GezaBMX

Hi Everybody,

After reading through pages and pages and pages of similar issues I still haven't found the exact fix to my problem.

So I have the M112 2.6 in my car and it doesn't always start most of the times on the first key, it cranks well but it doesn't catch.
When I first got it checked they told me that it's the rear O2 sensor on the drivers side. That got changed but the issue still remains, after that they told me that the MAP sensor is out so I ordered a new one and changed that also with some new hoses. The issue still persists. After reading more through the forums I was informed that this may be due to the CPS failing and this is a common issue with M112. Today finally I changed the CPS and the first time the car started up with a bit of hesitation but I didn't need to crank it twice. Went for a drive and the car seemed to run smoother then before. Got home, parked the car, cranked it a few times and it started no issue.
Finaly a few hours ago I went down to the car in the parking lot and yet again it didn't start on the first key.

I don't have an ODB2 reader so I can't check it now, need to take it to a mechanic but what the f... could still cause this problem?

I have read that fuel filter could also be the culprit... is it worth changing?
I have a CEL which I had from the MAP problem but, can it be that because the SAM was not notified by the fact that the CPS is replaced and it still thinks it's faulty ?

Any help will be appreciated since this is starting to get real frustrating

megacrazy

You need somebody with STAR to pull codes. If it cranks and doesn't start look at the usual culprits: fuel and spark. I am not sure why you're replacing O2 sensors and MAP sensors.

The crank position sensor doesn't need to be registered anywhere. It's plug and play. Take a look at fuel delivery (pump lines etc) and spark plugs, cylinder compression etc.

Oh and yes, the fuel filter could cause issues. Replace it if the codes you get are not helpful.

GezaBMX

The O2 and MAP were replaced since they were not working proper, codes came up when I took it to the mechanic. I don't like to just throw money at parts

GezaBMX

The funny thing is that it doesn't happen all the time, let's say 7 - 8 times out of 10

megacrazy

What kind of noise does it make while cranking? And you replaced the sensor with a new one that's known to be good?

GezaBMX

It makes the exact same sound as when you crank a totally healthy engine, nothing is missing or is extra. I replaced both the MAP and the CPS, got OE Bosch for both so I suppose they should be working.

The thing is that almost whole winter it started first key no problem, after the weather got warmer the issues started. When it "catches" it catches on the spot, it doesn't try like some cars that have issues starting. After start the engine runs perfectly, no strange noises no vibration. Since the sensors have been changed I can feel that the engine is smoother and seems to run better but this little niggle is getting frustrating.

megacrazy

Interesting. Another thing you might consider is the coolant temperature sensor. That can cause issues like this sometimes too. But like I said before, check codes and if nothing useful start checking wires, plugs and fuel delivery.

GezaBMX

The coolant temp sensor can cause "difficult" start ?
I'll get the car to the mechanic one of these days but cause of my schedule it's a bit more difficult. Honestly I'm still pretty confident and I think(hoping) it's some small bs problem that's why it doesn't just start. After the first failed turn of the key it always starts almost instantly on the second.

megacrazy

Yup... The ECU needs to make fuel adjustments based on temperature... If it's thinking it's colder than it really is it may be causing an incorrect mixture...causing issues.

Anyway best of luck. Hopefully it's nothing big.

GezaBMX

Thanks, well I'll get it to the mechanic as soon as I can to pull the codes and then we'll see what may be the culprit.

Rudeney

Unless you are getting a rough start, if it's just rotating and not firing at all, I believe it is a fuel delivery problem. Without a signal from the CPS, the fuel pump is disabled. So, if the CPS was replaced with a new, OEM part, then you can "probably" rule that out. I say "probably" because it is possible to get a defective part. The other possibility is the fuel pump itself. The proper check is for it's pressure and amperage draw. I can't recall them off the top of my head, but I know I've posted it before (if not here, then look at benzworld).

GezaBMX

I'm pretty sure the CPS is working since I don't think the car would even start without one, the rest of the parts that have been changed did make a difference since it can be felt that the engine is happier. I have to get a fuel pressure gauge to be able to check the fuel but first I want to just take it to the mechanic so we can pull the codes.

GezaBMX

This is not my engine, I just took the picture of the web. The little thing on which I have the arrow pointing next to the brake/ESP assembly, ticks from time to time, it's not loud but you can definitely hear it sometimes. Could this be the culprit or should this click ?

GezaBMX

The sound it makes is tick tick tick tick tick for a bit and then it stops, I have not found yet what makes it tick since it just seems to do it from time to time.

DanielFD

Take a look at one of the posts right under yours. Thats the Purge Valve, pretty unrelated to your problem.

GezaBMX

Earlier today I have found out that it's the purge valve, also I have read that this does "tick". Is this ticking the sound that it will make if it's going to fail? Or is this ticking just something that the purge valve does ?

GezaBMX

BTW, is there some "general" maintenance I could perform to maybe try and get rid of this issue? Like cleaning something out or .... ? Just asking since I could maybe do that before I take it the mechanic for the codes

megacrazy

Wtf...where did you find that engine bay. That's horrible hahaha.

No I don't think there's a general maintenance item that will solve all your problems . A problem like this is best approached by getting the codes and then troubleshooting step by step. The more you think about it without concrete tests and evidence the more it's going to confuse you.

Rudeney

A failing purge valve won't affect starting. Like I said, if it rotates and simply does not fire - i.e. smooth rotation, no partial running, no chugging, coughing, etc. then you're missing fuel.

GezaBMX

Unfortunately I'm reporting back with bad news. Was involved a few days ago in a crash so now the starting problem has to wait until the rest gets sorted out.
New hood, right fender, right headlight, bumper is needed and hopefully nothing else behind it.
I went to the old bats insurance since it wasn't my fault but any way it will take a few weeks until my car will get fixed.
Hopefully it will be at least as good it was before cause this is really the last thing that I needed.

DanielFD

really sorry about your accident. hope nobody was injured!
Your CPS sensor is still most likely your problem as it acts up in the heat. How much did u pay for the CPS sensor? cheap ones usually fail constantly or don't work all the time. Mine failed recently when a 2 day heat wave hit lebanon, had to fork out 160$ for the new part from the stealership but it works. Also get to a professional diagnostic that uses STAR it should be pretty easy to pinpoint as a failing/bad cps usually throws codes. Also on STAR you can read actual values from the CPS sensor and you can see if the sensor is giving out a weird reading. Also as Rodney said before, a failing fuel pump can also cause these problems, in my c230 i had a failing fuel pump that would giveout after a long drive. I'd wait 5 minutes and start up and run with no problems.. then after 30-40min of driving it would cut out again. Finally after 2 months i had enough money to change out the fuel pump and solve my issue.

GezaBMX

Now, I need to get the damage fixed before I can move on with the firing issue. This is how my car looks now:

Rudeney

Ouch! I don't know things work in your part of the world, but here int he USA, that would likely be a "total". You will need a new front bumper, new fender, new hood, each of which you can count on costing at least US$700 to replace and paint, so that's over US$2,000 just in the the body panels. You'll need a new headlight ($300), but it also looks like it probably will have damaged the radiator support. And when it does that, it usually takes a few other things with it, like the radiator, A/C condenser, coolant tank, etc. Over here, we didn't have the CLK240, but the similar CLK320 is worth under $5K. Most insurance companies will want to total it when the repair costs exceed 75% of the value. Of course since it's another person's fault, you would have some more leverage. But like I said, that's how it works here int he USA.

GezaBMX

The good thing is that as the headlight got pushed back it didn't damage other parts behind it. As I tried to avoid the old bats Renault, only my headlight hit her metal bumper and as the bumper pushed the headlight in the panels around it got damaged. The cross member that also has the grill mounting bracket got bent bunt only slightly, nothing a few whacks with a rubber mallet wouldn't fix.
Now, cause of my work schedule it's going to take more time to get the car fixed since I don't really have that much free time when I can take the car to a body shop.
The cost of repair is pretty much similar here as well, I could get panels from cars that are sold for parts but the insurance company of the woman already confirmed that new bumper, fender, hood and headlight is needed.
I want to figure out if it's possible to change my headlights to DEPO projectors since for the cost of one Mercedes headlight I could buy a set of Depo's here. At least like that they wouldn't look awkward cause if only the damaged headlight gets changed to a new one it will look funny that one light is a bit hazy and the other one is brand new.

GezaBMX

@Daniel

Yes the CPS was a brand new OEM part and once it was installed a difference could be felt. At this point I'm fairly certain that the Fuel Filter could be the culprit, I'm not sure of how much the pressure should be in the system. On the day when I had the crash I checked the little valve on the fuel rail but there was barely anything. This would explain "I guess" that this is why it won't start on the spot, but if I leave the key in position 2 for let's say 5- 10 seconds the car fires up almost instantly.

Can anybody confirm what is the correct fuel pressure when you check on the fuel rail ?
Can anybody confirm what brand or model is the correct (OEM) fuel filter ?

I checked pages and pages and pages regarding the subject and it seams like every forum has their "OEM" filter.

On a few websites everybody claims it's the Mann filter, on others it's the Bosch, on others it's the MAHLE ...KNECHT...
Since it's a known issue that after market filters have problems, I don't even want to spend time with it, I just want to get the OE and hope for the best.

At the moment the car is sitting in the body shop since I'm waiting for the insurance money. As soon as I have any updates on parts or progress I'll get back here