KillerPancake

Got a new one here, that I'm hoping the MBWorld may be able to help me narrow down before spending a ton of time on it. Have done zero diagnostics to this point since the issue really just started yesterday.

2005 coupe, manual trans, M271.

Go to start the car. Clutch in, turn key, get a few solid cranks then the starter stops turning over. Re-attempt and get the same thing, or no cranks at all. Re-attempt n times again and eventually get enough cranks for the engine to catch. This happened yesterday and it took QUITE a few tries - thought I might be calling for the hook but eventually it started up.

I think the battery can be ruled out at this point. No problems with accessories and no dimming of dash lights any time during the process. No other indicators whatsoever of a bad battery. When this happens it really reminds me of the odd time where I go to start the car and maybe let the clutch leg get a little lazy and the interlock kicks in and disengages the starter. Except in this case, I do have the clutch in firmly.

I'm thinking interlock, ignition switch or starter solenoid. Any other ideas? Anyone been down this road before?

Glyn M Ruck

Start by checking the starter relay in the front SAM. Interlock could be out of adjustment. Check for stored codes with an OBDII scanner.

https://mbworld.org/forums/attachmen...ompartment.pdf

KillerPancake

Thanks Glynn for the fast and great info!

The relay functions don't seem to be listed on this PDF description (although I could be overlooking that!). Do you know offhand which is the starter? I just finished checking them and most relays were seated OK but found "S" to be a bit loose and "R" was a bit looser. I pressed both in, and was able to start the car without issue, 3-4 times in a row. I'm very much hoping one of those is the starter relay!

Glyn M Ruck

S is the starter relay

KillerPancake

Well, no joy unfortunately. The problem continues. I even tried swapping relay S with the same type from another socket but that didn't help, so I think I can rule out the relay.

I've done a bit more checking:
- clutch interlock switch position is fine - it gets fully depressed, have not checked actual continuity on the switch yet though
- pulled the stored codes and got P0128 (thermostat) and P0301 (cyl #1 misfire) - doubt that either of these are related to the issue.

I've noticed a couple of other things. In a case where I turn the key and initially the starter doesn't turn over, if I hold the key for a second or two the starter will eventually begin to rotate and the car starts up. Also, in a case where the starter rotates and then disengages by itself, I get a number of relays operating both in the engine compartment and rear SAM when the starter disengages. Given this far reaching and seemingly coordinated event, it would seem that the SAMs are making a conscious decision to disengage the starter and not allow the car to start by disengaging the other electronics connected to these relays (e.g fuel pump?).

I also did a bit more forum searching and came up with this:

The symptoms described by MBC320 earlier on in the thread were identical to what I am seeing. In my case though, I don't have the V6 and have no stored codes for the CPS. Does the above seem plausible in my case at all?

Glyn M Ruck

The codes you are getting have nothing to do with this issue. Change thermostat (128) & check plugs etc.

A CPS can cause all sorts of crap but I've never known it prevent cranking. Frequently does not give a code though.

I hope we are not heading for an EIS problem here because it's expensive.

These car have a crank 'till start feature. If you flick the key to start position and release immediately it should go on cranking. Does it?

The other issue could be the engagement solenoid on the starter motor itself. It first kicks in the bendix gear & then makes connection to the starter motor itself to rotate.

Check all connections & earth before pulling the starter motor.

Russell Ormerod

cps is very much part of starting and can very well be your cause.
when you turn the key to crank you only sending a request to start to the
engine ecu. the ecu is what energises the starter relay and it needs to get the info from cps regarding engine rpm to determine when to disengage the starter. So if engine ECU gets no crank position input within about 3 sec after start request, it will switch the relay off, no matter what u do with the key

samaritrey

I wonder if an old CPS could be why my car seems to start slower than it use to I have been meaning to order one since it is a common issue and I know mine is on borrowed time at least 80k miles on it.

Glyn M Ruck

Most CPS failures on this forum have not effected cranking - only starting. That is my experience in SA as well. Replaced one on a friends C240 a week back. It just cranked away as usual but did not start. New CPS & she fired up immediately.

At your mileage Trey I think your starter motor is heading for brushes & bushes & a commutator clean up. C230 Sport Coup had to do a rebuild earlier this year. You are at similar mileage IIRC.

samaritrey

Oh fun this is why I love cars always something to work on lol

LILBENZ230

Every once in a while, I'll turn my key and the starter won't engage at all. It has happened maybe 2 times in three years, so I don't think it's anything similar to your issue. All other times my car starts as fast and as normally as it always has even though the battery is the original and I have 116.6k on it.

samaritrey

My battery is not even one year old and I only replaced the old one because I fried it by leaving my radio on and lights while I was working on it 3 times in one week. The first two times the car barely started the third time it was dead as could be and I decided to call Mercedes road side to just replace it. But over the last year I have noticed that it does not start as fast as it use to but until something changes and either it starts failing to start or causes an issue I will just wait. Back to the OP keep us updated

Glyn M Ruck

Guys - Just so you understand the inductively energised key, handshake & start process.

KillerPancake

Glyn, this is some excellent info. This leads me to a question and an observation which perhaps could only be confirmed by the firmware guys in Germany who wrote the code for the control modules, but let's see:

1) If we look at the DAS function diagram, we have 4 steps. I'm definitely making it past 1-3, no problems there. Depending on what's entailed step 4, "start authorization" could this point to an issue with my smart key and the IR function? I had originally discounted any key issues, since the EIS was seemingly doing it's thing.

2) In the "Tip Start Activation" diagram, it would seem to confirm in the diagram and step 2, that the CKP could be part of the equation that decides whether the starter relay gets engaged or not. Alarmingly, the ECT may also be able to make a call on that, although I am having no issues with the temp gauge so hopefully that's OK. It could be debated as to whether or not it makes real sense that the feedback from these sensors would have an impact on the crank/no-crank decision (vs. allowing crank, but no start). However, implementation would just be lines of code. If Herr G. Daimler wanted it that way, he'd just have to tell the programmers, and they'd make it so.

Anyway, my schedule is not conducive to this problem, but hopefully I'll have some time before next weekend to check/try some things and report back. Thanks to all for the feedback so far!

Glyn M Ruck

The temp sensor (ECT) is interrogated to map appropriate mixture at start.
Hot - closed loop etc.
Cold - open loop mixture enrichment etc.

The CPS (CKP) sensor is interrogated to ensure that the engine is not running so that you cannot crank the bendix into the rotating ring gear as you can on many vehicles with resultant noise, mayhem & potential damage. Once cranking the CPS identifies TDC for the ECU.

KillerPancake

This makes perfect sense in both cases.

How many times have we heard someone mercilessly grinding their starter gear against an already spinning ringgear? Locking out that little misstep is a great feature, outweighing the possibility of the sensors involved failing and causing a no-crank at some point!

Glyn M Ruck

The trouble with CPS's in my experience is that they become erratic & intermittent in their operation which seems temperature related. I sometimes wish they would just fail completely. This erratic operation can be very misleading when diagnosing gremlins. They frequently don't throw codes when intermittent.

I have never experienced a CPS on a Benz that has caused a no crank situation (only crank & no start) but I'm not writing it off. It's Russell's day job to diagnose these things. There could well be situations where the CPS causes no crank on a Merc.

I think if I were in your shoes I would replace the damn thing. I don't like throwing parts at a problem without full diagnosis but it is cheaper in the NA to toss a CPS & get a known trouble giver out of the equation than it is to pay a dealer for Star time.

KillerPancake

Yup, agreed. I started down this path yesterday and got a CPS on order. When it arrives I'll get the car up and replace it, along with checking anything else that could be related. We'll see what happens. Knocking on wood in the meantime and hoping that the car continues to start until I get around to this!

Russell Ormerod

Killerpancake, In post 1 you said that you, "turn your key and get a few solid cranks then starter stops turning over"

That is why I say it could be your cps, Glyn is correct in saying that a cps will not cause a no crank condition, very true. But if it cranks then stops thats when you need to look at cps. If there is no crank at all then you have to look elsewhere like starter or relay in front sam.

jtalbert

If a CPS is to fail in a car, is it a repair that is easily done yourself, or do you need to take it some place to get it repaired, and how much does it cost?

Glyn M Ruck

In the US a CPS costs about $50. It is a frustrating DIY that is well covered on the forum. You unplug it & remove a single Torx bolt & swap it out. It is located at the back of the engine between the engine & firewall which makes it a fiddle due to access. Easier on our C240's than the Quadcam M272 engines.

KillerPancake

Reviving my old thread here to give it some closure...

Replacing the CPS did not help, but what did help was the cooler fall weather setting in last year. Starting around September I had no further issues with the car until things started to warm up again this summer. The issue turned out to be highly affected by the car's temperature. After baking in the sun, a hot car was not a happy car and would put up a fight when it was time to start.

Brought the car to my indy who was able to diagnose the issues as the EIS with his star diagnostics. Unfortunately, and this was a new one to him, Benz would not sell him an EIS. Since the EIS is VIN coded and can never be re-coded to another VIN after being done the first time, Benz claimed that they stopped selling EIS modules to anyone as they were getting returns after mis-diagnosis of the EIS and the returned modules were no longer useful. Sounds like something that could have been easily solved with a simple no-return policy, but anyway... The indy did notice that the car started much more consistently by turning the key gently, JUST far enough to engage the starter, as opposed to turning the key all the way to the clockwise end stop. This little trick got me by for a while until I managed to get the car to the dealer who re-diagnosed the issue and confirmed the EIS. The EIS has been replaced and no starting issues since.

SkankZ

How much did the EIS cost?

LILBENZ230

He is in Canada so if you are in the US then it won't be the same. I've seen them cost anywhere from 1200-1800 in the US.

edgarinho10

I think it depends on the shop and whether you have taken the car apart or they have to since its a bit more labor wise