Rough running....diagnosis help

[acroflyrgirl]

MX quiz.

A few weeks ago I did a runup and had a bad spark plug, or so I thought. Mag drop low on one mag, EGT hot. Taxi back, remove #3 bottom plug due to the EGT tip. Put in a new plug and the plane flew great....for the next 13 hours.

Last weekend, flew a few flights, all was well. 2nd flight on Sat. The engine began running rough. EGT's & CHT's normal but rough between about 2000 and 2550 RPM, smooth everywhere else. Mag check good at all power settings.

Took all the plugs out and #3 bottom was a bit wet with oil. Cleaned all plugs, installed and the run up was fine. Took off at full power, 2600 RPM all is good, then as I start pulling the prop back it did the rough running thing again. Smooth at 2600 & above, but rough still between 2550 down to 2000. Smooth as silk at 1900.


I did a cold compression check. All cylinders were 70 to 76, and I removed the oil filler stick/cap and heard a little bit of air.....on each cylinder. At first I thought ahh hah, but on each cylinder, with good compression. I guess that is normal?

The local IA, who is mostly a Continental 520 guy, asked me about my mags.
I have Slick mags with 970 hrs on them. I had some trouble with them earlier this summer and had the internal timing adjusted, but did not overhaul (yellow tag) both mags.

This local MX guy thinks it's a mag issue. Does that sound right in your opinion? I'm assuming the good compression eliminates a valve or a ring problem.

[PCHunt]

Hi Cathy!
Carbureted or injected? 970 hours on Slick mags is a lot of time. There is a 500-hour AD on Slick mags.

The fact that your engine is rough at some RPM's and not at other RPM's might point to an injection problem if you are injected.

If carbureted, or for that matter, even if injected, might check for intake leaks.

"Grabbing at straws"

Pete
PS: How rough? What kinda rough? Have you done an airborne mag check at cruise power? Do you have an engine monitor that might provide data? Is the carb loose?

Lotsa Questions!

[RV10inOz]

Without a data file to study, here are a few things you should check first.

1. Plugs, gaps are 0.016-0.018" for massive electode plugs. The resistance needs to be below 5000 ohms too.

2. Carefully check your inlet gaskets and intake tube couplings. Do a GAMI Lean test both high and low altitude to detect leaks.

3. Get your mags overhauled and if the plugs have been there all this time the coils might be stressed. Make sure they get put back on and timed correctly, and you would be horrified how many times this is wrong.

4. If fuel injected the fuel pressure might be an issue if it is hot and the fuel flow is dropped back, by any chance are you running mogas? I doubt the injectors are dirty. What could be a problem is a build up of gum/sludge on the rubber diaphragm in the fuel control unit, and this can do funny things to the fuel flow. Usually from over priming or priming with hot starts.

5. you could have a good look at the EMS data file to see if anything is trending away from normal.

[AZtailwind]

Originally Posted by acroflyrgirl

MX quiz.

This local MX guy thinks it's a mag issue. Does that sound right in your opinion? I'm assuming the good compression eliminates a valve or a ring problem.

Cathy, I have a Slick Mag sitting here from the P-Mag conversion- It was overhauled about 400 hours ago if you need something loaned for diagnostics

[acroflyrgirl]

It is carbureted, I did do a full power mag check with normal results.
I am sending the mags out today for overhaul. That will eliminate one question at least.

I checked the induction, all snug. I'll know in a few days if the mags fix everything or I have to keep digging.

[ifixf15]

Cathy, before spending any REAL cash you may want to upload your Engine Monitor data to the SavvyAnalysis.com and e-mail a list of your symptoms to Mike Busch. Also, if you are sending your mags out, you may want to ask for an IRAN (Inspect and Repair As Necessary) instead of using the O word. With 970 hours, an Overhaul may be a bit of overkill.

Tom

[acroflyrgirl]

So, can I get info off my Dynon 180 that could point in the right direction for diagnostics?

[Pmerems]

Cathy,

If your D180 is set to record the data and the sampling rate is fine enough then you could download engine data in an excel format for review.