Engine issue diagnosis

[Flash]

I have an M20J with an IO-360-A3B6 that has about 1300 hours SMOH. Plane was flying great. Took it to a nearby airport to get propeller balanced. When the shop was done (and closed), I fueled and added oil. Had a normal run-up. In the takeoff roll, added full throttle and got much less than full power, plus lots of vibration. Did some additional run-ups and a high-speed taxi and did not get improved results. Re-sumped fuel after shutdown to confirm that wasn't an issue. Engine monitor graph is the second one below. Note how No. 1 cylinder EGT plummeted when I went full throttle and how No. 1 CHT sank, as well.

Shop took a look at engine the next day. Borescoped No. 1 cylinder. Everything looked good other than a loose fuel injector connection on the No. 1 cylinder. Did a careful runup. Flew the plane a couple of hours. Flew it a couple of hours the next day. Seemed slightly rougher than usual, but thought I might be imagining things. Also, EGTs peaked at 1 gph higher fuel flow than usual.

Flew it again two days later. Definitely rougher than usual, enough so that I decided to turn back to my home base rather than risk having AOG somewhere else. Downloaded the data and saw that the No. 3 cylinder had acted strange and then the No. 1 cylinder had cut out again. Engine monitor graph is the first one below.

Today, mechanic found a bit of fuel had leaked from the No. 3 cylinder but found no cracks and no current issue. He cleaned the lower spark plug on No. 3. He borescoped No. 1 but also saw nothing wrong with it. Compressions seemed good. Checked the spider and saw nothing wrong. Checked the No. 1 EGT probe, and it appeared to be working correctly.

I went to the run-up area after he'd checked out the plane, to see what would happen. No. 1 cylinder cut out at 1400 RPM.

Any diagnostic thoughts here?

Edited June 28 by Flash
images were in wrong order

[LANCECASPER]

5 hours ago, krowddardenonline said:

"Diagnosing engine issues is as easy as listening to the car hum—it practically tells you what's wrong. Most modern engines even fix themselves while you sip your coffee."  https://krowd-darden.online/

@mooniac58 looks like we have an AI member

[ArtVandelay]

I would replace the spark plugs because it’s relatively cheap and easy.

I would also do a injector test using jars to check the fuel flow is the same for all.

[Fritz1]

ask yourself what has been touched besides the propeller when the balancing was done, then be methodical, spark, fuel, air, whatever is going on may not just have one single cause, cleaning the injectors is easy, do a flow test, put each injector into a measuring cup, run boost pump for a couple of seconds compare contents of cups, look for intake leaks, how is the fuel pressure from the mechanical pump, test all the spark plugs

[PT20J]

I’d clean the injector nozzles and run some gas through the system with the nozzles out to flush the lines. Might be worthwhile to do the wobble test on the valves.

[Slick Nick]

Oh man, I just went through something similar. Took weeks to diagnose. Had the fuel pump replaced, had the servo flow checked, had the spider overhauled, had the injectors cleaned. All filters replaced and screens cleaned. 

Turned out the injectors were bad. They do wear out over time. 4 new Lycoming Injectors and I had a smooth running engine once again. They weren’t even that expensive. About 1/3rd the cost of GAMI’s. 

[Marc_B]

This is interesting as it looks like EGT2 starts out higher than the pack, but your EGT's all drop immediately on pulling fuel flow.  I would think that if it was a rich mixture and you're leaning that the EGTs would rise, peak and then fall.  And your CHT1is already dropping out of the pack well before the others while the EGT1 is staying relatively steady to begin with.  EGT 3 initially bottom of the pack but starts to rise as you drop the fuel flow while the CHT3 plummets.  After you start enriching mixture EGT2 rises back to the top quicker than the other.

Basically doesn't seem to fit a single injector or plug.  Seems it affects more cylinders than that.  Am I looking at that right?

Plug:  less burned fuel in cylinder = lower CHT + more fuel to burn in exhaust = higher EGT

Fuel Injector partially clogged:  if ROP runs more lean than the others so EGT/CHT both higher; if LOP then running leaner = lower EGT & CHT

Fully clogged injector: EGTs cold and CHTs dropping

https://www.savvyaviation.com/understanding-cht-and-egt/

 

[Flash]

6 minutes ago, Marc_B said:

This is interesting as it looks like EGT2 starts out higher than the pack, but your EGT's all drop immediately on pulling fuel flow.  I would think that if it was a rich mixture and you're leaning that the EGTs would rise, peak and then fall.  And your CHT1is already dropping out of the pack well before the others while the EGT1 is staying relatively steady to begin with.  EGT 3 initially bottom of the pack but starts to rise as you drop the fuel flow while the CHT3 plummets.

Plug:  less burned fuel in cylinder = lower CHT + more fuel to burn in exhaust = higher EGT

Fuel Injector partially clogged:  if ROP runs more lean than the others so EGT/CHT both higher; if LOP then running leaner = lower EGT & CHT

Fully clogged injector: EGTs cold and CHTs dropping

https://www.savvyaviation.com/understanding-cht-and-egt/

 

Thanks. There is no EGT2 in this graph. I think the line you thought was EGT2 is MAP.

[Marc_B]

8 minutes ago, Flash said:

There is no EGT2 in this graph. I think the line you thought was EGT2 is MAP.

Where's EGT2?

[PT20J]

4 hours ago, Slick Nick said:

Oh man, I just went through something similar. Took weeks to diagnose. Had the fuel pump replaced, had the servo flow checked, had the spider overhauled, had the injectors cleaned. All filters replaced and screens cleaned. 

Turned out the injectors were bad. They do wear out over time. 4 new Lycoming Injectors and I had a smooth running engine once again. They weren’t even that expensive. About 1/3rd the cost of GAMI’s. 

The nozzles shouldn't wear out, but there are a couple of stupid mechanic tricks that can screw them up. The first is using safety wire, a drill or some other object to clean them. That can bugger up or change the size of the orifice. The second is mixing up the inserts between the bodies. It's easy to test them. Just set up the baby bottle test and watch the spray patterns when fuel is flowing. It should be a stream about the size of a #2 pencil lead. If it is otherwise, then there is a problem. If it's a simple mix up of the parts, you can swap around inserts until they all have a coherent stream. According to Al Jesmer, that's how RSA assembles them at the factory. They just match parts until the stream is right.

[N201MKTurbo]

Everybody is assuming it is a fuel issue, but you never cycled your mags at high power when it was running rough. That’s the first thing you should do, that is why we have convenient switches to do that.

As far as an injector being bad, if you can find someone with an inspection microscope with a ring light, set the nozzle on the stage pointing up, focus on the end and inspect it, then focus down the bore. They are made with an EDM sinker. They should have an even sandblasted look to them all the way down with no scratches or burrs anywhere.