Mag/starting advice needed

[ELT]

1.During Annual the keyed ignition switch was replaced due to intermittent starting (it was bad).

2. Upon post annual run up when the switch is moved to the "L" position the engine looses ignition from both mags. If the right "P" lead is disconnected both mags fire normally.

3. Suspecting the new switch (new problem look at what was done)the old switch was reinstalled and still the engine looses ignition when the switch is moved to the ""L" position.

4. AI checked mags, shower of sparks, wiring and is pulling his hair out.

5. Engine kicks back on start (new problem)

6. Both Mags are 51 hours since OH.

7. Did not have this problem prior to annual.

8. Disconnect right "P" lead and it starts and runs fine

Any Suggestions

[N601RX]

Did he install the jumper on the new switch?

[ELT]

Yes the jumper was installed

[jlunseth]

It sounds suspiciously to me as though only the right mag is firing.  That would explain the engine appearing to run fine when the switch is on the R mag.  When it is on the L mag, the right mag is grounded out, and if the L mag is not firing it would appear as though both mags are not working.  R is working, but the spark is going to the ground (until you remove the R p-lead). 

 

There is one other possibility.  When starting, one mag is disabled and the engine starts only on the other mag.  I am not sure I remember the order correctly, but am pretty sure it starts on the right mag with the left mag disabled.  As soon as the switch is released from the start position, the other mag is then switched on and the engine runs on both mags.  It may be that the circuitry in the switch is somehow messed up so the switch is disabling the L mag as though it is in the start position, even though it is not.  However, that would not explain why it still does not work with the old switch in place.  The best explanation is the first one, the L mag is not working.

[N601RX]

The right mag should be grounded out during starting and it should start on the retarded breaker points in the left mag.  I used the Spruce ASC replacement switch a couple of years ago and did not have any problems with it.  I remember it had the jumper for the retard breaker and a diode for the starter relay. It seems like the wiring diagram was slightly different for it than the Mooney diagram, but it worked fine.

[ELT]

thanks All

Jlunseth, the shower of sparks system uses only the Left mag to start the engine. Thus if the left mag is not firing the engine would not start.

N601RX, Yes we suspect the replacement ignition switch is bad.  However it is strange that now both the new switch and the old switch now manifest the no run on Left problem.  The old switch did not have that problem before.  I saw the ASC switch but it requires a 337 form for use in cert. aircraft. 

[Mooneymite]

Just wanted to mention that Bendix has a rebuild kit for the L/R/Both/push-to-start switches.

Much cheaper than a new switch and an easy one hour job.

There is an AD against these switches to check for faults. Mine failed the test; the repair kit was all I needed. I think I still have pictures of the new guts being installed.

[moodychief]

http://www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

Good read!

[Greg]

It almost sounds like the key switch has been wired wrong.  It shouldn't be too difficult to check the new switch out to make sure it is working properly.  

[carusoam]

Since the old switch is now acting like the new switch...

Greg is making some good sense! Something to check on at least...

Best regards,

-a-

[Wildhorsesracing]

I had a similar problem, it seemed that the lead to the retard points was grounding out on an Adele clamp. Replaced the wire and it starts easily now.

[ELT]

thanks All,

Moodychief, We have a printed copy of that good read.

Greg, We did an impedance check of the new switch before and after install and it checked good. The old switch did check bad. Incorrect install is possible but IA and his AP checked, redone and have a wiring diagram.

Wildhorseracing, Were you able to start OK but when you moved the switch to "L" did the engine quit?

[N201MKTurbo]

I would ohm out the p leads back to the mags to make sure you have the wires properly identified.

[fatter36]

i had a starting continuity problem and found the issue by tracing the connections in all switch settings, L, R, Both, Start.  removed switch from panel, removed upper avionics access panel - used multimeter and electrical diagram to diagnose all positions working correctly.

 

based on your kickback and non-starting problem, you might have an issue with one of the connections being on the wrong terminal or grounded out somewhere along its path.  there are lots of wires on the back of that switch and it is easy to get them mixed up.

 

once the wires into the switch are positively identified, make your life easier and label all the wires for the next time you have to do some troubleshooting - paid lots of dividends for me.