252 and Encore pilots - ground run-up/ignition/mag check - leaned?

[nationwide]

Looking for input from operators of TSIO-360-MB and SB engines.  Do you conduct your ground run-up (ignition/mag check) full rich per the POH, or leaned?

Reason for asking:  I have an Encore-converted 252 with some mag issues.  (Discussed the latest here).  The plane was recently in the shop to have the TIT probe replaced (no other issues going in), and following that work, the shop said the plane failed the post-maintenance run-up due to excessive RPM drop.  They re-timed the mag--a mag with <25 hrs on it since coming back from repair, discussed in the thread linked above--to 21 BTDC, ran it up, and said it was now good.

When I picked it up I got excessive drop (>250 RPM) with good EGT rise on all cylinders, and notable engine roughness, which is uncharacteristic for the engine.  (Typical is 100 RPM and no/little roughness.)  The other mag was about 150 drop, also rougher than normal.  When I asked them about this, they said they checked it again, and got good numbers by leaning it out.  I've always done the mag check full rich, which is what's in the POH.  And the engine was fine full rich before this latest mag work but with no other changes (save for a new TIT probe), which makes me wonder about what's going on.

BTW I have read the threads about the validity/usefulness/effectiveness/pros-cons of on-the-ground mag checks, and the advantages/disadvantages versus an in-flight LOP mag check, and understand the issues there.  I am not looking for input on those issues, only what you as a 252/Encore driver do when you perform an on-the-ground test.  Or, A&P input on the issue, if you are one and have some.  Also, I do lean aggressively on the ground but had always gone full rich for the mag check (and for takeoff, of course).

[Jetrn]

I do my mag check @1700, mixture rich for about a minute or so on each mag.  Watching for corresponding temperature changes on the edm.

[gsxrpilot]

I do my mag checks leaned out a bit. But then I'm in Denver at 5600 ft on the ground. My 252 won't even start if the mixture is full rich.

[tmo]

Isn't the turbo already spinning with the engine at 1700 rpm?  Or is it not spinning enough to make up the 6" delta?

[gsxrpilot]

1 minute ago, tmo said:

Isn't the turbo already spinning with the engine at 1700 rpm?  Or is it not spinning enough to make up the 6" delta?

I think it's marginal. I just taken to having my Mixture knob pulled out about an 1" all the time when on the ground. Starting, taxiing, run-up, all of it. 

[kortopates]

Somethings wrong, it may not be the mags, but at Spokane's altitude I wouldn't expect that alone to be creating an overly rich condition. So I'd check the low Idle unmetered fuel pressure as well as the idle mixture adjustment - since its apparently behaving like its too rich. Perhaps the pump got adjusted along with the Mag work?

[anthonydesmet]

When your shop said “Got good numbers by leaning it out” are you sure they didn’t mean they ran the engine at 1700-1800 rpm lean for about 90 seconds with EGT’s in 1500 to clean the plugs and then did a normal full rich mag check?  That’s normal procedure isolate whether you have a mag problem or a plug problem when your plugs are fouled due to over rich conditions as @kortopates stated. I don’t think they did the mag check with your engine LOP. Sounds like a fuel metering issue vice mag?  How long has your airplane been sitting between flights also?

[carusoam]

Being leaned during the run-up...

Has one challenge attached to it...

Things are busy, and getting busier...

Have a good plan to make sure your mixture is set for T/O...  Before pushing the throttle in... 

It makes for a nice distraction challenge... but, can also be very tough on the engine... a pre-ignition challenge...

Best regards,

-a-

 

[nationwide]

On 5/29/2020 at 2:19 PM, carusoam said:

Being leaned during the run-up...

Has one challenge attached to it...

Things are busy, and getting busier...

Have a good plan to make sure your mixture is set for T/O...  Before pushing the throttle in... 

It makes for a nice distraction challenge... but, can also be very tough on the engine... a pre-ignition challenge...

Best regards,

-a-

 

I agree, it’s important not to take off leaned...that would be bad.

[nationwide]

On 5/29/2020 at 2:12 PM, anthonydesmet said:

When your shop said “Got good numbers by leaning it out” are you sure they didn’t mean they ran the engine at 1700-1800 rpm lean for about 90 seconds with EGT’s in 1500 to clean the plugs and then did a normal full rich mag check?  That’s normal procedure isolate whether you have a mag problem or a plug problem when your plugs are fouled due to over rich conditions as @kortopates stated. I don’t think they did the mag check with your engine LOP. Sounds like a fuel metering issue vice mag?  How long has your airplane been sitting between flights also?

They actually performed the test leaned out.  (I also tried clearing the plugs via the method you describe here when I was testing it—no improvement.)  It sat about 2 weeks this particular time.

[nationwide]

On 5/29/2020 at 12:40 PM, kortopates said:

Somethings wrong, it may not be the mags, but at Spokane's altitude I wouldn't expect that alone to be creating an overly rich condition. So I'd check the low Idle unmetered fuel pressure as well as the idle mixture adjustment - since its apparently behaving like its too rich. Perhaps the pump got adjusted along with the Mag work?

There was no work done to the fuel system this particular time, when this RPM drop issue arose.  But, it did recently (Nov) have the wastegate controller removed/readjusted/reinstalled and major adjustments made to the fuel controller following that re-installaton.  (I wrote about this on the Mooney Pilots FB page: https://www.facebook.com/groups/2226961823/permalink/10155850677521824/). The unmetered fuel pressure was bumped up considerably, and I now conduct ground ops with the mixture vernier out about 1-1.5” (used to be about 3/4 to 1”)...except for run up and takeoff, which as I said I have always done full rich.  Including after the fuel work, here at Felts (2000 MSL).  But no longer, as of this last trip to the shop and subsequent mag work, which is why I’m really vexed over the recent behavior.

The shop here insists that the FF numbers are all set up per book, and that it was wrong before.

If it was wrong before, and is now correct, it was apparently wrong for a very long time.  On my prior engine (MB), and this one (SB) before the controller/fuel work, I had a readable fuel pressure reading on the aftermarket fuel pressure gage that’s installed.  It’s installed on the unmetered side, and reads up to 30 psi.  Now it is pegged at >30 at almost any power setting save for idling on the ground or pulled back in the pattern.

[nationwide]

On 5/29/2020 at 11:25 AM, gsxrpilot said:

I do my mag checks leaned out a bit. But then I'm in Denver at 5600 ft on the ground. My 252 won't even start if the mixture is full rich.

I thought these fuel controllers were supposed to be altitude compensated?  Although, I watched a video from TCM (via a FAAST email link I got; it was “hosted” by American Bonanza Society) about their fuel systems and they’re really pretty basic/simple.

[kortopates]

6 hours ago, nationwide said:

There was no work done to the fuel system this particular time, when this RPM drop issue arose.  But, it did recently (Nov) have the wastegate controller removed/readjusted/reinstalled and major adjustments made to the fuel controller following that re-installaton.  (I wrote about this on the Mooney Pilots FB page: https://www.facebook.com/groups/2226961823/permalink/10155850677521824/). The unmetered fuel pressure was bumped up considerably, and I now conduct ground ops with the mixture vernier out about 1-1.5” (used to be about 3/4 to 1”)...except for run up and takeoff, which as I said I have always done full rich.  Including after the fuel work, here at Felts (2000 MSL).  But no longer, as of this last trip to the shop and subsequent mag work, which is why I’m really vexed over the recent behavior.

The shop here insists that the FF numbers are all set up per book, and that it was wrong before.

If it was wrong before, and is now correct, it was apparently wrong for a very long time.  On my prior engine (MB), and this one (SB) before the controller/fuel work, I had a readable fuel pressure reading on the aftermarket fuel pressure gage that’s installed.  It’s installed on the unmetered side, and reads up to 30 psi.  Now it is pegged at >30 at almost any power setting save for idling on the ground or pulled back in the pattern.

Your "fuel controller" is actually the fuel pump. The unmetered fuel pressure is only used to set the idle pressure setting at minimum rpm of 700 rpm. You can verify if its set properly by checking the your fuel pressure at exactly 700 rpm you want to see 6.25 to 6.75 psi. But the engine has to be fully warmed up first - such as after a lap in the pattern. This is one of 3 idle adjustments. The second one is the mixture adjustment which is just as important. To check mixture, after being idling above 1000 rpm for at least a full minute and again with a fully warmed up engine, bring the idle down to  minimum 700 rpm  (if it won't idle at 700 rpm then the 3rd adjustment,  idle RPM needs adjusting) and then at 700 rpm slowly lean till you kill the engine. As you lean the engine, you should see the RPM rise by at least 20 rpm to upto 50 RPM before it dies. If on the other hand, it rises a 100 rpm before it dies your idle mixture is too rich and needs to be adjusted leaner. Of course if its less than 20 rpm rise its too lean. I suspect from what you have described you'll find its too rich when you try it. Its possible the unmetered pressure was wrong before and is correct now and still possible its way to rich because of the idle mixture adjustment is off. 

On your fuel pressure sensor. If you are correct that its installed on the unmetered side (right after the fuel pump and in line with your Fuel Flow Transducer) you actually have the wrong fuel pressure sensor for a Turbo. Turbo fuel pressure is measured as the difference between upper deck pressure and metered pressure with a differential pressure sensor that is plumbed into both the the upper deck and off the Fuel divider.  These are pricey compared to just a pressure transducer used in NA engines. The differential metered fuel pressure is the important one to turbo operations and used to set the max metered fuel pressure. The unmetered fuel pressure is only used for idle fuel pressure. 

Edited June 1, 2020 by kortopates

[kortopates]

3 hours ago, nationwide said:

I thought these fuel controllers were supposed to be altitude compensated?  Although, I watched a video from TCM (via a FAAST email link I got; it was “hosted” by American Bonanza Society) about their fuel systems and they’re really pretty basic/simple.

Only normally aspirated engines have altitude compensating fuel pumps with an aneroid device on the fuel pump - such as the 300 HP TCM IO-550 on the  Bonanaza A36. Cirrus uses them also on the SR20 TCM IO-360. All turbo pumps also have an aneroid device, but they are always referenced to the upper deck pressure (never atmospheric pressure) since its upper deck pressure that the fuel injectors must overcome to get into the induction system. Next time you have the cowling off, notice the upper deck air tubes going to each injector to pressurize the injector with UDP pressure to atomize the fuel as it get sprayed out the injector

[carusoam]

Thanks for sharing these key details Mr. Kortopates...

There are so many details to know... 

Best regards,

-a-

[Tim Jodice]

29 minutes ago, kortopates said:

Only normally aspirated engines have altitude compensating fuel pumps with an aneroid device on the fuel pump - such as the 300 HP TCM IO-550 on the  Bonanaza A36. Cirrus uses them also on the SR20 TCM IO-360. All turbo pumps also have an aneroid device, but they are always referenced to the upper deck pressure (never atmospheric pressure) since its upper deck pressure that the fuel injectors must overcome to get into the induction system. Next time you have the cowling off, notice the upper deck air tubes going to each injector to pressurize the injector with UDP pressure to atomize the fuel as it get sprayed out the injector

How does a fuel injection system on a normally aspirated Lycoming work? What makes it reduce fuel flow as you climb?

[kortopates]

Lycoming RSA fuel injection is very different from TCM Continuous flow injection. Your RSA fuel servo meters the fuel to the fuel divider and injectors. See the attached diagram of the RSA system, notice the impact tubes at the bottom of the throat in the yellow area. These impact tubes measure the air mass density of intake air and there is an element of automatic mixtrue control since your RSA system is metering air proportional to the air mass density that is being measured by these tubes. This is actually a bit better and a bit more complicated than the TCM system which only senses manifold pressure whereas the RSA system is measuring density. But the drawback of the RSA system is that it isn't field adjustable - when its needs work or adjusting it needs to come off to be sent to a Fuel system specialist repair station. Which is a good idea every 10 years anyway.

The TCM systems, being a bit simpler, are entirely field adjustable and are likely to last to engine overhaul but of course there are lots of exceptions all around.   

I'l also attach a RSA FI Training manual which will step you through the entire system for a better understanding if you like.

RSA FI System Training 15-812_b.pdf

Edited June 1, 2020 by kortopates

[nationwide]

2 hours ago, kortopates said:

On your fuel pressure sensor. If you are correct that its installed on the unmetered side (right after the fuel pump and in line with your Fuel Flow Transducer) you actually have the wrong fuel pressure sensor for a Turbo. Turbo fuel pressure is measured as the difference between upper deck pressure and metered pressure with a differential pressure sensor that is plumbed into both the the upper deck and off the Fuel divider.  These are pricey compared to just a pressure transducer used in NA engines. The differential metered fuel pressure is the important one to turbo operations and used to set the max metered fuel pressure. The metered fuel pressure is only used for idle fuel pressure. 

Thank you for this.  I will try the tests you described (edited from quote) next time I fly.

Did you mean to say “The unmetered fuel pressure is only used for idle fuel pressure” in your last sentence?

[kortopates]

Just now, nationwide said:

Thank you for this.  I will try the tests you described (edited from quote) next time I fly.

Did you mean to say “The unmetered fuel pressure is only used for idle fuel pressure” in your last sentence?

exactly - unmetered. Thanks for noticing and correcting that. I corrected the post above too for anyone else.

[kortopates]

 

2 minutes ago, nationwide said:

Thank you for this.  I will try the tests you described (edited from quote) next time I fly.

Did you mean to say “The unmetered fuel pressure is only used for idle fuel pressure” in your last sentence?

BTW, you can buy the correct Turbo differential fuel pressure sensor from JPI. I have and use one on my EDM 900. Cheapest to generally buy them through Aircraftspruce.

[nationwide]

On 5/31/2020 at 8:59 PM, kortopates said:

Your "fuel controller" is actually the fuel pump. The unmetered fuel pressure is only used to set the idle pressure setting at minimum rpm of 700 rpm. You can verify if its set properly by checking the your fuel pressure at exactly 700 rpm you want to see 6.25 to 6.75 psi. But the engine has to be fully warmed up first - such as after a lap in the pattern. This is one of 3 idle adjustments. The second one is the mixture adjustment which is just as important. To check mixture, after being idling above 1000 rpm for at least a full minute and again with a fully warmed up engine, bring the idle down to  minimum 700 rpm  (if it won't idle at 700 rpm then the 3rd adjustment,  idle RPM needs adjusting) and then at 700 rpm slowly lean till you kill the engine. As you lean the engine, you should see the RPM rise by at least 20 rpm to upto 50 RPM before it dies. If on the other hand, it rises a 100 rpm before it dies your idle mixture is too rich and needs to be adjusted leaner. Of course if its less than 20 rpm rise its too lean. I suspect from what you have described you'll find its too rich when you try it. Its possible the unmetered pressure was wrong before and is correct now and still possible its way to rich because of the idle mixture adjustment is off. 

On your fuel pressure sensor. If you are correct that its installed on the unmetered side (right after the fuel pump and in line with your Fuel Flow Transducer) you actually have the wrong fuel pressure sensor for a Turbo. Turbo fuel pressure is measured as the difference between upper deck pressure and metered pressure with a differential pressure sensor that is plumbed into both the the upper deck and off the Fuel divider.  These are pricey compared to just a pressure transducer used in NA engines. The differential metered fuel pressure is the important one to turbo operations and used to set the max metered fuel pressure. The unmetered fuel pressure is only used for idle fuel pressure. 

Can you confirm the numbers above are for the 360-SB2?  I tried this test.  Idle was ok at 750 indicated, full rich.  I didn’t get any noticeable rise though doing the leaning test.  My fuel pressure gauge was reading ~15 (!) at closed throttle idle.  Looking at the log entry, the shop said they set unmetered to 31!  They must be talking about some other setting.  I will ask them.

Also, updating on developments—the aircraft does pass the ignition test (mag test) leaned out.  I did it myself.

[kortopates]

1 hour ago, nationwide said:

Can you confirm the numbers above are for the 360-SB2?  I tried this test.  Idle was ok at 750 indicated, full rich.  I didn’t get any noticeable rise though doing the leaning test.  My fuel pressure gauge was reading ~15 (!) at closed throttle idle.  Looking at the log entry, the shop said they set unmetered to 31!  They must be talking about some other setting.  I will ask them.

Also, updating on developments—the aircraft does pass the ignition test (mag test) leaned out.  I did it myself.

750 rpm is too high, fuel pressure goes up quickly with rpm. if you got 15 psi at 750 it will be lower at 700, but you won't know how much till you check it.

No noticeable rise at 700 while leaning to ICO is a problem. 

The log entry was referring to max FF of 31 - but using unmetered fuel pressure for max FF is wrong  (see note 2 below table - its for reference only and 31 is on the low side!) - it has be metered fuel pressure. The mechanic obviously does have the right equipment to properly set up the fuel system. But if you have confidence in your FF being accurate, which it should be, then I'd personally prefer to set up max FF using your ships FF - TCM approves of this (see note 4 below). But not using unmetered pressure - especially on a turbo.

Be careful not to change metered low pressure till you have the help to adjust all the fuel setup parameters - Idle at 700, low pressure idle metered pressure, idle mixture and metered max fuel pressure/max FF. Change the low end and it can effect the high end and vice versa, it an iterative process till its very small tweaks.

Improper fuel system setup is the #1 anomaly I see new turbo owners have and often while they're trying to ferry the aircraft home after purchase. Unfortunately it can lead to high temps and partial power losses right at a time when a new owner has no idea what to expect of their unfamiliar engine. The best advice I can give for TCM engines is abort any takeoff when TIT exceeds 1450F on the takeoff run.

Edited June 11, 2020 by kortopates

[Parker_Woodruff]

On 6/11/2020 at 11:45 AM, kortopates said:

 

Improper fuel system setup is the #1 anomaly I see new turbo owners have and often while they're trying to ferry the aircraft home after purchase. Unfortunately it can lead to high temps and partial power losses right at a time when a new owner has no idea what to expect of their unfamiliar engine. The best advice I can give for TCM engines is abort any takeoff when TIT exceeds 1450F on the takeoff run.

Paul, I see this with a lot of newly purchased aircraft as well - bad fuel setups.  Having flown several M20Ks, I recommend the takeoff fuel flow at the high side of the numbers published above.  In my experience, fuel flow wants to drop off a bit at altitude, so a full power climb to the teens or Flight Levels can get a bit too lean leading to higher CHTs.

[kortopates]

10 hours ago, Parker_Woodruff said:

Paul, I see this with a lot of newly purchased aircraft as well - bad fuel setups.  Having flown several M20Ks, I recommend the takeoff fuel flow at the high side of the numbers published above.  In my experience, fuel flow wants to drop off a bit at altitude, so a full power climb to the teens or Flight Levels can get a bit too lean leading to higher CHTs.

Yes indeed, we (Savvy) as well as RAM all recommend taking TCM's high number for the the spec FF and adding 0.5 to 1.0 GPH above that. so for example on the Encore we want to see 26.2 to 26.7 or about 26 1/2 right @ 39" with 2600 rpm. Even a little higher is okay, but really don't want to get carried away since we'll lose power going higher in FF and will feel the engine surge as it gets overly rich which isn't good either. 

Edited June 13, 2020 by kortopates

[flyer338]

On 5/29/2020 at 2:19 PM, carusoam said:

Being leaned during the run-up...

Has one challenge attached to it...

Things are busy, and getting busier...

Have a good plan to make sure your mixture is set for T/O...  Before pushing the throttle in... 

It makes for a nice distraction challenge... but, can also be very tough on the engine... a pre-ignition challenge...

Best regards,

-a-

 

I have found that leaning for ground operations so that applying full power results in misfire is a good way to provide an alert when the “full rich” for takeoff step is missed. I know this works with carbureted engines, I have not yet forgotten with my 201, so I am not sure. I have no idea about turbocharged engines.

More later, but my Mooney is flying again, and I am back.