Piper Archer engine vibration

Archer Jack

Archer Jack

Pre-takeoff checklist
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Oct 24, 2018
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Mansfield, TX
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Jack
I was returning home to Grand Prairie, TX a couple of days ago from Sugarland and had a serious engine vibration as I reduced power descending down to pattern altitude. Performance seemed a little sluggish during the flight but nothing terrible. The problem only happened when the throttle was pulled back. It went away at higher rpm. I did not try carb heat since temp was near 80F that day. Mixture was full rich in preparation for landing. Engine only has 65 hours smoh and annual was just performed a couple of weeks ago. Has anyone else had this problem? Thanks.
 
Do you have an engine monitor? Sounds like maybe a bad spark plug.
 
It might be a spark plug; did you do a magneto check while it vibrated to see if it got better?

My guess is that you have a tight valve/guide however.
 
Archer Jack said:
I was returning home to Grand Prairie, TX a couple of days ago from Sugarland and had a serious engine vibration as I reduced power descending down to pattern altitude. Performance seemed a little sluggish during the flight but nothing terrible. The problem only happened when the throttle was pulled back. It went away at higher rpm. I did not try carb heat since temp was near 80F that day. Mixture was full rich in preparation for landing. Engine only has 65 hours smoh and annual was just performed a couple of weeks ago. Has anyone else had this problem? Thanks.
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First, 80°F is no guarantee of not getting carb ice. The dewpoint matters every bit as much.

nyc02fa025_1.jpg


Aside from that, carb ice tends to be rarer in Cherokees but it's not impossible.

Throttling back tends to lean the mixture with a lot of carbs, and a lean mixture is harder to ignite if the engine is getting weak spark. A mag, ignition lead or sparkplug might be bad. And that mixture control linkage needs checking to make sure you are getting full rich.

A manifold vacuum leak could do it, too.

One more: a leaking or unlocked primer can cause lots of problems. With the throttle pulled back there's enough vacuum in the intake manifold to pull fuel out of the primer nozzles, making cylinders with nozzles very rich. Typical Lycoming only has three of the four cylinders with nozzles.

The statement that the performance seemed sluggish is a bit alarming.
 
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I don't fly many carbureted planes, but I think carb ice is more likely to be smooth and down on power than rough.
 
mondtster said:
It might be a spark plug; did you do a magneto check while it vibrated to see if it got better?

My guess is that you have a tight valve/guide however.
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If it was a stuck valve, would of continued even when he increased RPM. Don’t ask how I know.
 
Rcmutz said:
If it was a stuck valve, would of continued even when he increased RPM. Don’t ask how I know.
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Not always. I've had one that acted almost identical to what the OP is describing. Note I said "tight" not stuck, the engine I had trouble with flew and acted like it had a bad spark plug that never got better or worse when I'd do a mag check. I figured it out when I did the annual, the compression test on that cylinder was always low until I staked the valve. Then you could spin it through again and the valve would be slightly hung again. Firing pressure at higher loads seemed to help seat the valve and cause less trouble than lower loads.
 
As others said, check the easy/inexpensive stuff first--primer, spark plugs, mixture cable termini, and carb heat flapper (it could be on all the time). As Clip4 hinted, check the clamps on your induction hoses.

Also check the condition of your exhaust system. It is not uncommon for the internal muffler baffling to corrode, break, and obstruct exhaust flow causing a back pressure. Bouncing, vibration, turbulence, can cause the obstruction to be intermittent.
 
Very likely an induction issue or ignition. I’d pull plugs, inspect, clean, inspect again. Also check plug impedance with an Ohm meter. If all good check what others have said; carb heat mechanism, mixture cable, induction leaks, exhaust condition. Failing this, carb ice is a likely a factor. Perform a run-up after this inspection. Consider run up to higher RPM. If still rough I’d check mag timing.
 
Thanks everyone for your comments and suggestions. The guy who just did my annual a couple weeks ago is taking another look for me. Hopefully it's something simple. I agree carb ice can happen any time although this particular day was almost 80 degrees and dry. I have not had any icing situations even on much colder days in this plane, but there's always a first time.
 
Hoping you can update on this! I’m curious what the culprit was.
 
Archer Jack said:
I was returning home to Grand Prairie, TX a couple of days ago from Sugarland and had a serious engine vibration as I reduced power descending down to pattern altitude. Performance seemed a little sluggish during the flight but nothing terrible. The problem only happened when the throttle was pulled back. It went away at higher rpm. I did not try carb heat since temp was near 80F that day. Mixture was full rich in preparation for landing. Engine only has 65 hours smoh and annual was just performed a couple of weeks ago. Has anyone else had this problem? Thanks.
Click to expand...
Archer Jack said:
Thanks everyone for your comments and suggestions. The guy who just did my annual a couple weeks ago is taking another look for me. Hopefully it's something simple. I agree carb ice can happen any time although this particular day was almost 80 degrees and dry. I have not had any icing situations even on much colder days in this plane, but there's always a first time.
Click to expand...


What was the issue? I had the same problem yesterday…
 
Archer Jack said:
Thanks everyone for your comments and suggestions. The guy who just did my annual a couple weeks ago is taking another look for me. Hopefully it's something simple. I agree carb ice can happen any time although this particular day was almost 80 degrees and dry. I have not had any icing situations even on much colder days in this plane, but there's always a first time.
Click to expand...


What was the issue?
 
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