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Thread: Troubleshooting help needed

  1. #1

    Unhappy Troubleshooting help needed

    Before I drop dollars in a shop, can someone help me trouble- shoot my problem?

    My 1970 911S was running fine before I replaced the plugs and adjusted the valves following book "101 projects ..." . When I started up again, engine ran like it was cold, that is, lots of flat spots, trouble holding steady rpm. It had been sitting for a month so I took it out to get engine warm. After ten minutes, the performance did not improve. There are major flat spots between 3000 and 5000 rpm like I have never experienced. Once something inside seems to catch up, it runs powerfully up to red line under full throttle. It has trouble holding a steady rpm, that is, driving down the road at a steady speed results in surging. It has trouble accelerating under less than full throttle. Prior to my work, the engine tended to exhibit these symptoms, especially when cold, but never to the degree that I having now. This is unacceptable.

    So, back to garage and check everything obvious. Checked spark plug wires: connections are tight and leads are into the correct cylinder. Checked distributor cap: cap is on correctly, did not knock anything loose, and spark plug leads are tight from cap. Checked for anything loose: since I have the air clearner off there are disconnected hoses from it, otherwise nothing obvious.

    I was never aware of valve noise before. Although it is more than likely that it was my imagination, I thought that I heard loose valves. Not having found any reason for the poor performance, I decided that I would have to recheck valve clearance (pain!). To my puzzlement, valve clearance checks out fine.

    I start the engine and it still runs badly, as before, plus I really think that I am hearing valves noises. I have not run it on the road yet since we are experiencing a major rainstorm here but I am not optimistic since this is the way it ran last time.

    What now?
    I have repeatedly gone over everything in my mind. I am confident that I set those valves correctly but it is certainly possible that I am making the same mistake both times. Would I catch a problem on a third try? Did I not re-connect something or knock something loose? I am confident that the spark plug leads are correct and tight yet any problems here would explain a lot. I always turned the engine clockwise except for minor movement when lining up at the mark so could I have turned the engine the wrong way and damaged the tensioners? If I did, would that result in the problem I am having?

    I would like help with the steps to troubleshoot and fix these symptoms. I might be in over my head and if it must be that I need professional help, I will have to accept that.

    1970 911S Targa

  2. #2
    It may be a coincidence with the work just completed, but you have some symptoms of inconsistent fuel delivery. Could be an almost dead/intermittent fuel pump or clogged filter. A pressure and volume test will verify if it's okay.

    Maybe it's something you did while performing the valve adjustment. I'd check the easy stuff first. Did you mention checking the firing order? 1-6-2-4-3-5. The rotor turns in a clockwise direction. Locate no. 1 on the cap (dist. housing has a notch on it), then follow the wires to their respective cylinders:

    3 6
    2 5
    1 4
    fan is here

    If this is okay, check the continuity of each spark plug wire from the bottom of the distributor cap to the end of the spark plug connector. It should be way less than 10,000 ohms. If plug wires or connectors are old, handling may have brought on sudden ignition death syndrome (SIDS).

    Remove the spark plugs and check the gap (there should be some), then perform a compression test just to make sure the engine is mechanically sound. It has been known that some "adjust" the valves so much, the valves don't close when they should.

    Another test you can make requires some insulated pliers. With the engine idling or at the appropriate rpm, disconnect each spark plug in turn (at the dist. cap is fine). If each cylinder is contributing, rpm should drop equally. The cylinder that doesn't make a difference is the one to zero in on.

    Hopefully, you will have found the solution performing one of the above checks.

    Long distance guesstimate w/o buying new stuff. Hope some of this helps.


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