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Engine rough at 2400 RPM


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The mechanic who is now working on my plane (the one who did my annual is 150 miles away) seems very convinced that it is an ignition issue rather than a fuel issue. He changed my intake boot, installed an overhauled boost pump from Aeromotors and it is still running rough, though now at lower power settings. He says that his testing of the ignition harness shows that the wires are marginal. Previous mechanic says he tested them with a test box and they all tested good. The problem is still intermittent, sometimes its rough sometimes its smooth. I just purchased a JPI 830 (thanks teejayevans!) and I'm wondering if install it first would help diagnose the problem or if I should wait until the mechanic hopefully figures it out. Stupid question, but would it be worthwhile to install it now or would an install be essentially worthless before the engine is running correctly? What really sucks about this is I'm only about 2 hours by air from Don Maxwell but can't get the plane to him.

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See if I have this right...

1) you have a diagnostic tool that would help everyone (including MSers) diagnose the engine’s challenge.

2) With data, you can’t fairly play the game called ‘Swaptronics’.  The expensive replacement of working devices...

3) 

What is causing the delay of installing the diagnostic tool?

PP thoughts only. not a mechanic or magician...

Best regards,

-a-

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  • 2 months later...

Update: my plane is finally out of the shop. Installed a JPI 830, overhauled the fuel servo and distributor, cleaned the injectors and its running like a top. Previous commenters were exactly right about the servo. The overhaul shop couldn’t even perform a pre-overhaul flow test. Apparently the diaphragms in the servo were ?loose? causing the intermittent roughness. Thanks for all the input, it is much appreciated.

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Congratulations 18Q !!!  

I just read this thread and we certainly do have a wealth of knowledge here. Sounds like the advice you got not only helped you diagnose and fix your plane, but maybe even saved your life. 

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16 minutes ago, Yetti said:

Thanks for the update and happy for a good running plane.   Who did the servo and divider OH?

Martin Induction Systems in Enid Oklahoma. About $2300 for servo and distributor overhauls and injector cleaning. 

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