Lycoming IO-360 Stumper!

[KSMooniac]

I've noticed a change in my IO-360 operational behavior lately, and am puzzled... any hints or suggestions/ideas would be appreciated!

Used to fly LOP in cruise reliably and had a 0.0-0.2 GPH GAMI spread. All was great. Lately it has increased to 0.5-0.7 and obviously that is sub-optimal, especially compared to what I had. #3 now always peaks first, followed by #4 0.2-0.3 after, and then #1 and #2 at 0.5-0.7 and they're always close together. I've always had some fuel staining around the injectors, and lately #3 is noticeably more stained than the others.

So far, we have swapped #1 and #3 injectors with no noticeable change. Next up was a fuel flow test with graduated jars, with and without injectors, and all 4 appear to be flowing equally. My mechanic then put his thumb over the fuel line on #3 to see if the line might have a crack, but it held the fuel pressure just fine. I had suspected an induction leak on #3, and we also changed the gasket and seal on that tube carefully. We haven't pressurized the induction system yet. 

Next up will be a compression check (they were all high earlier in the summer), and perhaps a valve lift dial measurement. The induction tube looked OK visually when we had it out, but we didn't do any kind of NDI or pressure test on it yet. I can't say I've heard of induction tube cracks on Lycomings, but I suppose that is possible. 

Possibly related or not, twice in the last 2.5 months on a cold start I've had a dead cylinder, but it was #4. We checked the plugs and moved them to #2 for grins to see if/when I get another dead one if it moves. Leads all tested good. Borescope on the valves showed no issues with even patterns and clean stems. (I fly LOP all the time in cruise/descent) I feared it was a sticky valve, but the mechanic doesn't think that is the case based on ~450 hours since cylinder work on all 4 and the visual inspection. He believes if the valve guides were too tight it would've shown up very early.

Any other ideas?

 

[N201MKTurbo]

It sounds like you have the fuel and induction system covered. I would service the mags. Check/replace the points and set the internal timing. Then set the timing to the engine. Unequal firing times will change the combustion process quite a bit.

 

The mags are split top to bottom from left to right, but your change seems to be front to back which is a bit weird.

[N601RX]

I would put all the injectors in a jar of Hoppe's and drop them in a ultrasonic cleaner for a few minutes before spending to much time looking at other stuff. 

[larryb]

Your peaking order follows mine almost exactly. 3/4 followed by 2/1 0.5 gph later.

[kmyfm20s]

Spark, gas and air. It sounds like you have eliminated gas and air!

[mike_elliott]

It sounds like more than one cylinder is involved here, Scott, from your gami spreads now vs. then. Air and fuel are the things that change that. With nothing changing on #3 after you a) swapped injectors and insured the intake wasn't leaking at both ends, It might pay to pressurize the intake system as a whole. Since you went from a .02 across all four to a .07 between #3 and #2, and .05 between #3 and #1 it would warrant a closer inspection of the flow divider. Also look down the servo opening and see if the ram tubes are leaking when the system is pressurized.

[MB65E]

Might have a few issues, The valve wobble check SB is right around 400 hrs and sticking valves are due to carbon build up. Induction leaks are possible, but it looks like you addressed that. Like turbo says look into the mags, and hoppies for the injectors. A 500 hr inspection/ overhaul could do wonders. Check the harness and plugs. Also, we all know the champion plugs are having their issues lately.

Fly safe!

[jetdriven]

Check the flow divider for debris inside. We have this problem too and that's what I'm checking when I get back to the house

[KSMooniac]

I'm pretty sure the spark is fine.  Plugs are tempest fine wires with <200 hours on them.  Mag has <250 hours on the overhaul.  Leads all tested fine, and mag check behavior on a LOP cruise power mag check is all good as well.

 

I'm pretty sure fuel flow is fine as well, although I'll confess to not fully understanding the RSA fuel injection system as I've not studied it in detail.  That might be my next step.  We did the fuel flow test into jars as I stated above, and fuel delivery with and without injectors is very even to all four.  I wonder if something in the RSA system could change that, though, at less than full rich mixture settings.  I might repeat the test with a half-rich setting and see if that changes fuel delivery for some reason.

 

I think pressurizing the intake and inspecting the ram tubes under pressure would be good next steps.

 

Keep the ideas coming please!

[KSMooniac]

Check the flow divider for debris inside. We have this problem too and that's what I'm checking when I get back to the house

Byron, do you think debris in the divider would show up during the baby jar flow test?  I assume so, but perhaps not, especially with lean settings... that is what I'd like to learn about.

[jetdriven]

I would think it would, but that diaphragm and needle valve inside there starts to affect fuel flow below around 7-9 gph. It may be sticking or wearin out. I'm not sure i can't find data. But I am about to pull ours apart. Our gami spread was .2-.4 on a fresh factory engine. Then it went to .8 gph and i put in gami injectors. After three rounds of tuning, I have the richest (F) injector in #2 and a-c in all the other 3. 1-3-4 all peak together. #2 peaks .8 gph sooner. It's aggravating. Full rich takeoff EGTs are all the same however.

Perhaps performing the baby jar test with the mixture at 7 gph might reveal something.

[testwest]

Scott, you may want to have a look at your cam with a borescope. I hope you are not looking at a rounded off cam lobe. However, that much wear should have shown up in the oil analysis.

[pinerunner]

I have one thought to add, seeing as I just swapped injectors for the first time. Hehe. I noticed you mentioned fuel stains around the injectors. Injectors screw in using NPT threaded fittings which are tapered and "snug up". Mine don't show blue stains. If they were loose enough you might have enough backword flow in between intake strokes to send some of the fuel from A to B or at least to change air to fuel ratio in A since it is getting extra air. A bit of wear or corrosion on the NPT fiting might create too much leakage. I'd try just a little snugging up on the fitting.

[mike_elliott]

I have one thought to add, seeing as I just swapped injectors for the first time. Hehe. I noticed you mentioned fuel stains around the injectors. Injectors screw in using NPT threaded fittings which are tapered and "snug up". Mine don't show blue stains. If they were loose enough you might have enough backword flow in between intake strokes to send some of the fuel from A to B or at least to change air to fuel ratio in A since it is getting extra air. A bit of wear or corrosion on the NPT fiting might create too much leakage. I'd try just a little snugging up on the fitting.

please use caution here, cracks in Cyl heads are caused by overtightening. More than likely, the blue fuel stains are from the screen in the injector itself

[Awful_Charlie]

I can't say I've heard of induction tube cracks on Lycomings, but I suppose that is possible.

 

I'm afraid I've not only heard of it, I've had them - on an IO360B1E in a brand P.  The cracks were around the flange that mates with the cylinder head, one was apparent due to fuel stains running down, but it took an inspection of the others to reveal one other needed to be replaced too.  I seem to remember we took the opportunity to replace all the rubber joints to the sump at the same time, as they were all elderly.

 

You've got some great other suggestions too, but I never suffered from fuel staining around the injectors.

Good luck!

[Jsavage3]

Recommend you have your fuel injectors cleaned IAW GAMI first...  I had this issue recently and the cleaning took care of it...

[kmyfm20s]

Just found this article on injector maintenance. Very helpful for my understanding of them.

http://www.kellyaerospace.com/articles/FuelInjection.pdf

[jetdriven]

I use a harbor freight ultrasonic cleaner and Hoppes #9, remember to do them separately because the inserts are supposed to remain with each injector body.

 

15 minutes in the ultrasonic and they come out like new.

[tony]

I found an ultrasonic cleaner on eBay, every other annual I throw the injectors in a baby jar of MEK and then put that in a tub full of water.  After 30 minutes you'd be amazed at the junk that comes out.

[KSMooniac]

The injectors are believed to be clean... they were cleaned at annual (against my wishes) and there are two bits of evidence to show it isn't a fuel problem.  I swapped #1 and #3 with no change in behavior for either cylinder, and did the baby jar fuel flow test with and without injectors installed and got even fuel distribution to all four cylinders.

[MB65E]

Check the servo finger filter. Make sure the little orings get replaced on the screen too.

[Parker_Woodruff]

Scott,

Here's the best resource I have for the Bendix/RSA system. I use it with all my students.

http://www.precisionairmotive.com/Publications/15-812_b.pdf

I had a time this summer where my spread got so out of whack right after an injector swap. We pulled the offending injector and found nothing. Re-seated the injector and put some DC-4 compound around the threads on one of the fuel lines. Problem solved. Still No idea how it happened. Spread got right back in line.

[KSMooniac]

Thanks, Parker.  I've gone through that pdf and it is very helpful.  I'm pretty confident the fuel flow is even to all 4 after doing the jar tests, with and without the injectors.  I didn't think about leaking through the threads and that could be a possibility.  I'll ask my A&P about it and see what he thinks.

 

This weekend I hope to do a hi-altitude and lo-altitude GAMI lean test, a compression test, pressurize the induction system and check for leaks, and lastly measure the valve lift for all 4 cylinders to (hopefully) rule out cam or lifter issues.

[jlunseth]

I second the recommendation on the mags.  I will bet that you are seeing a larger drop during your runup than you did when the engine was behaving, and I also bet there is a bigger differential between the two mags.

[KSMooniac]

Mag is the least likely problem IMO at this point in time, and my mag expert (Aaron @ Select in Lancaster TX) agrees.  I have the D-3000 with <250 hours on an overhaul.  In cruise flight the LOP mag checks are good and consistent.  There is no difference in drop on either side.  If I don't find a smoking gun with my second round of planned checks, then I'll likely send my spare mag out for IRAN and swap it with what is on there currently.