I'm flying a new to me 182 with a 470, I noticed it sounds like it could be misfiring a bit at idle power when taxiing but it passes mag checks. It has 75hrs on new mags, my normal ground leaning is to lean until it runs rough then richen enough to smooth it out. Egt gauge doesn't show any dead cylinders. My A&P heard it as I was passing by and checked it over.

Above 800rpm or so it runs and sounds fine so I figured it was just loading up since I was busting around the pattern for a bit. I played with the boost pump to see if it had any effect, and enrichening to full rich doesn't seem to change anything either. Figured I would see if you guys had any advice before he starts replacing parts. If it were low fuel pressure I assume it would be running worse at higher power settings.

The big bore continentals have a pretty good lope at idle, due to valve overlap. Could this be what you're hearing?

Is it a fuel injected 470 on a 182? I ask because you said it had a fuel boost pump.

It could be allot of things obviously but one of the most common are loose intake hose clamps. That engine has about 20 intake hose clamps that like to get loose. It's usually only noticeable around idle and if really loose the engine will run lean in cruise. Pop your cowl and check all your clamps and look for fuel stain around the intake hoses.


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I haven't noticed any change in cruise temps, but I'll check the clamps. Yes fuel injected, I am thinking to have him check the fuel pressure and clean the injectors.

Is it a bendix fuel injection or continental? Either way if you lean it out and it doesn't get better or u turn on the boost pump to richen and it doesn't get better it's not likely a fuel pressure issue. If you have a multi prope EGT you would likely notice an overly lean injector.


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What are the "mag checks?" Just your run-up on individual mags for smoothness and rpm drop? Or something more involved? Might not rule out ignition yet.

Like Jered said, big bore continentals idle with a lope below a 1000rpm. Have you had someone who is not new to 182 sit in the airplane and listen to/feel it? Could be nothing

Next time you have the cowl off, you might want to check the plugs with an ohmmeter. 5000 ohms or less.

http://www.aircraftmagnetoservice.net/m ... ting-guide

Jeredp wrote:The big bore continentals have a pretty good lope at idle, due to valve overlap. Could this be what you're hearing?

Could you explain this? Does this mean that one cylinder starts its power stroke before the previous one has finished?

Valve overlap means that the intake and exhaust valves are partially open at the same time. This can help exhaust scavenging and cylinder filling at RPMs where the air column carries enough momentum to keep moving in the proper directions, but at idle where the air columns have very low momentum it causes gas reversions, which can cause a rough idle. The engine is sort of choking on its own exhaust.

Here's a sweet, sweet sounding extreme example. And yeah, I miss that car.

https://vimeo.com/74698960

As mentioned, loose induction clamps (vac leak) are a potential culprit. Simple to find, simple to fix. Cowl off, someone in cockpit to idle engine, and spray wd-40 sparingly around the cuffs (yeah, standing right behind the prop), including the crossover tube. The engine will go from idle to 1200 or so in a hurry when there is a problem leak.

Zzz wrote:What are the "mag checks?" Just your run-up on individual mags for smoothness and rpm drop? Or something more involved? Might not rule out ignition yet.

The rare times I am on asphalt I will run the engine up for 20 seconds or so per mag and watch the individual cylinder egts. I did take a buddy out that commented it idles smoother then his stock 470 so I am not as concerned. I put about 20 hours on it since I first posted and haven't noticed anything amiss since. Probably just loaded up and the a&p was bored and wanted something to look at.

Sounds pretty normal to me, but checking the intake clamps is a good easy idea as previously mentioned. Your ground leaning doesn't make any sense though. You can't lean until rough and richen until smooth out at idle. If you try, as soon as you add a touch of power to taxi the engine dies.

ONce upon a time I had a weird engine thing going on-- not really rough, just seemed to be less smooth than usual.
Mag checks at 1600 rpm were fine.
I did a single-mag ops check at cruise power and the roughness on the RH mag was readily apparent.
New points & condenser fixed it.
Same thing with the LH mag a hundred hours or so later.

I'm curious about your ground leaning. I agree with "aggressive leaning" while idling or taxiing, to minimize plug fouling. But can I assume that you're enrichening the mixture again before take off? As low elevation as Fairbanks is, and with a DA today of -750', you sure don't want to be leaning for take off or until you're at least a couple thousand feet in the air, if then. You'd be way above 75% power, and improper leaning could easily cause damage.

Caveat: I've never flown an IO-470--plenty of hours behind O-470s, but none behind the hybrids.

Cary