Starting issues and fuel pump ?

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robains
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Starting issues and fuel pump ?

Post by robains »

I'm able to start the Bonanza (manually) about 30% of the time. I can start it 100% of the time using Auto Start but where is the fun in that?

I've gone over the video and the manual and the checklist and although the video varies (Alt is turned on after engine start) from the checklist, neither method reliably works.

Fuses - all good
Fuel - left or right tank makes no difference
Fuel pump - sometimes the pump reaches 10-12 but sometimes it only makes it to 5-6 - puzzled? Why would the fuel pump sometimes register 10-12 and sometimes only 5-6 even after a battery change?
Overhaul - makes no difference
New Battery or different battery - makes no difference
Throttle 1/4 (although manual says FULL, then also 1/4??)
Mix - full Rich
Prop - full (but any position doesn't make a difference)

I'm beginning to suspect some sort of incompatibility with GoFlight SECM but even when I use VC controls/switches I still have the same issue.

The 30% of the time I can start, I have no idea why, using the same exact sequence.

Questions:
Any known issues with GF SECM? (SECM does turn on the FUEL PUMP and CARB HEAT and COWL, no way to really override)
Why is the fuel pump so inconsistent?
Any other clues on how to get the engine to start more consistently?

Cheers, Rob.
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robains
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Re: Starting issues and fuel pump ?

Post by robains »

A clue ...

viewtopic.php?f=108&t=35884&sid=d44fcbe ... a&start=15

different aircraft but, I'll check this out and see ...

Cheers, Rob.
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AviationAtWar
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Re: Starting issues and fuel pump ?

Post by AviationAtWar »

Your hard start is most likely related to the amount of time you're running the pump when priming. Here's how I've started the Bonanza since the beginning.



https://www.youtube.com/watch?v=4JuFDSDRa4w

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robains
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Re: Starting issues and fuel pump ?

Post by robains »

Thanks for the video.

After inspecting (Shift + 7), it reports as "flooded". This is a cold start and I followed the procedures exactly and ran the fuel pump for very short duration as in the video's I've seen (several) and still floods the engine. So I go thru the process to burn off the excessive fuel (throttle full open, mix set to full lean/off, fuel tank selector off, crank for a few seconds and repeat two or three times). I follow start procedure but this time I do NOT touch the fuel pump and the engine fires right up.

I don't know how off/dormant duration is being logged, and if it's based on PC date/time or sim date/time to establish a "cold start" flag, but it seems any use of the fuel pump (I stop it as soon as it touches green) and that results in an engine flooded. So I've removed the fuel pump On/Off from my checklist and just always leave it off and the Bonanza is starting 100% of the time now.

I don't know if this is a bug or just something specific about my setup?

Cheers, Rob.
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AviationAtWar
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Re: Starting issues and fuel pump ?

Post by AviationAtWar »

The reason you're seeing the different fuel flow readings when priming is because of different throttle settings. A lower throttle setting will produce a low fuel flow reading, wide open throttle will produce the highest flow.

I found that opening both the throttle fully and mixture fully and then waiting until the needle gets to the green makes it easy to flood, as you have also. I start mine with the throttle cracked, mixture rich, and run the fuel pump just until the needle stops climbing.

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robains
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Re: Starting issues and fuel pump ?

Post by robains »

Manual suggests:
1/4 throttle
pump reaches green
mix rich

that hasn't worked for me ... so far no fuel pump at all does work 100% of the time ... I'll stick with that unless it doesn't start ... then I'll try your throttle "crack" option and fuel pump.

What puzzles me is the IO-520-BB is fuel injected so don't really understand how or why they need fuel pump priming?

Cheers, Rob.
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AviationAtWar
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Re: Starting issues and fuel pump ?

Post by AviationAtWar »

I haven't tried starting without priming at all - I will now because I'm curious - but I'd be surprised if it didn't start more quickly with prime than without. Assuming an amount of prime that the engine is happy with, of course.

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robains
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Re: Starting issues and fuel pump ?

Post by robains »

But like I said, the engine is fuel injected, so turning a fuel pump ON doesn't activate injectors (those are controlled either electronically via a solenoid + ECU or mechanical pressure distribution pump) so no fuel would enter the combustion chambers.

https://www.twincessna.org/pdf/SID97-3G.pdf

Page 26

Maybe I'm missing something, but it seems to me the engine must be turning over in order for the injectors to spray fuel (see fuel manifold valve assembly)?

Cheers, Rob.
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AviationAtWar
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Re: Starting issues and fuel pump ?

Post by AviationAtWar »

The injectors are a fixed orifice, not solenoid controlled like a car. If fuel flows to the injectors under pressure it's coming out of the nozzles, which is why the fuel flow gauges climbs with the boost pump on and moving the mixture handle toward rich.


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robains
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Re: Starting issues and fuel pump ?

Post by robains »

This diagram shows the fuel going thru a manifold pressure control valves. It also seams to be a return system (most cars are returnless these days)

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Mechanical or electronic control, it would NOT make sense that turning on a fuel pump will flood all the cylinder chambers with fuel. If that were the case, if someone had accidentally left the fuel pump on when then turn they engine off it would most likely result in a fire and/or catastrophic damage.

Cheers, Rob.
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AviationAtWar
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Re: Starting issues and fuel pump ?

Post by AviationAtWar »

That's what would happen if the mixture and throttle were left open with the electric pump on. The engine is stopped by moving the mixture control to idle cutoff, which stops the flow of fuel to the injectors, so there wouldn't be any fuel flow out of the injectors after the engine is shut off if the pump was left on. The electric pump in the Bonanza wouldn't be on in any normal situation anyway, it's only use is for priming or emergencies (mechanical pump failure)

If there is fuel flow to the injectors, there is fuel flow through the injectors.

Leaving the electric pump on without the engine running and the mixture and throttle open will flood any of our injected A2A planes including the Connie.

Running the electric pump with throttle and mixture open is also how the injected 172 and 182 are primed.

AviationAtWar
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Re: Starting issues and fuel pump ?

Post by AviationAtWar »

All Continental Motors fuel-injection systems are considered continuous-flow injection systems, because fuel is delivered to individual cylinders at a constant pace without regard to intake-valve opening or crankshaft position. These simple systems, while fuel-wasteful by design, eliminate the need for spring-loaded injector nozzles and complex injection-timing devices. Fewer moving parts and relatively trouble-free operation are the trade-off against the efficient burning of fuel and air. There are four basic components to this system, only two of which are field adjustable.

The engine-driven fuel pump sends fuel under pressure to an injector assembly, which controls the amount of fuel directed to the manifold valve. The supply of fuel from the pump is determined by pump speed and relief-valve adjustment. How much of this supply is allowed to flow to the engine is determined by metering valves within the injector assembly. Both the pump and the injector are ground-adjusted to a predetermined fuel-flow rate at any given power setting. A mixture-control feature is included to allow the pilot to override these pre-set adjustments in order to properly lean the engine during cruise.

Metered fuel from the injector is then routed to the manifold valve, which has two main functions. The primary goal is to equally divide metered fuel between all six cylinders. The secondary objective is to provide a positive means of stopping all fuel flow when the mixture control is placed in idle cut-off. From this point, metered fuel is then fed through stainless-steel injector lines to the fuel nozzles. Injector nozzles are equipped with a calibrated orifice installed in the upper chamber, which controls the amount of fuel injected under a set pressure. The lower portion of the nozzle is used as a mixing chamber for fuel that has already passed the calibrated orifice and ambient (or deck) air, which is introduced for atomization.

Whether normally aspirated or turbocharged, operation of this fuel-injection system is the same. Fuel is pumped under a set pressure to the injector, which mechanically calibrates this flood for the power selected and sends the resulting flow through the divider valve (or manifold valve) to the nozzles. Excess fuel is sent back to the fuel pump from the injector to be reintroduced to the pump or returned to the aircraft fuel tanks, as demand dictates.

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robains
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Re: Starting issues and fuel pump ?

Post by robains »

Very interesting, thank you!

Definitely not efficient in terms of fuel economy but given the era, certainly better than carburetor(s).

Back on original topic, still able to start the engine without a short prime on fuel pump. But more testing and it seems fuel pump on just enough to get the pressure needle to move seems to work also (less than 2 seconds). Any more than about 2 seconds and that seems to trigger a "flooded".

Cheers, Rob.
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