Doug Schumacher

carusoam, gsxrpilot, Yetti, Marander and others, Thanks for your feedback and yes I 100% agree with you about collect and analyze data, and then act according to the data. Part swapping is for the A&Ps or owners that don't know how to do it the right way. We reached out to you for your knowledge and experience and we thank you very much for your time helping and guiding us. This particular problem is very very subtle (very small vibration) and only happens for 1-2 seconds, so it is not acting like bad gas, valves or fuel delivery. I'm 1 of the 3 pilots that fly the M20J and I'm not the owner, so I've been sharing your comments with the other 2 guys. The owner has bought a new set of fine wires and mag capacitors that will be installed during the annual. The mags and prop were rebuilt about 100-200 hours ago. If the problem exists after the annual we will swap the plugs to see if the problem moves with the plugs. We have not downloaded the data or setup a Savvy account, but we will try to do this after the annual is complete if the problem remains. Thanks again, we are grateful to have you guys as a resource,.............I'm listening and learning.

Plane is in annual. Owner is installing all new spark plug wires to see if this fixes the hiccup. Non related, we are doing the valve wobble check as the engine has about 1500 hours. We will keep you posted on any results we find. Thanks again for the suggestions.

Thanks for help and I’ll let you know what we find

We will try the plug swap, then wires and then mags. Also we will try to switch mags when it it happening to see it it is one of the mags.

Carusoam, thanks for all the feed back. This not a strong vibration. I will see about downloading the data, we did it once but not sure we still have this July flight still on the device. I will look into the Savvy site. There is no doubt in our minds that the engine hiccup/vibration/misfire is trying to be compensated by the prop governor and that is why we see the rpm vary.

We do have the fine spark plug wires. We have the ability to download the data from the engine monitor but we did not think it would be helpful where the problem only happens a most a few times for 1-2 sec over a 3 hour flight, and we do not know where in the data the problem happened as the RPM is not one of the data streams.

Thanks for the additional comments. Prop and Mags were rebuilt at last annual (about 100 hours ago). I've posted the video to youtube and the link is below. The video is under-whelming to watch, but when you are in the plane in cruise and the problem happens you know immediately something "wrong" happened. You can feel a slight vibration as if the engine missed a beat. But it goes back to perfect in 2 sec or less. It took me a long time to notice that the RPM was changing, as all I knew for sure was that it felt like the engine pulsated. Normally the RPM holds rock solid, maybe +/- 1 rpm. So in this video before and after the hiccup the RPM is still not as solid as usual. In other words I think this video caught a big hiccup but there were still smaller ones (or settling down) before and after the big one. Before I graphed the data I could not really see any difference between the cylinder exhaust temps. If the hiccup lasted longer than 2 seconds (like 10 sec) I think the temperatures would vary alot more. The first time I noticed it I was flying from Laconia NH to York PA and everything was fine for a hour or so and all of a sudden there was a slight vibration for 1-2 sec. I could not see anything out of place and it did not happen again for about another hour. Of coarse I thought I was imagining things. I then had my phone ready to record if it happened again, and this time it happened a few times with several minutes between each occurrence. I decided to stay overnight in PA and have an A&P have a look. We spent $1,200 with the A&P at York. Bore scope, compressions, replaced intake tube o-ring gaskets, and adjusted idle mixture (he may have checked a few other items). The entire flight home and the next several flights the problem did not show up. But it happened again in September. We checked plugs and fuel injectors and test flew, and it happened a few hours later. We sent out the fuel servo for rebuild and reinstalled a few weeks ago. We had a few successful flights, but then it happened to me again in 12/8/18. https://youtu.be/XkIehU2X-7U

Thank you all for your responses. The engine monitor does not collect RPM, but we have a digital tachometer. So I was able to take a video of the engine monitor and the tachometer and then pause the video each second and record the data. Please see attached graph. You can see Cyl-4 looks different then 1, 2 and 3 during the vibration and RPM hiccup, and note that the vibration and RPM hiccup only lasts 1-2 seconds. The hardest part about this problem is that it only happens for 1-2 seconds (never for >3 seconds), and sometimes you have to fly for hours to see it happen. Also I assume that the tachometer responds a few seconds faster than the EGT temp probes, so the temps should probably be shifted to the right a few seconds. Data from July-2018 video.pdf

I'm new to this MooneySpace and this is my first post. I share a 1981 M20J with 2 other pilots. Starting in July 2018 we have been trying to find the cause of an intermittent hiccup with the engine. Some back ground about the plane; about 1500 hrs on engine, 150 hrs on prop, 150 on Mags, and A&P has checked: fuel injector flows, cleaned plugs, and rebuilt fuel servo. Problem: You can fly for a long time (sometimes 2, 5, 10 hours) without any problem, and then all of a sudden you can feel a slight vibration and you can see the RPM fluctuate +/-10 RPM (sometimes a bit more and sometimes less). This only happens for 1-2 seconds and then it goes away completely, and then it will usually come back again many minutes later. We have a engine monitor and we were able to videotaped it happening. Upon close examination you can see cylinder #4 does change temperature several degrees during the hiccup, so it appears cyl-4 is miss-firing for 1-2 seconds. Any thoughts of suggestions would be great, as we are spending $ without results.