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Mercedes-Benz engine repair questions and answers

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  • joanne.bermudez
    joanne.bermudez - 2007 Mercedes Benz C230 - Engine - 9/25/2013
    Check engine light on
    intake manifold gasket was just changed a week ago
    • Jimm
      9/25/2013 Jimm
      The check engine light is located on the dash and stays on if the computerized engine control system detects an engine performance or emissions problem.
      First step - have the stored fault codes or check engine light scanned - for free - at any local auto parts store; Advance Auto, Auto Zone, NAPA. Then, post a reply as 'add answer' with the specific code for more assistance. There may be a fault code stored in the OBD memory which may not be displayed as a check engine light
  • rmcelroy1
    rmcelroy1 - 2003 Mercedes Benz ML320 - Engine - 9/20/2013
    My car will not start right away. Turns over many times before it fires
    It happens more after sitting .
    0 answer
  • UCME48
    UCME48 - 2001 Mercedes Benz SLK320 - Engine - 9/14/2013
    Need to pin point the # 4 plug #5 pin in the ECM to correct a short
    Im having ny ecm rebuilt and he found that on the ecm the #4 plug #5 pin was the problem, I need help in pin pointing the wire and its use,,thanks, Don
    • HouseCallAuto
      9/13/2013 HouseCallAuto
      The #4 cylinder and #5 pin is a wire that runs from pin 5 of the engine control module to pin 3 of the ignition coil for the #4 cylinder. If this is what was failed within the ecm then replace the ignition coil for cylinder #4 and confirm that this blue white wire is not shorted to ground anywhere alomng the run form the ecm to the coil and if it is too difficult to follow the full length of the wire to see it then run a new wire and splice it a few inches away from the ecm and a few inches away from the coil. Done.
      9/13/2013 UCME48
      I didnt explainmyself very well, im speaking of the ECM #4 SOCKET and the #5 pin in the socket, ita a brown wire i think goes to the 02 sensors. Sorry about the confusion
    • HouseCallAuto
      9/14/2013 HouseCallAuto
      Ok I see a brown wire that runs from the #5 ecu pin and goes to both DOWNSTREAM O2 sensors. Probable cause of ecu failure is a shorted out O2 sensor heater. That means replace both rear O2 sensors and confirm that this brown wire is not shorted to any other wires. O2 sensor is the more likely cause.
      9/14/2013 UCME48
      Thanks so much for your help, I will change both and check before i get finished,, Thanks again,,,,,Don
  • UCME48
    UCME48 - 2001 Mercedes Benz SLK320 - Engine - 9/11/2013
    ECM plug 4 #5 pin what does it control
    Im having my ecm rebuilt and they found that the #4 plug #5 pin was the cause of my short, My Alldata diagram showes a different wire sequence then mine does..
    0 answer
  • jpuett
    jpuett - 1998 Mercedes Benz ML320 - Engine - 9/10/2013
    How to install combination switch assembly on vehicle
    do you have to remove steering wheel
    • bear.1216
      9/10/2013 bear.1216
      You have to remove steering wheel and disassemble steering column until you reach the switch.
  • UCME48
    UCME48 - 2001 Mercedes Benz SLK320 - Engine - 9/7/2013
    O2s sensor shorted ecm
    I sent my ECM in to be rebuilt and after looking it over he found that the O2s sensor on the left bank low side after the TWC was the cause of my short. any ideas on why this sensor could effect and distroy my ECM, I did find that it had some oil on it >>
    • Jimm
      9/7/2013 Jimm
      The ECM monitors / looks for a signal from the O2 sensors of a certain milliamp (mA) and voltage range (variation) during the O2 sensor normal operation. The O2 sensor produces a voltage based on oxygen content in the exhaust. The voltage varies between 0.1 and 0.9 Volts, with 0.1 indicating lean and 0.9 indicating rich. The ECM constantly monitors this voltage while in closed loop to determine how much fuel to inject. If the ECM determines that the O2 sensor voltage was too low (less than 0.4 Volts) for too long (for more than 20 seconds (time varies with model)), then a fault code is set in the OBD (On-board diagnostic) system.
      If there is a short in the O2 sensor or the sensor wiring, then the ECM will simply have an out-of-range signal and will not be able to monitor. It is unlikely the O2 sensor has directly caused the ECM malfunction or failure.

      Today’s sensors are quite sophisticated and rarely require replacement unless they are brought outside of their operating window due to engine malfunction or contamination. On OBD II equipped vehicles, the ECM monitors 02 sensor voltages and triggers a check engine light if the voltages fall outside a predetermined value. A bad sensor is reasonably easy to diagnose with a common scan tool. The voltage of the front sensor should fluctuate rapidly from approximately 200-800 millivolts, if it does not or does it slowly, chances are the sensor is bad. However, it is very difficult to detect a functional but degraded oxygen sensor. They do however, even during perfect operating conditions, degrade over time due to the depletion of the platinum electrodes inside the sensor.
      As they degrade, the output voltage is reduced and as the output voltage is reduced, the ECM compensates from what it reads as a lean A/F ratio, compensating by adding more fuel. An increase in fuel consumption not remedied by a tune up often points to an oxygen sensor that has deteriorated.
  • cannalside
    cannalside - 1983 Mercedes Benz 380SL - Engine - 9/6/2013
    Engine missing, blows carbon out of tailpipe and fouls all plugs with carbon
    could not find vacuum problem replaced o2 sensor 1 year ago, could this cause problem? using bosch wr9dp plug, should I replace with hotter plug? appreciate all help.
    • bear.1216
      9/6/2013 bear.1216
      Sounds like engine is running to rich engine is getting to much fuel. You should do fuel pressure test may have high pressure or leaks. Common causes are faulty EGR valve bad fuel pressure regulator spark plug misfires leaking injectors leaky canister purge valve. A restricted exhaust system would also cause your symptoms like bad catalytic converter. A bad oxygen sensor could cause this but any underlying problem would cause the o2 sensor to read rich.
      9/6/2013 bear.1216
      If plugs are wet with raw fuel suspect fuel or ignition problem. If covered with dry black carbon suspect exhaust emmisions problem.
  • karl
    karl - 1995 Mercedes Benz E320 - Engine - 9/4/2013
    Car wont turn over and I now hear tone by e-brake
    started car a tone started going off some where near the e-brake so I turned off to restart turn key on tone started again but car now does not turn over why
    0 answer
  • fcowlin
    fcowlin - 2008 Mercedes Benz CLK550 - Engine - 9/2/2013
    When I start the car and the air is in the on position the engine races. If the air is off no problem. Why?
    The car has 48000 kms and this problem just started. No warranty. It happens no matter if the engine is warm or cold. It happens frequently but not all the time. It started last year. The engine light is not on. No other lights on. I must turn the car off to ...
    • wbrockstar
      8/27/2013 wbrockstar
      The engine is supposed to idle up a few hundred rpm,s to compensate for the added load of the ac,but it shouldnt be racing.Your IAC valve either needs to be removed and thoroughly cleaned or replaced.
    • ESASLLC2006
      9/2/2013 ESASLLC2006
      It is difficult to diagnose a problem sight unseen but I will give it a try. It is possible that the throttle plate has a lot of build up around it. This car has the M273 V8 and does not use an IAC motor/solenoid, but a throttle actuator that uses the throttle plate to adjust idle. I have seen them with so much gunk that the engine will not start because it basically suffocates the engine. The idle should increase slightly but come back down to normal idle and it may be getting stuck. I hope this helps.
  • mkatzpa
    mkatzpa - 1997 Mercedes Benz E320 - Engine - 8/28/2013
    Starting car issue: The car ALWAYS starts immediately when cold, but needs 3-5 x's if sits for 20+ minutes...
    This has been occurring for no less than a year and the Mercedes dealership cold not diagnose problem; finally, they determined it was the "crankshaft position sensor"...After replacing it with the wrong sensor, then having difficulty removing the wrong one and ...
    • wbrockstar
      8/28/2013 wbrockstar
      Does the starter drag at all when its taking you 4-5 times to start car??Or does the starter turn over fine but the engine just wont start until the 4th or 5th time??I had a similiar thing happen to my mustang .It started fine when cold but after the engine would warm up and I turned the car off,it would drag and wouldnt start until after the 5th or 6th time.It turned out bein a spot (on the cable that runs from the starter relay down to the starter)about 6inches long where the insulation had been completely worn down to the bare wire-caused because the cable was rubbin against bottom of oil pan.This situation basically caused a short in the starting and electrical circuit.Check for any bare,corroded,and loose wiring or harnesses.It wouldnt hurt to purchase some electrical cleaner and qtips,unplug and clean any and all harnesses under the hood.Check grounds really good to.Computer controlled cars are notorious for having problems arise from bad grounds and dirty connections so check em good.It also sounds like engine heat is directly responsible for whatever part is defective since
      it starts just fine when the engine is cold.I would look at the sensors that only work when car reaches operating temperature or its possible that a sensor that mainly only works when engines cold and then shuts off when car reaches oper temp,may be continuing to run and adversely affect engine instead of cutting off like its suppose to do.
  • johnchar393
    johnchar393 - 1984 Mercedes Benz 300TD - Engine - 8/27/2013
    Where on the engine do I install the block heater for this car?
    heater mercedes benz part no is Q6200009
  • don.spears
    don.spears - 1988 Mercedes Benz 560SL - Engine - 8/14/2013
    Cold idling black gas smoke out tailpipe, black smoke reduces when engine warms
    Revving when engine will produce a little black smoke. What is the mechanism that increases gas for cold starts then reduces for warm run? On old carb cars it was an automatic choke. This car has fuel injection.
    • wbrockstar
      8/14/2013 wbrockstar
      On your model of car,the only two sensors that have that job are
      1) O2 - Oxygen sensor
      2) ECT - Engine Coolant Temperature sensor
  • UCME48
    UCME48 - 2001 Mercedes Benz SLK320 - Engine - 8/13/2013
    What woud cause a ECU to fry and smoke
    I pulled in a driveway and hit a bump and the car went into limp mode, i shut it off and then tryed to start it , it started one and never started again, it smoked the ECU computer.
    • wbrockstar
      8/13/2013 wbrockstar
      Theyre designed to take a lil bit of vibration and bumps so thats odd.Something inside the ecu couldve jarred loose.The wiring harness
      to ecu might have a bare wire that shorted on metal when you hit bump.There are a few resistors inside ecu that have been known to burn up rite where they meet circuit board.Moisture couldve been in the near by viscinity,bump could have jarred the case loose enough for moisture to seep in.Too much voltage couldve also burnt it up as in a sudden unexpected surge of voltage.The ecu works off of very small voltages( 5v) and if any circuit on the car shorted to/through ecu,it would fry because everything not related to the ecu on the car works on ( 12 volts)....You cant pass 12v through a 5v circuit
      8/14/2013 UCME48
      I think u ht it with the surge. would a short do it also? what would be the best way to track t down if there is any,,?? thanks for your help i really apperiate it.
    • HouseCallAuto
      8/13/2013 HouseCallAuto
      Is the area the computer is in look like there is or has had water intrusion?
  • micheleadibe
    micheleadibe - 1992 Mercedes Benz 300SE - Engine - 7/31/2013
    Why is my car over heating
    after 4 miles it over heats, it started two days ago
    • wbrockstar
      7/31/2013 wbrockstar
      Low coolant in system,thermostat stuck in closed position(a good test to check is,turn heater on when engine starts to overheat,if its blowin only luke warm instead of hot,thermostats stuck-replace) Malfunction in cooling fans.Radiator could be clogged.Faulty water pump.Faulty radiator cap failing to maintain proper pressure on cooling system
  • wendald clark
    wendald clark - 1997 Mercedes Benz SL320 - Engine - 7/30/2013
    Engine starts then shuts off emediatly
    Turns over then dies
    • frankiedonnn
      7/30/2013 frankiedonnn
      If it stalls as soon as you take your hand off the key sort of thing check the ballast resistor.Also check intake manifold for leaks, insufficient fuel flow check fuel pressire and fuel filter : if the fuel filter is not in the tank it maybe easy to do this yourself .No point in dropping the tank unless you are sure of the diagnosis.