Sensors dead when engine running

[Flying Canuck]

I'm on the home stretch towards final inspection - scheduled for Thursday. I've got a handful of squawks left, anyone have any tips/experiences with these?

For context, I've got a Dynon SkyView HDX with the EMS module, an IO-320 engine and the 4 cylinder Kavlico probe package.

My oil pressure sensor works when the engine isn't running - I had cross wired the oil and fuel pressure transducers so I swapped the plugs before my first engine start (caught that on the engine pre-oil). I swapped them back and changed the EMS pin assignments before my second start today. In both cases my oil pressure goes offline immediately on start and comes back online immediately on shutdown. The fact that I've tried this on 2 different wiring paths (and don't have the same issue with the fuel pressure sensor) tells me that it isn't a loose electrical connection.

My #4 CHT temperature sensor is doing something similar - I get room temperature readings with engine off, the temperature reading goes down when I start the engine and then the sensor goes offline. I checked the connector and it appears solid and stable.

My engine is running quite smoothly once it settles in and I bring the mixture back - no crazy vibrations going on.

I'm also not getting anything on my amps shunt (offline on the display) - but I suspect that this is because I'm not getting anything coming from the alternator when I enable the field. My battery voltage isn't going up, so I'm sure that means no charging. I've got a VP-X in there, I have a few things I can check on this next time if I hook up my laptop.

These issues and the fuel level sender that I've posted elsewhere about make up most of the outstanding items I have before inspection. As always, the collective wisdom of this community would be most gratefully appreciated.

[Mike S]

My first thought is a bad ground. But that is almost always my first thought with wiring issues.

My second is electrical noise from alternator or ignition.

Last thought, is the oil sensor being fed from a lower voltage such a 5v?? If so, make sure the voltage stays good.

[n82rb]

Go to the page that shows the raw voltage data on the pins and watch what the do as you go from power up until shut down. That will give you an idea of what's going on.

Bob burns
Rv4 n82rb

[lr172]

what happens to your voltage readings with the engine running. My first guess would be some type of electrical interference coming from the alternator, second would be an issue with the EMS module. I would try running with the alternator offline and see if the problems persist.

Do you have mags? Those can shed a lot of interference if you have a problem with the shields on the wires.

Larry

[Flying Canuck]

Thanks for the input. I've thought it through and the one thing that makes the most sense is interference from the mags. I routed the p-leads through the same firewall pass-through as all of the engine sensor wires - I see from reading some older posts that this is a bad idea. I'm going to drill another hole and move my p-leads to it this afternoon. Hope that fixes it.

As far as my alternator problem - I'm almost certain that I didn't even run a ground to the alternator, just the field and b-lead. Clearly that's wrong, so I'll check that when I head out to the airport today.

Thanks again for the responses.

[Carl Froehlich]

Originally Posted by Flying Canuck

Thanks for the input. I've thought it through and the one thing that makes the most sense is interference from the mags. I routed the p-leads through the same firewall pass-through as all of the engine sensor wires - I see from reading some older posts that this is a bad idea. I'm going to drill another hole and move my p-leads to it this afternoon. Hope that fixes it.

As far as my alternator problem - I'm almost certain that I didn't even run a ground to the alternator, just the field and b-lead. Clearly that's wrong, so I'll check that when I head out to the airport today.

Thanks again for the responses.

If your engine starts, your alternator is grounded. This is not your alternator output problem.

Recommend you do a ?strategic pause?. Instead of chasing individual items get another builder to review your wiring documentation, verify that it is in compliance with the SkyView and other component installation instuctions, and then verify actual wiring is per your documentation.

If you found this many problems on engine start, you have others yet to be found.

Carl

[Flying Canuck]

I see now that there?s no ground connection required for the alternator. I quickly found a problem with my installation though. My b-lead lug was contacting the alternator case, that can?t be good.
I just talked to the avionics guy who shares my hangar and he urged me to talk to Dynon before moving my p-leads. I?m doing that now.

[krw5927]

I think you found the problem...

Originally Posted by Flying Canuck

I see now that there?s no ground connection required for the alternator. I quickly found a problem with my installation though. My b-lead lug was contacting the alternator case, that can?t be good.
I just talked to the avionics guy who shares my hangar and he urged me to talk to Dynon before moving my p-leads. I?m doing that now.

[lr172]

Originally Posted by Flying Canuck

I see now that there’s no ground connection required for the alternator. I quickly found a problem with my installation though. My b-lead lug was contacting the alternator case, that can’t be good.
I just talked to the avionics guy who shares my hangar and he urged me to talk to Dynon before moving my p-leads. I’m doing that now.

That's a dead short for the alternator and any electrical system connected to it. If you have a fuse between the alternator and your master buss, you should find it blown. You must have one or you would have several melted wires and possibly a melted plane. This explains why you have no reading from your shunt.


That's a pretty serious error and I would suggest, like others, that you re-trace all of your electrical work and identify other isssues before flying, at least on the power circuits. At a minimum, I would want someone experienced with electrical work to inspect it.


Larry

[lr172]

Originally Posted by Flying Canuck

Thanks for the input. I've thought it through and the one thing that makes the most sense is interference from the mags. I routed the p-leads through the same firewall pass-through as all of the engine sensor wires - I see from reading some older posts that this is a bad idea. I'm going to drill another hole and move my p-leads to it this afternoon. Hope that fixes it.

Thanks again for the responses.

The P lead does not pass any current, and therefore no interference, unless you close the switch, which disables the mag. This is typically done only in a runup or other testing scenario. Proper procedure is to use shielded wire with the shield as the return path. This helps to nullify the magnet fields from the two wires when the mag is grounded. My P lead is only an inch or two from my min-x EFIS and have never had an issue. If your P lead is unshielded with a frame ground, they can throw of an oscillating and powerfull field.

Larry