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badmrb

Active Member
I've got an RV6 with an O-360, 10:1 pistons, one mag and one electronic ignition, GRT engine monitor. The problem is I can't get the engine to lean correctly and need some ideas.

Normally, at cruise, 2450rpm, I'd lean till one or even two cylinder EGT's start to drop and then go 100 degrees ROP. Might get a little drop in RPM but never any roughness, but I didn't go too far on the lean side.

When just flying local I'll run 2100rpm and lean till one or more cylinders start to drop EGTs and then a turn back in to bring EGTs back to peak. This usually give about 5.5 gph and 120kts to 125kts. Again, I'd get a slight RPM drop but never any real roughness unless I really lean aggressively.

Something has changed. I was putting around locally the other day and when I went to lean it up, it began running rough like it had a real miss until I richened it up. Now I can't get it to lean. No cylinder will drop EGT before I get roughness. Actually feels like a miss.

I've done ground run-ups as well as play with it in the pattern. No miss on either mag or EI. No difference on runup when just running on either ignition. I've tightened the intake tubes thinking it might be a leak. Plugs look good. Compressions are good, so I haven't lost a cylinder.

My A&P is stumped as well. We ran it at different power settings on the ramp and couldn't any cylinder to drop temp before beginning to run rough. All the EGT's are relatively close, no big difference.

ANY other ideas? Anyone had something similar?

Thanks
 
Sure sound like you're sucking intake air from somewhere... intake hose, gasket, I've even seen leaks at the sump connection. Look a little closer, check the carb gasket too. :)
 
This just happened to me...

Last month, very similar symptoms.

Mine is IO-360-A1A, one mag, one EI, and I can normally run very lean with no roughness.
All of a sudden, any leaner than peak egt and it would miss badly.

The plugs had 70 hrs on them. Swapped them out for fresh plugs, problem solved. Even though the plugs look great, I think there are lead nodules down around the bottom of the insulator that need to be cleaned out.

Reiley -- why do you say big problem if crimped? This may be a religious argument, but many say solder bad, crimp good.... is there something special about the coil leads?
 
scsmith said:
Reiley -- why do you say big problem if crimped? This may be a religious argument, but many say solder bad, crimp good.... is there something special about the coil leads?
Click to expand...

With the coils under the cowl in the turbulent intake cooling air, baffled or under a plenum the crimped connectors take a beating. Most of the time you can look at the insulator and see that the wire (lead) has been arching. This could and eventually will damage to the EI controller. If you can get the best of the best crimp, you might not see this for a while. Adding a dab of silver solder will give you a little support. You don't want to go overboard and make the wire brittle!! :)
 
Mag runs top aviation plugs. . . EI runs bottom auto plugs. It acts the same when running on either ignition alone. . as well together. Engine monitor doesn't show any EGT drop when I start getting the roughness/missing. . so I can't see one cylinder in particular acting up. I suppose something in a particular batch of fuel could have left some deposit on all the plugs. A&P is thinking it might be carb related since one cylinder or ignition isn't standing out.

Its funny, if this were a cessna, I wouldn't even be worrying about it.. .pull mixture until rough. . .add fuel back in. I wouldn't even have noticed a difference. But this thing has been so smooth and with the 4 cylinder EGT has been very predictable. Im trying to figure out what has changed.

Might have to pull the carb, inspect gasket etc. If this were a car, I get my can of ether or carb cleaner and start spraying gaskets listening for an RPM change. Its a little harder to find an intake leak (if thats what it is) with that big fan on the front.
 
Unashamed plug?

If you were running 114 series E/P-mags and a EICommander, you could simply display the screen shown below and it would tell you the condition of your ignition harness.

Preflight%20-%20green%20TDA%20b.jpg


The four vertical bars indicate the condition of a harness in a dual 114 E/P-mag installation. Bars to the left of the green box are for the left ignition and those to the right are for the right ignition. White indicates cylinders 1 & 2 while blue indicates the cylinders 3 & 4. (Two cylinders are fired by one dual coil pack.) Numbers blow the box indicate a fowled plug or shorted wire, numbers above the green indicate an open lead or broken plug.

The 114 series E & P-mags have the ability to measure the duration of the spark; too short (low number) and there is a fowled plug or electrical short, too long (high number) and there is an open lead or broken wire.
 
badmrb said:
Mag runs top aviation plugs. . . EI runs bottom auto plugs. It acts the same when running on either ignition alone. . as well together. Engine monitor doesn't show any EGT drop when I start getting the roughness/missing. . so I can't see one cylinder in particular acting up. I suppose something in a particular batch of fuel could have left some deposit on all the plugs. A&P is thinking it might be carb related since one cylinder or ignition isn't standing out.

Its funny, if this were a cessna, I wouldn't even be worrying about it.. .pull mixture until rough. . .add fuel back in. I wouldn't even have noticed a difference. But this thing has been so smooth and with the 4 cylinder EGT has been very predictable. Im trying to figure out what has changed.

Might have to pull the carb, inspect gasket etc. If this were a car, I get my can of ether or carb cleaner and start spraying gaskets listening for an RPM change. Its a little harder to find an intake leak (if thats what it is) with that big fan on the front.
Click to expand...

Hot summer days?

Leaning seems a little weird to me also but if you wait a while the EGT's do show LOP. What I've been doing is leaning to rough and then forward a bit to get a smooth operation. No indication of peak EGT, but if I recheck the EGT monitor 5 minutes later, it is showing LOP. (?)

I've written this off as a low altitude, hot weather anomaly. Same weird indications during very cold winter ops at low altitude.

Take the machine up to 8 or 10 grand and try LOP there. It is probably OK as is. Some days I get normal indications down low, some days not, which of course means I don't really know what's going on. But it always performs well at altitude.
 
check the tubes

In the sump, unless it's a horizontal inducted engine. Grab ahold and twist. If they move you have an induction leak.
 
Thanks for the ideas guys.

I tightened the induction tube hose clamps but I didn't really check the sump tubes themselves. Ill look closer at those, might have to drop the tubes from the heads and see if anything moves that shouldn't goin into the sump.

As far as fuel deposits, I might just replace the auto plugs. . .they're cheap enough.

The other thing I might do is drop the carb down and look at the gasket or just make sure the carb is still tight. Nothing felt loose, but I never put a wrench on the nuts.

I hope to be able to get back to the airport and check these this weekend.

Anybody else have similar symptoms? and what was a the cure?
 
Realized I never posted solution.

Just thought I'd post a followup since I often find posts with problems and then no solution.

I was talking with a friend who still thought it sounded like an induction leak. I kept on it. It was suggested I trace out all the lines on the primer system since a break there could be a problem. I was going to pull and plug all the lines to eliminate them as a source of air. They all looked intact.

I decided to have my son work the primer hard and I was going to look for leaks. .. guess what, primer didn't work. I hadn't used it since last year. I never could get better results priming then using the previous owners method of pumping throttle several times while cranking. Apparently the O-rings had dried up bad enough they werent sealing at all. A couple of new orings and no more problem!
 
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