Fuel Pump Adjustment TIO360 TCM rebuilt 300 hours ago and fresh out of annual inspection.

[lvpazik]

Purchased 1980 M20K 231 N922PT. Had complete annual inspection done as part of prebuy including rebuilt mechanical fuel pump. Ferry pilot flew it across the country from Florida to Pahrump NV with no issues. I flew the airplane once for 1 hour total time and it has sat for 60 days. Now won't idle and have to keep hitting low boost or primer. Local mechanic who is an excellent mechanic but has no Mooney experience did some adjustments. Mooney mechanic in Florida that did the annual and works mostly on Mooney's said "these engines don't like to sit and you'll have to completely readjust the fuel flow and pressure settings. They adjusted the rebuilt fuel pump at "sea level" and our field level here is 2700 feet if that matters.

After some adjustments we've got it starting fine however it's still running too rich and the fuel psi on the EI instrument won't go over 5.7 whether at idle or 2000 rpm. When we "lean" her out from idle speed of 650, she rises almost 200 rpm before she starts to die and I believe the manual says it should be around 60 rise before it starts to die.

 

We seem to be chasing the issue. Any advice or any qualified Mooney mechanics in Vegas area that can drive out the 60 miles to my hangar in Pahrump, with the gauges they need, adjust the airplane with my mechanic so he "learns" the system and get her flying? I have another plane/pilot and could pick you up and bring you back if you don't want to make the drive. Local mechanic has all tools except what I believe are some specialized gauges to properly adjust this injection system. Thoughts?

[carusoam]

Turbo Continentals are the most complex Mooney engine to set up properly...

They are also the most complex engine to start and operate for Mooneys too...

Could be operator or engine set up...

Before going out of the way to get the proper mechanic... are you familiar enough with the engine..?

Never mind... I see you have had a mechanic make changes already...

 

When in the Vegas area... I ask questions to @Jeev.  Jeev has an aviation business and is really helpful...

Best regards,

-a-

 

 

[jlunseth]

The information that the engine malfunctioned because it sat for 60 days and "these engines don't like to sit" is just flat wrong. My engine has sat for as long as three months and it is the same the next time I start it up.  Being at 2700 should make no difference at all in a turbo engine. Some of your other numbers are not making sense though. I don't idle my engine below 1100 (I have the LB), for one thing it does not really like to idle that low, but mainly because the alternator will not be charging and you will very quickly see a LOW VOLTS on the annunciator, or if you have an engine monitor, a low buss voltage warning of some kind. I am not sure my engine will even idle at 650, I doubt it. An idle rise of 200 is too much, it should be around 75, but my guess is that the fuel flow is set to support a higher idle level than you are operating at and therefore, if the engine runs at all at 650, it is way overrich. An added problem is that at low idle, the back two cylinders, which are furthest from the throttle, may not operate at all or at very low power when you are low idle. Get the idle up to 1100 and they will fall into line.

Try running it at 1100 for an idle/taxi speed, it is not an NA. I had a veteran Mooney instructor once ask me, as we started down the taxiway, do you ride the brakes or watch the light flash? Meaning, you either need to idle with enough RPMs that you need to hit the brakes a few times when you taxi, or you need to be ok with watching the low volts warning, there is no in between.

With the 231 you should be more concerned that the fuel flow, at full power, will hit the numbers in the POH, which are 22.5 - 24.0 GPH. There are many more problems on that side of the engine's operation if the engine is not running very rich (hot temps), than on the idle side.

I think you will find that you need to lean the engine a fair amount for taxi, and also when you are pulling the throttle back on final approach. If you pull the fuel flow back on final, first, I am not talking about pulling it back to the point where you cut the engine off, just enough to stop the "burbling," which is what the engine does when it is overrich on final. I am just talking about leaning it out some. But you have to remember to put in some fuel flow on the runway after landing. If you don't, once the prop and engine are not being helped by the airstream the engine can die.

I am not sure what is going on when you say you have to hit the low boost or primer when the engine is idling. It is not an unusual problem to have the engine fire on start up but then die, especially in cold weather, after the engine has sat for awhile. The problem is that the fuel drains out of the fuel lines, you prime the engine, start it, and then it promptly dies because it has used up all the prime and there is no fuel in the lines yet. The fix is to switch the boost on briefly after the engine fires and starts to run, that will keep it going until the mechanical pump has had a chance to fill the lines. I leave the safety cover on the high boost to do this, and just press one corner of the switch. It acts as an instant on -instant off switch so the pump stops as soon as you stop pushing. But I really think that at an engine RPM that low probably nothing is working well in the engine. Try 1100 and see if that works better. Let us know

[Bravoman]

Pahrump is the home of the (in)famous Chicken Ranch which I heard has or had a runway

[jlunseth]

PS my fuel pressure when taxing is in the 3. something level, say 3.7 GPH. Even at 2000 RPMs it won’t be very high but I can’t say I look at it very often during runup (which is when it is at 2000). It is not a redline number in the 231, fuel flow is more important.

[tmo]

+10 for all of jlunseth's comments - he is very well versed in the intricacies of our engines.

I sometimes need to give the engine a little bit of extra fuel when starting up cold - as jlunseth said, there is air in the lines and it needs to be forced out if the engine stumbles when starting up. I use the prime switch for that, but I guess the electric pump one would be more proper and actually easier to reach with the left hand, as one let's go of the ignition key.

While mine will idle slower than his without any significant roughness, definitely well under 1000 RPM, I leave it there only briefly upon cold start, and then go to around 1000 rpm for the remainder of the warm up. That is at around 2 GPH; my taxi takes more power, last weekend it was 2000+ rpm just to get going on the wet grass. When shutting down, I barely get any RPM raise, but I'm already idled out deeply for taxi, so I might already be LOP.

Having low idle is crucial for being able to land

My FF at full power 40"/2700 RPM is right around 24 GPH and as jlunseth said, it is crucial to keep the engine cool.

I never lean on final, and aren't aware of any issues resulting from that. The POH calls for "MIXTURE FULL RICH" in Section 4, BEFORE LANDING. One less thing to think about on a go-around.

[jlunseth]

10 hours ago, tmo said:

I never lean on final, and aren't aware of any issues resulting from that. The POH calls for "MIXTURE FULL RICH" in Section 4, BEFORE LANDING. One less thing to think about on a go-around.

You are right that the POH recommends full rich. People on the ground, though, will tell you your engine was missing on final. As I indicated in my post, I lean out and that takes care of the burble. Its a little different from a true misfire, its  more of a suppressed fire, but it is there. The recommendation to put the mixture in full rich is in the event a go around is required. But it is easy enough to push both knobs in, in that event. It is certainly ok to do the final approach full rich though.

This is probably a very fine point, but if I do a landing where I think that a go around is a possibility I will deliberately let the plane fall behind the curve on final approach, which allows/requires putting in more power, which in turn allows me to enrich the mixture without incurring burbling.

I spoke to a friend with a Bravo today. He tells me he idles at 1070 and has the same issue with taxiing that we do in our 231’s, if he reduces the idle speed he will get a low volts warning. If I were being as precise as he, 1070 is about the exact idle where the low volts problem goes away and the engine runs well. I just go for the bigger rounder number, 1100.

[kortopates]

The OP merely needs to find a mechanic that knows how to set up a TCM fuel system - it's really nothing to do with Mooneys except the caveat that an intercooled 231 needs it's Max FF set at the reduced MAP redline of ~37.5" rather than 40"

But once idle unmetered pressure is reset it will require checking metered full power psi or max FF per the TCM spec. - changing one often changes the other.

Idle unmetered psi is from 6.5 to 6.75 psi at 700 rpm from memory.

 

You have to ignore good intentioned folks references to fuel pressure unless they know unmetered from metered - they are very different. And that goes for what ever your monitor reports without knowing which one it is. But metered pressure requires a dual inputs from fuel pressure and UDP.

 

 

Sent from my iPhone using Tapatalk

[kortopates]

Pahrump is the home of the (in)famous Chicken Ranch which I heard has or had a runway

There was even a wreck still parked there for years too - don't know about present status though.


Sent from my iPhone using Tapatalk

[jlunseth]

20 hours ago, jlunseth said:

PS my fuel pressure when taxing is in the 3. something level, say 3.7 GPH. Even at 2000 RPMs it won’t be very high but I can’t say I look at it very often during runup (which is when it is at 2000). It is not a redline number in the 231, fuel flow is more important.

PPS I realized that is my fuel flow at idle, not fuel pressure, sorry.

[carusoam]

For reference...

The IO550s will idle at 700rpm or so...

Using near 2gph close to SL...

About 4gp full rich, until warmed enough to lean...

1k rpm is used to make sure oil is being distributed by splash mechanism...

At idle, I get the low volts...

At 1k rpm, I get a speeding ticket on the taxi ways... 

 

My O360 was very generous for telling me when I forgot to enrich the mixture...

The IO550 is too polite to tell you you made a mistake...

 

PP thoughts only, not a CFI...

Best regards,

-a-

[Guest]

From the K model manual.  Also in the Downloads engine section there is information on set up procedures.

Clarence

[kortopates]

On 11/12/2020 at 10:38 PM, carusoam said:

1k rpm is used to make sure oil is being distributed by splash mechanism...

True of your old Lycoming but one of the pluses of TCM lower cam is that its getting sufficient splash at much lower Idle RPM - no need to idle any higher than necessary to keep the alternator low voltage light off!