Boost Pump and Starter work only with Avionic Master on - strange (Update: possible incorrect error description by a mechanic on site, see ff.)

[M20J-Uwe]

Mooney save back at home !

M20J MSE 243164 (1990)

The issue (description by local mechanic on site, at that time I'm 240nm away at home): 

Battery Master and Alternator ON: The fuel pump and the starter do not work, the lights are working. Battery is full charged, no issue.
To make the boost pump and starter work, have to put the avionics switch ON, then everything works. The engine can be started.

But, if avionics ON the boost pump can not switch OFF (beside pulling the CB). It’ just running, even the boost pump switch is off.

Technically I could fly the plane home for further inspection and repair. I’m now afraid about a possible short circuit somewhere.

Any Idea? 

__________________ Update 6/6/22 pls see below too _________________________

Thank you very much for all the support and good advice. The error description above came from the French mechanic in Colmar LFGA. I had tried, on the way to Colmar, sitting 10h in a train, to trigger Mooneyspace as additional support, typed on the iPhone. To me, the description seemed so strange, I had tried to have you as such a good source on my side. 

On site, I then had remote support from my avionics professional who did the avionics conversion (2xG5, GNS 530/430 WAAS+210, AT1, ADL) two years ago, as well as from another avionics examiner, both from Germany.

On site, the situation turned out to be different than described by the French mechanic. The boost pump did not work. Navigation switch on or off did not matter. I did measured through the boost pump switch, which is also a CB - Mooney standard wiring. It works normally. A separate Boost Pump CB does not exist therefore also. the French mechanic has probably confused that with the fuel flow CB. Probably just the boost pump is defective or has/had a short circuit. We are now clarifying this at home.

I was able to start the Mooney without the boost pump, normal procedure, but with the avionics switch off. So, at least for me, there is no longer any connection of the issue with the avionics bus, as far as can be seen at least now.

I had wondered about an error that had already occurred 2 months ago. Therefore, I had a possible dependency with the avionik relay not seen as entirely impossible. The Alt Field CB jumped out once, but could be pushed in again. No further issue. This occurred again on the flight to Colmar. Not on the return flight. I can't see any connection with the boost pump. Maybe it's just "lause and fleas" at the same time. We are now looking into this at home.

Again thank you all. Any advice on both problems is of course highly appreciated by me.

 

 

[ArtVandelay]

My boost pump switch is the circuit breaker. Makes me think someone did some rewiring? Is this 28v, maybe they changed it in later years. I would crawl under the panel, check the starter/master/avionics switches wires for any lose wires.

[N201MKTurbo]

Check your AUX buss jumper, it is a branded cable near the top of the circuit breaker panel. Mine broke once and it did weird stuff like that.

Edited June 4, 2022 by N201MKTurbo

[Fly Boomer]

  On 6/4/2022 at 5:21 AM, M20J-Uwe said:

I’m now afraid about a possible short circuit somewhere.

Expand  

If we can get a minute of his time, @M20Doc may have an idea.

[chriscalandro]

If it didn’t do this before you should absolutely not fly it. 

[PT20J]

Does this airplane have the standard factory wiring? You mention avionics "button" but Mooney used a circuit breaker rocker switch. You also mention that pulling a circuit breaker shuts off the boost pump, but Mooney used a circuit breaker rocker switch for the boost pump and there is no other circuit breaker except the AUX Bus which will kill everything powered through the rocker switches.

The MSE should have three buses: Battery Bus powered by the master switch (through a relay), the AUX Bus (powered from the Battery Bus via the AUX Bus circuit breaker), and the Avionics Bus (powered from the Battery Bus via the avionics relay. This relay is normally closed so that the bus will be powered if the relay coil or Radio Master switch fail. The relay coil is energized via the Aux Bus when the Radio Master switch is OFF).

The starter is powered from the Battery Bus through the Starter/Cigar Lighter circuit breaker and thence to the ignition switch and finally to the starter solenoid.

The boost pump is powered from the Aux Bus through the boost pump circuit breaker rocker switch.

I could see how you might get the boost pump issue if somehow the boost pump power lead was connected to the avionics bus, but this would seem hard to do since the avionics bus is in the circuit breaker panel and the boost pump is wired far away to the switch on the pilot's panel. Likewise, if the starter solenoid was disconnected from the main bus and reconnected to the avionics bus it would work as described. But, without rewiring, it is difficult to see how something could fail to produce these symptoms.

Skip

[Ragsf15e]

Gonna need a digital volt meter and patience to trace power with only the master on.  Check for power at the bat bus and aux bus.

[A64Pilot]

I’m thinking English could possibly be a second language, if so don’t read too much if button or switch or whatever are misused, that’s just a guess though.

From what little I know of my 201, I’d be suspicious of the Aux bus as well, if I pull my Aux bus CB I think it turns on my Avionics, so there is some kind of connection there.

‘I don’t understand it as well as PT20J apparently does

Edited June 4, 2022 by A64Pilot

[PT20J]

  On 6/4/2022 at 7:43 PM, A64Pilot said:

if I pull my Aux bus CB I think it turns on my Avionics, so there is some kind of connection there.

Expand  

The avionics relay connects the avionics bus to the battery bus to power the avionics. The relay is normally closed and the Radio Master switch is actually on in the OFF position holding the relay open. When you turn the Radio Master ON, it removes power from the relay. It's a fail safe design to prevent a failure of the Radio Master switch or the relay coil from preventing the radios from getting power. The avionics relay coil gets power from the aux bus (through the Radio Master switch) so that's why the radios go on when you pull the aux bus breaker.

Skip

[A64Pilot]

So the failure mode of the avionics relay is that you can’t turn the avionics off with the switch?

I found the to me odd behavior looking for hidden functions in my CB panel, for instance I have no idea where my aftermarket intercom gets it’s power.

Edited June 4, 2022 by A64Pilot

[carusoam]

  On 6/4/2022 at 9:58 PM, A64Pilot said:

So the failure mode of the avionics relay is that you can’t turn the avionics off with the switch?

I found the to me odd behavior looking for hidden functions in my CB panel, for instance I have no idea where my aftermarket intercom gets it’s power.

Expand  

welcome aboard Uwe!

Using AOG in the title describes your situation… code for aircraft on ground, needing assistance…
 

failure mode of the avionics switch…

The switch operates the avionics buss relay…

The relay is normally closed (believe it or not) supplying power to the avionics bus when power becomes available…

The master relay powers the avionics master relay to open… (surprise?)

It closes again when the avionics switch is turned on….  Fail safe mechanism for Mooney avionics panels…

It works really good until the avionics master relay fails in the open position…

It gets interesting when the avionics master gets turned on before the master relay gets turned on…

It gets disappointing when the master relay stays open when switched on…

 

This is an unlikely source for the OPs fuel pump being enabled solely by having the avionics master relay on… unless there is something wrong with the Master relay…

So….

Master relay sounds like it is not operating correctly… try whacking it to get it to work once…

Replace when able…

+1 for asking @M20Doc to stop by….. (dead master relay?, back powered by turning the avionics relay on…

 

To have the fuel pump come on…. Something has to deliver electricity to it… a lot of electricity…

Back powering the main buss using the avionics relay… wouldn’t turn anything on if it’s individual switch is off…

Check that the fuel pump can be turned on and off with its circuit breaker / switch…

 

Sounds like more trouble shooting may be needed…

Either way… major electrical system error with no explanation… is reason enough to spend more time finding out where the electrons are coming and going to and not flying it…

PP thoughts only… not a mechanic…

Best regards,

-a-

[carusoam]

More about the normal operating conditions of the electric fuel pump…

The circuit has only a few things…. As wired at the factory….

1) Power from the main bus

2) A circuit breaker (often part of the switch) aka CB Switch…

3) The switch

4) the ground…

5) If the switch is off, power can’t get to the pump…. Wired the way the factory does it….

6) Some planes going to Europe get re-wired as part of the importation process… usually adding another switch to supply electricity in the event the avionics relay fails in the open condition…

 

It is really super odd that the fuel pump is able to stay on with its switch in the off position….

it is kind of odd to have a separate circuit breaker for the electric fuel pump that has a CB Switch….

Find out WHAT is powering the electric fuel pump…

Let us know what you find out…

PP thoughts only…

-a-

[M20J-Uwe]

Thank you very much for all the support and good advice. The error description above came from the French mechanic in Colmar LFGA. I had tried, on the way to Colmar, sitting 10h in a train, to trigger Mooneyspace as additional support, typed on the iPhone. To me, the description seemed so strange, I had tried to have you as such a good source on my side. 

On site, I then had remote support from my avionics professional who did the avionics conversion (2xG5, GNS 530/430 WAAS+210, AT1, ADL) two years ago, as well as from another avionics examiner, both from Germany.

On site, the situation turned out to be different than described by the French mechanic. The boost pump did not work. Navigation switch on or off did not matter. I did measured through the boost pump switch, which is also a CB - Mooney standard wiring. It works normally. A separate Boost Pump CB does not exist therefore also. the French mechanic has probably confused that with the fuel flow CB. Probably just the boost pump is defective or has/had a short circuit. We are now clarifying this at home.

I was able to start the Mooney without the boost pump, normal procedure, but with the avionics switch off. So, at least for me, there is no longer any connection of the issue with the avionics bus, as far as can be seen at least now.

I had wondered about an error that had already occurred 2 months ago. Therefore, I had a possible dependency with the avionics relay not seen as entirely impossible. The Alt Field CB jumped out once, but could be pushed in again. No further issue. This occurred again on the flight to Colmar. Not on the return flight. I can't see any connection with the boost pump. Maybe it's just "lause and fleas" at the same time. We are now looking into this at home.

Again thank you all. Any advice on both problems is of course highly appreciated by me.

[jaylw314]

  On 6/6/2022 at 6:21 PM, M20J-Uwe said:

Thank you very much for all the support and good advice. The error description above came from the French mechanic in Colmar LFGA. I had tried, on the way to Colmar, sitting 10h in a train, to trigger Mooneyspace as additional support, typed on the iPhone. To me, the description seemed so strange, I had tried to have you as such a good source on my side. 

On site, I then had remote support from my avionics professional who did the avionics conversion (2xG5, GNS 530/430 WAAS+210, AT1, ADL) two years ago, as well as from another avionics examiner, both from Germany.

On site, the situation turned out to be different than described by the French mechanic. The boost pump did not work. Navigation switch on or off did not matter. I did measured through the boost pump switch, which is also a CB - Mooney standard wiring. It works normally. A separate Boost Pump CB does not exist therefore also. the French mechanic has probably confused that with the fuel flow CB. Probably just the boost pump is defective or has/had a short circuit. We are now clarifying this at home.

I was able to start the Mooney without the boost pump, normal procedure, but with the avionics switch off. So, at least for me, there is no longer any connection of the issue with the avionics bus, as far as can be seen at least now.

I had wondered about an error that had already occurred 2 months ago. Therefore, I had a possible dependency with the avionik relay not seen as entirely impossible. The Alt Field CB jumped out once, but could be pushed in again. No further issue. This occurred again on the flight to Colmar. Not on the return flight. I can't see any connection with the boost pump. Maybe it's just "lause and fleas" at the same time. We are now looking into this at home.

Again thank you all. Any advice on both problems is of course highly appreciated by me.

Expand  

Lots of head scratchers there   I'm guessing the original mechanic pulled the Avionics Bus relay CB and found that the starter works.  Since all the radios were on, he assumed the Radio Master switch was ON.