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  #1  
Old 05-03-2021, 04:48 PM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
Posts: 571
Default One quirky cylinder

I trying to get some dual instrument time in that I need before I can write my instrument rating written test next week. My engine is having other ideas, had to scrub several flights over the last 2 weeks because my engine is just not right.

Some baseline information, I have a IO-320 built to zero time with 2 Bendix mags, Precision Airmotive Silverhawk EX fuel injection. I have 178 hours on this setup. Last year I had a fuel starvation event on takeoff that resulted in replacing the bearing kit on the FI servo. The mixture wasn't setup correctly after that reinstallation (way too rich) and I had a couple of engine quits on rollout before that was fixed. Recently I noted a 400 rpm mag drop on the right magneto on runup and also had the timing on the left mag fixed (from 27 degrees to 25). Everything ran well after that, but I didn't get much time in. I changed the oil and filter a week ago.

Now my current issue. Last week I was taxiing for departure and found my engine was running roughly, almost like it was running on 3-1/2 cylinders. #1 CHT was higher than the others and #1 EGT was more than 100 degrees colder. Cancelled that flight and did some inspection. Injector and fuel line from the flow divider were clear. Spark plug (R mag) tested good (L had been checked 2 weeks earlier). My mechanic/engine builder pulled the R mag and replaced a weak coil, it tested good as new. Reinstalled the mag and did a couple of good runups. Mag drop was still a little high, right around 200, but much better and the engine seemed to run fine.

Today I went to try a test flight and after a fairly long ground run (with mixture leaned for ground running) I entered the runway and immediately did a 180 to come back off. Engine was stumbling badly. Did another runup and my right mag drop was pushing 260 with the last 60-80 coming with a lot of roughness. No real roughness on the left mag, 120 drop or so. #1 cylinder temps were 40F higher CHT (350) than the others and 100+F lower EGT (1000). Other cylinders were all similar temperatures. The roughness was getting worse, but was not constant - maybe 1/2 the time on a 30 second cycle or so. Taxied back to my hangar and shut down. My mechanic had me do a per cylinder fuel flow check. With a 2 second boost pump burst, front cylinders delivered less than the back ones, not by a lot, maybe 90%. #1 was the lowest flow but only by a slight amount.

In what may be nothing but coincidence, I had radio TX issues today too. RX was good but tower was having difficulty hearing me, saying there was a lot static. One radio was worse than the other and I'd never had this issue before. Maybe this is a hidden clue, maybe it's nothing.

Next troubleshooting session is tomorrow morning where we are going to check the flow divider, particularly at the #1 port and test the ignition harness. The thinking is that there is either something inhibiting fuel flow intermittently or the ignition wire from the right mag is faulty.

Anybody have any ideas what else might be causing these issues? My mechanic doesn't think that it should be a sticky valve, the engine isn't all that old (2-1/2 years) and has been well maintained. I just want to trust it again.
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Claude Pitre
RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018

Added GPS 175 and authorized for IFR April 1, 2021

Interactive map of all of my flights here
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  #2  
Old 05-03-2021, 05:10 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 290
Default Engine Monitor?

Do you have a full 4 point engine monitor, like a JPI (color), Dynon, or something? Can you dump the engine data, and upload to Saavy Analysis? Then we can see plots of CHT etc.

A 10% difference in fuel flow is a lot (in my opinion). Open up the divider and clean it. Won't be surprised if you find some small junk in there.

Check really carefully for any fuel leaks or places that the system can suck air instead of fuel. Carefully check the injector lines from the divider to the injectors for cracks.

The mag drop sounds high as well. Just pulling a C-172 checklist, max is 125 rpm, and a max difference between mags is 50. So if one mag drops 100, the other needs to drop at least 50. 200??? That's a NO GO.

I think you have multiple issues. Don't stop when you find "something".

What air temps are you having?
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Last edited by blaplante : 05-03-2021 at 05:12 PM.
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  #3  
Old 05-03-2021, 05:30 PM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
Posts: 571
Default

I do have a Dynon engine monitor, but I didn't bring the logs home. Maybe I'll run out and grab them.

We've been in the 7-10C range for OAT.
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Claude Pitre
RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018

Added GPS 175 and authorized for IFR April 1, 2021

Interactive map of all of my flights here
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  #4  
Old 05-03-2021, 08:22 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,215
Default

The mag drop is not consistent with mixture or valve sticking. It surely seems like ignition. Plugs, wires, etc. Even carbon tracking in the mag. If the mag tested for even spark (4) on a bench either under pressure or large test gaps and good, then back to downstream of the mag. 2 cents
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  #5  
Old 05-03-2021, 10:33 PM
RV3Kev RV3Kev is offline
 
Join Date: Sep 2017
Location: Traralgon Australia
Posts: 46
Default

try replacing the spark plug wire and spark plug to #1 cylinder. insulation could be breaking down giving the erratic operation.
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  #6  
Old 05-03-2021, 11:16 PM
rv8ch's Avatar
rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
Posts: 4,133
Default

Quote:
Originally Posted by RV3Kev View Post
try replacing the spark plug wire and spark plug to #1 cylinder. insulation could be breaking down giving the erratic operation.
This is what it sounds like to me too. I had one ignition wire which worked perfectly sometimes and then badly others, depending on the bend of the wire. Turns out it was the connector between the wire and the spark plug. I also had intermittent radio "static" and clicking.
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  #7  
Old 05-04-2021, 06:18 AM
Nashpdman Nashpdman is offline
 
Join Date: Sep 2020
Location: Nashville
Posts: 12
Default

"In what may be nothing but coincidence, I had radio TX issues today too. RX was good but tower was having difficulty hearing me, saying there was a lot static. One radio was worse than the other and I'd never had this issue before. Maybe this is a hidden clue, maybe it's nothing."

This would lead me toward an electrical issue. Maybe a ground issue? Check your voltage and load test while running if possible. It has been my experience not a lot happens by coincidence.
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  #8  
Old 05-04-2021, 07:04 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,537
Default

On the high CHT / low EGT on #1, assuming that only low RPM operations are like this and high power is consistent with other cyl's, I would open the spider and check for debris in the four V shaped slots. At Idle and low 1000's RPM, fuel is partially metered in the spider, not the injector, like in higher RPMs. Debris in the spider can cause leaning on individual cylinders and create the symptoms you describe, but typically only at low RPM operations. If the debris is lodged in the bottom of the V, the leanness can prevail into the runup RPM range. I had a buddy with the exact symptoms as yours on two cylinders and we addressed it by cleaning out the debris in the spider. His was a new installation, where this is much more common.

As to the mag drop, I would put an ohmmeter on each plug wire and each plug and ensure they all test to spec. I also would pull the mag and look at the cap / rotor for excessive wear. Problems like this overwork a coil and can cause early failure. Given the failed coil, you want to be looking for sources / issues that would cause overworking of the coil and the most common are excessive cap rotor clearance and excessive sparkplug gap. 200 RPM on mag drop, assuming symmetrical timing across the two mags, is a lot and an indication that something is not right somewhere. Not as likely, but if the mag is reassembled with the gear off one tooth, weak ignition can result as the cap and rotor are not in proper alignment. It is easy to get this installed incorrectly when the mag is not on a fixed stand, as the magnet is pushing the armature away from the spot where it needs to be when installing the mag top. Given that you still have 200 RPM drop, I speculate that another issue is lurking and caused the coil failure.

Larry
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Last edited by lr172 : 05-04-2021 at 07:22 AM.
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  #9  
Old 05-04-2021, 09:21 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 290
Default

Quote:
Originally Posted by Flying Canuck View Post
I do have a Dynon engine monitor, but I didn't bring the logs home. Maybe I'll run out and grab them.

We've been in the 7-10C range for OAT.
Too cool in my opinion to be getting any vaporization in the fuel lines (which will cause surges and all kinds of odd running).

The engine monitor logs can show a lot if you can point out at what time you did run-up, mag-check, etc. I had a funny idle for a long time. Once I had my JPI installed I could see that one cylinder 'went funny' at idle speed. A tiny bit of stuff in one of the V's of the FI spider.

As others said... check plug resistance, and also condition / corrosion of the plug wire spings and the plug top end 'socket' the spring goes into. The comment about the mag being assembled off one gear is right on too - that's the mag "internal timing".
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  #10  
Old 05-27-2021, 10:55 AM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 290
Default Well?

I'm sure curious as to what you've found!
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