Odd Engine behavior

[Gino230]

RV8, IO-360 (actually O-360 which was converted to fuel injection by the builder) Catto 3 blade FP prop.

Taking off yesterday, the airplane seemed a little sluggish, not performing exactly like I'm used to. Looking back, I realize now I was about 50-100 RPM low at full throttle for T/O. Fuel pressure normal, MP normal, mixture full rich. With the Catto I usually see 2100, 2150 as I get rolling static TO RPM. I was about 2050 by the time I noticed.

Once I reached cruise, the acceleration to cruise speed / RPM seemed a bit slow- then when I began the leaning procedure, it was definitely not behaving as usual- EGT would not reach the "normal" range (1300 ish peak) before the engine became rough. I tried several things, Alternate air (no change) Mag check (functioned properly) boost pump on or off, no help. I kept attempting to lean, back to full rich and tried several times. this was at 7500'. After several attempts, the engine stumbled, then seemed to return to normal operation, but still could not reach the EGT I'm used to seeing.

CHTs were normal, each about 300 degrees which is in line with what I usually see.

30 min later I'm back on the ground. Idles fine, runup at 1800 RPM Normal. So its only a full throttle or high power setting problem.

I let her cool down and pulled the upper cowl looking for the obvious stuff. Plug wires all tight, no fuel stains anywhere or exhaust leaks, in short nothing obvious. The one thing I found, is the #2 injector (the forward left cylinder where the injector is exposed to cowling opening) had alot of blue staining and when I wiggled the fuel line (spider to injector) it was slightly loose at the injector. I tightened it, cleaned it up, ran the boost pump a couple of times and saw no leaking.

Took off the next morning and all was back to normal. The other part of the puzzle, the day before the flight in question, I flew about 35 min of acro, so alot of time running around richer than normal. So possibly a couple of dirty plugs? Plugs were replaced 50 hours ago and haven't been out since.

Airplane is new to me with about 40 hours in the last 3 months of me getting to know it.

I'm aware of the Lycoming SB regarding fuel injectors, but this seems to be a concern with the horizontally installed injectors (mine are not horizontal) but could possibly do with a cleaning, not sure when it was done last.

Could the loose line have caused the running issues I had? This was the only injector with the blue stains, I understand there's a bleed hole on these injectors so it's not unheard of to see fuel staining? But the other 3 are clean.

Looks like a little solder has chipped off of the fuel line, should this line be replaced?

 

[rv8ch]

I'd compare the fuel line to the others to see if looks very different - these are cheap so might be best to just order a new one. Not sure it's easy to repair. They typically come straight and you get to bend them as you like.

I'd look at that airfilter and the rest of the snorkel - it looks like it's seen an "induction backfire" - or something that's damaged it from inside the induction system. Induction backfires can also do damage to the throttle system. Not sure the technical term is "induction backfire", but I think you know what I mean.

 

[Gino230]

I'd compare the fuel line to the others to see if looks very different - these are cheap so might be best to just order a new one. Not sure it's easy to repair. They typically come straight and you get to bend them as you like.

I'd look at that airfilter and the rest of the snorkel - it looks like it's seen an "induction backfire" - or something that's damaged it from inside the induction system. Induction backfires can also do damage to the throttle system. Not sure the technical term is "induction backfire", but I think you know what I mean.

The air filter has looked like that since I got the plane, I've never liked the fit and finish of the air filter mounting and after seeing how some others finished the top of the snorkel / baffle ramp mine is lacking, although functional for now. I have a new filter and the plan is to mold the top of the snorkel around it, then install a new baffle ramp sandwiching the filter in.

But to your point, I've never experienced a backfire or any kind of popping.

The fuel line looks similar to the others, except for the color where I cleaned it up with scotchbrite. I'll probably replace it for piece of mind. Appreciate the input.

 

[bjdecker]

@Gino230 Lycoming SI 1275_C applies to Fuel Injectors, regardless of the servo orientation (horizontal or vertical).

I agree with Mickey -- the air filter and the mount looks...Janky...

FWIW - I mounted mine from beneath the front ramp, and I used the temperature "riser" from the RV-14 Baffle kit with modifications; I expanded the guard in front of the #2 injector body, which seems to eliminate the fuel staining...

 

[Gino230]

@Gino230 Lycoming SI 1275_C applies to Fuel Injectors, regardless of the servo orientation (horizontal or vertical).

I agree with Mickey -- the air filter and the mount looks...Janky...

FWIW - I mounted mine from beneath the front ramp, and I used the temperature "riser" from the RV-14 Baffle kit with modifications; I expanded the guard in front of the #2 injector body, which seems to eliminate the fuel staining...

View attachment 102944

Yes, the bulletin was mostly concerned with cleaning fuel injectors and making sure that horizontally mounted injectors are clocked correctly to prevent fuel from dripping out of the air passage after shutdown. It doesn't give an hour recommendation for when injectors need to be cleaned, just a how to on cleaning them "when engine operation dictates".

Part of my problem is that this engine had fuel injection added by the builder, so it's kind of a hybrid and not exactly easy to figure out part numbers, etc. Welcome to the world of experimentals!

That baffle ramp and filter looks great, did you fabricate the metal brackets and attach them to the snorkel as per plans?

 

[lr172]

Moderate performance reduction with all egts cooler than normal brings these possibilities to mind

Fuel flow / servo issue causing lean mixture
Fuel flow / servo issue causing rich mixture
Timing advanced too far
Reduced airflow / obstruction.
Sticking piston in spider

As you leaned, was the egt rising or falling. If all the egts were abnormal, it is systemic and not one injector.

The back to normal the next day does add a twist and need to start with things that could change each flight. Have EI or are both mags? Also think about what systems the acro could have affected l

 

[Gino230]

Moderate performance reduction with all egts cooler than normal brings these possibilities to mind

Fuel flow / servo issue causing lean mixture
Fuel flow / servo issue causing rich mixture
Timing advanced too far
Reduced airflow / obstruction.
Sticking piston in spider

As you leaned, was the egt rising or falling. If all the egts were abnormal, it is systemic and not one injector.

The back to normal the next day does add a twist and need to start with things that could change each flight. Have EI or are both mags? Also think about what systems the acro could have affected l

Dual Mag setup, mag timing was last checked at condition inspection 60 ish hours ago? Not sure why it would return to normal the next day?

Reduced airflow seems possible, but I would have thought I would notice a difference when trying alternate air- which I did not.

When I was attempting to lean, I was using #4 cylinder as my reference- that's what I use most of the time (hottest) and then I reference the others. EGT was rising as I was leaning, however it wouldn't get to within 100 degrees of "normal" before the engine began stumbling. To be honest, I don't recall what the other EGTs were doing or if I even checked- It's one of those selectable EI gauges that only displays one cylinder (EGT or CHT) at a time.

Another thing to note is when leaning this engine in cruise, it generally doesn't get rough- it just smoothly loses RPM as the EGT drops on the lean side of peak. So my technique has been to lean to the RPM loss, then enrich a bit and generally run 75 deg ROP on the hottest cylinder. But during the flight in question, as I attempted to lean, it would get rough.

Unfortunately, My #2 cylinder EGT probe is bad, the new one is sitting in the toolbag, I was planning to install it when I got back this week. Since that's the cylinder with the loose injector line and blue staining on the injector, I'm unsure if that had anything to do with it.

Another piece of the puzzle, the airplane was freshly fueled the night before- both tanks sumped as usual. Probably has nothing to do with it.

I think the best course of action is injector cleaning followed by the fuel flow test (filling up the bottles with the injector lines) and cleaning the fuel screen in the servo?

 

[lr172]

When I was attempting to lean, I was using #4 cylinder as my reference- that's what I use most of the time (hottest) and then I reference the others. EGT was rising as I was leaning, however it wouldn't get to within 100 degrees of "normal" before the engine began stumbling. To be honest, I don't recall what the other EGTs were doing or if I even checked- It's one of those selectable EI gauges that only displays one cylinder (EGT or CHT) at a time.

So, if egts rise as you lean from full rich and get stumbles before reaching peak, that points away from a fuel issue. You need to see if this is happening on other cylinders as well. Several things it could be if only one cylinder that it can’t be if all cylinders. Need that info to get a whole bunch deeper without guessing.

When leaning, was the stumble gradual as you leaned or everything fine until it hit a wall and stumbled?

 

[pilotkms]

I just dealt with the exact same symptoms the other day. I thought it was one of my 2 Pmags that had started to fail. No outright failure but a lessening spark kind of operation. So I replaced the (apparent) malfunctioning Pmag. I have a spare. Didn’t fix it. Pulled the #1 top spark plug. Surprised to see an obvious fouling. 50 hours on current plugs. FIRST time I’ve seen a fouled Auto plug in 1300 hours. Will be test flying tomorrow to verify problem solved. But I think it’s obvious. Check the simple stuff first

 

[lr172]

I just dealt with the exact same symptoms the other day. I thought it was one of my 2 Pmags that had started to fail. No outright failure but a lessening spark kind of operation. So I replaced the (apparent) malfunctioning Pmag. I have a spare. Didn’t fix it. Pulled the #1 top spark plug. Surprised to see an obvious fouling. 50 hours on current plugs. FIRST time I’ve seen a fouled Auto plug in 1300 hours. Will be test flying tomorrow to verify problem solved. But I think it’s obvious. Check the simple stuff first View attachment 103004

You sure? When a cylinder is running on one plug, the egt on that cylinder typically rises 150-200*

 

[Gino230]

So, if egts rise as you lean from full rich and get stumbles before reaching peak, that points away from a fuel issue. You need to see if this is happening on other cylinders as well. Several things it could be if only one cylinder that it can’t be if all cylinders. Need that info to get a whole bunch deeper without guessing.

When leaning, was the stumble gradual as you leaned or everything fine until it hit a wall and stumbled?

First, thank you for your input.

Second, if I'm being honest, I was not in full analysis mode so I can't be precise when answering this question. I was more thinking do I need to find a runway because this thing isn't running right? I'm returning to GA after 20+ years flying at the airlines so I'm a bit more nervous than the average RV pilot when I'm not sitting on 2 massive engines. These airplanes are pretty robust though and will keep on flying even if conditions aren't perfect, thank goodness for that!

But I would like to understand the "why" behind certain things so I will keep you posted as to what I find.

Keith, thank you for your story, I'm going to check plugs as well. I'm running standard massive electrode plugs BTW.

 

[pilotkms]

> Will be test flying tomorrow to verify problem solved.
Yep. Just flew for an hour and she’s back to normal. $24 for 8 new plugs.
Sorry to say, I jumped to the conclusion it was a Pmag problem. I’m sorry Brad/Trent.