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Engine Rough/Black Smoke/Quit

John Tierney

Well Known Member
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Today I had my IO-360 run rough at low RPM and quit on short final. Witnesses report seeing black smoke puffing from the exhaust before the engine quit. I was able to roll out and off the runway on a taxiway. Then after a couple of tries the engine restarted and seemed to run like normal, including smooth idle and normal RPM rise on shutdown. I’m asking for hints at where to look for problems.

I was doing a local area flight after some unrelated airframe adjustments. The plane took off fine, climbed and flew at high cruise just fine, but since it was a local flight, I wanted to conserve fuel, and throttle back to 2200 rpm. I overshot my throttle pull back and felt some engine rumbling, so headed back for my home field. Orbited the field at 4000 AGL to troubleshoot, and the engine roughness felt like it would shut off if I got below 1200 RPM, so I kept the plane high on base and final and aimed for a long landing in case it shut off. Well, it did quit and I was high, but forward slipped it (a little faster than flap speed) and landed OK.

I DID NOT try the alternate air (filter blockage), or cycling the ignition (wanted to keep her running). Engine seemed to run a tiny bit smoother with leaning, but not too much leaning.

OAT was warm, but not above 90F. I have an AVSTAR (Bendix standard) injection system with dual PMAGs. About 140 hours on the airframe, and just last week did a 4 hour out/in cross country with no squawks. I pulled the top cowl after flight, but no evidence of a problem. Will pull the lower cowl tomorrow.

Any ideas?
 
You have fuel injection but I had a situation with my carbed engine that resulted in the same results as your incident.

A tiny piece of trash got lodged in the carb needle. This stuck the valve open which caused the smoky, rich condition. I felt mine go rough at 1300rpm on a mile final, kept the rpm up and it quit on the runway. I had to take the carb apart to clear the needle and seat.

Looks like you were dealing with a very rich mixture for some reason. Maybe a close look at the fuel servo is in order.
 
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I would start it and check each ignition. I know someone who had his timing change that experienced similar symptoms.
 
Check the injector nozzles. Your experience was similar to one my buddy and I experienced with his IO-360. Turned out one of the injector nozzles had an obstruction blocking fuel flow which caused others to run rich. Removed the obstruction and cleaned the injector nozzels with Hoppes #9 and all was good afterwards. Just a suggestion.
 
Check the injector nozzles. Your experience was similar to one my buddy and I experienced with his IO-360. Turned out one of the injector nozzles had an obstruction blocking fuel flow which caused others to run rich. Removed the obstruction and cleaned the injector nozzels with Hoppes #9 and all was good afterwards. Just a suggestion.

I had a similar situation after paint - a small piece of something blocked one injector. The servo keeps pouring in the same amount of fuel and the extra goes to the other 3 - super rich mix with black smoke on three cylinders and dead lean on the 4th. Makes for an interesting takeoff attempt, I'll tell you that.
 
I had a similar situation after paint - a small piece of something blocked one injector. The servo keeps pouring in the same amount of fuel and the extra goes to the other 3 - super rich mix with black smoke on three cylinders and dead lean on the 4th. Makes for an interesting takeoff attempt, I'll tell you that.

We were in a Cozy MKIV pusher. Couldn't see the fan behind us. The shake was so bad we thought we lost a jug or a prop blade. We were in the circuit doing required practice IFR approaches at Punta Gorda. Declared an emergency to get on the ground ASAP. The inbound heavy's were being vectored out to accommodate us. They were probably annoyed but better safe than sorry.
 
At aroiund 1200 RPM, the mixture is mostly controlled by the dedicated idle mixture circuit. By 1000 RPM, it is fully controlled by the idle circuit. First, be sure that the spring is still on the square arm connected to the throttle linkage. This spring holds the star shaped wheel that controls idle mixture. If it is missing, the mixture will change from vibration.

Black smoke would indicate richness. However, if it was only seen just as the engine died, it would not be definitive that richness was the problem during the roughness event. If you suspect richness as the source, I would start by insuring the idle mixture is correctly set. Warm weather requires leaner mixtures than cold weather. The normal setting can handle the temp swings pretty well, but if you are on the rich side of normal, it would run well in the winter and start to get a bit rough in the hot weather. This is why I try to set the idle mixture on a 50* day, as it represents the mid point of ambients that I see in my flying.

Also, on final in hot weather is the most difficult regime for dealing with boiling fuel downstream of the servo and this can cause roughness if it happens. Has anything changed that would increase heat absorption in these fuel lines? Upstream of the servo, fuel is at 25 PSI, but downstream it is only 2 PSI at idle. This drops the boiling point quite a bit.

+1 on the other recommendations about partial injector blockage. However, if that were the case, you should have noticed a significant lean condition, via EGT & CHT, on one cylinder during the high power portion of your flight. Happened to me once and noticed in cruise a power reduction with no roughness, as well as both EGT and CHT indications that something wasn't right on one cylinder. Also possible that the debris broke loose and clogged as you hit the pattern.

Larry
 
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Thanks, still troubleshooting

Thanks to everyone for your suggestions. I checked all the usual suspects and found no smoking gun so far. The EMS download showed all CHT and EGT matched during the problem period, so I haven't pulled the injectors yet. Fuel flow and pressure download was as expected. Wires and MAP hoses to the PMAGs were secure.

Ran the engine un-cowled today up to normal runup speeds, and everything functioned fine, including idle and rise in RPM as mixture twisted to ICO. No evidence of blue staining except one spot, on the outside of the rubber hose segment between the #1 intake tube and the sump, between the hose clamps. No signs higher up on the engine, so wonder if it could be excess prime coming out of the snorkel drain hole and blowing back.

Plan on timing the PMAGs on next trip to the hangar and I am cleaning/recharging the K&N filter tonight (nothing found in the snorkel). Wil chat with the local A&P Monday.
 
Instrumentation

Is your plane equipped with an engine monitor ( fuel flow, fuel pressure, 4 EGTs and CHTs)?
Since you haven't mentioned it, I guess not but if you do have one and have data, that may help identifying issues.
 
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