Piper Challenger Starting Issue
I own a 1973 piper challenger 180, it is basically a piper archer with the old hershey bar wing. I had fine wire plugs put in at annual in September. Since then I have had trouble starting. Engin is always pre-heated. I do not think it is due to the fine wire plugs but that is the only thing that has changed. During oil change today, the Machanic had same problem. He indicated that he found that once it sounds like the engin is trying to start and you let off the key, you need to depress the key to turn the starter, the engin will start. I will try this tomorrow but I have never had to do that in the 7 years I owned the plane. I always just turned the starter until the engin started. He indicated that with the key depressed, one mag is disabled and the fact the the starter is engaged will not let the engine turn over at full speed and that is why it appears to be trying to start but will not go because the starter is keeping it from full revolutions. While that does make some sense, I have never had to worry about that before. I am going to try this new proceedure tomorrow but am wondering if anyone has any ideas what could have caused this change. I have always just primed 3 times and then pushed the key in to engage the starter and held the key in until the engin started.
Any thoughts woudl be appreciated.
Any thoughts woudl be appreciated.
Comments
If I understand correctly, your START switch is a twist and push operation. That is the same as my -161. You should twist and push and hold until engine start, just as you have experienced in the past. What is happening when your mechanic "lets off" on the key is both mags start to fire, that is the P-lead is no longer grounded on the non-impulse coupled mag. The inertia of the rotating prop simply carries the engine through one or two ignition sequences and the engine starts. The key position/push or no, has no effect on keeping the starter from "full revolutions." That said, any time you can isolate the onset of a problem with the timing of a change of parts in the engine, that should be your first point of review. New plugs can be bad. Have your mechanic look up the resistance specification of the new plugs and test them. If that doesn't locate a problem, return the massive style plugs to the engine for a trial.
Other potential sources of the problem,
1. The timing of the mags was likely adjusted during the annual. Re-check the timing.
2. The twist & push style switch is known for wear in the START contacts. When that happens the switch may become resistive and cause the START relay to fail to fully engage. This is easily tested by bypassing the START contacts at the switch or jumpering at the START solenoid. Since you have to hold the key against the spring tension to perform this test, it is easier to do with a helper.
Let us know what you learn.
VFRs, without TFRs,
Dennis_ARR
1978 PA28-161
KARR Aurora, Illinois