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99 E430, 01 E430 Sport, 00 SL500
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3,266 Posts
Discussion Starter #1 (Edited)
Lately, my car (130K miles) developed the problem with cranking. The cranking got longer and longer before it started. On one short trip to get some fast food, it could not start so I had to leave it there, came back a few hours later then it started on the first crank. Sounds like CPS symptom that some members described?
To buy a new CPS, I had to know either the engine serial number or the plug (1 locking tab or 2 locking tabs). I located where the CPS was, fished a camera in there to take a snap shot, pulled out the plug to make sure, it was 1-tab plug, plugged it back in. Didn't have the right torx socket so the work got to wait. I did not order the new CPS yet.
Today, I started the cars several times, the cranking was gone. I also did 2 long test drives with the old CPS in it. The car started fine every time.
I think the heat might have caused problem to the plug, not the CPS because my car's cranking-starting symptom disappeared after I pulled the plug then plugged it back. Moreover, the CPS is described as magnetic inductor. It either works or does not work. It can't be heat related to be intermittent. The crank shaft got magnetic pins on it, inside the CPS is probably just a coil that produces inductance when the crank shaft turns. If the coil breaks, the car can never start.
What do you think?
 

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Premium Member
1998 E320 sedan
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450 Posts
Hi Mebvis, here is a quick link with a basic description:
a couple of things could of happened you may have made a better contact removing and replacing the connector (plug) which suggest you should take the opportunity to remove it again and use contact cleaner I use a touch of silicone spray on the connectors to keep the seal conditioned! If you were to remove the cps then check the end for rust I just came across one that had a fine layer of rust which likely adds to resistance wouldn't heart to pray it with cleaner and a wipe.
Patch's
 

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99 E430, 01 E430 Sport, 00 SL500
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3,266 Posts
Discussion Starter #3
>>you may have made a better contact removing and replacing the connector (plug)

If anyone thinks his car's CPS needs to change, try unplugging the plug then plug it back in (Unplug: Squeeze the top of the locking tab then pull) (Plug: Push the plug in, the locking tab will click in place).
I'm really curious to know if the working CPS has been wrongly replaced. It might just be the unplug/plug action that helped fix the bad contact that caused cranking problem.
I'm going to do another short test drive to the same fast food joint to see if I'll be stranded.
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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7,035 Posts
1) Never use silicone spray at/around the engine compartment

2) Some have cleaned the sensor with MAF cleaner, but no reports on long term success

2) At mileage at/over 100K best to replace the CPS with any suspicion based on warm engne CPS symptoms, replace with the OE Bosch only and avoid the frustrating nightmares from retail auto parts store no name China replacement CPS. Single clip Bosch OE about $45 in aftermarket but make sure you are ordering the Bosch, and not the China sensor.

Keep the beat !
 

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99 E430, 01 E430 Sport, 00 SL500
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3,266 Posts
Discussion Starter #5
I've just gone on the same route, stopped, bought some food, engine started fine, got home. So today, engine started many times without the cranking problem.
But one car can't be enough to prove the plug/unplug fix...
 

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1999 E300 TD
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2,045 Posts
The CPS is just one part in a large system of parts that aids in successfully starting and providing even engine running.

Just because the car is hard starting does not immediately mean that the CPS is faulty.

The CPS voltage pulse is monitored constantly by the engine control module and for the CPS to fault the pulse to pulse that is generated,at a given RPM, must not change by a defined amount. If there is a time difference your check engine light will come on-Did yours come on????

I say this because if your CEL did not fault a CPS then your question is almost impossible to answer correctly with out placing a scope on your car to determine and validating the quality of the CPS pulse .

My answer is that a hard starting engine question can't be solved by---------
 

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E320/E250 Bluetec Ford F350 6.7l
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36,038 Posts
I had lot of experience that quite often it is the connection that is bad, not the sensor itself. Than mechanics always replace sensors to start with and the owners will newer know.
I had fuel temperature sensor light twice in last 3 years. Still have the original senor, just cleaned the plug.
Than on ML55 the CPS was easier to replace via wheel well.
Than magnetic inductor do malfunction before final failure. I had one in my Ford. The Vehicle Speed Sensor was acting for 5000 miles before I replaced it.
 

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Premium Member
1998 E320 sedan
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450 Posts
"1) Never use silicone spray at/around the engine compartment"
OK fabbrist1 I'll bite, why
Patch's
 

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Premium Member
1998 E320 sedan
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450 Posts
A scope is nice but not the only way to check, there is a measurable low voltage when cranking, there should be pulse at coils seen with a time light or circuit tracer and if the contacts are corroded then that can add resistance and lower the potential to trip a slow start or the ecm not reading the correct voltage. Of course there are many other possibilities that can cause poor starting or failure to start.
Patch's
 

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2000 E320 Sedan, 2002 E430 Sedan
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84 Posts
It might be the plug!

Based on my recent experience, I would like to suggest that it may be very worthwhile to investigate into the CPS plug before doing a full-on CPS replacement. I would suggest pulling the plug and spraying it down with electrical contact cleaner. Then, most importantly, with a sharp tipped tool (set of tweezers or very skinny needle nose pliers), gently crimp down each the 2 female connector terminals that are inside the plastic housing of the plug. The idea is that the plug will now give a cleaner contact and tighter grab onto the prongs of the CPS.

My recent toils with a starting problem and the CPS are documented here: http://www.benzworld.org/forums/w210-e-class/1920673-chalk-up-another-one-cps-3.html#post9964521, and a happy ending was finally achieved precisely by what I've suggested above. I, too, now wonder how many CPS units have been wrongly accused.
 
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