX
'11 SL550 - '08 ML350
Changed the fuel filter on Labor Day and no more issue starting. I do now hear the whir of the fuel pump for 2-3 seconds when I turn the key on but not once the car starts.
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Thread Starter
Senior Member
Joined: Mar 2003
Posts: 448
Likes: 4
From: San Antonio, TX
'11 SL550 - '08 ML350
Things worked fine for a couple of months but cranking is difficult again. I changed the crankshaft position sensor and cleaned the MAF again. Still it is hard to start. I have to turn the key to the on position and wait literally a minute or two before trying to start. This may take up to 4 times to start.
What might need the key to be on for a long time? Could the fuel filter be clogging again (possible fuel contamination), the fuel pump is going out, the MAF is going out? Any suggestions?
What might need the key to be on for a long time? Could the fuel filter be clogging again (possible fuel contamination), the fuel pump is going out, the MAF is going out? Any suggestions?
Super Member
Joined: May 2009
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From: Toronto, Ontario, Canada, eh!
2003 C230 Sports Coupe, Paprika Metallic Red, Auto, Pano, Leather
Did you recalibrate the CPS? My understanding is that the car can do the recalibration itself without STAR,... with the car in PARK, rev slowly up to 2500RPM in 2 minute (idle is 700RPM, so you're adding about 150RPM every 10 seconds,... very slowly!),.... then hold the rev at 2500RPM for 30 seconds; then drive,.... that should recalibrate the CPS. If you had NO cps faults prior to change then no recalibration needed.
What`s your mileage,....
Did you change fuse 52 from 15A to 20A,.....
What voltages are you getting in dyno mode,.... before start, at start, at idle and at 2000RPM,...
What`s your mileage,....
Did you change fuse 52 from 15A to 20A,.....
What voltages are you getting in dyno mode,.... before start, at start, at idle and at 2000RPM,...
Thread Starter
Senior Member
Joined: Mar 2003
Posts: 448
Likes: 4
From: San Antonio, TX
'11 SL550 - '08 ML350
Did you recalibrate the CPS? My understanding is that the car can do the recalibration itself without STAR,... with the car in PARK, rev slowly up to 2500RPM in 2 minute (idle is 700RPM, so you're adding about 150RPM every 10 seconds,... very slowly!),.... then hold the rev at 2500RPM for 30 seconds; then drive,.... that should recalibrate the CPS. If you had NO cps faults prior to change then no recalibration needed.
What`s your mileage,....
Did you change fuse 52 from 15A to 20A,.....
What voltages are you getting in dyno mode,.... before start, at start, at idle and at 2000RPM,...
What`s your mileage,....
Did you change fuse 52 from 15A to 20A,.....
What voltages are you getting in dyno mode,.... before start, at start, at idle and at 2000RPM,...
Mileage is around 135,000
What good would increasing the amperage on a fuse do? If a 15A doesn't blow, putting a 20A won't do anything. Am I missing something here?
I haven't checked any voltages.
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Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
The start enable fuse 52 is underated. Benz put out a bulletin to increase to 20 amp. It's in the Wiki. Fuse is not your problem. The car would not crank if 52 was blown.
