My C172 engine "hiccupped" - why?

Texguy

New Member
Hi I was in a rented 172 and the engine sputtered for 1 second. It was scary and I want to avoid it in the future if I did something wrong. Kinda sounded like "rrrrrrrrrrrr Putt Putt rrrrrrrrr."

More details: It was night, about 80-85 degrees on the ground. I went up to 5000. The Mixture knob was leaned out about 1 1/4 inches. I put the plane in a 150 fpm descent. At 4000 I enrichened the Mixture slightly so the knob was just 1 inch out. The hiccup was about 4 minutes later at 3500 feet. Reflexively I turned on the carb heat. The engine was fine from then on (I doubt the carb heat did any good). I was on the ground 5 minutes later.

Any guesses? Maybe the mixture was too rich? Maybe it wasn't my error - the plane is from the 1970s but seems decently maintained.
 
carb ice? water? By your description it would seem your mixture position was at least "in the ballpark"... you might be right, though I would suspect too lean over too rich.
 
There are dozens of things that could cause an engine to sputter like that. It could have been the mixture or your decent could have shifted some water around in the tanks and it just took a couple minutes to get to the carb. Did you do a mag check afterwards?
 
I've had enough hiccups to count on one hand and each one was unpleasnt. Prior to the hiccup and after the hiccup the engine showed no indications of roughness, loss of RPM, sputtering or anything... was completely normal before and after each one which revealed no definite indication of what may of caused it.
 
My guess would be water but there are dozens of other things it could of been.

I was pretty lucky in the 172 I never really got too many hiccups but once I got into the 210 that thing has some very dramatic coughs. Scared me the first few times that it happened...
 
I had MX explain this to me once - and I can't for the life of me remember what they said it probably was - but I remember them saying it wasn't serious, and happens from time to time.
 
I've had enough hiccups to count on one hand and each one was unpleasnt. Prior to the hiccup and after the hiccup the engine showed no indications of roughness, loss of RPM, sputtering or anything... was completely normal before and after each one which revealed no definite indication of what may of caused it.

I've had it happen in a C172 as well. Certainly a little nerve-racking.
 
I have grey hairs from engine sputtering at night.

Honestly, from your discription, sounded exactly like a little bit of carb ice to me. Not a mechanic.
 
Temp was 80-85 degrees and you were at 3500? Hmm doesn't sound like a carb ice issue to me. Maybe excessively lean or had some water?

I've had an engine hiccup. We were flying a Navajo when we switched tanks to the inboards. The right engine started sputtering and the RPM was going up and down. You could feel the plane yawing from the differential thrust from the left engine, and the RPM rising and falling from the right engine. To add to the excitement it was about 10:30PM and we were 1000ft above the downtown buildings in Orlando.
 
It sounds like the perfect recipe for cab ice to me. 80-85 on the ground makes it 60-70 at the altitudes you were flying. What was the dew point? Look on this chart to see where they intersect. I'd be willing to bet you were in the "Serious Icing (glide power)" zone.
 

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The only thing worse than an engine sputtering is an engine sputtering at night.

That is exciting.

I had one night (back when I sprayed mosquitoes for a living) where I had a R-985 on the Beech 18 not only sputter, but backfire about 3 times when going across town about 300 AGL. Talk about an attention getter!:eek:
 
My guess would be water but there are dozens of other things it could of been.
I would guess the same thing, but I cannot emphasize enough that is a pure "guess".

However, if you haven't heard of it, be sure to ask your instructor about "auto rough". Airplane engines are notorious for going into the auto rough mode at night, over water, and in the mountains.
 
Back tot he topic, isn't is SOP to go full rich when descending?

Definitely not in most Lycomings. You're gonna have all sorts of hot start as well as cold start fun when you start putting around full rich. The trick with something like an O-360 for always being able to hot start easily and always pass a mag check is to lean the crap out of it on the ground, and DON'T go full rich in the decent.
 
Nope.
There isn't a silver bullet.

You do what is needed.
I was coming back into a pattern on downwind after over an hour at 5,500 and I had put the mixture full rich over the course of a couple minutes and the engine sort of "coughed" or rumbled once on downwind. I called my cfi asking about it and he gave me some explanation about enriching the mixture too quickly causing it. This was in a 172R.
I'm assuming yours happened in cruise from what you're saying. I know in most planes if you advance the throttle too quickly it will sputter or cough. Had it happen on takeoff in a 150 and I ended up aborting and going back to the runup. Everything checked out fine.
 
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