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Thread: Sporadic RPM and GPH

  1. #1

    Sporadic RPM and GPH

    I have an AF2500 (updated from ACS2002) in my RV-8/IO-390/Dual Lightspeed Plasma III with your Tach Interface Board. Lately the rpm starts to take a DC offset anywhere from 20-100 rpm and also fluctuates about 20-30 rpm. The engine itself is steady as is proven by a secondary tach (Lightspeed's rpm/MP/Deg meter). At the same time the GPH meter starts to read about 2 GPM high. Every once in awhile the problem goes away and everything reads steady and correct. I have tried turning a bunch of other electronic items on/off in flight to see if it has an effect but it doesn't. I replaced the main interface cable (from analog board to screen) recently due to other problems (see my other post) and everything has worked great until recently. I also recently rerouted my two Lightspeed power lines from the "always hot" buss straight back to the battery + terminal......shouldn't have made any difference. Any ideas?

  2. #2
    Advanced Flight Systems Shawn McGinnis's Avatar
    Join Date
    Sep 2012
    Canby, OR
    It sounds like your RPM problems are being caused by additional noise. I would recommend checking your alternator ground, engine ground, or spark plug wires. One of the simplest tests is to take jumper cables and grab the engine / alternator and the airframe. To check the spark plug wires insert a multimeter set to continuity mode into both ends of the spark plug wire then gently pull on both ends to see if the meter stops beeping.
    Shawn McGinnis

    Advanced Flight Systems

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