P-lead wire and start issues

catmandu

catmandu

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Catmandu
IO-360, hard to start. Does not fire for a while, then magically comes alive with a smooth running engine. Cold, hot, flooded, you name it, same results.

However, fires right up when you remove the P-lead on the 25 hour old left mag (which has the only impulse coupling) in each and every situation.

Initial action was to check the resistance of the wire from the Bendix ignition switch to the mag, no variance in resistance when moved at several places along the line. Checked continuity of same wire to ground while moving it at several places, none found. Replaced Bendix ignition switch with new, but problem persists.

Thoughts? :dunno:
 
Something inside the mag case? Maybe that mag lead to the switch is grounding on the airframe?

I had a similar problem with a SOS lead grounding through a wound tube of dialectric paper inside the case that was to serve as an insulator. Would intermittently ground and kill the system. But no, if it was a short in the case, removing the lead wouldn't do nuttin.

Whoops, never mind. Just read you checked for a short to ground...
 
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P-leads in wrong mags? If they're switched you're grounding the left mag in the start position.
 
Norman said:
P-leads in wrong mags? If they're switched you're grounding the left mag in the start position.
Click to expand...

Yup, or wired wrong at the switch meaning you are trying to start it on the mag that has no impulse coupler. Have you noticed any kick-backs?
 
Tom-D said:
Bag ignition switch. high resistant short to ground, in the start position.
Click to expand...

This!

Aircraft ignition switches are the biggest joke. Unreliable in any number of ways. I hand one you could do mag checks all day, even turn the switch to off and watch the engine die, yet when you removed the key, one mag would still be hot.
 
flyingron said:
This!

Aircraft ignition switches are the biggest joke. Unreliable in any number of ways. I hand one you could do mag checks all day, even turn the switch to off and watch the engine die, yet when you removed the key, one mag would still be hot.
Click to expand...

I never have liked keyed switches. I prefer toggle switches and start with the right mag off.
 
Greenhead said:
Maybe dumb question but curiosity got me. Why the right mag off on start?
Click to expand...

Do some research on impulse couplings.

You want to start with the non-impulse coupling grounded (off) - and traditionally the non-impulse mag is installed in the right position.

-Skip
 
Because most engines have one mag w/impulse spring and one without. You want to start on the impulse mag only. A key switch is wired to kill one mag while the switch is in the start position.
 
catmandu said:
IO-360, hard to start. Does not fire for a while, then magically comes alive with a smooth running engine. Cold, hot, flooded, you name it, same results.

However, fires right up when you remove the P-lead on the 25 hour old left mag (which has the only impulse coupling) in each and every situation.

Initial action was to check the resistance of the wire from the Bendix ignition switch to the mag, no variance in resistance when moved at several places along the line. Checked continuity of same wire to ground while moving it at several places, none found. Replaced Bendix ignition switch with new, but problem persists.

Thoughts? :dunno:
Click to expand...


Well, I have gotten **** new parts before. More likely the magneto, but it could be the switch.
 
Norman said:
P-leads in wrong mags? If they're switched you're grounding the left mag in the start position.
Click to expand...

Winner. I got sloppy when doing the mag check with the left lead disconnected, did not recognize the single mag drop was on the wrong mag.

Whether it happened at the engine at some point, or on the switch, who knows, but it is fixed, so life is good.

Thanks, all. I knew many brains would be better than one, especially my limited one. :rolleyes:
 
catmandu said:
Winner. I got sloppy when doing the mag check with the left lead disconnected, did not recognize the single mag drop was on the wrong mag.

Whether it happened at the engine at some point, or on the switch, who knows, but it is fixed, so life is good.

Thanks, all. I knew many brains would be better than one, especially my limited one. :rolleyes:
Click to expand...

Another reason why I don't like key switches, but I guess a guy could get the toggle switches mis-wired also. :rolleyes2:

Glad you found it!
 
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