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Can't seem to run LOP after a long climbout

bullojm1

bullojm1

Well Known Member
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!
 
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.
 
airguy said:
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.
Click to expand...

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.
 
rv6ejguy said:
I'd be really concerned about this in flight where high fuel flows should be keeping the fuel moving and relatively cool.
Click to expand...

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.
 
airguy said:
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.
Click to expand...

Thanks for the suggestion! This actually does make a lot of sense. I will order some firesleeve to add a second layer.
 
airguy said:
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.
Click to expand...

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.
 
Lean mixtures are very sensitive to ignition issues, I'd be looking at the ignition system (mags?) and plugs.

Like airguy said the high fuel flows at power pretty well rule out heated fuel issues.
 
airguy said:
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.
Click to expand...

This past week I wrapped an extra layer of fire sleeve around my fuel line between the servo and the spider. I only have two flights under my belt with this configuration, but so far it looks to of cured my issues.
  • After a steep climb out with my CHT's above 350, I can lean now.
  • My cruise CHT's seem to be lower because I am able to run further LOP than I could before

Below are some pics of my installation.

DSCN5105.JPG


DSCN5106.JPG
 
I haven't done it on mine, but you could also wrap aluminum tape on the firesleeve for a barrier to radiant heat. I figured just providing the layer of insulation would be enough, in my case (and apparently yours too) it was enough.
 
Aluminum Fitting?

bullojm1 said:
Below are some pics of my installation.

DSCN5105.JPG
Click to expand...

It appears that you have an Aluminum pipe to AN fitting on the inlet to the flow divider. FYI, Lycoming uses a steel fitting in that location, and this is definitely one place where I would want to use steel instead of aluminum...

Skylor
 
skylor said:
It appears that you have an Aluminum pipe to AN fitting on the inlet to the flow divider. FYI, Lycoming uses a steel fitting in that location, and this is definitely one place where I would want to use steel instead of aluminum...
Click to expand...

Skylor,

I am 99% sure that fitting is steel. Typically the aluminum pipe fittings have a blue anodized coating on them. This one appears like all of my other steel fittings. Next time I have the plenum off, I will get my magnet out to further inspect.
 
bullojm1 said:
Skylor,

I am 99% sure that fitting is steel. Typically the aluminum pipe fittings have a blue anodized coating on them. This one appears like all of my other steel fittings. Next time I have the plenum off, I will get my magnet out to further inspect.
Click to expand...

The AN816 adapter fitting appears to be blue in the picture which is why I asked, but it could just be that the black oxide finish appears blue. The flex-line end itself appears to be stainless.

Skylor
 
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