#5 & #6 not firing on 3300 Jab with new Aeroinjetor

[NARROBB]

Hi guys,

I just fitted the Aeroinjector on a Jab 3300. On ground testing, #5 & #6 are not firing and obviously the engine is shaking with two cylinders not firing. This is visible from the CHT/EGT monitor and the cylinders are cold after shutdown.
Though I noticed if I push the power higher (1800+) they start to fire and the engine get smoother; lowering the engine back to idle the CHT/EGT drops all the way on these two cylinders and the engine back to shacking.

Swapped #2 & #6 plugs to see if the issue moves with no luck. Thinking it is going to be highly unlikely both distributors/rotors are failing on the same cylinders; this seems to be the air/fuel mixture getting to all cylinders except 5/6 being the closer to the aeroinjector. I did open both distributors and seems both are okay. Not sure if this can be associated with the aeroinjector needle (#3 needle used) and the engine cut off when ¾ of the way out on the mixture cable.

I am using the K&N RX-4040 direct hookup for air-filter. trying without the air filter attached is the same. Thinking of putting a spacer hose between the engine & aeroinjector, maybe the air/fuel is only getting mixed correctly further down the path and #5 and #6 are only getting mostly air on idle?! Anyone experienced this before? any new ideas or hints is highly appreciated.

Thanks

[builderflyer]

That's a new one, Narrobb. I've never experienced what you describe nor have I ever heard anyone else describe what you are experiencing. You may likely find that cylinders # 5 & 6 will be running lean at WOT but not at idle in the way you describe. Have you set up the Aeroinjector in the way the manual indicates? But my experience has been that if the the Aerocarb or Aeroinjector is set up to be too lean at idle, the engine won't fire at all, not just starve the back 2 cylinders of fuel.

Have you run this engine before with a different carburetor? Oh, one other thought........did you remove and replace the ignition wiring while you installed the Aeroinjector? Let us know what you find.

Art,,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,Jabiru 3300 #261

[NARROBB]

Aeroinjector is setup per the instructions. Engine got about 120 hrs with the Bing but airplane sat for a year before the change. Only change was the aeroinjector and direct filter. Wiring not changed. Ground static gives 2650 rpm with the aeroinjector (all cylinders firing). Ohmmeter check is consistent across all ignition wires. Plugs are D9EA so no resistor in plugs but in the wires. What’s the standard plugs wire resistor expected?

Can the Jab ignition system be checked by hand rotating the prop similar to Lycoming or this type needs faster prop rotation to see a spark? (By taking out all plugs, lay one by one on the engine to ground it and rotate the prop by hand to see a spark).

Planning to check the intake valves with a camera, also will try a spacer between the aeroinjector and engine.

I rerouted the throttle cable from the previous location so it’s not going to be easy to put back the Bing just to test it but could be done as a last resort.

Thanks for your reply.

[sonex1566]

I know that this sounds nuts....is it possible to rotate the Aeroinjector a bit either way? At part throttle settings with a Bing carby it can be possible for the air/fuel mixture to be directed towards one side of the air intake tract. I know that it can be a pain in the butt with cables etc getting in the way, if it was possible to do it with the engine running and not chop your arm off you could see the effect it has.

[sonex1374]

Narrob,

You mentioned that the AeroInjector was set up properly and that static WOT you're getting 2650 rpm, but I wouldn't rule out a basic mixture setting that's not quite right. Static rpm with the typical Sensenich prop should be a bit higher than 2650 (say 2700-2800). The fact that the rear cylinders are not firing at idle suggests you may be too lean and may need to enrichen the needle setting a bit and see how that works. Before you can really digest what's happening at low power we need to make sure the WOT tuning is correct.

A few questions to help paint a diagnostic picture:

1) What are your WOT EGTs, and what kind of rpm/EGT increase do you get when you pull the mixture knob out say 1 inch while at WOT?
2) What were the outside air temps when you were doing your tests (cold air won't atomize the fuel very well on a cold engine)?
3) What fuel flow rate are you getting at the carb fuel inlet when draining freely? Did you eliminate the fuel pump when you removed the Bing, or is it still in the fuel circuit? If any of this changed when switching to the AeroInjector you'll need to re-verify your fuel system performance.
4) Did you oil the K&N filter, and is it possible there is an airflow restriction (say too much filter oil)?
5) It would be helpful to know what intake manifold style you have (we can make an educated guess based on engine SN and not have to physically open the manifold to inspect it) - the older manifolds were changed internally duel to uneven mixture distributions, and this is even more significant with an AeroInjector.
6) How many hours on the plugs, and what gap are they set with?

Jeff

[DCASonex]

I would check the short hoses that connect the two halves of each of the intake pipes running up to those two cylinders. Being at back of engine they might have been displaced while removing the Bing carb, or while installing the Aeroinjector, and if so the leak would make them run lean at Idle but might not be noticeable at WOT. Those pipes are also sealed where they exit the intake chamber, and if seals have been broken might see same result.

David A.

[tx_swordguy]

Did you happen to look at the plugs in the suspect cyl? Were they black and fouled looking or clean and lean looking? Lots of times just changing or cleaning the plugs will fix running issues at least temporarily but it is odd that both back cyl were not running. The main reason I got rid of my aeroinjector was number 6 would not go below 1400 egt on wot take off. I had to throttle back to keep it in check. I was also having other issues (started running stupidly rich on all cyl no matter how lean I ran it) and had just had enough of that carb. Also you might make sure your plug wires are secure on the distributor and making good contact. I am leaning toward a fuel issue but the ignition side is also pretty easy to clean up quickly.How many hrs?
Mark

[NARROBB]

All great ideas. Thanks.

Here are some more info and observations;

- Did try rotating the aeroinjector. I can only do it a few degrees CCW (pilot view). No effect.

- Engine is Ser 1460. (Early hydraulic lifter that was fully converted to CAMIit solid-lifter when at 70 hrs). This flew about 60 hours more after the conversion with no issues.

- Plugs changed 30 hours ago, plugs color are text-book perfect. Yesterday, I did replace #2 & #6 with Resistor type Iridium NGK just to check, #2 replacement was just as a control test to make sure #2 will continue firing with the added resistor. #2 kept firing with no issues; are the plug wires expected to have 4 to 5kOhm resistance on their own? anyone tested this on their wires? All my wires are consistent between 4 and 4.7Kohm resistor within the wire itself. #2 kept firing fine with 5KOhm added resistor within the plug (NGK Iridium) so looks like there is no need to replace the wire with a low-resistance wire (180 ohm/f) type similar to the ones I am using on Lycoming (with Auto plugs)

- Don't think the engine is too lean at idle if its running better at WOT and not quitting. I really did not spend much time on WOT due to the fact the engine is shaking really bad with 4 cylinders firing only. On idle, while shaking, EGT on running cylinders is pretty normal (900's, and 1200-1300's on WOT).

- K&N is brand-new out of the box with nothing done to it, testing without any filter attached is the same.

- Everything so far pointing to the fuel/air mixture; yesterday I've removed the aeroinjector to disassemble it to make sure (again) the needle is oriented correctly (tapered side towards the engine), marked the beginning of the taper and inserted it again per the manual so the marked line just shows up on the slide. A very interesting change of behavior; Pulling the throttle all the way back, mixture 1" out (from full rich) does start the engine immediately with all cylinders firing; idle RPM is 780-820. Any change in throttle will stop #5 & #6 immediately and can be seen by the fast drop of temp on the EGT for these two cylinders (and shaking engine), further change in throttle kills the engine. So looks way-over-rich? Though trying to advance the throttle a little bit with the mixture almost cut-off does not make the engine run better, I figured the mixture control should get the mixture very lean when just a little bit opened from fully closed. Next trip out there will start pushing the needle further down in one turn increment and see what difference this will produce. I now understand what people were referring to the "pain" in tuning the aeroinjector.

- Engine mechanical pump not eliminated but a Holly 1-4 PSI regulator is after the pump; going to look into this further. Will probably rig a gravity feed bottle to feed the aeroinjector with fuel to check and eliminate issues with the regulator.

- Distributors/Rotors; may bite the bullet and spend the $200!!! on getting these replaced. They do look fine and clean. What should be the approx. length of the spring-loaded carbon brush when new?
Anyone knows a compatible replacement from the automotive market that can (at least just for ground testing) be used to check? I really dislike the design of these distributors/rotors.

While talking about these; why not having both rotors exactly parallel have no impact on the timing?

Mine are “slightly” off, the left one (Pilot view) is a few degrees ahead of the right one. I remember a few years back reading about this and from memory the writer said “The ignition rotors are attached to the rotor shafts. In most cases the rotors
will not be parallel but this will not affect ignition timing."

Tried to look again to find the writeup with no luck. Is this true or I am just getting old and talking nonsense? I think not having them exactly parallel should affect the timing.

A while back, I’ve designed a control system which requires a full 360 degrees shaft rotation detection with 0.1 degrees of accuracy running at 5000 RPM. I am leaning towards just putting a magnet on the rotor shaft and use my board design to control an externally mounted 6-cylinder ignition pack to fire precisely at 25 degrees; the initial aim is for sure to keep a fixed advance but can be easily upgraded as testing progress on one side; then make both sides! I think it would be a nice experiment while I am figuring out these aeroinjector issues!!

[WaiexN143NM]

Hi all,
I dont think the aeroinjector can take any fuel pump. just gravity flow and no ram air intake.
can u do your test w the gravity flow only ? no pump or regulator. it maybe too rich.
good luck and let us know your results.
anyone else concur??

be safe fly safe

WaiexN143NM
Michael

[tx_swordguy]

as was stated try gravity only and no ram air. When I used the aeroinjector cyl 1,2 and 5,6 were the leanest and 6 being unreasonably lean at WOT no matter what I did to the needle. Try backing the needle out 1/4 turn (richer) at a time and see what it does. Also you may pull the intake tubes out and reseal 5,6 at the intake manifold to be on the safe side. You can do that without disassembling the manifold.The manual tells what kind of sealant you need, it is a non hardening type but I don't remember exactly. Mine, when I had it running as good as I could get it at cruise 1,2,5,6 I could get up to about 1300-1350 3,4 would be 1200ish EGTs. In my experience you won't get even temps with the Aeroinjector. I just replaced mine with a rotec tbi and got my first ground run yesterday (have not flown yet). In installing the rotec I put an air stream straightener on the intake side. Perhaps you could try something similar on the aeroinjector to get 5,6 to take the fuel better.