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Thread: Cold start issue

  1. #1
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    Default Cold start issue

    Hello guys,
    In the past couple of days (since it has become cold here) my Z is having a hell of a time starting, that is, it cranks for a long as hell time, (i usually do 3-5 second bursts, takes a few of these to get it done) when it finally does it runs at really low RPMs and when I try to accelerate I get a lean condition and prefiring (backfiring in the intake).

    Things I have done
    1. New cold start valve from autoparts store (green stripped one, not sure if that tell anyone anything)
    2. New Thermotime switch (along with the temp sensors)
    3. Cleaned all terminals.

    Any ideas? Could I have a defective CSV? Does the AFM do anything in the starting procedure? I'm at a wits end here and this is killing my battery. It use to work perfectly fine in the cold, start on the second crank and rev to 1.5k until the car it temp. Now it just sits at idle (~1000) and I have to sit there for a good couple of minutes before I can drive the thing without leaning the hell out of it.

    All six injectors are new, along with the lines, regulator pump and really anything you can name fuel related.

    Thanks
    Jan
    1976 280Z
    HLS30288273

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    Could be a shorted water temperature sensor circuit. The lower the resistance the hotter the engine looks to the ECU.

    Low fuel pressure is a possibility, on the hard starting and the lean intake popping. Have you measured it?

    The low RPM after it starts could be a stuck closed AAR.

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    Pressure at the line between the filter and the fuel rail is the same it has always been (~37psi) and if it was a fuel problem wouldn't it persist the entire time, not just when the car is started? It hasn't changed since I installed the new pump four months ago. The AAR is not even a year old. The short sounds like it might be an issue, how would one check this?
    Last edited by Pomorza; 11-11-2011 at 10:44 AM.
    1976 280Z
    HLS30288273

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    Jan, I don't know the appropriate terminals for the '76 (probably the same as for my '78), but you can unplug the big connector from the ECU and measure resistance across the CTS and all its wiring right there. If there's a problem, that's where you'll be able to see it. Check your FSM for the correct terminal numbers.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Yeah, I'm betting water temp sensor as well. If not, also check the intake are temp sensor.
    1978 280z 4sp

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    Cozye, the water temp sensor is also new, I went ahead and replaced all three sensors while I did the thermotime switch. Does the intake temp sensor have anything to do with the cold start?
    1976 280Z
    HLS30288273

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    Registered User cozye's Avatar
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    Quote Originally Posted by Pomorza View Post
    Cozye, the water temp sensor is also new, I went ahead and replaced all three sensors while I did the thermotime switch. Does the intake temp sensor have anything to do with the cold start?
    Not directly related to cold start, but it is related to cold weather. There is a cut off temp that it riches the mixture up. It's described in the fsm. I don't remember the temp, but it's like 59 degrees or something like that. I could see a possibility that that if it were not working, you would be lean on cold weather. It's a long shot but worth checking.

    Does the car run good when warmed up?
    1978 280z 4sp

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    Another test you can do to gets more info, pull a vacuum line off the manifold when running cold to see if it helps or hurts. This will introduce more unmetered air. It does sound like your aar could be acting up, although I know you said it was replaced not long ago
    1978 280z 4sp

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    The car runs perfectly fine when its hot, it actually richened up a bit. I took it up and down Mt. Lemon here in Tucson last night the temps up there was in the low to mid 40's car drove great. I'll pull a vac line and see if it helps.

    Thanks
    Jan
    1976 280Z
    HLS30288273

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    Jan, the air temp sensor has relatively little influence on mixture and absolutely no influence on the CSV circuit. The CTS has the most influence on mixture (but still no interaction with the CSV). As Eric says, the CSV is only switched on for temps below some threshold temp somewhere in the 50's.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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