engine trouble; need groups collective wisdom

[gsengle]

I need some suggestions from this group - I have a sick M20R, and we are puzzled.

In flight last week at 12k feet cylinder #6 (which we later realized was mis-wired to the engine monitor so it was actually cylinder #1) on the IO-550 stopped firing. I had had a questionable run up earlier in the day, but seemed like a fouled plug, which cleared, so I departed.

Rather than spend a ton of time diagnosing the problem, when it misfired 30 mins later in flight and I couldn't keep it firing (because of course, who knew what was going on) I declared an emergency and landed. I was in IMC, so I was pretty busy, but saw a couple of things. I was able to get the cylinder back for 15 seconds or so with mixture, but then it went out again. When the CHT went cold, on my descent, I noted that the EGT was a few hundred degrees hotter than the other cylinders - we think this was the unburnt fuel maybe burning as it hit the exhaust system?

Unfortunately my landing was far from home at a remote field with no maintenance, so I flew back with my instructor/A&P a week later to see about repair/diagnosis, and maybe bringing the plane home. Everything looked fine and we pulled the plugs etc on what we thought was the bad cyl and those looked fine, so we ran it on the ground, and it ran like crap - same problem. So we went out and realized that the problem cylinder was a different one (#1 was cold, not #6). We pulled the plugs, and they looked badly fouled. The engine is high time and does burn some oil, so we thought, ok, this isn't common but we'll replace the plugs and see how it runs. It ran fine. So, thinking that we had solved the problem, we set out to fly back - I flew the 'chase plane' and my instructor flew the Ovation - on the theory if it acted up he had a great deal more experience to diagnose. Sure enough, the longer we flew (we had a 400 mile flight home) the more trouble the engine gave him. Evidently he had to run it pretty far ROP to keep that cylinder firing. The new plugs looked pretty ugly when we got home. Even more mysteriously though, the original two plugs while ugly, tested fine. So I suspect the plugs are not the root cause...

So what could be going on here? 1) Bad fuel? nah, it is just 1 cyl. 2) Bad injector? Maybe? That would explain needing to run the whole engine rich, but would running overly lean on that cyl cause plugs to get ugly? 3) Rings? Too much oil in that cyl? 4) Valves? Seems unlikely since I was able to get immediate changes by playing with mixture. And up until this - my oil analysis has been fine 5) Spark? Seems unlikely since a bad mag wouldn't be one cyl would it, and would a misfire in that cyl cause these symptoms? It just goes dead cold on the CHT.

I'm a layman here - but after having a similar issue in my Arrow a few years back (in that case was cam lobe spalling on one cyl intake valve) I know just enough to know that it can get expensive quickly if one isn't smart about diagnosis... So I turn to this groups collective wisdom for ideas! What causes a cyl to intermittently miss with these symptoms?

thanks much in advance,

Greg

[N601RX]

I had a similiar problem in an IO 360. I couldn't keep the plugs in one of the cylinders clean. It was obvious lots of oil was getting into the cylinder. When we pulled the cylinder off, the rings fell out in pieces. It was burning about 1-1/2 quarts of oil hr. The top compression ring was not broken, just the middle and oil ring. Compression testing didn't show anything abnormal.

If your plugs are oil fouling that soon, your not going to have much choice but to pull the cylinder. But be sure it is oil fouling and not an overly rich cylinder fouling them.

[M016576]

I had a similar problem with my IO-360 a while back and it was a plugged injector. I'm not an expert, but that's what it sounds like to me....

[KSMooniac]

I like the broken ring hypothesis. You might also check the plug wire very carefully before pulling the jug and see if it is shorting out somewhere and compromising your ignition.

[danb35]

There does seem to be a potential problem with the broken ring hypothesis, that being that more than one cylinder is involved. However, it should be easy (and inexpensive) enough to determine with a borescope, as there would likely be scoring of the cylinder walls if that's the case.

[Taracka]

Did u switch mag to see if that affects the way it ran? You could have a magneto going bad. How many hours on them? Worth checking before you pull a cylinder.

[gsengle]

Let me add to the puzzle - at around the same time, my fuel totalizer was starting to act up. On a previous flight, and the last flight, at start up, I got abnormally high fuel flow readings, but that settled down before take off. I saw flows going up to 100 gph during a test run up, even as the engine was running fine (and clearly no huge pool of 100gph fuel under the cowl on shutdown). Anyone have their shadin start to break in this way, and could this be related? Piece of something getting stuck in the fuel lines downstream of the impeller? How do these things work?

thanks,

Greg

[N601RX]

The transducer generates pulses as the impeller rotates and the display counts these pulses. The K factor is then used to convert these pulses to GPH. It would seem to me for it to read that high that it must be picking up noise from the ignition or from a loose connection between the transducer and display.

[Awful_Charlie]

I don't know the Continental setup, so not sure if this is relevant, but the fuel flow transducer will report wildly high figures if there are slugs of air in the flow. If you provide your engine with a poor supply of fuel, then all bets are off as to how much power it can make and how

[gsengle]

I promised to update. Ok, I'm still skeptical, but it seems to be nothing more than a clogged injector, whew...

[jetdriven]

Let me add to the puzzle - at around the same time, my fuel totalizer was starting to act up. On a previous flight, and the last flight, at start up, I got abnormally high fuel flow readings, but that settled down before take off. I saw flows going up to 100 gph during a test run up, even as the engine was running fine (and clearly no huge pool of 100gph fuel under the cowl on shutdown). Anyone have their shadin start to break in this way, and could this be related? Piece of something getting stuck in the fuel lines downstream of the impeller? How do these things work?

thanks,

Greg

Greg, that indicates an ignition system failure. Let me develop. That FF sensor wiring is supposed to be shielded. Our new install we shielded ours. If you have a plug wire arcing under that cowl it could definately cause havoc with the transducer signal. It may also be a magneto if more than one cylinder is affected.

[gsengle]

It seems to be one cylinder, sounds like I better inspect the ignition wiring...

[butchgilbert]

I had a similar problem, turned out to be broken oil rings. If the plugs are really fouled, I would pull the cylinder and inspect, oil in the cylinder can really screw up the ignition and eventually you'll see very high oil consumption.