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Rough engine with take off power


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Run up was OK. Mag check was about 75 RPM drop on either side. Prop cycled OK.

I flew from KWHP to KVNY for some pattern work and do a ground VOR check. I land at KVNY, perform the VOR check, then take off for some pattern work. The first touch and go was fine. On the second one, I think I might have heard a few pops like backfiring but I am not sure. The engine was still producing full power at this point. On take off from the third touch and go, I noticed a much slower climb, rough running engine (possible infrequent backfiring and more than usual vibration), and very low CHT / EGT on cylinder 4. By very low I mean it wasn't registering above 200°F. The airplane was in the take off configuration, full throttle, mixture full rich, boost pump on, turbo normalizer off. Pulling the throttle back to about 50% to 70% reduced the engine vibration to normal and cylinder 4 CHT/EGT returned to normal range (300° to 400°F) with the other cylinders. In fact, cylinder 4 might have been briefly hotter than the other cylinders after reducing power. I continued in the pattern and observed the same marginal power, engine roughness, and lowered CHT/EGT on cylinder 4 in the fourth touch and go. Leaning in flight didn't seem to help, only reducing power would restore normal engine operation. I then returned to KWHP without issue at 50% to 70% throttle in a brief cruise.

Some other information:
- The engine had been running for at least 40 minutes prior to the 3rd touch and go, mostly in flight
- Ground operations were leaned aggressively, but all pattern work was done with full rich mixture, cowl flaps open, boost pump on, turbo off
- Just before flying, I topped off with 47gallons of 100LL. (It was definitely NOT Jet A. KWHP doesn't self-serve Jet A, and I sumped both tanks to check fuel after refuel).
- The airplane experienced loud backfiring on take off about 5 flight hours prior to this flight (a few weeks ago). Immediately following the significant backfiring event, I removed, cleaned, and gapped all spark plugs except cylinder 2 & 4 bottom plugs as I was having a hard time removing them with limited tools. The airplane performed fine for approx 5 flight hours until today's flight. The CHT/EGT monitoring was not observed on the initial flight with backfiring. 
- Oil pressure and oil temperature were fine, observed 6 quarts of oil in pre-flight check.
- 1977 M20J Lycoming IO-360 with turbo normalizer


What do you think the problem is?

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My guess fowled plug. I found doing patterns full rich and always going full rich on final I would fowl some plugs so much as to not be able to burn it off and would end up picking out lead beads.  Some ALCOR every few tanks and leaning in the pattern has cured my issues.

Did you do a mag check on ground or in air after this issue? Do you have engine monitor to observe EGT/CHTs of all 4? 

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7 minutes ago, kmyfm20s said:

Sounds like a timing issue but do you have an engine monitor with data or down load? 

No data. Insight Avionics GEM 603 engine monitor.

1 minute ago, J0nathan225 said:

My guess fowled plug. I found doing patterns full rich and always going full rich on final I would fowl some plugs so much as to not be able to burn it off and would end up picking out lead beads.  Some ALCOR every few tanks and leaning in the pattern has cured my issues.

Did you do a mag check on ground or in air after this issue? Do you have engine monitor to observe EGT/CHTs of all 4? 

What is ALCOR? 

I did another mag check after the issue on the ground and couldn't reproduce it any issue. This might be because I had leaned aggressively in taxi and then did the run up.

I'm also leaning towards fowled plug because they had a lot of deposits on the plugs when I cleaned them and the issues seem correlated to mixture being too rich.

Perhaps I need to always lean appropriately in the pattern or find a better take off mixture? It wasn't a high altitude airport (field elevation 800 feet).

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Usual recommendations for new2MSers...

1) Hold off on TnGs until things are running as smoothly as expected... added complexity can work against you in a few ways...

2) Fuel igniting in the muffler... often a too rich condition, or an ignition challenge, or fuel ratio challenge...

3) Lots of things can be ruled out by posting EGT and other data from the JPI...

4) If you got it, work on getting it uploaded to Savvy, Click the share button at savvy, copy the link here...

5) Study up on running a really good run-up... how to set the data rate properly...

6) It could be as simple as some champion spark plugs aren’t behaving very well any longer...

7) Great detailed Pirep, Preston!  You gave Plenty of detail to work with...

8) Do you have a FF meter? Leaning for T/O would only be normal for higher altitude/DA...

I bet we can find where the issue is immediately, what is causing it, right after that... then any next steps...

PP thoughts only, not a mechanic...

Best regards,

-a-

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Cylinder 4 going cold indicates that it wasn't producing power. The likely causes would be ignition, fuel or a stuck valve. Ignition seems unlikely as it would have to affect both plugs. The fact that it seems to run at reduced power but not at full power could indicate a restriction in the fuel flow. When was the last time the injectors were cleaned?

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I should have been clearer...

ignition being the spark wasn’t happening...

Not so much the mag wasn’t doing its job...

Could be a shorted wire as well...so inspect the wire when you get the cowl off...
 

Either way...start at the plugs and work your way out from there...

inspecting the plugs... oil, lead, missing parts, high resistance, wear... things that mess up the spark...

if you are familiar with leaning during taxi... your lead build up will probably be tiny...
 

PP thoughts only, not a mechanic...
 

Best regards,

-a-

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1 hour ago, PT20J said:

Cylinder 4 going cold indicates that it wasn't producing power. The likely causes would be ignition, fuel or a stuck valve. Ignition seems unlikely as it would have to affect both plugs. The fact that it seems to run at reduced power but not at full power could indicate a restriction in the fuel flow. When was the last time the injectors were cleaned?

Skip

+1 on this.   A clogged injector nozzle or line or debris in the flow divider might do this.    I've had injector nozzles clog and unclog and reclog themselves before, so it seems like it does happen.   A partial clog will run fine at lower power settings, but once it gets past where it can supply sufficient fuel then the affected cylinder starts to go lean.

 

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The next homework assignment would include checking the logbooks to determine how long the fuel injection system has been in place...

Over time, an OH is often a good idea...

If you go to cleaning out the fuel injectors... there is a test for that... run them into four identical containers... this is called the baby food jar test...  all four should fill at the same rate... if one is partially blocked the results will be obvious...sometimes the spray is more dribbles or squirts... cleaning the FIs is often done using a vibratory cleaner and something called Hopps#9

PP thoughts only, not a mechanic...

best regards,

-a-

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+1 on it being unlikely an ignition problem.  You'd only see slightly higher EGT and minimal CHT change (basically the same effect as a mag check), unless it happened simultaneously to both plugs or on only those two leads from the mags.

Seems less likely to be a stuck valve or morning sickness, since it happened after the initial flight, but I suppose that's still a possibility

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