Car cranks but won't start
Thread Starter
Member
Joined: Jun 2018
Posts: 249
Likes: 44
From: San Antonio, TX
2005 C55 AMG
Car cranks but won't start
So I drove my car to work today and it ran fine with no issues (60 miles each way), but when I got in it to get lunch it started right up as usual, then sputtered and died. It now cranks over but will not start.
I don't believe it is a CPS since it happened when the car was cold. My first guess was bad fuel and/or a clogged fuel filter (car has a little under a half tank), but then when I plugged in my MB 2.0 scanner, it won't communicate with the ECU or TCU but will scan everything else in the car. Tried my Bluetooth obd scanner and it won't connect at all.
Ideas?
I don't believe it is a CPS since it happened when the car was cold. My first guess was bad fuel and/or a clogged fuel filter (car has a little under a half tank), but then when I plugged in my MB 2.0 scanner, it won't communicate with the ECU or TCU but will scan everything else in the car. Tried my Bluetooth obd scanner and it won't connect at all.
Ideas?
Member
Joined: May 2013
Posts: 109
Likes: 31
C32x2 RIP, 2005 C55, 2020 GLB 250, 2014 E550
Does the car start intermittently? If you disconnect the battery and re-connect, does it start? Is the fuel pump engaging? How many miles do you have on your car? I recently replaced my fuel filter as preventative maintenance at 185K.
Thread Starter
Member
Joined: Jun 2018
Posts: 249
Likes: 44
From: San Antonio, TX
2005 C55 AMG
No. It only started that one time. It only cranks now. At least it's home now after a $165 tow bill...
I disconnected the battery, after which it let me scan the ECU and TCU, but of course any codes that might've been there were gone.
I don't hear the fuel pump running and the Schrader valve on the fuel rail didn't squirt any fuel when pressed with the ignition on. The fuel pump fuse is at least visually good, so evidence points to the fuel pump.
I'll go through the electrical system and check the CPS, MAF, and fuel filter anyway just to be thorough (mostly because I don't want to do the fuel pump, still hoping it's something else...). Currently at 161k mi.
I disconnected the battery, after which it let me scan the ECU and TCU, but of course any codes that might've been there were gone.
I don't hear the fuel pump running and the Schrader valve on the fuel rail didn't squirt any fuel when pressed with the ignition on. The fuel pump fuse is at least visually good, so evidence points to the fuel pump.
I'll go through the electrical system and check the CPS, MAF, and fuel filter anyway just to be thorough (mostly because I don't want to do the fuel pump, still hoping it's something else...). Currently at 161k mi.
Senior Member
Joined: May 2007
Posts: 457
Likes: 61
asdas
I believe the fuel filter is integrated into the fuel sender, and removal requires removal of the fuel pump anyway (both under the rear seat). At 161k miles I'd just replace both while you're in there.
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Senior Member
Joined: May 2007
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asdas
The fuel sending unit is a separate part from the pump. If yours is the original from 2005, the replacement will be an updated part that will require a wiring plug adapter. Don't forget the cap seals too. Make sure you buy the right fsu and fuel pump. Some online websites will list the "lesser" W203 parts as fitting the C55, so you've got to double check.
https://mbworld.org/forums/c32-amg-c...fill-up-2.html
A bigger PITA than doing an external canister filter, but if your fsu, filter, and pump are all original and have 161k miles on them, you are well past due anyhow.
https://mbworld.org/forums/c32-amg-c...fill-up-2.html
A bigger PITA than doing an external canister filter, but if your fsu, filter, and pump are all original and have 161k miles on them, you are well past due anyhow.
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Senior Member
Joined: May 2007
Posts: 457
Likes: 61
asdas
This video is of a 2007 C230. I guess at some point Mercedes switched all W203's over to the in tank FSU/filter unit. Small details may be different from the C55, but this video gives you and an idea of the kind of job you're looking at if you DIY.
Last edited by brauhaus313; Dec 7, 2021 at 07:53 PM.
Newbie
Joined: Nov 2019
Posts: 8
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2005 C55
And by the way, it is in the fuel tank, and the filter is integrated like others have mentioned. A2094700494 and A2094700594 are the part numbers for the pump and sending unit modules. They are on AutohausAZ and a couple other sites.
Senior Member
Joined: Mar 2011
Posts: 324
Likes: 2
From: Bella Vista, AR
05 C55 AMG
Question. I did the fuel sending unit already and had to use a modified harness to get the newer part to hookup to my wiring harness in the vehicle. I want to do the fuel pump now, do you know if this will also require a special harness or do I just buy the fuel pump, A2094700594?
Thread Starter
Member
Joined: Jun 2018
Posts: 249
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From: San Antonio, TX
2005 C55 AMG
Well, after checking everything else (MAF sensor, cam position sensor, etc) before committing to spending nearly $500 on a new fuel pump and sender, I had to admit defeat and bite the bullet. So, new fuel pump and sender are in (not as bad a job as I anticipated), car fired right up and runs great. That being said:
Now my fuel gauge doesn't work. Floated around a half tank for a while until I filled it with 14.3 gallons, then settled down to reading empty (no light on though).
I checked resistance on pins 1-3 and pins 1-4 and they read 155 and 350 ohms respectively (consistent with a nearly full tank and checked against old pump sender assemblies). Edit: The full range of both the original senders is about 50 Ohms (full) to 1k Ohm (empty). The actual pump is on the same connector and there are no problems there. I suspected maybe my car's connector had an issue with the sender common (pin 1), but it reads fairly high resistance (in the kilohm range) as expected. There is no mention of a fuse or SAM control over the fuel sender. Ideas?
Quickvr4: No, you only need the adapter harness for the LH sender unit. It is for the tank pressure sensor. The bigger connector is for both the senders and the pump.
Now my fuel gauge doesn't work. Floated around a half tank for a while until I filled it with 14.3 gallons, then settled down to reading empty (no light on though).
I checked resistance on pins 1-3 and pins 1-4 and they read 155 and 350 ohms respectively (consistent with a nearly full tank and checked against old pump sender assemblies). Edit: The full range of both the original senders is about 50 Ohms (full) to 1k Ohm (empty). The actual pump is on the same connector and there are no problems there. I suspected maybe my car's connector had an issue with the sender common (pin 1), but it reads fairly high resistance (in the kilohm range) as expected. There is no mention of a fuse or SAM control over the fuel sender. Ideas?
Quickvr4: No, you only need the adapter harness for the LH sender unit. It is for the tank pressure sensor. The bigger connector is for both the senders and the pump.
Last edited by Spooky55; Jan 29, 2022 at 11:13 PM.
Thread Starter
Member
Joined: Jun 2018
Posts: 249
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From: San Antonio, TX
2005 C55 AMG
Just an update: fuel gauge issue solved. Totally my bad - the driver's side sender unit's float looked like it might get hung up on the hoses that cross between the two tanks, so I clocked it about 30 degrees away from the hoses, unwittingly pinning the float against the front of the tank. I loosened the retaining ring and straightened it out. Problem solved. Crappy thing is that I had everything out of the tank at least 3 times and kept repeating the same mistake. The gauge reading totally empty was an error condition that was cleared with my scan tool that actually detected the stuck float. I guess the moral of the story is don't second guess Mercedes engineers...
Just for general info, (in case anyone is interested) it looks like the sender unit on the driver's side is a simple siphon pump. It will nearly completely empty that side while keeping the passenger side with the actual pump full. The two floats are simple variable resistors that range from 55 ohms in the "full" position to about 950 ohms in the "empty" position. They are wired independently but with a common ground. The rear SAM than sums them together and runs them through an analog to digital converter with a combined full range of 100 ohms empty to 1900 ohms full. If you measure them at the connector, pin 1 is common and pins 3 and 4 are the two sides. Pins 2 and 5 are the fuel pump power. The drivers side tank will always read lower because of the way the siphon pump is designed, but since the computer adds them together, any slosh from one side to the other is negated at the gauge.
Just for general info, (in case anyone is interested) it looks like the sender unit on the driver's side is a simple siphon pump. It will nearly completely empty that side while keeping the passenger side with the actual pump full. The two floats are simple variable resistors that range from 55 ohms in the "full" position to about 950 ohms in the "empty" position. They are wired independently but with a common ground. The rear SAM than sums them together and runs them through an analog to digital converter with a combined full range of 100 ohms empty to 1900 ohms full. If you measure them at the connector, pin 1 is common and pins 3 and 4 are the two sides. Pins 2 and 5 are the fuel pump power. The drivers side tank will always read lower because of the way the siphon pump is designed, but since the computer adds them together, any slosh from one side to the other is negated at the gauge.
Last edited by Spooky55; Feb 22, 2022 at 02:44 AM.
