Ultralight Aircraft - Added fuel injection and now burns more fuel and 212* cyl temp difference

Reporting from France-

I was helping my uncle with his ultralight airplane, which is practically a kite with a Rotax 4 cyl engine. He converted from carb to fuel injection with some kit and now it burns 15% more fuel then before. It was supposed to save 15% of fuel. One symptom is cylinder number one is an astonishing 212* cooler than the other 3 which match.

The other day, he flew across France to the guy who makes the kit and had it checked out. Everything checked out ok, but they replaced some sort of pressure sensor and the ECU anyway. 5 minutes after take off, the pressure sensor failed and the engine stalled forcing a emergency landing in a cornfield. Luckily nothing broke, they replaced the sensor and he flew back to where he lives.

Today, we replaced the fuel rail and both injectors which feed cylinders 1&3 (#1 is the one that is colder) and also the fuel pressure regulator. Still no difference. We also swapped the easy-to-get-to spark plug on #1 to #2 and no difference. Then we checked to see if there was a difference in temperature if we ran the motor one spark plug bank#1, spark plug bank #2 and with both running. No difference.

Cylinder #1 running too rich has to be the culprit for the extra fuel consumption and temperature difference right? I just don't see what could be the issue if the guy who makes the kit says everything checked out right, and we've replaced pretty much the entire kit ( now ecu, pressure sensor 2x, injectors, fuel rail an regulator). Vacuum leak? But I would think that would make it run more lean. Any other ideas?

Today, we replaced the fuel rail, inject

I have no answer for you, but I am fascinated by this. Please keep us updated.

It sounds to me more like a dead cylinder, that puts the temp on #1 at something like 90*? We're talking in Fahrenheit here right? Check the compression on #1? Ignition system fault? If its port fuel injection I cant see how one cylinder would be able to go rich like that, and you would see it on the plug color, plug 1 would be black.

I think Kenny is onto something there. Check the compression

+1 on compression check.

I'm guessing its a 912/914? If the aftermarket injection is like the original carb setup, cylinder 1 and 3 should be fed by the same port. If you have no more compression on cylinder #1, you might be unable to ignite the fuel, so it stays un-burned inside cylinder #1. So the computer would detect a lean condition on cylinders 1 & 3, and would dump more fuel in. Try to smell the oil. Does it stink of gas?

Edit: keep us informed, I didn't even know someone made an injection system for the 912/914.

Possibly a fuel Injectors leaking? swap it around with another and see if the issue moves cylinders. Kenny is dead on though with a compression test.

I'd also pull the valve cover for the offending cylinder and have a look for anything out of the ordinary. Maybe it wiped a cam lobe?

Holy crap those are expensive!

Rotax engines cost nice car money!

In reply to motomoron:

That's a E36 M3load of cash for what's basically a fancyass VW motor.

Other than asking why #1 is getting more fuel than the others, I can't really help.

I would ask however how an Ultralight gets a 4 cylinder engine. The pic below is what I think of as an Ultralight. Is Unc's ship perhaps a Light Sport plane? <150hp, can't fly IFR and not at night. (looks like an airplane, not a hang glider).

The definition of ultralight depends on the country. For example, the following planes are considered ultralights in Canada:

It only has to follow the three following rules:
-Maximum 2 seats
-Maximum 1200 lbs gross weight
-Maximum stall speed 45 mph

I think France has similar rules.

^^ what fanfoy said. Our LSA = everybody else's "ultralight"

Ah, got it.

Thanks.

If it was indeed a compression issue wouldn't a 4cyl run audibly awful on three cylinders? And be way down on power? Is it possible it's "just" dumping lots of fuel into #1 for some other reason?

JoeyM wrote: ^^ what fanfoy said. Our LSA = everybody else's "ultralight"

This is making more sense to me now.

ebonyandivory wrote: If it was indeed a compression issue wouldn't a 4cyl run audibly awful on three cylinders? And be way down on power? Is it possible it's "just" dumping lots of fuel into #1 for some other reason?

The way I'm reading it now, its got two injectors, one per bank. Unless the computer went reallllly dumb, there's almost no way this is fuel related.

Im still betting on a dead cylinder.

Kenny_McCormic wrote: It sounds to me more like a dead cylinder, that puts the temp on #1 at something like 90*? We're talking in Fahrenheit here right? Check the compression on #1? Ignition system fault? If its port fuel injection I cant see how one cylinder would be able to go rich like that, and you would see it on the plug color, plug 1 would be black.

We are talking Fahrenheit, but only because of my conversions. With the laser thermometer on the exhaust manifold, 3 cylinders were running at 310 Celsius, cylinder #1 at 200. When he flew to the guy's place who builds the kit, they did a compression check and everything was fine. The plane is only a year or so old and my uncle is extremely meticulous with maintenance so I would be surprised if it was a compression problem. Also, plug one was black.

fanfoy wrote: +1 on compression check. I'm guessing its a 912/914? If the aftermarket injection is like the original carb setup, cylinder 1 and 3 should be fed by the same port. If you have no more compression on cylinder #1, you might be unable to ignite the fuel, so it stays un-burned inside cylinder #1. So the computer would detect a lean condition on cylinders 1 & 3, and would dump more fuel in. Try to smell the oil. Does it stink of gas? Edit: keep us informed, I didn't even know someone made an injection system for the 912/914.

I think it's a 912 but I will double check. 1 and 3 are fed by the same intake manifold/TB but there are two injectors, one for each port. Also, there is no sort of o2 sensor on this setup (which was curious to me) so I don't see how the computer would detect a lean condition to begin with. I'll smell the oil and see if I notice anything.

ebonyandivory wrote: If it was indeed a compression issue wouldn't a 4cyl run audibly awful on three cylinders? And be way down on power? Is it possible it's "just" dumping lots of fuel into #1 for some other reason?

I would think so but it runs/flys fine (minus the emergency landing in the corn field). Sounds good too. I believe he flew the plane like this all the way to Romania too. He says it runs great. It can idle at a lower speed and he says it feels smoother, but it burns 15% more fuel than with the carbs, which is the opposite of what it's supposed to do.

Kenny_McCormic wrote: The way I'm reading it now, its got two injectors, one per bank. Unless the computer went reallllly dumb, there's almost no way this is fuel related. Im still betting on a dead cylinder.

Yes. I kinda agree but if it runs so good / no noticeable loss of power how could that be? Compression check checked out, maybe we will pull the valve cover or do a leakdown test.

His rig:

Is that the bridge at Millau?

pull the valve covers and check that the valves are moving properly. Now that I see what the engine looks like, I bet it is like an air cooled vw. With two pushrods in seperate tubes beneath the cylinders. you could have a bent rod or a loose rocker arm or rocker shaft

Ah, exhaust manifold, I thought you meant cylinder head temps. The only things you really haven't ruled out are a bad injector driver(depending on if its batch or not) and something wrong with the valve train(wiped cam, bent pushrod, etc) or ignition.

You've ohmed out all the wring to that injector, right?

motomoron wrote: Holy crap those are expensive! Rotax engines cost nice car money!

I'll say they are...but why does the 2-stroke 2 cyl cost so little (relatively speaking)?

mad_machine wrote: pull the valve covers and check that the valves are moving properly. Now that I see what the engine looks like, I bet it is like an air cooled vw. With two pushrods in seperate tubes beneath the cylinders. you could have a bent rod or a loose rocker arm or rocker shaft

Thanks, we will take a look.

Kenny_McCormic wrote: Ah, exhaust manifold, I thought you meant cylinder head temps. The only things you really haven't ruled out are a bad injector driver(depending on if its batch or not) and something wrong with the valve train(wiped cam, bent pushrod, etc) or ignition. You've ohmed out all the wring to that injector, right?

Bad driver would be the computer right? That has been replaced once already, as had both the injectors on that side.

Nope, we have not. So just make sure good wire going to/from the injector? It's brand new but worth a shot.

As far as the possible valve train issues, I wonder if we can rule that out. He keeps track of fuel consumption all the time, and as soon as he swapped to the fuel injection he dropped 15%.

Thanks for the suggestions everyone! I will report back with what I find.

On a side note, somewhat surprised that no one finds the TDI 4motion Tiguan completely badass.

Missed the new computer, if that's the case I'd be tempted to say the EFI is fine, potential wiring issues aside. I dont think it would work at all with the injector hooked up backwards or I'd suggest that. From whats been provided, I do think the EFI conversion might be coincidental to the actual problem.

How is ignition controlled on one of these? Id assume any HV leak would show up on the radio as noise, so if its ignition related it would have to be on the low tension side or a bad plug.

Enyar wrote: On a side note, somewhat surprised that no one finds the TDI 4motion Tiguan completely badass.

I do, but was trying to stay on topic...