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75 Merc 350SL Warmup Problems

  • 07-02-2008 2:05pm
    #1
    DJD
    Registered Users, Registered Users 2 Posts: 58 ✭✭


    Hi,

    I have a 1975 350SL (Electronic Fuel Injection) that has problems with cold starting and warming up. It runs very rough initially and cuts out unless you keep the revs at about 2000rpm. Once it has reached normal running temp it smooths out like a switch has been flicked and keeps going with no problems.

    I have seen posts that refer to a warm-up regulator, but as far as I can see the electronic fuel injection version does not have a warm up regulator, and the Haynes manual makes no reference to it.

    Has anyone had similar issues with warm-up?


Comments

  • #2
    Dades
    Moderators, Society & Culture Moderators Posts: 25,558 Mod ✭✭✭✭Dades


    Hey DJD,

    I've a 72 350SL that has some cold-start quirks too. Mine will start, but "hunts" for a couple of minutes (i.e. revs up and down) before settling at a steady idle. The PO was told by M Benz that something called the "warm up air slide" was at fault, but as the issue never caused the car to cut out neither of us did anything about it.

    Does this sound similar? I think your '75 has same FI system.

    There are other real MB heads here who may be able to help!


  • #3
    DJD
    Registered Users, Registered Users 2 Posts: 58 ✭✭DJD


    Hi Dades,

    Thanks for that. My car does have the same FI system as yours. The problem with mine is not hunting though, but very rough running and cutting out (unless you keep the revs up)

    Dave


  • #4
    mike65
    Closed Accounts Posts: 88,972 ✭✭✭✭mike65


    That should be a D Jetronic system. The issue is not enough fuel by the sounds of it - cause be a dodgy air temp sensor giving the ECU a wrong readout and so not enriching the mix.

    http://members.rennlist.com/pbanders/djetfund.htm
    TS2 sensor is a negative-temperature-coefficient resistor (resistance goes down as temperature goes up), mounted on the cylinder head. The ECU has a warm-up enrichment circuit that senses the resistance of the TS2 sensor and corrects the mixture for the engine temperature.

    You might just have an air-leak - that will bugger up cold starting and cold idle.

    Mike.


  • #5
    MercMad
    Registered Users, Registered Users 2 Posts: 4,266 ✭✭✭MercMad


    The early car has the warm up slide, which causes the hunting, right at the front top of the Motor you will see a small unit with rubber pipes going into it. Take it off and clean it, then check every rubber pipe you can see for splits and cracks, replace as neccesary !

    The later one does sound like the cold start/cold running system is not operating and as Mike says its most likely the coolant temperature sensor. If it behaves like an old car that has a manual choke, which isn't working, then thats my best guess ! again its imprtant to make sure none of the vacuum hoses are split and drawing in air which leans out the mixture ! These cars have an auxilary air valve which should be cleaned if it does hunt a lot.

    Good luck !


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