A new to me car has a cold start problem. Car is 1999 SLK230 Komrpessor with the M111.973 engine.

First start of the day, it catches with rough idle for a couple seconds then smooths out. After that it is fine. PO said it's done that since he owned it (3 years!). What some people will put up with!

I'm leaning towards an FI problem. In my 560SL there were check valves and a fuel accumulator that can allow fuel pressure to leak down overnight and that's what I think is happening here...anyone know if the M111.973 has a similar check valve/accumulator? I looked at fastlane's parts listings and saw nothing but injectors and a fuel pressure regulator. I don't think it is the FPR unless that also acts as a check valve after shutdown...

So, anyone can help with the cold start problem???

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I'm bumping this because nobody responded to the first post but I have more clues so I am hoping someone familiar with the fuel system can help.

The cold-start issue seems definitely due to fuel pressure leak-down overnight. I changed the plugs and they were all the same in appearance so if one injector was leaking down it isn't leaving any clues on a spark plug.

I replaced the fuel pressure regulator but that was not the problem. When I removed it there was no fuel pressure in the system.

I've found that I can cold-start the car smoothly if I put the key to position 2 for long enough that the fuel pump shuts down (building pressure) then start, but if I start it right up it will stumble for a second or two before it smooths out. After that eveything is flawless....idles smooth as glass and accelerates perfectly. Warm starts are fine too.

So, since I now have pinpointed it to a fuel pressure issue...can someone tell me what device maintains fuel pressure from the supply side? Is there a check-valve built into the fuel pump? I'd rather not pull the injectors at this point since the problem is minor, but will do so if there is no other alternative. I'm considering pinching off the supply line overnight and seeing if pressure still drops off, I guess that would tell me if it is leaking at the injectors or the pump itself...

The fuel pumps are relatively cheap ($100 as OE aftermarket pierburg) so my question basically is, does anyone know if there is a check valve built into the pump to hold pressure on the supply since there isn't one I can find anywhere else should I assume that is the case?? I'd try replacing the pump next since the injectors are both costly and more difficult to service than the fuel pump is.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Yes there is a check valve in the pump, you are right.

I have heard of an auxilliary valve that can be fitted into a system but do not think it is a part one can buy. As an alternative, I would suggest fitting a pressure acculmator off another Bosch system, provided it meets upto the holding pressures required. I do not know if the Bosch K-jetronic accumalator could do as a substitute.

Thanks, I found an aftermarket inline fuel check valve (8mm) on ebay that I will install downstream of the pump in the supply line and see if that clears up the problem. Since the pump seems otherwise to be fine I think this will help pinpoint it as the source if it clears it up.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I'm reviving this thread since I was not succesful so far at resolving this problem and thought others might benefit from what I have found. I replaced various parts trying to fix it but it still did the same thing. I replaced plugs, wires, fuel pressure regulator, K40 relay and fuel pump and filter. Each time the car did the same rough cold start accompanied by an abrupt first shift.

Then I susbscribed to STAR Tekinfo and found a technical bulletin which describes exactly what I am experiencing. The number is 22/99. Unfortunately the fix is to replace the engine control module (a $2000 part - list price).

The car had apparently experienced this since new but none of the PO's cared enough to get it fixed, they just lived with it. Since I have verified the old PN is still in there I am going to try and convince the dealer who originally sold the car and did all the service on it to goodwill the repair since they told the PO to ignore it when he complained.

For those who suffer from the same problems I can say if your ECM has the PN 023 545 83 32 or 024 545 57 32 then that is probably to blame for rough cold start and abrupt shifting when cold. The modified PN is 028 545 44 32. I've attached a copy of the bulletin. A similar bulletin exists for other engines BTW, so I recommend you check with STAR Teknifo if you have this trouble with another model.

Attached Files

Bulletin 2299.pdf (15.3 KB, 1026 views)

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz