dastard

04' C240 - changed plugs, couple days later wouldn't start on cold morning

Turns over strong, but only sputters here and there. As the day warms I can play with the accelerator and get it to run. Once running, will run fine all day, off and on, until the next cold morning.

Replaced battery, was a bit weak and original
Fuel pressure is 55 psi
No codes
Unplugged MAF - still no start
Dash reports engine temp close to outside temp

* Pulled fuel pump fuse - starts right up! No hesitation.

I've searched here and a couple other forums for a couple hours and only found one other similar problem that was fixed with an ECU reflash.

Is there anything I should check before taking to the dealer to try a reflash?

Russell Ormerod

Did u fit the correct plugs
Not sure if ME2.8 is flashable

dastard

Used bosch 9652 plugs. Those are correct replacements right?

Russell Ormerod

What plugs came out? Can't remember off the top of my head but I think it's a FR8DP22+ bosch plug or something. Plug gaps ok? .8mm. Strange ir will only start with relay out. That relay would be in rear sam? Sounds like you need to lean the mixture out to make it start.

dastard

The ones that came out were the original ones, with the MB emblem on them. I'm not sure the number, I already had the replacement ones when we replaced. Gaps were good.

Yes, it's running very rich like it's flooding when I have the problem. It is fine when the outside temp is 50 degress F or higher, no starting problems.

Yes, rear sam. I'm actually pulling the fuse, but I guess the effect would be the same with the relay. I did see a bit of corrosion under the relay. I dismounted the sam and checked each harness or cable plugged in one by one, everything else looked fine. Is this sam possibly bad? Is there a way to get inside to find/clean any internal corrosion?

Russell Ormerod

No it won't be a Sam issue. We must find out why it's so rich. Do you have Star? The only thing is you don't see actual value for air mass in ME2.8 dunno why they don't show it..but you can select further actual values and see it there. Or look under full list of fault codes search.for airmass. And.go thru the tests. It may be easier if just try another airmass sensor genuine only please. U can also check if fuel pressure is not too high. Unplugging airmass is not a good test.

dastard

My buddy has a snap on scanner. I don't think it has Star?

Sounds like my best bet is stick a new MAF on there? Can you suggest best place to buy OEM?

The fuel pressure stayed around 55 psi, give or take 2-3 psi. I think the highest I saw while running was 58 psi.

Russell Ormerod

Not sure where in your country. But either genuine or directly from bosch

dastard

Thought I'd update this since it was finally resolved. The car was set to run e85 for some reason, though we've never run that. Ended up having to reflash the ecu and she's all good now. Local non-dealer shop with access to Star fixed it.

Russell Ormerod

Some after market scanners do funny things to ecu setting without you even knowing it.

dastard

Funny you mention that. After changing the plugs my original guy used his snapon scanner, which he had previously used to quickly and accurately diagnose 2 other problems, to "reset the fuel/air mixture" or something along those lines, which was supposed to help the car reset with the new plugs.

Is it possible the snapon scanner inadvertently put the car into e85 mode, you think?

Russell Ormerod

Not impossible! Anytime a tester has write access to a ecu anything can happen. At least with star you know it is always doing what's intended. I have seen aftermarket testers do mixture adaptation resets and when you check live data with star nothing is reset.

dastard

Thanks for the feedback and help in this thread. Really appreciate your time!!

Russell Ormerod

No problem. Glad u fixed it