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Thread: 1995 c280 hard to start at medium coolant temperature

  1. #1
    Member
    Join Date
    Sep 2014
    Location
    Surrey BC, Canada
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    66

    1995 c280 hard to start at medium coolant temperature

    Up to the next problem that Im facing.
    Background:
    1995 C280 160k km
    My regular fuel consumption is about 10.3 L/100 km, at some point about 2 month ago I noticed my car running rough and fuel consumption gone up to abot 12L/100 km, no CEL so I plugged an OBD2 scanner and it gave me a misfire on one of the cylinder. Changed one coil - that fixed it, in about a week after that another coil went bad. So I pulled 3 coils from my 1997 S320 and replaced all of them. I thought that should bring my fuel consumption back to normal, but it still stays high (also outside the temperature dropped below freezing I guess it doesn't help either)
    Now I noticed I have hard time starting the car if I leave it for 1/2 hr -1 hr, It cranks but no start. I have no CEL, I have no problem starting cold or hot only if I leave it for a period of time. I watched my temp gauge and I can see this problem occures when coolant temp is below 70-75 deg C. If I floor accel pedal it starts but the RPM goes up and down for a sec untill settles.
    When it starts cold my RPM goes up and down for a sec until settles at high RPM as it should at cold start, I do get a blip once in a while, but the RPM goes down as it warms up. When hot RPM goes up and down for a sec until settles at~600 -650 rpm.
    I've check throttle body linkage and seems to work OK, it doesn't bind.
    Another thing that I've notice and not sure what to make out of it: using ELM327 OBD2 adapter I get a reading on the LTFT (long term fuel trim) and it always stays at minus 3.9. There's no reading for a STFT (short turm fuel trim). I feel that LTFT should change a bit as I open or close the throttle, not sure if it reads the correct port. This car is 1995, pre OBD2 so limited info is available.
    Im not really sure what systems are involved during the car start, anyone would give me a suggestion where to start the troubleshooting.

    This is a plan I formulated so far :
    1. Check/test Crankshaft position sensor
    2. Check/test Camshaft position sensor (got a new one coming)
    3. Clean MAF sensor (I can see it working OK on OBD2)
    4. Clean Intake temp sensor (I can see it working OK on OBD2)
    5. Replace OVP relay (I had some problems with it so I have a new one coming)
    6. Check all available systems for faults at 38 pin diagnostic plug. The ELM327 adapter for OBD2 port doesn't give much info.
    7. Run a diagnostic on the A/C control module for potential faults.
    7. Replace coolant temp sensor (4 pins one, I think it sends coolant temp to the gauge and also used for fuel injection system) got a new one coming

    Any other suggestions?
    1995 C280 charcoal metallic

  2. #2
    Member
    Join Date
    Sep 2014
    Location
    Surrey BC, Canada
    Posts
    66
    well...problem solved....
    too bad I didn't see any interest from the forum members...
    1995 C280 charcoal metallic

  3. #3
    Senior Member
    Join Date
    Apr 2011
    Location
    Antarctica
    Posts
    551
    Quote Originally Posted by andy_1100 View Post
    well...problem solved....
    too bad I didn't see any interest from the forum members...
    Any word on what the problem was and how you fixed it? This information could still help others with similar issues.

  4. #4
    Member
    Join Date
    Sep 2014
    Location
    Surrey BC, Canada
    Posts
    66
    Turned out...its a leaky fuel pressure regulator.
    The fuel was leaking into the vacuum line creating reach condition.
    Interesting enough that i did a complete fuel system check and pressures were all to spec.
    Installed new pressure regulator, it starts good and fuel economy is back.

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