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  #1  
Old 04-13-2016, 10:26 AM
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bullojm1 bullojm1 is offline
 
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Question Can't seem to run LOP after a long climbout

I've noticed an issue recently where I cannot seem to run LOP smoothly after a long climbout. Going down to SNF I was flying relatively low - 4500' to avoid the headwinds. My CHT's on climbout only got up to about 300 degrees. I had no issues with the engine running smoothly LOP, burning 7.8-8.2 GPH, and leaned out to roughly 20-40 degrees LOP.

Coming back I climbed up to 9,500'. On climbout the CHT's reached 370 degrees. When I tried to lean, the engine would surge and stumble any any mixture setting leaner than peak. I pulled back the throttle to cool the engine down. Once the CHT's went down to the low 300's, I could easily lean the engine LOP.

This is not the first time this has occurred, and it always is correlated to highest CHT's. I am running a Superior IO-360 with a vertical sump, Precision Fuel Injection with the Sam James short cowl and plenum. Oil temps are always around 180 degrees. OAT doesn't seem to matter. It happens with the OAT across the board (except when it is too cold for the CHT's to get above 300).

My thought it is has to be related to the fuel system getting hot - either the fuel divider, fuel pump or the lines going from the divider to the injectors. Before I invest in some thermocouplers to take temperature readings on my fuel system, I thought I'd see if anyone else has had this issue and can offer some advice.

Thanks and I appreciate any assistance!
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  #2  
Old 04-13-2016, 10:31 AM
bkthomps bkthomps is offline
 
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Boost pump running the whole time? Sounds like classic vapor lock, share an engine monitor datalog
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  #3  
Old 04-13-2016, 10:31 AM
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airguy airguy is offline
 
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I discovered a similar issue early in Phase I on my 9A, I wrapped a second layer of firesleeve around the fuel lines from the firewall penetration all the way to the servo, and from the servo to the baffle penetration going upward toward the spider. This seemed to solve the issue, and now I'm testing 91 premium auto fuel alongside 100LL with this setup.

I will say up front that the 91 premium does not provide the same results as 100LL - I can't run LOP with it, the engine runs a fair bit warmer with it, and I appear to lose perhaps 5% power on the same fuel flow - but the ability to save $1.30 per gallon (local current prices) in cruise flight is pretty attractive.

I guess my results with autofuel testing are similar to the auto-engine guys - it's fun doing it, but it's not what the marketing would have you believe. If you want book numbers without having to jack around with it, run 100LL.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 900 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #4  
Old 04-13-2016, 10:42 AM
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Quote:
Originally Posted by bkthomps View Post
Boost pump running the whole time? Sounds like classic vapor lock, share an engine monitor datalog
No boost pump, just engine pump.
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  #5  
Old 04-13-2016, 10:46 AM
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Quote:
Originally Posted by airguy View Post

I guess my results with autofuel testing are similar to the auto-engine guys - it's fun doing it, but it's not what the marketing would have you believe.
Many of the auto conversions using EFI, run Mogas, including me for 200 hours- no issues. Same goes for a number of our Lycoming customers. The higher pressures with EFI give higher resistance to boiling.

I'd be really concerned about this in flight where high fuel flows should be keeping the fuel moving and relatively cool.
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  #6  
Old 04-13-2016, 10:57 AM
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Quote:
Originally Posted by rv6ejguy View Post
I'd be really concerned about this in flight where high fuel flows should be keeping the fuel moving and relatively cool.
It wasn't so much then that I was seeing the problem - but during longer low-power ops I was getting heat-soaked on those fuel lines and seeing vapor bubbles, so I added the insulation.

I think I want to change to a smaller injector orifice too, to raise the pressure downstream of the servo to give myself a little more margin against the boiling point. My fuel supply pressure using the AFP pumps (dual electrics, no engine-driven pump) is a stable 38psi so I've got some room to play there.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 900 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #7  
Old 04-13-2016, 10:58 AM
bkthomps bkthomps is offline
 
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Quote:
Originally Posted by bullojm1 View Post
No boost pump, just engine pump.

Any logs? If vapor lock your fuel flow numbers would decay
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  #8  
Old 04-13-2016, 11:02 AM
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bullojm1 bullojm1 is offline
 
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Brian,

No logs - I'll enable them the next time I go up.
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  #9  
Old 04-13-2016, 01:39 PM
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bullojm1 bullojm1 is offline
 
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Quote:
Originally Posted by airguy View Post
I discovered a similar issue early in Phase I on my 9A, I wrapped a second layer of firesleeve around the fuel lines from the firewall penetration all the way to the servo, and from the servo to the baffle penetration going upward toward the spider. This seemed to solve the issue, and now I'm testing 91 premium auto fuel alongside 100LL with this setup.
Thanks for the suggestion! This actually does make a lot of sense. I will order some firesleeve to add a second layer.
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RV-7, Flying!
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The Best FAA N-Number Availability Search Engine -TailNum.com
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  #10  
Old 04-14-2016, 07:04 AM
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rleffler rleffler is offline
 
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Quote:
Originally Posted by airguy View Post
I think I want to change to a smaller injector orifice too, to raise the pressure downstream of the servo to give myself a little more margin against the boiling point. My fuel supply pressure using the AFP pumps (dual electrics, no engine-driven pump) is a stable 38psi so I've got some room to play there.
That was the first thing Don Rivera recommend for my RV-10. He swapped out the 0.28s for 0.25s before we started the balancing process.
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