IO-360 engine stumble

[HRM]

So, took my E (The Mistress) out a week ago and everything was good up until application of full power (for TO) and she stumbles and misses.

This evening, with A&P/IA on board, we experience the same thing.

First thought, fouled plugs. We do the high-power run-up under lean conditions. Second thought, mag timing, we do the dynamic mag check, no joy.

So, what should we look at next? Injectors?

Run-up (2000 RPM) goes fine. Everything collapses on full-power for TO.

[takair]

Is it momentary stumble or does it get better?  Engine monitor?  Can you see individual EGTs?  Could be servo issue too...

[Pasturepilot]

How many hours on tour mags? My C model had similar issues a couple years before I bought her and we chased all sorts of leads: Carb rebuilt, replaced intake seals, all sorts of stuff. 
 
Carb heat helped. (But that’s not gonna help you a bit)

it turns out, the 500 hour inspection was about 200 past due. Sent them out and not a hiccup since. 

Edited December 23, 2019 by Pasturepilot

[HRM]

6 minutes ago, Pasturepilot said:

How many hours on tour mags?

Sh*t. They were last rebuilt in 2000. Two decades. Damn.

[ragedracer1977]

7 hours ago, HRM said:

Sh*t. They were last rebuilt in 2000. Two decades. Damn.

2000 couldn’t possibly be 2 decades ago.... can it? 

[tmo]

Must be that Y2K bug....

[ArtVandelay]

Sh*t. They were last rebuilt in 2000. Two decades. Damn.

How long have you owned the plane?
Might want to check the last time the landing gear motor was serviced while you’re at it.


Tom

[HRM]

3 minutes ago, ArtVandelay said:

Might want to check the last time the landing gear motor was serviced while you’re at it.

I checked. Believe it or not, the landing gear motor has NEVER been serviced! Must be made of nonexistium.

[67 m20F chump]

Does the rpm rise when you pull to idle cut off?  IE is the mixture too lean and when you add more air it stumbles.

[HRM]

47 minutes ago, 67 m20F chump said:

Does the rpm rise when you pull to idle cut off?  IE is the mixture too lean and when you add more air it stumbles.

We (my A&P was with me) checked that. All the dynamic (throttle in/out; mixture in/out; flow, etc.) checks were fine. Push it to full throttle and it stumbles.

Here's the Savvy chart. FF follows MAP exactly. This was last week when I was solo. I need to get the data from yesterday and upload to compare.

[takair]

EGT 3(?) seems to have something going on. Note the sinusoid vs the others. That may be a valve?  Borscope May help there. That said, not sure if that would cause what you describe. If you keep full power does it continue to stumble?  Is it popping, violent, etc?  Or is it a momentary loss of power that recovers?  Could be as simple as an injector clogged or partially clogged. 

[HRM]

Just now, takair said:

EGT 3(?) seems to have something going on. Note the sinusoid vs the others. That may be a valve?  Borscope May help there. That said, not sure if that would cause what you describe. If you keep full power does it continue to stumble?  Is it popping, violent, etc?  Or is it a momentary loss of power that recovers?  Could be as simple as an injector clogged or partially clogged. 

It's a sustained stumble, but not violent (like detonation). My first thought was injector and that's an easy check. 

I'll have yesterday's data up in Savvy later today, on the taxi back we ran it up, ran it down, MAP in, MAP out, etc. Should show something.

[Bob - S50]

I think that's #4 you are talking about.

[MikeOH]

54 minutes ago, Bob - S50 said:

I think that's #4 you are talking about.

I think he's referring to the waviness BEFORE about the 0:09 minute mark in #3

[ArtVandelay]

EGT #4 goes up when the rest go down, making the wave pattern, I would pull plugs (clean&gap) and check the FF, might as well borescope it at the same time.


Tom

[takair]

Looking at this on phone. Waviness is #3 at the pre 9 min mark. I see the #4 now post 9 min. That could certainly hint at things. As suggested, check plugs and injectors there. 

[Bob - S50]

Could also be a mixture issue.  If #4 is getting less fuel it will be operating closer to peak EGT.  That could be the fuel distributor, the line to the injector, or the injector itself.  I'd be tempted to swap the injectors between #4 and one of the others and see if the problem follows the injector or not.

[HRM]

Here's the data from our testing yesterday, something definitely wonky with #4. Its intake pipe is where the port for the Precise Flight SVS goes. Now I am wondering if it has gone leaky and is letting air into the manifold.

[ArtVandelay]

The 2 dips in EGT #4 is the cylinder not firing, it’s unlikely a spark problem, fuel or sticking valve?

Standard disclaimer: I’m just a PP....

 

Tom

 

[carusoam]

Are those screen shots?

Or is there a link to the actual data?

It helps to be able to click on all the details and see other things...

Usually a link shared to the savvy site does this...

Data at the run-up is a great way to determine things about the mag health...

Best regards,

-a-

[HRM]

1 hour ago, carusoam said:

Or is there a link to the actual data?

Here you go—I just recently learned about sharing.

[Marauder]

Here's the data from our testing yesterday, something definitely wonky with #4. Its intake pipe is where the port for the Precise Flight SVS goes. Now I am wondering if it has gone leaky and is letting air into the manifold.

You definitely have a dead #4 cylinder showing up. It’s possible that both spark plugs went offline at the same time but not likely. I had 2 spark plugs in the same cylinder firing intermittently but it looks like both of your’s went dark.

You need to look at common factors (injectors, manifold, valves, etc.) to start eliminating things. Good luck, I know how frustrating these things can be.


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[Marauder]

Another thought. I subscribe to SavvyAnalysis and have the folks there look at stuff for me when I can’t sort it out. Another set of professional eyes can help.


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[ArtVandelay]

It’s interesting that FF jumps up when cylinder 4 stops firing, could you have leaking injector? Your fuel pressure drops as well:

 I would check #4 injector.

 

Tom

 

 

[HRM]

Thanks all (so far). The goal of this exercise is to drive what gets looked at next