rpm break up at 5500rpm

[travish325]

Help me out. Stock m20 hitting a sputter what feels like spark break up at 5500rpm. Ran fine before I parked it then the engine bay got filled with snow lol

Changed plugs they were shot looked over heated
changed rotor it was corroded
changed cap also corroded
changed wires
changed coil

Nothing fixed it, sometimes it will rev past 5500 to redline but not often. It hits 5500 and just sputters. Idk where else to look. Im thinking a fueling issue but the snow in the engine bay could have shorted something but I dont know what.

[JP-X]

Sounds like the engine may be running lean. The issue at that particular rpm range may be due to a worn out track on the stylus in the AFM. There should be some width on the stylus that will allow you to adjust where it rides. There is a black plastic cover that is siliconed on the electronics there. If you open that area up you should be able to adjust the card so it rides on a fresh path.

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[Chessmaster]

^ that is probably the most likely cause. See if anyone local has a good one to try outfirst. i have a few for sale If you need a good one. I also have few set of rebuilt, flowed, and claned 4 pintle injectors for $40 a set if it ended up being injectors.

[travish325]

Ive got lots of spare parts laying around. Just getting ideas before I go changing everything

[jlevie]

Data from the AFM is not used above 4500rpm if the WOT switch in the TPS is closed. This sounds like it could be a bad TPS, CPS, or engine harness.

[JP-X]

It's pretty easy to check and adjust the AFM you have, and you can watch how the stylus changes as you operate the throttle under the hood. As you sweep the rpm band you will see the stylus move. If it starts looking like it has an unstable behavior, then it is likely the AFM is part of the issue.

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[JP-X]

Data from the AFM is not used above 4500rpm if the WOT switch in the TPS is closed. This sounds like it could be a bad TPS, CPS, or engine harness.

I'm not familiar with this part of the system specifically, but this sounds like a good thing to check too.

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[JP-X]

Can you post pics of the old plugs? The color of the electrode will help you know if you were running lean. This isn't always the greatest indicator, since the color can change relatively quickly during the running cycle.

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[travish325]

One had the electrode nearly melted to the post. Im gonna say thats not right hahaha

[JP-X]

Basic color read is
Black is running too rich
White is running too lean
White with a bronzed look to it is about right.

Melted plug ... Not sure I've ever seen that happen before.

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[enigmaticdream]

AFM adjustment. I had a similar problem above 5300. Adjusted the AFM and the car runs like a top.

[travish325]

Afm it was. Grabbed and extra I had laying around and problem solved.