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  1. #1
    John Jardine
    Saab Fan
    Join Date
    10 Dec 2011
    Location
    Lumberton, New Jersey, United States
    Posts
    30
    Saab(s)
    1991 900S convert, 1985 900s 4door,1985 900 Turbo

    Head gasket change wont stay running

    Hi all. We have a 1985 900s 8valve that we changed head gasket because we had installed upside down causing oil leak on shut down. Car was running now will only start when cold and not idle. Car stalls once heated up. We question if fuel relay might be bad or if main fuel pump might have a problem. Car does have new vacuum lines,cool start injector and and fuel injector. Car ran great before except for oil leak. This is a daily driver, garage kept with 180000 miles. Any help or ideas thanks.

  2. #2
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
    Join Date
    14 Aug 2010
    Location
    Medford, MA
    Posts
    684
    Saab(s)
    '90 900 LPT with a flat-nose conversion
    From your description, the mixture sounds rich. I wonder if you didn't put some fuel component on wrong, or break a line during reassembly. I think breaking a fuel line would cause it to run lean, though. Can you try unplugging the cold start injector and seeing how it affects things? How about swapping back the old fuel injectors to see if it makes a difference? It sounds like you have a good basis for some solid trial and error work here. If all else fails, just install Megasquirt and enjoy the extra mileage and power (and freedom from K-Jetronic).
    Ask me a question about your c900! I promise I either can answer it or know someone who can

  3. #3
    Edward G
    Saab Enthusiast
    Join Date
    10 Mar 2011
    Location
    Victoria Australia
    Posts
    121
    Saab(s)
    T5.5 84 900T8
    no it sounds mixture lean to me - a fuel pressure gauge would easily confirm this -

    starting when cold and dying when hot is commonly caused by a bad warm up regulator on an 8v. the warm up regulator controls the mixture, and gradually leans it out when hot. When the WUR gets blocked then the fuel pressure ends up being higher than its supposed to be. the higher fuel pressure restricts the movement of the fuel distributor piston and causes a lean mixture - that is how K jet functions...

    the warm up regulator raises the fuel pressure by a plate deflecting as it heats up.

    crack the left line on the warm up regulator loose so fuel runs out with engine running (have fire extinguisher and cloth underneath) if car idles better/runs longer then my above diagnosis is correct and you need to either rebuild or replace the WUR.

    it could also be a fault with the fuel distributor, there is a WUR metering hole that can get blocked causing the same problem... often a good test of the entire system is to get the engine to the point where it stalls, remove the injectors put in 4 equal containers, jumper the fuel pump relay socket so the pump runs, remove the airbox intake bellows and use a magnet to raise the air flow sensor plate in the airbox, this will run the injectors... look at the spray pattern and note the volumes (that there isn't a 10% difference between the injectors) if the injectors are spluttering or cut out all together its likely the fuel pressure is much too high!

    also check the simple things - like the frequency solenoid valve has it's power plug attached, and the vacuum lines are attached correctly to it.

  4. #4
    John Jardine
    Saab Fan
    Join Date
    10 Dec 2011
    Location
    Lumberton, New Jersey, United States
    Posts
    30
    Saab(s)
    1991 900S convert, 1985 900s 4door,1985 900 Turbo
    Hi all. got the old baby running again. Car had bad fuel pump and fuel distributor. Had tto make a brass bushing new fuel pump alittle smaller. Car started to run but not sending fuel to allinjectors. Found a rebuild fuel distributor for $79 car runs like brand new.

 

 

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