Watch My Video--Diagnose That Sound!

[Brian Scranton]

Mooniacs...here's a little sleuth work for ya. 

M20F, RayJay Turbo, IO-360, 1000 SMOH, High Alt Airport (5759'), not hangered....it's been pretty cold but no cold starts. 

About 100 hours ago I cleaned the injectors. About 50 hours ago I cleaned the plugs. About 10 hours ago I changed the oil. Recently, and sporadically but increasingly (sorry for all the adverbs) over the last few months, on my take off roll I've been getting a burp in the engine as I advance to full throttle. It happens around 2000 rpm, the fuel flow tweaks a bit, the engine sounds like it's backfiring, and full power doesn't happen. So I abort. Exit the runway and do a few full power run ups, leaned, then full rich, then leaned again, and the issue always resolves--I depart without issue. Now, I don't even bother taking the runway until I have done these high power run ups a few times to clear out whatever is going on.

I've checked for water in my fuel lines. None. I've checked to see if maybe I was too lean. I wasn't. Too rich. Nope. So I took this video and brought it to my A&P who thinks I might have a stuck (or sticky) valve. What do you guys think? Thanks!! B   

Mooney vid.mov

[gsxrpilot]

A sticky/stuck valve would show up easily on the engine monitor.  I couldn't tell what monitor you have, but if you can "normalize" the EGT's and then do that same procedure. A stuck valve will stick out on that monitor like a big old middle finger.

[nels]

Video doesn't work for me.

[Brian Scranton]

27 minutes ago, gsxrpilot said:

A sticky/stuck valve would show up easily on the engine monitor.  I couldn't tell what monitor you have, but if you can "normalize" the EGT's and then do that same procedure. A stuck valve will stick out on that monitor like a big old middle finger.

I have an older Insight GEM, EGT/CHT/TIT--but my A&P said that a sticky valve specifically wouldn't show up because its happening in such a quick fashion. Ie, it's there and then its not. Maybe a newer monitor would though? Either way... 

[Randy_B]

A couple years ago I was in for annual and the shop had an E model with Ray Jay turbo in there as well.  The E had a bad stumbling and loss of power problem on take-off.  The shop went through everything; electrical, ignition, fuel system, hoses, and valve train with no resolution.  They were frustrated and running out of ideas.  I searched MS and came across a post on the symptoms of a bad fuel selector.  The problem ended up being a bad o-ring in the selector.  The unit would pass a pressure test all day.  However, a vacuum test would produce bubbles, presumably from around the selector stem.  The unit was sent to Lasar for rebuild and the plane ran perfectly after it was reinstalled.  MS has a lot of great information and insight.  

[carusoam]

I forgot how to save the video to replay it...

do you have a FF indicator?  Are you seeing more FF to match the colder denser air being inducted?

I'm with randy on this one, something related to fuel flow, just a small bit off from normal.

FF probably hides the air bubbles that Randy mentions.

PP ideas only...

 

Best regrads,

-a-

[Yetti]

I vote  fuel issue.  the Fuel pressure should not burble like that.  Probably should start with the simple stuff.  Servo check, Mechnical pump check, finger screen.

 

[Marauder]

2 hours ago, Brian Scranton said:

I have an older Insight GEM, EGT/CHT/TIT--but my A&P said that a sticky valve specifically wouldn't show up because its happening in such a quick fashion. Ie, it's there and then its not. Maybe a newer monitor would though? Either way... 

Brian -- as you may be aware, I was dealing with some issues with my F as well. Mine turned out to be spark plug related. I have a recording engine monitor and was able to upload the data for Paul from SavvyAviator to look at. My plane faltered like you are showing during my run-ups. Ended up being a resistance issue with both plugs in one cylinder. Not sure what kind of plugs you are running. But it is an easy resistance check. I would look at #3 cylinder first. I had a GEM for years and the #3 seems to be moving up a bit faster than the other cylinders. Worth the effort before digging into the more complicated and expensive possibilities.

[Brian Scranton]

You guys kick such major ass--thanks! 

[bradp]

I was going to vote o ring in the fuel selector.


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[Mcstealth]

Since I have no idea, how about the Flux Capaciter?

[bonal]

I had same type of issue after a long taxi and hold on a carbed  o360 same rpm range misfiring and back fires. cleared after full power run up and leaning turned out to be plug fowling even though i lean heavy on start and taxi operations.  i would agree with B26 check the easy stuff first

[kortopates]

I vote for the new engine analyzer with downloadable memory - especially with a turbo! But it needs MAP, RPM and FF too.

But so far there are no signs of a sticky valve. At least not yet with the limited data. Also no data to discern whether its a mixture issue or ignition issue but you can give the ignition issue a good preliminary check in the run up using your EDM730. Really what you should be doing at every runup if not already: At run-up RPM, let EGTs stabilize and the put it into normalize mode. Select a single mag e.g. Right and look for a good rise on every plug, then back to both allow EGTs to drop back down and then select the other Mag and once again look for a good rise on every cyl. See one go cold or one without a rise and then you know you have a or fouled bad plug. 

Your A&P is got the right idea - he is thinking of things that could go away as the engine warms up. Ignition is also a possibility if an oily plug bottom at startup is being cleaned off by burning it clean. An o-ring on the fuel selector is seems less likely to clear up as the engine warms up.  Eliminate the easy ones first.

I assume you don't have ability to download data which if adding to your diagnostic challenges.

 

[Guest]

I too can't make the video run.

In many cases a sticking valve is evident on initial start, and one cylinder will show no or very low EGT.  As the cylinder warms the valve begins to run normally and the engine operation smooths.  I had this on my E model.  Reaming the guides cured it.

If the problem is regular and repeatable, start the engine and run on one mag at a time over to sucsesive starts to see if you can isolate it to either ignition system or to the same cylinder indication on both mags, as in Chris's example of bad plugs in the same cylinder.

Clarence

[Brian Scranton]

1 hour ago, kortopates said:

Your A&P is got the right idea - he is thinking of things that could go away as the engine warms up. Ignition is also a possibility if an oily plug bottom at startup is being cleaned off by burning it clean. An o-ring on the fuel selector is seems less likely to clear up as the engine warms up.  Eliminate the easy ones first.

I assume you don't have ability to download data which if adding to your diagnostic challenges.

You're right! A new GEM would be sweet and you're also right--no ability to download. I'll try the mag check, though I check mags at every run up and have not noticed anything out of the ordinary as suggested. Thanks!!!

[N201MKTurbo]

The fact that the sudden drop in fuel pressure precedes the stumble indicates an air bubble in the fuel line. Do you have the boost pump on? If you do try it with it off or vise versa. Does it do it on both tanks? How long has the engine been running before you advance the throttle?

[Brian Scranton]

1 hour ago, N201MKTurbo said:

The fact that the sudden drop in fuel pressure precedes the stumble indicates an air bubble in the fuel line. Do you have the boost pump on? If you do try it with it off or vise versa. Does it do it on both tanks? How long has the engine been running before you advance the throttle?

Boost pump isn't on--and the engine was running for 3 mins prior...haven't tried switching tanks either. But, when it happens on the runway the boost pump is for sure on, so it happens in both environments. 

 

[gsxrpilot]

My first Mooney didn't have a proper engine monitor when I bought it, so I figured that into my offer and had the Insight G2 installed within a month of purchase. The second Mooney, the 252, had an engine monitor, but I felt the turbo warranted a better one. So again, the very first purchase was a JPI EDM-900.

I wouldn't want to have my own money tied up in a plane that I was flying without a good engine monitor. Engines are just too expensive.

[Brian Scranton]

Ok. Went back and tried some of your suggestions. Had my A&P in the right seat. It was 40 degrees out. I taxied super lean over to the shop. He hopped in. CHTs were all above 200, oil above 100--while lean I advanced the throttle and it did the same thing (cough, burp, BLAP!) right around 1700rpm, power back, leaned even more, then we did it again full rich and it went away. Added the turbo. Full power. No problem. Reduced to 2200rpm and did a mag check. All clear. So ignition and fuel seem to be fine. And once it was warm, I couldn't duplicate the burp. So he's increasingly thinking that its a slightly sticky exhaust valve. Annual in a few weeks--we'll take a look and I'll report back. 

 

[Brian Scranton]

On January 10, 2017 at 8:28 PM, Marauder said:

Brian -- as you may be aware, I was dealing with some issues with my F as well. Mine turned out to be spark plug related. I have a recording engine monitor and was able to upload the data for Paul from SavvyAviator to look at. My plane faltered like you are showing during my run-ups. Ended up being a resistance issue with both plugs in one cylinder. Not sure what kind of plugs you are running. But it is an easy resistance check. I would look at #3 cylinder first. I had a GEM for years and the #3 seems to be moving up a bit faster than the other cylinders. Worth the effort before digging into the more complicated and expensive possibilities.

Well...the young lady is in annual right now. I pulled, cleaned and gapped the plugs--then did a resistance check. Lower plug in #1 was DEAD. It also had a bit of oil on the lead. I hope I found my problem because that was certainly easy to fix. Now, the oil on the lead--I wonder if my rings are starting to go on the cylinder. I'll keep ya posted once I fire her back up...

Also, FYI, replacing the hoses on the RayJay; what a bitch. 

[Marauder]

Well...the young lady is in annual right now. I pulled, cleaned and gapped the plugs--then did a resistance check. Lower plug in #1 was DEAD. It also had a bit of oil on the lead. I hope I found my problem because that was certainly easy to fix. Now, the oil on the lead--I wonder if my rings are starting to go on the cylinder. I'll keep ya posted once I fire her back up...
Also, FYI, replacing the hoses on the RayJay; what a bitch. 

Hope that fixes it for you.


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[FloridaMan]

I had similar behavior once with a clogged #3 injector (IA said it's always the #3 for whatever reason). 

[Shadrach]

Watching the video, this sure looks like a momentary fuel starvation event. It seems unlikely that the simultaneous drop in fuel pressure is a merely a coincidence.  I hope I am wrong, but I think you and your A&P are barking up the wrong tree. Glad you caught the out of spec plug, but a single bad plug on one cylinder would not cause that kind of burble.  When was the fuel servo last serviced?  Go through the process and watch you EGTs during the event even if you have to watch them cylinder by cylinder.  You should upload the vid to youtube. Not everyone is cool with downloading and executing files from a web forum. 

 

[Guitarmaster]

I agree with Ross...  Looks like a fuel issue.  Seems like something that would happen when trying to run up with the mixture too lean.  What happens when you lean the mixture while it's doing this?

[Brian Scranton]

On February 21, 2017 at 11:51 AM, Guitarmaster said:

I agree with Ross...  Looks like a fuel issue.  Seems like something that would happen when trying to run up with the mixture too lean.  What happens when you lean the mixture while it's doing this?

Never tried--since it happens full rich on the runway. I'm putting her back together today and we'll do a leak check. I'll report back.