Checking the timing on a 308 QV | FerrariChat
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Checking the timing on a 308 QV

Discussion in 'Technical Q&A' started by gt500blue, Feb 15, 2009.

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  1. gt500blue

    gt500blue Formula 3

    Oct 18, 2006
    1,851
    Texas
    Full Name:
    GT
    #1 gt500blue, Feb 15, 2009
    Can some one post the correct procedure for checking the timing on a 83 308 QV? I'm still chasing a mis-fire and I'm wondering if my very greasy crank sensors might be the culprit. I have checked the plug wires and changed the spark plugs (the previous ones were fine and less than a year old - but since I was checking them, I replaced them - cheap). Still have the low RPM mis-fire under load. After 500 RPM above idle, it starts to improve, but still there.

    I have a timing light/gun that I have used many times on a Nissan and other US models. But where do I see the timing marks? Through the small opening in the bell housing? Which cyl is actually #1? Both valve covers are labeled #1-#4?? Finally, what is a good 12 volt source in the engine compartment? My other cars are all front engine and the battery is obviously not in reach on the 308.

    Would one of the sensors on the crank cause a mis-fire if faulty? I have not pulled the distributor caps yet as I didn't want to break the gasket just yet until I checked the timing. Also, the vacuum line from the Digiplex seems brand new, so I don't know if I need to pull the carpet out of the trunk just yet to check the two units.

    Any photos of how to check the timing on it with a timing light? thanks!
     
  2. fastradio

    fastradio F1 Rookie
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    Apr 26, 2006
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    David Feinberg
    #2 fastradio, Feb 15, 2009
    JW,

    If this car were in my shop with these symptoms, I would in this order do the following:

    -Pull the plug extenders and inspect them very carefully for any fine cracks or pin holes. Also, I would ohm test eash one. (8 times out of 10, a bad plug extender will cause the type of mis-fire you're experiencing.
    -Pull the distributor caps and inspect the center carbon contact for wear or damage.
    -Verify that the cap and/or rotor doesn't have green corrosion growing on them. The cork gaskets are neither here nor there...and the car will run fine with them, or wothout them. Worst case, just buy new ones....
    -Ohm test the ignition wires, being sure to "wiggle" the wires at the ends to ensure that you don't have an intermittant connection.

    As far as a 12Volt source for your timing light, I use a separate lawn tractor battery as a power source...Works just fine. A quick test to determine if you have an intermittant mis-fire would be to connnect your timing light to each cylinder and observe the sparking frequency of your timing light. The light should flash at a constant rate for all cylinders. If the light "seems to miss a beat" every once in awhile, that's the cylinder you should further explore.

    If you want to observe the advance curve, remove the semi-triangular plate on the bell housing...and shoot your light in there. The number 1 cylinder is the rightmost one, on the bank closest to the fuel distributor.

    David
     
  3. gt500blue

    gt500blue Formula 3

    Oct 18, 2006
    1,851
    Texas
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    GT
    #3 gt500blue, Feb 15, 2009
    David,

    Thank you so much for the reply! Okay, I pulled the wires and visually checked the extenders when changing plugs. All looked very good. THey are only a couple of years old, but I guess I should still Ohm test them. I do have an Ohm meter, but how do I exactly check the extenders? Pull them out of the wires and measure resistance from the inside plug connector and the connector that goes into the wire? What should the value be?


    What about the wires? I'm assuming I need to pull each off the distributor caps and check resistance from end to end with the meter? What should the resistance be for a good wire? I will wiggle to be sure.

    Good tip about the lawn mower battery. I have an extra in the garage I can use.

    Finally, could a dirty, oily crank sensor cause the misfire as well?

    Thanks again!!
     
  4. fastradio

    fastradio F1 Rookie
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    Apr 26, 2006
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    David Feinberg
    #4 fastradio, Feb 15, 2009
    JW,

    Check your PM...

    David
     
  5. spiderseeker

    spiderseeker Formula 3

    Jul 22, 2005
    1,718
    Colorado
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    Steve
    #5 spiderseeker, Feb 15, 2009
    * I'm not an expert in this area but I believe there are three crank sensors, 1 for each bank of cylinders and 1 to drive the tach, so my answer would be yes, a bad crank sensor could affect the firing of one bank. Sometimes just cleaning the crank sensor connectors can help.(my PO said that he had to clean mine once)
     

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