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Topic-icon Rough engine running in winter 1967 Arrow I

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2 years 10 months ago #391

Our 1967 Arrow I will experience very rough, but quite intermittent, engine operation in very cold weather. I've noticed this "hiccup" shortly after departure and also on taxiing after landing. The coughing stops but it is somewhat unnerving on departure. This does not happen in the summer during warm weather. The airplane is kept in a heated hangar. Temperatures during flight are ranging from 20F to -20F.
The engine driven fuel pump was replaced last winter which seemed to resolve the problem. However, this quirkiness has reared its ugly head again this winter.
Speculation has suggested frost on plugs, injectors turning to water and being ingested into the fuel or possible air intake blockage.
Any suggestions would be most welcome!
Thank you.

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2 years 10 months ago #392

Hi Marcus,

I'm hoping that our resident expert, Steve Ells, will chime in here. He may have the help that you need. Fingers crossed.

Scott Sherer
N344TB

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2 years 10 months ago #399

Hi Marcus,

I've been thinking about this... I know you've replaced the fuel pump already and are considering other devices in the engine as being the culprit, but perhaps it's too rich due to the cold, dense air. Have you tried leaning a bit?

Best,
Scott Sherer
N344TB

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2 years 10 months ago #400

Scott, thank you for the suggestion. It is definitely something we're considering. On a cursory inspection we have found one plug fouled with lead, suggesting to me she's running a little rich.
I'll be flying it back today from a different airport since the engine failed on taxi the other day and couldn't be restarted. Flooded, no doubt. On return, we'll clean or replace all the plugs and see how that affects performance.

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2 years 8 months ago #450

Additional information on this topic:
1) This phenomenon only occurs in cold weather
2) Primarily occurs in a nose up pitch attitude
3) Did not occur before we had a heated hangar
4) There is a delay of at least 30-60 minutes after leaving hangar before it happens. Evidently dependent on outside temperature
5) When it occurred for the first time last winter it took about 45 mn and was departing DLH, nose up.
6) Perhaps water is condensing because of temperature change from hangar to outside cold, somewhere in the fuel system, probably on the right side, and then freezing creating ice crystals causing a partial restriction of fuel flow
7) I’m wondering why it occurs in a nose up pitch. Is a vent getting blocked?
8) Electric fuel pump has no effect.
We have replaced the fuel pump and had the fuel servo rebuilt; although these parts were in need of repair, they evidently did not contribute to the problem.
I will fly today and will do a significant drain on the right side fuel tank, fly for an hour or so and see what happens. If the problem occurs, I will rtb and add isopropyl alcohol to the tank and fly again to test.

I'm looking forward to suggestions for this extensive, helpful knowledge base. Thank you!

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2 years 8 months ago #451

Hi Marcus,
I'm going to take a screen print of this thread to my mechanic tomorrow and ask for his opinion.

Scott Sherer
N344TB

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