From new, my 915is had much more lane drop than my 912is. About 150-175rpm. My 912is was always pretty close to zero and I've hear the 915is should be the same. I am checking at 2500rpm (although 4000 rpm is only a bit better). Eventually it went over 250rpm and I've grounded it for now. I replaced the spark plugs, no change. I checked the logs with BUDS and did find a crank position sensor error and discovered that the engine cradle was making slight contact with the crank position sensor. I spaced that out and I am not seeing any more crank position sensor errors. Fuel pressure is perfect.

I was going to check the resistance of the ignition coils and spark plug wires. I see the procedure and the resistance values for the coils in the heavy maintenance manual but I cannot find the values for the spark plug wires.

Anybody know what they are supposed to be? Any other ideas for things I should check? Thanks.



  • Re: 915is > 250 RPM drop on lane check

    by » one month ago

    In the 915 MMH, section 74-20–00 refers you back to section 76-70-00 for instructions on how to test the ignition cables.  Unfortunately, section 76-70-00 tells you how to do a general resistance test, but does not give you a value for spark plug wire resistance… at least as far as I can see. I see from your post you already found the ignition coils test procedure, which is well described   

    You can do a comparative test on the plug wires, looking for a plug wire that is significantly different than the others.  Each wire will be slightly different, but you are looking for an obviously higher reading.  Also, check the tightness of the screw on plug boots, and also where they are screwed onto the coil prongs. If you find a loose connection that won’t take up by turning clockwise, you can snip off 1/4” of the cable and thread the boot back on.  

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