Rotax 912 switched to Fuel Injection. Engine still wont run Right. Any ideas?
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- Опубліковано 7 лют 2025
- I went to help Tom tune his new Edge Performance fuel injection system that he had just installed on his Rotax 912. He went to fuel injection because he was having issues with the carburetors for quite some time.
he flys a Rans S7 bush plane.
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The engines still in KS, new parts in, cam and lifters, probably back on the test stand tomorrow to confirm he for sure found the problem, and hopefully back in the FEDEX system Monday, just in time, mark my words, to ALMOST make it here for next weekend, but not quite!
So how did we get to this stage ? I was waiting to see the results from one of your previous comments about you having taken the valve covers off. Did this guy you sent your engine to actually have findings? Please reply, thanks.
Im interessted as well did you have any updates?
Always good to see Tom in one of your vids!
Cool! I loved every minute of this. Tom's a cool cat - thanks for introducing him to us. Your camera/computer/phone juggling was impressive...and entertaining, crazy man.
Thank you!!
Tom was a good watch on your channel! But, he left us hanging how many fat girls had been in that back seat 😂😂
Rotax 912 are famous for coil ignition issue, genuine ones are mounted in top of the engine, taking vibrations and heat. An easy trick is to heat them up with a hair dryer, and test your engine with hot coils.
Easy, cheap test.
Had a similar issue with my rotax few years ago,ended up being a bad trigger coil. You can check the continuity at the coils. They also have a gap between the coil and Mag that is important to have corect. Good Luck
Checked it.
I learned to fly at Utah State Aeronautical Program in Logan, 1954. We had two Aeronca Champs, T, Craft and an L5 which we rebuilt in the Lab for the club. Cost was $5/hr dual and $2/hr solo. I spent a lot of time flying the air currents around Mt. Logan and harassing's the groups of elk and deer My buddy Jay Carter and I rebuilt a champ, using student labor and surplus dope and fabric. I envy your instruments. We had a wire on a cork for fuel, tack and air speed as well as a compass. I believe we also had a turn and bank indicator. Some things never change. Dean Reese was our instructor and Hugh, Summers and Louie ran the Aero Dept.
Dave Hansen
She's all ready to go! I ran it up and all seemed real good, now I'm just waiting on the weather, but not until I fly it at cruise power for a while will I know for sure it was the camshaft. Before, it also started and ran fine during runups (which I limit to about 3500 rpm) , it was only in flight and at 5,000 RPM that the real bad missing started, and persisted.
What was wrong with the camshaft, was it worn out?
@@Ayastracci It may have been defective, but the lobs, one in particular, were badly worn, clearly visible when eyeballing it.
For me, it turned out to be the injector pump and or valve stem, in one way or another. First thought was a leaking center body seal, but they tested for that and no joy. Finally, since we've changed out every other part over the past few years we installed an overhauled injector pump and stem. That fixed the issue. even the issue didn't show on the pc.
The possible root cause was one of two items. Some internal damage inside the pump, but NOT a leaking center body seal, or when installing the pump the mechanic noticed that the two nuts holding the top of the pump on were not as tight as they should have been.
His airstrip is crazy! Open the door and off to work!
OK, I've now watched the video and followed through with some research.
First, I'd check fuel pressure at the rail before the injectors could be partially plugged fuel filters or a below peak performance pump.
Second, timing advance, I know depending on how old the Rotax is it changes the advance from 4 degrees to 26 degrees could be something with it.
Third, i don't disagree with valve springs and floating valves at high rpms.
My synopsis would be to start with the most simple and check fuel pressure where it started suddenly but has been persistent this would be a great starting point!
Good luck guys let us know what you find
Agree issues is fuel delivery, hoses, vacuum or pressure. Something in that is probably the issue. Maybe even fuel tank problem.
Pressure and vacuum test all the fuel systems: hoses, rails, injector connection points, pump pressure, tank pick up, flared fittings or dissimilar metal connections (example: brass to steel, hose barbs). Fuel injection fuel delivery is pretty complicated and MUST be perfectly efficient through all rpms with flow input and return correctly designed and calibrated. Since this was a carbed engine before may have had different fuel line requirements.
From hearing it run in the video at 5000+ it does not sound like a “miss” but a starve for fuel, fuel restriction issues.
After changing ignition coils and plugs, I'd want to look at valve springs. Could have a problem there which could affect rpm at the same place, valve float.
*Good Idea. An over heated engine could take much of the temper out of the springs especially the exhaust-valve-springs.*
That and valves might not be seating properly or hard enough or too hard.
I concur.
@@garyt6591 *I had this happen and it drove me CRAZY! It turns out the Exhaust valve springs where so weak they where sucking in hot fumes from the exhaust manifold and giving me a crapy burn at high RPM!*
@@johnsluggerunbelievable- I sold a plane because I couldn't figure out this issue. And dumbass mechanics couldn't correlate why an rpm drop with overheating.
trigger coil gap (be sure and use brass feeler gauge) check all grounding wires
Checked, all good.
Trigger coil gap. I believe the specified air gap range is 0.012” to 0.016”. Worth a check to make sure they are in Spec.
I have the edge FI on my 912 in a zenith 750. When I was carbureted I had more trouble with it generally between the 3800 to 4800rpm range, but it will consistently run smooth now with the fuel injection through that range but with my prop all I've ever seen is about 5300 RPM.
The biggest in improvement I noticed on the fuel injection is throttle response and instant power, there's no lag like in the carburetors.
I did notice that my cylinder head temperatures did go down on average about 10 to 15°F With the fuel injection
It was a costly addition but if you wait six months and then look back on it you will say it was a great purchase.
I'm gonna say he's got a cracked porcelain or something on a plug or two.
Check plugs for correct resistance, may be breaking down under high pressures, also lots of counterfeit ngk plugs around now made with poorer quality.Should be around 5000 ohms. I've found some that were way out of spec.
45 yr mechanic and i tend to be in the valve spring train of thought. first inspect but after that they gotta come off for real spring pressure testing
I am leaning towards the valve spring issue, after chasing down rabbit holes for the last 2 months (could be this, could be that, anything is possible) BUT I do have a non stock cam, developed by Hal Stockman and installed by him about 900 hours ago.
generally speaking a vacum gauge should bounce at higher rpm or any rpm depending on how bad it is. but by the time it hits 5k and to stumble vacume will bounce so its a test you can do but experience is key @@portnuefflyer
*Check the Exhaust for obstructions!!!! I found 2 dead Rats and a large nest in my exhaust pipe that had turned to carbon and at different times they would land just right and block the exhaust.*
I found a intake valve stem retainer clip partially broken, 2 piece normally, this was in 3 pieces when removed. The first anomaly I've found in chasing down this gremlin, while it appears the broken clip was still doing it's job in retaining the valve stem, I am of course replacing it. Also new springs on that cylinder, test flight coming up, depending on the weather and my work schedule.
i was thinking a valve spring / sealing issue oddly enough i just fixed a Honda pressure new low low hours with odd running issue ported head lapped vales re jetted drill out one size up it in and now its golden but lol, God bless frUm east tennessee
So where are we at with this issue ? Did you get to run it yet ? Has the weather been good enough to fly it yet ?
Great filming job, under tricky circumstances!
Engine back, got another 3 or 4 hrs. to finish the re-install, that's means probably one more full day! It ran great on the Kansas test stand.
Hope you figure out your engine problem. You are looking good. Take care.
OMG Autronic!
That is an ancient ECU that is about twenty years old tech.
Things have moved on so much.
Excellent tech help on the phone to which I agree with his assessment that the problem is not related to the ECU but elsewhere.
Over advanced ignition timing at rpm will cause an engine to run rough. Find or mark an accurate TDC then check actual timing with a timing light against what the ECU is indicating.
This was my first thought
@@jeremymason1684I'm assuming they've checked the basics like huge plug gaps or broken valve springs.
Lots of advice. Hope it helps.
100% plug wires for sure should be first thing to check.
Ignition coils ! Could also be the ignition boxes. Had a similar issue and I had to get coils and a stator fron Hal Stockman a few months back. Remember to call him Jonas he is the go to for this sort of issue and parts.
Interesting put some iridium plugs in there or a little hotter or somethings lose when it hit maximum power and vibration definitely check that or try both fuel pumps at the same time 👍👍👍🇺🇸
It's on a FEDEX truck on it's way back to me, after the new cam and lifters were installed, and put back on the test stand, Mike ran it full power for an extended period and it now kicks ass! So, it would appear the initial problem was indeed caused by a cam with bad lobes, resulting in improper valve actuation. I'll post here again when it's back in the plane and flown.
Autronic ECU ; truly an experimental install, like most ECU companies; including Autronic; they do not like aircraft installs; so it is impossible to get support if you tell them it is an airplane.
I use a Haltech ECU on my Mazda 13B rotary; with much success including rotor balance adjustment on the cockpit panel as well as mixture control as you would if it was a carburetor. Love it.
I'm no airplane mechanic....but I did stay at a Holiday Inn Express last night. My first thought after hearing about the issue before AND after the fuel injection upgrades was valve springs.
Might be...
Another test flight showed the valve spring work didn't change a thing, the same exact issue occurs as before and after the EDGE EFI install, so obviously the problem is not fuel intake related. I decided to ship it, after building a heavy duty crate for it, scrouging material from a few construction sites I was already on anyway (free) to the Kansas EDGE dealer Mike, not because I suspect the EFI but because he's a expert Rotax wrencher, with a test stand, AND an EDGE guy also. Hal would have had to re-convert it back to the carbs before putting it on his test stand, and that would have confused things possibly. I should have some results in a few days.
I agree with the valve spring or a timing issue if your springs are weak that would cause them act to slow or possibly a stretched timing chain that has the timing off just a tad
Rotax 912 series engines do not have timing chains
1. Coil packs might not be getting enough power from wire danmage exc. 2. Valve issues. Both in my mind could start at higher cylinder pressure. I could be wrong but it doesn't hurt to check.
Is Tom planning to adopt someone? I really want to be adopted by Tom. I can drive trucks and cut trees. Tom is absolutely awesome and I want to him to live 150 years. We need people like Tom.
Good morning from Minnesota! Huh???
I made a tool for checking the compressive strength of the valve springs, without the need to remove them from the engine. After going around twice, just checking one exhaust valve in each cylinder (I'll need to flip the tool around and maybe do a little mod to it to check the intake valves, ) and found them all real consistent, except for one cylinder, it was 25 to 30% weaker than the others. I have no idea if that's the issue, but I ordered 2 new springs just to eliminate the possibility.
I test flew it today for 2 hours, the EDGE EFI is complete and as far as I'm concerned totally airworthy. My original problem, that started on 6-25-23, with the carbs, persists however! Badly missing, crapping out, around 5K RPM. Whatever it is, it has nothing to do with the EFI, fuel flow, or the electrical system. Floating valves is looking more and more as a possibility, just using the process of elimination.
Thanks for the update Tom!
test your plugs under a pressure load. NGKs are known to break down under pressure loads for no reason!
Sure good to hear the familiar names. Jonas, Tom and Hal. what a bunch of great guys. Hope you get the problem figured out. But you didn't state why or advantages of switching over to fuel injection over tried and true carbs. I'd be curious.
The EDGE comapany site does a pretty good job of that.
I like your suggestion on the different size prop to get it up to a higher RPM
The same prop the last 2500 hours, it's not the issue.
have you figured out the problem yet @@portnuefflyer
I’ve seen spark plugs lose spark under pressure in a champion spark plug testing unit.
For what it's worth, I just solved an intermittent issue with a Polaris engine. The coil was the problem. Spark is good
ok time to get out a PicoScope and all so check the grounds and conectors for the green crustys its electrical for sure
If you are running spark plug caps that screw on...remove them from the wires and check their resistance as they normally have a small pellet resistor inside and they'll deteriorate with time which increases their resistance. Sooner or later it gets so high that it limits how much pressure the spark will still jump. I'd do that first before digging in any farther as we've seen these cap resistors go bad lots of times on motorcycles and automotive applications. Resistance should be right on 5K ohms.
Also...when you pull the cap off of the plug this can stress the connection of the cap to the wire core....so it's good practice to nip 1/4" off of the end of the wire which should expose fresh core for the cap screw to dig into for a good connection. These things cost $0.00 and should be eliminated before spending any money.
Tom is a pretty amazing guy.
No change, after replacing the valve springs, I'm out of options and have pulled the motor, my next move will be to see if I can get Hal Stockman to put it on a test stand in his shop.
Valve springs!
I had something very similar happen with my engine. It turned out that both ignition modules and all the coils were grounded with one large wire, and most of the strands of that wire were broken at the ring connector. It didn’t have enough grounding at higher rpm’s
Rev limiter going off...?
Focus on your ignition system only. If spark is falling out then it's ignition. Systematically go through each component with careful attention to coil (high voltage and pickup) and all connections and grounds in the ignition.
Did that, months ago.
@@portnuefflyer Do it again with separate eyes.
Had a very similar problem in a truck. It was plug wires. 🤷.
Tom when mine hits around 190 cht it will start missing on both mags but if you let it cool down while in flight to just below 185 it will smooth out and as long as you hold it below 190-195 it runs fine, but I have the the aftermarket boxes on it with the 12 volt wire on them to hook to direct 12 bolts with a switch and turn the switch it will run smooth at 190-195 all day long if you turn the switch off at those temps it will start missing again. It’s a mystery that was the reason I changed from rotax boxes to the aftermarket ones but the same thing. I also put in a stator new fly wheel the only thing I haven’t done yet is to air gap the triggers.
Tom and yourself need to make a channel
Sounds like spark wire problems; the high RPM (full load) and if you have distributor cap.... LOL writing while watching the video... when the guy on the phone said the same thing.
The higher the load the higher the spark voltage is required and it is more likely poor wires will spark to ground intermittently.
A dirty (conductive film of oil or dust) will cause the spark to dance around inside the cap to ground or other plugs.
I'd just replace the dist cap and wires (like 8mm wires).
Coils or plug wires would be my next stop and change the crank sensor
It still could be a FI issue, make sure that crank sensor produces a very clean edge, use a scope. Maybe your SW already does this? If it's an ancient ECU -- have a new replacement on hand, they do get hurt from just a couple of mis-connections in years gone by. IMHO if I had an ECU in my plane, I would have switchable pair just like your mags.
The crapping out issue has been ongoing for a couple months before I installed the EFI.
Change every sparc plug cable and connector to the spark plugs. Look how the electrodes look. Is there debries between the electrode and ground?
LOL I Love my Prius ! Only Real men drive a Prius!
have you checked the fuel filter just to make you you are getting the correct flow?
I'm a automotive guy, never been around planes. But it really sounds like a ignition trigger system problem.
How is the EFI getting crank signal?
Is it the same pulse as the ignition system?
Some ignition trigger systems will start to fail and only loose higher RPM trigger definition, especially under higher loads, but idle and run fine otherwise. Best way to see it is with a oscilloscope of some sort. One meant for ignition systems would be better. Your looking for a lose of pulse, a weak pulse, or a wide pulse (wide will overlap at high rpm, and fake a high flat line).
Broken valve spring(s). Everything else has been ruled out, it's likely mechanical.
5000rpm...broken valve springs? This has been going on for a LONG time and the top end is not damaged?
Maybe not broken, but weakened? Heat tempering from overheat can cause it.
Magneto, or a Firing Coil or Distributor can also brake down.
Gotta be fuel or ignition. Has the mag been timed correctly? Are all the ignition wires on right, and securely?
looks like that propeller stops very very fast when you killed the engine seems like something is restricting the movement check pressure
Sounds centrifugal...
You got dirt in your fuel injector and there’s a little Jets in there that have dirt in them that’s why it’s not throttling up
I know nothing about aircraft engines. But in what I know about high rpm engine stumbling I would check / replace the fuel filter first
Check compression and do a leak down check
Sounds like power loss at the spark plug caps or plugs themselves.
I was thinking problem with the air amount until he said AFR were good.. wonder if it needs more or better engine ground wires.
Were the ignition modules swapped at the same time the system was installed? If so, are they the soft start ignitech modules? I put those in my 912 as well and when wired with the soft start I would see something along the same lines. Pull the soft start connection and see how it runs
Anything weird on the MAP sensor side when that happens at 5000rpm?
Maybe try closing the gap on the plugs. See if that makes a difference. If it changes something that might help diagnose the problem. I gotta say I’m not a fan of the FI. I did a larger X over tube and messed with the carbs and got my 912s running sweet.
As did I, for over 3000 hours, plus a BigBore low comp from Hal S., totally trouble free and then this issue came out of nowhere. BUT, progress of a sort just now: I enlarged the supply line from my 3 gallon header to the fuel pump assembly, from 1/4" (original) to 3/8", and got rid of a un-needed valve that added even more restriction. Pumps like to push, not suck, and though my in flight fuel burn will be the same or less as before (I had a HacMan Leaner), the FI will be moving a lot more fuel, I missed that fact and the runup I just did since increasing the supply line went great. But a static runup for a couple minutes is one thing, still need to fly it, WX permitting.
@portnuefflyer
Progress is great! I’m curious though, what about the changes you made would have made the running condition a sudden change with the original components? The fuel lines and valves would have continued to flow the same amount of fuel all the time unless something suddenly got caught in the system causing a slight blockage or a valve had gotten moved slightly slowing down the fuel flow.
Additionally, was the fuel line hard line or were there sections of rubber line? I have seen rubber line close up on the suction side and limit fuel flow.
@@tw6896 Partial hard line, a short section of new 1/4" hose, all good, and flow testing at the firewall pre EFI install showed the usual flow rate, many times more than needed for normal operation. Inspection of the header tank finger screen, the first time I had pulled it in over 3000 hours, showed zero accumulation of any foreign objects or debris.
@portnuefflyer
Ok. The reason for my question is I’m trying to help figure out why you had a successful run up after you changed the fuel supply lines from 1/4” up to 3/8”. I’m assuming that is the first successful run up since the issue began.
So, if I read your issue correctly, you said that initially the engine ran just fine on the original 1/4” fuel supply lines. Then at some point, it began experiencing the running issues above 5,000 rpm and that has remained constant until the 3/8” supply swap. If it continues to run fine on the new fuel lines, something had changed in the old system because initially it ran good on that system too. It seems to me that only a blockage or restriction of some sort could cause that issue to pop up all of a sudden as long as you didn’t alter the fuel tank venting in the process. That blockage or restriction could have been a foreign object which you said you could not find. It could have been something wrong with the valve you removed. It could have been a slight collapsing of the fuel hose under heavy suction.
I have had multiple instances of fuel hoses collapsing under suction over the years. It is nearly impossible to detect as well because as soon as the heavy suction is removed, it springs back out. I have also had fuel hose separate internally such that only the inner lining of the fuel hose was collapsing and the outer section of hose never changed.
Regardless I’m hoping it’s still running better after the fuel supply change as you initially indicated. If so, something in the old supply system had “gone bad.” If it continues to run poorly, then you can disregard all of this.
Jonas, you have obviously never been to the Just Aircraft "factory" in South Carolina.......check the videos for taking off and landing there.
Is it at almost 6,000', like this one? I've seen it, looks like fun, I know Troy, my kind of pilot!
You might want to check the prop pitch, it might be too coarse.
Stator/spark failure, air filters, gearbox issues.
Valve float.
I would try running it with the exhaust and air induction systems removed to see if the problem persists. Maybe there’s a restriction?
Stupid question... by any chance might be there is some RPM safety limiter? In program...
Also what was changed, and what was kept from the old system? Can you check if fuel pressure drops on 5000 RPM? Does wideband sensor shows rich, lean or normal mixture on 5000 RPM?
Tell us about the $50 louvers on the radiator
Fuel Pump low voltage - bad ground?
Jonas, About your Airbike, have you looked into Gocart/ Racecart braking systems? They go real fast now days and have way more substantial rotors/ calipers than mountain bikes.
What was done just prior to the problems started? Back up and work from there. I haven't watched the video yet but that's the first thing that comes to mind.
Clogged injectors?
Basics: it is either lack of fuel or lack of spark. Faulty Fuel system and starving for fuel supply. Regardless of the correct EGT's and mixture, confirm it with pressure gauges and volume checks. Faulty spark, replace what they recommend; wires, caps, plugs. I'm guessing fuel.
All that matters is that you physically rule these out before wasting your time. BASICS
If it was fuel starvation the AFR would start climbing to a very lean condition indicating lack of fuel causing a reduction in RPM. It’s gotta be ignition related.
Would agree about the AFR going lean in a carburated setup as you dry out the bowl at high flow rates, but FI with fluctuating pressures at high pulse rates could hold back max power with starvation without showing up in the AFR which is an average over time.
What about the snow bike???? Lol
It's called a Ruffian SEND-E, made in NH.
Tom did you try to see how far it will rev when around 180 cht to see if it works like it should?
Is there water in the gas?
What was the fix ? What was wrong?
You tried not having the blast shield at the back there?
Is the ECU doing the ignition timing as well or is it just fuel injection? Its coil on plugs controlled by the ECU? If so what timing did your tuner put in? If not perhaps its time to change to automotive coil packs and control them from the ECU so you can set the timing.
An automotive ECU would learn the tune as you do have a wideband O2 sensor (i heard him mention it) - the wideband will keep the mixture right and he was reporting it was right however its no good have a good ratio if the timing is not advancing at the right rate for the RPM.
I think your tuner was right and it is ignition. You maybe need the ECU doing ignition through racing coil-packs if you are not.
😎
The prop?
Do you know what that device is he has for his oil cooler? I have RANS S 7 and have trouble getting warm in the winter as well.
If it was a fuel problem couldn't you verify by running both pumps?
Its always ignition "ALWAYS!!!!
Same ignition right? like same mag or whatever..ITS A NO GETTING SPARKY ISSUE FOR SHIZZLE
I was hoping you would give us a better look at that snow bike. looks to be electric? what's the make/model?
I’ll do a separate video on it.
Not the valve springs
Throwing out guesses that it’s a ground wire connection.
It’s out of gas. Yep….
I would try closing the spark plug gap by .001 to.003 thousandths just to see if it changes anything.
Can't hurt I guess, but the gap on new plugs is already at a minimum, as it was when the issue started. And that gets back to "why doesn't switching the mags effect any difference when it craps out" issue, which would seem, unless BOTH sides of the electrical system were at fault, which is really unlikely.