Is my airplane haunted?

Briar Rabbit

Briar Rabbit

Line Up and Wait
Joined
Mar 22, 2017
Messages
626
Location
Albion, Nebraska
Display Name
Display name:
Rob
Nice day yesterday so decided to practice a few touch and goes at dusk/dark. Ice in front of the hangar so a bit of a challenge getting the bird out. Preflighted, climbed in, pulled out the checklist and got to the point where I turn on the fuel pumps. IO-520 so a low and high boost pump. The low does not operate until the throttle is open and starter is engaged. So to initially prime the system you have to run the high boost pump. I always turn on the low pump first and then watch the fuel flow gage for movement when I turn on the high pump. When the needles come off the peg operate for about 3 to 5 seconds and then off with the high pump. So I am at this point and turn off the high pump when the starter engages on its own and turns the prop about 10 inches??? WTF? I then turn on the key and crank the prop about 4 revolutions - no fire so again run the high boost pump a bit, turn off the pump and the starter again moves the prop another 10 inches or so. I know it is going to be a nice flight but I have never had an engine want to start on it’s own?

I just had the fuel pump replaced and they also replaced the two boost pump switches. Obviously there is a gremlin in there so it is going back to the shop next week. Also I noticed that the charging system is not working during climb out, negative 4 to 5 amps above 2600 RPM but normal at all RPMs below that weird? Went negative on every climb out about 8 times and started working when I throttled back, even when taxiing back in at idle. And my panel lighting has an issue with the two rheostats turning on the same lights. This will be the third attempt by the avionics shop to get the new panel lighting wired correctly.

Must be haunted!
 
You flew the plane after the boost pump activated the starter twice? :eek:
 
Salty said:
You flew the plane after the boost pump activated the starter twice? :eek:
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I had a phone discussion with the mechanic that works on the airplane before flying it and was told that the issue was related to the low pressure boost pump switch. He had seen that issue before. When that switch is turned off it would not be an issue. But I am going to get it fixed before flying it again.
 
Keep flying it. What’s the worst that could happen? We’re trained for emergencies. Use that training. “Use it or lose it,” I say.
 
Briar Rabbit said:
I had a phone discussion with the mechanic that works on the airplane before flying it and was told that the issue was related to the low pressure boost pump switch. He had seen that issue before. When that switch is turned off it would not be an issue. But I am going to get it fixed before flying it again.
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What is the purpose of having an electric fuel pump on your plane? What the purpose of the switch? Rule 1, don’t take sick airplanes into the air.
 
JOhnH said:
Sorry I can't help, but I do have a question:
What plane do you have? I have an IO-520 in my V35 but only one boost pump.
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It is a Cessna 210K. The only time the boost pumps are used is during the starting sequence. The boost pump switches are never turned on again after the engine is started.
 
Briar Rabbit said:
It is a Cessna 210K. The only time the boost pumps are used is during the starting sequence. The boost pump switches are usually never turned on again after the engine is started.
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FIFY, read your emergency procedures. If you lose a fuel pump that switch has to work properly.
 
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In an “IO-whatever”, I think you want the ability to have a boost pump in case your “regular” injector fuel pump goes out.
 
Good point. Even though it is a new engine with a new pump and given I never left the pattern and that the low boost pump which would be the one turned on in that scenario still worked you are probably correct. Adequately chastised.
 
Ryanb said:
Agree, especially after about the age of 65, but they also have medication nowadays that assists with those emergency situations...
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Already got a script, at your age? Wow.... I am just assuming you only know of these meds if you need them...
 
That pump system has a "start" function that turns the pump on when you hit the starter if the switch is set to "Start." The mechanic has miswired the new switches so the starter is getting fired when you switch off. It's firing the contactor, perhaps because the diode is shorted or missing. Or something else altogether is possible, implied by the poor cranking when that happens.

That system has other problems. There are specifications for pump pressures, pressures that are adjusted by moveable contacts on a pair of power resistors on the firewall. I often found them WAY off, a real problem if the pilot lost the engine-driven pump and had to use the emergency boost function but didn't get the right pressures at the right throttle settings. And to add to the misery, Cessna started supplying Weldon pumps instead of the original Dukes pumps just a few years ago, and the Weldon provides the same pressure on less current** than the Dukes, so it runs too fast and the existing resistors are inadequate to reduce the pressures to within limits. I complained to Cessna about it and got some different resistors, but they never issued an SB on it. One has to wonder how many incorrectly-calibrated systems are flying around now. Too many folks just replace the pump without checking the system for accurate pressures and throttle switch setting.

See this: https://www.jpinstruments.com/wp-content/uploads/2012/08/SID97-3F.pdf

If you have a new Weldon pump, you likely need more than just corrected wiring at the switch.

**Less current means that the resistors don't drop the voltage as far as they would with a larger current through them. So the Weldon pump runs too fast and creates pressures above the limits and the resistor ajustment range is inadequate. Your mechanic needs to talk to Cessna.

There was an SB back in 1996 to replace resistors to suit the Dukes pump. The original resistors were physically too small. A lot of airplanes never got this done, too, since it wasn't an AD. Near the end of the document are the schematics for the wiring for various models.
https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=22254
 
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