Excessive fuel consumption advice needed

Seeking fuel consumption advice! I'm running a 4-cyl AEIO-360-A1E with a fixed pitch prop. The engine has run great for 700 hrs and all the operating parameters are terrific except for cruise fuel consumption @ approx 2500 rpm has risen from 10.5 gph to more than 14 gph over the past year!! I?ve asked for input from some of the best engine guys in the business and none have been able to even offer a theory about what might be causing it. Before I start spit balling rebuilding components I?m hoping that someone in this forum might be able to offer some direction.

I don?t have an engine monitor so I simply lean in cruise by pulling the mixture until the engine slows and then richening it until the engine runs smooth, and then richen it a bit further. Specifically, the engine will start to run rough when the mixture has been pulled 1.5?. Pushing it in a ?? causes the engine to run smooth, and then I?ll richen it another ?? to operate approx. 50-75 deg rich of peak. The mixture knob positions, EGT and CHT readings have not changed at all since my excessive fuel consumption problem developed.

Compression checks are excellent. The spark plugs look perfect and show no signs of excessive rich running. I don?t smell any fuel and have mounted gopros all over my belly to look for leaks out the vents and can?t detect any leaks. I have no fuel residue anywhere on the exterior of the plane or fuel tank.

Any input would be GREATLY appreciated!!!

Dave Scott
www.scottairshows.com
[email protected]

Without an engine monitoring system, how are you measuring fuel flow? By fuel consumption fill up to fill up?

If so go back to the one fact you have, you are using more fuel than before. The extra fuel going into the engine is just one cause.

At 14gph in cruise and you still lean as discribed, my first guess is the fuel is leaking somewhere. You report no blue stains but perhaps a closer look? As this is a new issue, I?d look at the engine driven fuel pump diagram drain port. Fuel?

After that look at the usual suspects.

Carl

couple ideas

idea one - does your plane sit out? Someone stealing fuel?

OK, maybe a more serious thought... I recently found that one of my sump to intake tube hoses had migrated enough to cause a bit of an air leak. I don't have a full engine monitor, but I have a hunch that would cause that one cylinder to run a bit leaner. Then if you lean 'by sound' I think the engine would start to run rough when that one cylinder gets too lean. Hence you'll end up with the mixture set good on one leaking cylinder, and too rich on the other 3.

Other than that, leaking fuel somewhere sounds reasonable too.

-Bryan

If you are pulling out 1.5? to rough and then going back in 1? i?d Suspect that you are way more than 50 degree ROP. Have you tried pulling out to rough and leaning to smooth and just leaving it there?

Not much help here.

OK, you have a good one. Most of the up-draft carb. engines are pretty simple systems. If you have confirmed that you do not have any leaks from the tanks or lines or a stuck or bypassing float needle valve. There are a couple three things to check before you start pulling out your hair. The fuel pumps on our flat fours will start weeping after many or even a few hours if a diaphragm gets leaky. That is why we put that drain tube down and out the exit air hole, so that if it does the fuel will go out into the slip-stream. You may not see any blue streaks or stains on the belly if this happens. And for the most part a diaphragm rupture will slowly increase in the size of the leak over time, " Not always". The enrichment valve in the Carb. also is another place to check as well as the float valve and seat. Some times the enrichment valve will get out of whack and direct a little more fuel into the mix than wanted. The float valve and seat are just like the one in your throne at home. The seat or needle will get trash in them or just get old and not seat well together and bypass some fuel and over fill the bowel so that it get sucked up into the mix.
These are only a few things to look out for, but they are the starting points for a fuel problem of this type. As an engine get older and has more wear it will pull less air through the pump and not more so if the system is working and has no faults, then you should expect the fuel consumption to decline not increase, so I would not think you have a problem with that end of you concern. Just some ideas. Not set in stone, but food for thought.

Yours, R.E.A. III # 80888
P.S. My bad, went right past the IO post at the top. You can pull the lines off after the fire-wall and pressure test them, all the way to the induction even the nozzles can be bench checked , BUT, yes it would be nice to have a full four channel EGT for this question. And if you are using a Red cube or transducer it would not be the first one that has gone astray, you can bucket test most of them with some small degree of accuracy. If you have a diaphragm pump the above still holds.

Looks like an injected engine from the description...

"I don?t have an engine monitor"

As you wrote "I don’t have an engine monitor"

How are you determining your fuel consumption? By pump tickets at fill up time / tach hours since the previous fill up? Weight carried and G's pulled will add dramatic fuel flow. If this is an S1 the G's much more than weight. But you don't state what airframe so we don't really know about the weight.

A cracked injector line or even a leaky solder joint on one of the lines at the spider can evaporate a surprising amount of fuel with no visable stains on the cowling. Stains on the belly are not always present, depending on where a leak location is.

Too many unknown or unstated variables here to offer much help.

Where do your fuel tank(s) vent?

Just a side note: 50deg to 75deg ROP is considered the worst place to run your engine.

If everything is the same and fuel consumption rises by 40%, I would start by checking for leaks downstream of the red cube as well as confirming that the red cube is still performing correctly and not giving bad readings. These do fail, though they seem to be erratic or report low when they do.

Pull the cowl and start looking for blue staining. If your fuel pump overflow is routed overboard, look for staining there or temporarily route it to a container to see if that is the source.

In theory, if that extra fuel was making it into the cylinders, you should see changes in the EGT from the higher fuel flow.

Larry