Jump to content

Mixture too lean; misfires; 0.7 GAMI spread


Recommended Posts

 

Now that I have a working EDM-830 (saga), I’ve been trying to figure out what’s going on. I’ve been working with the folks at Savvy, etc.

It’s a work in progress, and I’m going to go up and do some calibration and gather more data, but issues that have come up so far:

  • Departing my home airport, which is at 100’ MSL, my EGTs are over 1400F, which the Mooney specialist at Savvy says is “on the lean side” and outside the cohort of F/J models they’re tracking (usual range 1250-1350). Fuel system is almost all new (servo, mechanical fuel pump replaced ~100 hours/~6 months ago). Is there an adjustment that can be made? I have the quadrant throttle (blech). Edit: “Your max FF is a little on the low side of what we typically see...”
     
  • When I went about 15F LOP (which was at 7.5 gph at 8500’), EGT1 and 4 spiked about 40F each, “showing us that both #1 and #4 are misfiring.” Ignition System should be dialed in; same service ~6 months/~100 hours ago, had the following done: IRAN’d mags, new ignition harness, new p-leads, engine timed. Within the past ~5 months/~80 hours, all new spark plugs. Run-ups are fine, including mag checks (100 rpm drop both sides). What should I check / have checked first? (Could just be a couple of dirty plugs? I lean pretty aggressively for ground operations including the mag check...)
     
  • I’m going to redo the gami spread test a few times, but my initial run, ~22” MAP, 2500 RPM, 8500’ peaked EGT4 at 8.3 gph, 1 @ 8.1, 3 @ 7.7, 2 @ 7.6, a spread of 0.7, higher than the <= 0.5 gph required for LOP operation. Per the Savvy analysis, I have what “appears to be poor mixture distribution - which is unusual for this engine. It usually does fine. ... Its rare these engines need gami's - very few need them. But if 0.7 is accurate that's not going to support smooth LOP ops.” Which would be just my luck, I get one of the only Lyc IO-360s that needs GAMIs. I’m going out this morning to get more data, but if the 0.7 is accurate, is there anything short of swapping the injectors to GAMIs I should look at?

Sent from my iPad using Tapatalk

 

Edited by chrixxer
Formatting
Link to comment
Share on other sites

There is a way to set rich and lean.  There is a manual for your fuel servo.   You need a new mechanic.  no I am not kidding on the new mechanic.

Current mechanic has never looked at the fuel servo (until this deep dive, I didn’t know I needed him to). The guy who did the work after Pt. Mugu, I agree wholeheartedly, was ... “less than stellar.”

 

Edit: I’ve read through the Precision Airmotive manual and don’t see where take-off fuel flow can be adjusted on the RSA-5AD1? Idle settings are fine... (I’ll double check them today, though.)

Link to comment
Share on other sites

I assume the mechanic has verified that the throttle travel goes to the stop. You should be seeing close to 18 gph FF on take off at sea level. If that's not happening it would increase EGTs as Savvy (probably Paul @kortopates ) pointed out. 

Injectors checked?

Plugs checked for resistance? Champions or Tempest? I know they're nearly new but... 100F drop on MAG check is a little on the high side.

When was the fuel servo last overhauled? If the simple stuff is okay it is a likely culprit. Mechanic should disconnect the throttle linkage and verify the control level moves freely stop to stop. I don't think servos are field serviceable. ICBW. 

My comments are based on personal experience and discussions with @AGL Aviation. Paul/Savvy has forgotten more than I know...

 

  • Like 1
Link to comment
Share on other sites

Have you verified that you have no intake leaks or a stuck sniffle valve.  As you know the fuel servo is not field adjustable. However, it is adjustable buy a fuel service specialist during rebuild/IRAN. It may be possible to request that the fuel flow be set at the Max range of spec but I don’t for sure. As a data point, my 67F typically has EGT‘s in the mid to high 1100s at full throttle, full rich, when departing my field (701’).  The servo is remarkably good at maintaining mixture the during climb. I only lean to hold takeoff mixture and then because there’s no reason to be that far ROP as power drops off.  Our engine was torn down for overhaul into thousand, torn down again due to a case crack in 2010. Various intake tubes have been off at other times in the last 20 years for mx.  All four injectors were replaced due to a ham fisted technician over tightening the B-nuts and cracking the injectors.  EGT probe’s I have also been removed, reinstalled and/or replaced.  None of those situations have had any effect on max power EGT’s, fuel distribution or how the engine runs in general. 

 It’s post like these I think of whenever I hear somebody parrot the line that raw EGT‘s don’t matter. It is indeed true that the +/- 30-60 per cylinder means nothing. But when all of your numbers are in a place that couldn’t possibly be the desired setting, then it’s time for concern.  If all of your EGT‘s are over 1400, How could you possibly be 250° ROP or better on takeoff?  Normally aspirated Aero Engines of don’t generate EGT numbers in the  1600° plus range when properly timed with both plugs firing.

The first thing I would do if I were you is take off and level of 1000’ AGL. Do a quick lean from full rich to peak on your leanest cylinder.  That outcome will determine whether or not you have an instrument issue, an ignition issue or a fuel flow issue. If at 1000’agl (1300msl)  at full rich it is not at least 250° ROP then I would stop flying the plane and have the fuel service sent out for maintenance. If you are able to get to 250° ROP (high 1500-1650° range), Then I would check the mag timing.  If somebody used the wrong mark and the timing is retarded, that could explain your increased EGT’s.

Edited by Shadrach
  • Like 3
Link to comment
Share on other sites

About that Gami spread... 0.7 isn’t horrible, but it isn’t that tight either...  the big question that follows... is there one cylinder that peaks before or after the other three... (signs of an air leak near one cylinder)

Full throttle fuel flow should tell you a great deal about how things are set up.

As Bob pointed out, his FT-FF is around 18gph for the IO360...

This much fuel is going to be near 2-300°F ROP...

So... rolling down the runway, with T/O power... quick review of MP, RPM, and FF... gives me the comfort I need to continue on.

 

At the other end of the spectrum... throttle pulled all the way back... engine turning about 700rpm, FF 1-2gph...?

 

Savvy is telling you that something is failing a spark plug, or two...

 

You have the skills and equipment to determine exactly which two plugs are not working...

 

If they are champion... their resistance has gone high...

If they are the other guy’s... It is missing the center electrode...

 

Can you post a JPI graph that includes the flight where you saw 40°F EGT jumps caused by the misfires?

 

Keep in mind when a plug misses, iow, doesn’t fire... it sends some small amount of excess raw fuel with the exhaust.... it continues to burn... raising the EGT...

 

Expecting that there are two failing plugs, because you have two cylinders that are showing instances of higher EGTs... focus on things where the plugs can be tested...

The run-up is a good way to start... nice and slow, allowing time for EGTs to rise, peak, and stay... before switching to both, waiting to see the EGTs descend, bottom, and stay...

All eight plugs should behave the same way... there are going to be two that may start looking slightly different....

 

If Nothing stands out on the ground based run-up... the mag check in cruise is surely going to confirm what Saavy is telling you...

There is going to be a learning experience in here... you will learn what plugs are not working as expected... or you will learn that you are going more lean than you have expected... ie. leaning until there isn’t enough fuel near the plugs to burn evenly...

Leaning slowly, takes a bit of time... take the effort to know you are actually going from ROP to LOP... at less than 65%bhp, you are free to lean, un-lean, and lean again to find exactly where peak is occurring...

 

For leaning experiments... set the MP to the low level needed for 65%bhp... no need to climb to get there...

Higher MPs are easier to lean deep...

Lower MPs are not as easy to lean deep...

A well balanced engine... (like my old IO550)

  • down low, the engine could run 90°F LOP before turning off...
  • up high, the engine could run 50°F LOP before turning off...
  • power drop is huge going this far LOP... It is just for an experiment of how well balanced the air/fuel mixture really is...

Post a link to your savvy graphs if able... if you can feel a plug skip, it will be in the graphs... if you can see a 40° EGT rise, it will be in the graphs too...

Raw EGT data gets a bad rap... but, it isn’t very easy for most people to use... it usually requires comparisons to previous flights, or other planes with similar installations.... because the raw EGT is very sensitive to distance between sensor and exhaust valve....

PP thoughts only, not a mechanic...

Best regards,

-a-

Link to comment
Share on other sites

as @Shadrach pointed out, the fuel servo on the Lycoming IO-360 is not adjustable.  IIRC, this is an issue on Continentals.  My full power, full rich FF is about 16.5, which is on the low side, but I'm about 300degF ROP

My GAMI spread is between 0.5-0.8 gph and I can run about 50 degF LOP.  When I had bad internal timing on my left mag from cam wear, I had the same problem LOP.  Interestingly, when I ran as lean as possible and did an in-flight mag check, it did not demonstrate any problems, so I don't think the in-flight leaned mag check is very sensitive.

You do realize the visual tape indicators on the 830 can be changed from the settings menu?  It's annoying, but takes 15 minutes.

 

Link to comment
Share on other sites

@chrixxer

EGT1 has fallen compared to the other three... first graph.

The second graph shows EGT #4 not behaving particularly well, and #1 still misbehaving...

Looking more like the plug issues discussed...

Fortunately the traces begin right at start-up... no need to flight test, when running on the ground is pretty telling...

Slow run-up on the ground... to see each response for each plug on L,R, and B mags...

Find the two misbehaving plugs, remove and inspect...   (check the logs first to see what plugs you have, how old they are...)

Pp thoughts only, not a mechanic...

Thanks for posting the JPI graphs so quickly...

Best regards,

-a-

  • Like 1
Link to comment
Share on other sites

Thanks for posting the Savvy graphs.

I don't see a good run-up mag check on either. Or if there is a good mag check there, you've got some ignition issues.

Do a nice and slow mag check. Set power to a steady RPM, I use 1500. When you switch off one mag, let it run there for 30 seconds. Then back to both for 30 seconds, then the other 30 seconds. 

Better yet, go fly and do an inflight mag check, nice and slow, just as prescribed in the Savvy Test Profile.

Post the resulting data.

And what @Yetti said, get a different A&P.

  • Like 2
Link to comment
Share on other sites

2 hours ago, carusoam said:

Full throttle fuel flow should tell you a great deal about how things are set up.

As Bob pointed out, his FT-FF is around 18gph for the IO360...

 

Well, Jay says his are 16.5gph on take off. The reality nobody knows what exact fuel flow ought to be on a given day. It varies depending on DA, and can vary quite a bit. What’s important is that the engine is adequately rich with all the knobs forward. Depending on conditions that could be anywhere from 15 (departing Leadville in July) to 21gph (Rockland, ME in Feb). The servo is capable of delivering far more fuel then an IO360 needs.  No need to complicate it.  The engine is 250° to 300° ROP or it isn’t.

Edited by Shadrach
  • Like 1
Link to comment
Share on other sites

1 hour ago, jaylw314 said:

as @Shadrach pointed out, the fuel servo on the Lycoming IO-360 is not adjustable.  IIRC, this is an issue on Continentals.  My full power, full rich FF is about 16.5, which is on the low side, but I'm about 300degF ROP

My GAMI spread is between 0.5-0.8 gph and I can run about 50 degF LOP.  When I had bad internal timing on my left mag from cam wear, I had the same problem LOP.  Interestingly, when I ran as lean as possible and did an in-flight mag check, it did not demonstrate any problems, so I don't think the in-flight leaned mag check is very sensitive.

You do realize the visual tape indicators on the 830 can be changed from the settings menu?  It's annoying, but takes 15 minutes.

 

The servo is not field adjustable, but I believe the metering jet is adjustable by a fuel servo tech when removed from the aircraft. I believe the continental fuel servos are indeed adjustable in the field by an A&P.  The RSA-5AD2 does have field adjustable FF, but that is not the servo our engines utilize.

Link to comment
Share on other sites

Thanks Ross!

I missed the important detail... my numbers are at 125’ MSL... :)

Bob’s are in the Carolinas...

 

The cool device in the LB panel is the EGT gauge that is calibrated with °F... very easy to tell how ROP one is while flying... at a glance.

2-300°F ROP is depicted by a blue box...  white box on the G1000...

All things that can be checked before leaving the ground...

Easier at SL because the numbers are well documented...

More of a challenge when at higher alts where the engine data is less well documented... MP, RPM, FF in the POH....

 

+1 on good run-up on the ground... most likely individual plugs, but could be caused by a failing mag...

how many hours on the plugs, how many on the mags...?

What plugs are in there?

Are the failing plugs all in the low position... they could be getting oil soaked... (visible when plugs get pulled)

Are the failing plugs all in one mag... the mag could be slowly failing... (check To See the mag hasn’t gotten loose)

 

So for next steps... determine which exact two plugs are showing the problem, using the slow ground run-up...

slow... 30 seconds on L, 30 seconds on B, 30seconds on R...  1.5 minutes and the data collection should capture it... based on the graphs we are seeing today...

I use 30 seconds in this case, because my JPI takes multiple seconds to get one reading...  if the JPI is at its highest capture rate of two seconds... this would be better... the usual six second capture rate makes this 30 second wait time kinda necessary....

And yeah... the run-up should be very visible in the JPI graphs... where’d they go? :)

PP thoughts only, trying to help Chrix understand what he is seeing under ordinary Mooney conditions on the ground, not a mechanic or CFI....

Best regards,

-a-

Link to comment
Share on other sites

On takeoff on the second graph, your fuel flow is only 12.3 but within 3 minutes, with no logged reduction RPM, it goes up to 12.8 with an accompanying drop in EGT. Do you recall doing anything to increase fuel flow, such as giving it more mixture, when you left Mountain Valley? I interpret the initial FF to be a result of your leaning to accommodate the DA at your departure airport. Since you are climbing out it would seem counter-intuitive to me to enrich the engine, but being a flat-lander, I don't know if any knowledge I have would apply here. I think the biggest concern for me would be if you made no adjustment to the mixture, and the monitor recorded an uncommanded change.

My Savvy report card I just received (IO-360) shows Max Fuel Flow of 17.9 gph to be the 50% and 17.1 gph to be the 25% number so even the max of 16.3 gph on your first graph would be low.

 

  • Like 1
Link to comment
Share on other sites

4 minutes ago, Oldguy said:

My Savvy report card I just received (IO-360) shows Max Fuel Flow of 17.9 gph to be the 50% and 17.1 gph to be the 25% number so even the max of 16.3 gph on your first graph would be low.

Mike Busch at Savvy makes a big deal out of ensuring the full rich fuel flow is high enough, but again, his experience and Savvy's client base are much more from Continentals rather than Lycoming's (correct me if I'm wrong, @kortopates).

Link to comment
Share on other sites

Jay roughly speaking...

Max FF for the IO550 (310hp) 27.2gph according to the STC at SL.... some people bump that up closer to 30gph for improved cooling

So using the continental numbers adjusted for the hp of the IO360.... a 200hp engine would have... 18.1 gph to 20gph using the same MSL and ROP....

which kind of matches the discussion above...

So Chrixxer’s max FF at 240’ (?) MSL 12.1 and then 12.7 later on... desires an explanation... (great call OG)

 

Confirm That the T/O...

  • was full rich, at full throttle, full rpm... 
  • what caused the .5gph increase in FF later on... ?

 

An increase in FF is usually accompanied by...

  • increase in MP
  • increase in rpm
  • or an increase of mixture...
  • it is difficult to get more FF when all knobs are pushed in and climbing

I probably missed something.... now waiting for Ross to enlighten me... :)

So more things to consider if the fuel servo isn’t quite right yet...

Got to love the JPI data recorder, and Savvy graph capabilities...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

  • Like 1
Link to comment
Share on other sites

1 hour ago, jaylw314 said:

Mike Busch at Savvy makes a big deal out of ensuring the full rich fuel flow is high enough, but again, his experience and Savvy's client base are much more from Continentals rather than Lycoming's (correct me if I'm wrong, @kortopates).

Continental or Lycoming, the amount of surplus fuel needed to slow the combustion event is the same. Full rich, max power FF should be .55 to .60lbs/hour per horsepower. So a 200hp aero engine on a standard day should require between  (.55*200)/6 and (.60*200)/6 which is 18.3-20gph. Chrixxers numbers on take off appear to be way low and  inconsistent. At sea level he’s getting 12 to 15gph at 2700 RPM. Manifold pressure appears to be low and inconistent as well. Even on a hot day at 100 feet MSL I would expect more than 24 inches. The other Flight shows 29.1 inches and 16.3 gallons an hour, better but still FF is still low.

Edited by Shadrach
  • Like 1
Link to comment
Share on other sites

1 minute ago, Shadrach said:

Continental or Lycoming, the amount of surplus fuel needed to slow the combustion event is the same. Full rich, max power FF should be .55 to .60lbs/hour per horsepower. So a 200hp aero engine on a standard day should require between  (.55*200)/6 and (.60*200)/6 which is 18.3-20gph. Chrixxers numbers on take off appear to be way low and  inconsistent. At sea level he’s getting 12 to 15gph at 2700 RPM. Manifold pressure appears to be awfully low as well. Even on a hot day at 100 feet MSL I would expect more than 24 inches.The other Flight shows 29.1 inches and 16.3 gallons an hour, better but still low.

I was just talking specifically about the point of adjusting full power fuel flow, MB beats that like a dead horse, but it has little bearing on the Lycoming people.

I haven't looked at @chrixxer's numbers, someone else had suggested he was leaning for altitude?  That would make sense if he got up to 16.3 gph on other runs.  Like I said, I get 16.5 gph and I'm at sea level in Oregon, so I probably get more standard days than the average person here :) 

  • Like 1
Link to comment
Share on other sites

18 minutes ago, jaylw314 said:

I was just talking specifically about the point of adjusting full power fuel flow, MB beats that like a dead horse, but it has little bearing on the Lycoming people.

I haven't looked at @chrixxer's numbers, someone else had suggested he was leaning for altitude?  That would make sense if he got up to 16.3 gph on other runs.  Like I said, I get 16.5 gph and I'm at sea level in Oregon, so I probably get more standard days than the average person here :) 

He took off from a 100msl field on both flights.  Max FF on the first was just over 16GPH. max on the second was just over 12GPH.

Edit -  I understand your locale is given to mild weather at sea level.  That does not change the fact that the recommended full power FF is .55 to .60lbs per hour, per horsepower.  Your FF instrument could be off a little and your Servo could be set up on the lean side of spec. Eitherway, you're on the lean side. If it's working out, I'd not sweat it too much.

1733110427_05-18at1746.thumb.jpg.3517869eb2e557af7505ac096b5506b2.jpg

1137195262_05-18at2116.thumb.jpg.a943d5674dc51179d8e57d49a882270a.jpg

 

Edited by Shadrach
  • Thanks 1
Link to comment
Share on other sites

2 minutes ago, Shadrach said:

he took off from a 100msl field on both flights.  Max FF on the first was just over 16GPH. max on the second was just over 12GPH.

Ah, thanks, I couldn't get to the Savvy site to work on this computer.  Yes, 12 gph does seem way low, lower even than full throttle at best power

Link to comment
Share on other sites

24 minutes ago, Shadrach said:

He took off from a 100msl field on both flights.  Max FF on the first was just over 16GPH. max on the second was just over 12GPH.

One minor correction, Ross: second flight took off from L94 which is ~4,200 MSL. That is why I was wondering if the initial FF was set lower but then increased on its own or as a result of a change he made. I could see dialing back FF based on DA, as I think you mentioned earlier, but he has not indicated how he set the controls for the second take off.

One of those "inquiring minds want to know" things.

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

34 minutes ago, Oldguy said:

One minor correction, Ross: second flight took off from L94 which is ~4,200 MSL. That is why I was wondering if the initial FF was set lower but then increased on its own or as a result of a change he made. I could see dialing back FF based on DA, as I think you mentioned earlier, but he has not indicated how he set the controls for the second take off.

One of those "inquiring minds want to know" things.

Good catch!  I would argue that both settings are way on the lean side. 

My POH numbers @ 2700 RPM for 5K and 7.5K:

5K says at 25" MAP the fuel flow should be 16.7GPH

7.K gives 23" MP the Fuel flow should be 15.4GPH

Incidentally the POH FF for Sea Level max power full rich on a standard day is 18.6GPH.  It does not give a FF for those 30.75" days when the OAT is 12 and the DA at the airport I'm departing  is -3400'. On those days it should be pushing 20gph.

 

Edited by Shadrach
  • Like 1
Link to comment
Share on other sites

4 minutes ago, Shadrach said:

Good catch!  I would argue that both settings are way on the lean side. 

My POH numbers @ 2700 RPM for 5K and 7.5K:

5K says at 25" MAP the fuel flow should be 16.7GPH

7.K gives 23" MP the Fuel flow should be 15.4GPH

Incidentally the POH FF for Sea Level max power full rich on a standard day is 18.6GPH.  It does not give a FF for those 30.75" days when the OAT is 12 and the DA at the airport I'm departing  is -3400'. On those days it should be pushing 20gph.

 

Absolutely they look lean! My J is pushing about 19 GPH during a full rich T/O from my home field on the mythical standard day.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.