R

Remag

Well Known Member
Hi, I'm a long time reader, first time poster. I have wanted an RV for ever and have just purchased one . It is a great machine and built in Texas before being imported into Australia this year (RV-7 built in Texas by Wayne Baker).

PROBLEM: After commencing flight, the engine instruments (all Vans steam gauges) and Tach will fail. The avionics will continue working. On most occasions, if I flick the Master off and back on (Avionics go off and on as well), the instruments will commencing working again, however, sometimes they won't and I land, wait a while and restart the master at which time they work again. The problem is isolated to engine instruments only.

If it was a faulty master switch, the Avionics would also fail; but they don't. I don't have a wiring diagram for the plane.

Any ideas?
 
Since you don't have a schematic for your plane, that's step one. With out one, you'll just be guessing at what is wrong. It doesn't have to be fancy or be put into a CAD application. Draw all you instruments on a paper, then start tracing all the wiring and drawing their path on the paper.

This will accomplish a few things. This first will be getting the electrical schematic documented, you will also become much more familiar with your plane's electrical design, last but not least, you'll probably find the issue.

I suspect that just by tracing each wire and inspecting both ends, you may find your problem. I would tug on each wire to ensure that all connectors are firmly attached. Look for chafing that may be grounding a circuit. Also look for oxidation and/or corrosion that may be impacting the circuit.

I suspect that the problem is a loose connection. Since it impacts multiple engine instruments, it may be a shared ground.
 
Welcome to VAF!!!!

Remag said:
Hi, I'm a long time reader, first time poster.
Click to expand...

Mark, welcome aboard the good ship VAF.

I agree with Bob's assessment, my first thought was a loose ground, or connection from the master switch.

This may take a bit of time to track down, but certainly sounds like you need to start following the wiring from end to end.

Good luck, and again, welcome.
 
Instruments

Is your Alternator switch on?

Pat

Remag said:
Hi, I'm a long time reader, first time poster. I have wanted an RV for ever and have just purchased one . It is a great machine and built in Texas before being imported into Australia this year (RV-7 built in Texas by Wayne Baker).

PROBLEM: After commencing flight, the engine instruments (all Vans steam gauges) and Tach will fail. The avionics will continue working. On most occasions, if I flick the Master off and back on (Avionics go off and on as well), the instruments will commencing working again, however, sometimes they won't and I land, wait a while and restart the master at which time they work again. The problem is isolated to engine instruments only.

If it was a faulty master switch, the Avionics would also fail; but they don't. I don't have a wiring diagram for the plane.

Any ideas?
Click to expand...
 
Welcome to VAF! Its like having Oshkosh on your desktop :D

Good news is the failure tells you its something in the wiring (probably) since all eng insts are affected. So, my first guess is its a wiring problem.

Are all the eng insts wired through a single breaker or fuse? Is there a single power feed to all the eng insts? I'd be looking for the single point that affects the engine stack.

I do agree you should work up a wiring schematic for the plane. Can you still contact the builder?
 
I had a Van's ammeter go bad and cause several other engine instruments on my instrument bus to behave strangely. I remover the ammeter and everything returned to normal. If the suggestions of a bad common ground or power connection turn up nothing, you could try removing one gauge at a time and see if the rest start working.

Paul Danclovic
Jamestown NC
RV-8A N181SB
 
I agree with Bob. I would start tracing your power and ground connections and draw a schematic as you go. First of all your assumption about the master switch may not be correct if the master switch is a double pole. The avionics and the instruments could be on the same switch, but not the same circuit. Start at the master switch and follow the wiring to your instruments. You may have to pull one at a time to check the connections. It sounds more like a loose connection on a common connection so start looking at the areas where the connections would be to all of the instruments. For example the first guage in a string or the ground connection to a grounding block.

Good luck.
 
Do all of the Vans gages go to a single fuse or breaker?

It would be easy to check by puling fuses/breakers, and if so, that would be a good place to start looking.
 
A relay...

could be the culprit. I use relays in several higher amperage circuits controlled by switches on the panel. If it is it should be fairly easy to track down. especially if it's mechanical and not solid state.(a clicking sound would be noticible.
Just my .02:confused:
 
Thanks for the help guys, I will most definitely have to produce a schematic.

It seems that the master switch may be a DPST according to the Vans accessories catalog. As we know, these work like two separate switches in one throw. So I'm thinking that one pole of the switch (the pole that supplies the Engine instruments bus) might be faulty while the pole which supplies the avionics master continues to work. It seems strange that I can get the gauges working again by toggling the master on and off a couple of times (may also be a faulty relay but i don't think I have any on that cct). It will only cost me $20 to find out if the switch is the problem by changing it out.

On another note, as Paul has suggested, the fuel pressure gauge appears to be intermittently faulty even when the other instruments come back to life. Perhaps this is bringing the others down. Either way, it will have to be changed out. I will disconnect this gauge and see if it makes a difference. Other than that, it will be a process of checking earths and connectors etc.

My aircraft has only one CB being an alternator breaker. I don't know what it is using for circuit protection on the other circuits (need to do the schematic).

Thanks for all your help, I am just loving flying the RV. These aircraft are amazing.

Mark.
 
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Remag said:
I don't know what it is using for circuit protection on the other circuits (need to do the schematic).
Click to expand...

The wiring kit supplied by Van's includes combo switch/circuit breakers and one CB for the alternator. That may give you a start.
 
A ground wire run in series (from gauge to gauge then ground) will cause problems. Make a jumper wire and replace one ground wire with a known good one. Don't have any other grounds on that gauge. Then do a test run to see if that gauge works. Grounds in series will also cause the gauges not to be accurate. You will really see this in the fuel gauges.
 
So if you have a DPST switch it should be very easy to tell if the two poles are wired separately. Just pull the switch or try to look at it somehow. If you have wires on one side only then both poles aren't wired. If you have them on both sides then both are used. I wouldn't buy a switch without looking first.
 
Rustic29 said:
The wiring kit supplied by Van's includes combo switch/circuit breakers and one CB for the alternator. That may give you a start.
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Great, that will explain the lack or breakers. Everything on this aircraft is stock Vans design, no mods, so I expect the switches will be a switch/breaker. Can't get out to the plane until Thursday and will spend the day with a multi-meter and screwdriver.
 
Problem Solved!

Went to the airfield today, had a play with the plane and located the problem.

It turned out to be a bad crimp on a blade connector at the back to the PCB behind the switch block. Problem solved, time to go flying...

Thanks for your help.
 
Remag said:
Went to the airfield today, had a play with the plane and located the problem.

It turned out to be a bad crimp on a blade connector at the back to the PCB behind the switch block. Problem solved, time to go flying...

Thanks for your help.
Click to expand...

Glad you found the problem, and thanks for posting the answer.

Have fun flying:D
 
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