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28 May 2022, 16:39 [ UTC - 5; DST ]


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 Post subject: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 02 Apr 2022, 18:02 
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In a FAAST webinar last week, the presenter talked about turning the aux fuel pump on for takeoff and landing on fuel injected 1xx-series Cessnas, even though the POH doesn't call for it. His rationale was that should the engine hiccup, turning on the fuel pump is one of the first steps to be taken so you're that far ahead.

I checked the fuel system diagram for both of my club planes that are fuel injected ('79 182RG and 2001 172S), and neither shows a return path for excess fuel. So wouldn't turning the fuel pump on potentially be pushing too much fuel into the engine?


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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 02 Apr 2022, 18:19 
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Username Protected wrote:
In a FAAST webinar last week, the presenter talked about turning the aux fuel pump on for takeoff and landing on fuel injected 1xx-series Cessnas, even though the POH doesn't call for it. His rationale was that should the engine hiccup, turning on the fuel pump is one of the first steps to be taken so you're that far ahead.

I checked the fuel system diagram for both of my club planes that are fuel injected ('79 182RG and 2001 172S), and neither shows a return path for excess fuel. So wouldn't turning the fuel pump on potentially be pushing too much fuel into the engine?

No, unlike the CMI system, the Bendix system on Lycomings doesn’t use fuel pressure to control flow. Providing you have in minimum required pressure. For the two engines discussed, the minimum pressure is probably about 18psi. Max is around 45 or 50.

Boost pump on is SOP for Bendix FI systems on TO and LG in case the engine driven pump fails. The head pressure provided by the high wing is insufficient to keep things running.

Jeff


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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 03 Apr 2022, 07:33 
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Unless he has data to support his conjecture; no, nope, non, nyet, nein.

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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 03 Apr 2022, 11:06 
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Lycoming systems should have the boost pump on. Continental should have it off. They are very different systems. A Continental can go too rich and falter with high boost pump pressure. Lycomings don't have that issue.


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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 03 Apr 2022, 12:43 
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Location: Ann Arbor, MI (KARB)
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Username Protected wrote:
I checked the fuel system diagram for both of my club planes that are fuel injected ('79 182RG and 2001 172S), and neither shows a return path for excess fuel. So wouldn't turning the fuel pump on potentially be pushing too much fuel into the engine?


The R182 (aka 182RG) and 172RG normally have carbureted Lycoming engines (O-540 and O-360 respectively) with engine driven fuel pumps and aux fuel pumps. There are STCs for fuel injected engines for the R182 so your club R182 may have an IO-540, in which case the POH supplement should be your guide.

My 172RG POH advises to use the aux fuel pump in case the engine driven fuel pump cannot maintain 0.5psi minimum fuel pressure, and also instead of priming with the manual primer for starting the engine when warm.

My understanding is the carburetor installations in the R182 and 172RG are unusual to make room for the retractable nose wheel under the engine, so the head pressure from the high wing tanks is a bit less than non-RG carbureted 172 and 182 models. Hence the need for fuel pumps especially during climb at high power.

The fuel system diagram for my 172RG shows the aux fuel pump in parallel to the engine driven pump, and the POH says the following: “When the auxiliary fuel pump is operating, it draws fuel from a tee located between the strainer and the engine-driven fuel pump, and delivers it to the carburetor.” So in this case I think running the aux fuel pump and the engine driven pump simultaneously “just in case” might not be a good idea since it draws fuel before the primary pump.

The FAASTeam presenter making this blanket statement about aux fuel pumps and 100 series Cessnas strikes me as poorly informed, unless it was directed specifically at the injected Lycoming in the 172R/172S and delivered with a strong caveat to consult your POH for overriding guidance.

My comments here are not directed at the OP as much as for others who may see the thread and assume the discussion applies to their 182RG.


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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 03 Apr 2022, 13:23 
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I made a mistake in my cold-induced head fog, associating the aux fuel pump with fuel injection. Obviously not the case, duh.

The 182RG does indeed have a carbureted Lycoming O-540, and the system diagram shows the aux fuel pump in parallel with the engine-driven pump. The only mention made of it in the Normal Procedures section of the POH is in the before takeoff checklist, where it says to look for a rise in pressure, then turn it off again, or to use it if the engine can't maintain 0.5 psi fuel pressure without it.

The 172S has an IO-360, and the only mention of the aux fuel pump in the Normal Procedures section is during engine priming. There's no pre-takeoff check for it. The diagram shows the aux pump in series with the engine-driven pump. Ours has the earlier version of the fuel system, with no fuel return line from the fuel/air controller unit.


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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 03 Apr 2022, 18:05 
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Username Protected wrote:
I made a mistake in my cold-induced head fog, associating the aux fuel pump with fuel injection. Obviously not the case, duh.

The 182RG does indeed have a carbureted Lycoming O-540, and the system diagram shows the aux fuel pump in parallel with the engine-driven pump. The only mention made of it in the Normal Procedures section of the POH is in the before takeoff checklist, where it says to look for a rise in pressure, then turn it off again, or to use it if the engine can't maintain 0.5 psi fuel pressure without it.

The 172S has an IO-360, and the only mention of the aux fuel pump in the Normal Procedures section is during engine priming. There's no pre-takeoff check for it. The diagram shows the aux pump in series with the engine-driven pump. Ours has the earlier version of the fuel system, with no fuel return line from the fuel/air controller unit.


Do not use the aux fuel pump while taxing in the carbureted O-540 PA-24 Comanche. The fuel in the engine driven fuel pump will be bypassed, heat up, and vapor lock. When the aux fuel pump is turned off after takeoff, the engine will die due to the vapor lock.

The fix is to not taxi with the aux fuel pump on so that fuel is going through the engine fuel pump. The aux is only used for a short period during the actual takeoff. I would assume the same thing can happen in your C-182RG.


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 Post subject: Re: Fuel pump on or off for fuel injected Cessnas?
PostPosted: 05 Apr 2022, 05:02 
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Joined: 09/09/13
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Location: Ballarat, Australia
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In my 177rg I am happy to follow the POH. It does not call for the auxiliary fuel pump on takeoff and landing. I figure Cessna knows better than me.


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