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M20J Fuel pressure drops as engine warms up


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Yes, we ran the boost pump with mixture at idle cut-off. Cowling removed. Could not see any leaks! It doesn't make sense that the pressure would drop as the engine warms? The people that sell fuel pumps are telling me that ii is a weak fuel pump? Maybe, although I have never had to replace a fuel pump on any plane I have owned. I have had to replace boost pumps! This pump was new at major overhaul 715 hrs ago! 2002. I would like to run some sort of test on it to prove the mechanical pump is bad before I start removing enough accessories to get at it and take it out! 

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1 hour ago, Robert A. Reed said:

Yes, we ran the boost pump with mixture at idle cut-off. Cowling removed. Could not see any leaks! It doesn't make sense that the pressure would drop as the engine warms? The people that sell fuel pumps are telling me that ii is a weak fuel pump? Maybe, although I have never had to replace a fuel pump on any plane I have owned. I have had to replace boost pumps! This pump was new at major overhaul 715 hrs ago! 2002. I would like to run some sort of test on it to prove the mechanical pump is bad before I start removing enough accessories to get at it and take it out! 

The fuel pressure should be confirmed with a mechnical test gauge connected the system.  If your plane has electric an pressure gauge they are know to mis read.  You should be seeing 25+/- psi

Clarence

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52 minutes ago, M20Doc said:

The fuel pressure should be confirmed with a mechnical test gauge connected the system.  If your plane has electric an pressure gauge they are know to mis read.  You should be seeing 25+/- psi

Clarence

Thanks Clarence! Do you think the fuel pressure transducer could be the cause of the change in pressure as it warms up? That would definitely be an easier fix than a new fuel pump! I see that Chiefs has them for $36.50, and they are a lot easier to get at than the fuel pump! I am a new Mooney convert! Don't want this to spoil my introduction to the 201! Just sold a Bonanza that always had some problem when I needed to use it!!

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29 minutes ago, Robert A. Reed said:

Thanks Clarence! Do you think the fuel pressure transducer could be the cause of the change in pressure as it warms up? That would definitely be an easier fix than a new fuel pump! I see that Chiefs has them for $36.50, and they are a lot easier to get at than the fuel pump! I am a new Mooney convert! Don't want this to spoil my introduction to the 201! Just sold a Bonanza that always had some problem when I needed to use it!!

It could be the transducer, wiring connections, poor grounds etc. It will tke a bit of diagnosis to determine the trouble.

Clarence

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50 minutes ago, M20Doc said:

It could be the transducer, wiring connections, poor grounds etc. It will tke a bit of diagnosis to determine the trouble.

Clarence

Thanks! After seeing all of the threads, I am skeptical as to weather it is a fuel pump problem! I will follow your advice and do some more diagnostics! I will post what we find! My mechanic is on vacation in Florida now and I am trying to get a jump start and give some advice as to what he may want to do to fix this problem when he returns! You guys are very helpful!!

any other solutions would be appreciated!

 

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Unhappy coincidence here, I have been chasing a similar issue with the fuel pressure in my 201. I have been seeing 25 psi cold that falls to 14 psi when warm. I have checked the calibration of my sender and gauge which appear ok. 

The system research I have done says the mechanical fuel pump controls fuel pressure in the system, so I am planning to replace the fuel pump soon. I'm not looking forward to the job, these planes were never designed for service!

I have about 700 hours since rebuilding the engine with a new fuel pump. 

Greg

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13 hours ago, GregF said:

Unhappy coincidence here, I have been chasing a similar issue with the fuel pressure in my 201. I have been seeing 25 psi cold that falls to 14 psi when warm. I have checked the calibration of my sender and gauge which appear ok. 

The system research I have done says the mechanical fuel pump controls fuel pressure in the system, so I am planning to replace the fuel pump soon. I'm not looking forward to the job, these planes were never designed for service!

I have about 700 hours since rebuilding the engine with a new fuel pump. 

Greg

I am glad to hear that I am not the only one experiencing this problem, which is usually the case! I am going to start with the first piece of equipment in the system. If it is warm enough to lay on the hanger floor tomorrow, I will clean the gascolator and boost pump screen. I have read that if there are no fuel leaks, it could be sucking air. Sucking air with no fuel leaks would have to put the problem in front of the boost pump? One person had a crack in the line, another had a bad gasket! My mechanic comes back into town tomorrow, and hopefully has some more ideas! Replacing the fuel pump is not my idea of fun either!

I will keep you posted on anything we find! Please do the same. Thanks

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23 minutes ago, carusoam said:

Everything upstream starts with blocked fuel tank vents and includes things like fuel selector valve and everything in between...

 

Good luck with your search.

Best regards,

-a-

Yes, thanks. I am checking fuel vents. I have switched tanks several times with no change in pressure! Would a bad selector valve cause these problems?

Bob

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Tank selector valve can have a shaft leak.  Air bubbles enter the fuel line here...

If you have a FF indicator that is giving funny data, suspect air bubbles entering the system upstream...

keep in mind I'm only a PP, not a mechanic.  Ideas I have learned by reading a lot of MS...

Best regards,

-a-

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On ‎3‎/‎16‎/‎2017 at 1:59 PM, carusoam said:

Tank selector valve can have a shaft leak.  Air bubbles enter the fuel line here...

If you have a FF indicator that is giving funny data, suspect air bubbles entering the system upstream...

keep in mind I'm only a PP, not a mechanic.  Ideas I have learned by reading a lot of MS...

Best regards,

-a-

Could the gasolator drain have the same problem? Sucking air around the shaft? I have noticed some fuel stains on the shroud around the drain "pull handle" inside the plane! I also smell some fuel inside the cabin if I do not turn the fuel selector to "off" .

Bob

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There are a few variations of the selector valve and the drain valve.  But they both can let fuel out or air in if not in good condition.

Lasar is known to rebuild these pieces for a few dollars. Dan at Lasar is really good at describing how the rebuild process works.

I don't recall any details on OHing the drain valve.  There has been discussion regarding the effects of draining using a sample cup.  One of the seals is subject to getting messed up if not careful.

If you see blue stains around the The pull ring shaft that is a subtle hint of fuel escaping.  Could be related to the selector valve if they are close together in your ship.  Leak in one area and evaporate in the other... air is less viscous than fuel.  So if fuel is leaking while the plane sits.  Air might be entering while the plane flies...

do you have a FF gauge?  Often air bubbles can cause some erroneous display issues, and inaccuracies...

I am only a PP, not a mechanic...

Best regards,

-a-

Edited by carusoam
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Hello, just checking back in with the symptoms (or lack of) with my J fuel pressure issues. 

I have a fuel flow meter, it's indications are rock solid under all conditions. 

I have had no evidence of any fuel leaks around the selector, gascolator, or anywhere else. All of these systems were rebuilt or new since 2009. 

I'm a few weeks away from a mechanical fuel pump replacement as a next step in solving my falling fuel pressure issue. I will report back if I learn anything  

Greg

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12 hours ago, carusoam said:

There are a few variations of the selector valve and the drain valve.  But they both can let fuel out or air in if not in good condition.

Lasar is known to rebuild these pieces for a few dollars. Dan at Lasar is really good at describing how the rebuild process works.

I don't recall any details on OHing the drain valve.  There has been discussion regarding the effects of draining using a sample cup.  One of the seals is subject to getting messed up if not careful.

If you see blue stains around the The pull ring shaft that is a subtle hint of fuel escaping.  Could be related to the selector valve if they are close together in your ship.  Leak in one area and evaporate in the other... air is less viscous than fuel.  So if fuel is leaking while the plane sits.  Air might be entering while the plane flies...

do you have a FF gauge?  Often air bubbles can cause some erroneous display issues, and inaccuracies...

I am only a PP, not a mechanic...

Best regards,

-a-

Yes, I do have FF gauge. Haven't noticed anything unusual, but have been so focused on the fuel pressure that I may have missed something! I have a small black gob of stuff in the bottom of the gascalator bowl. May be remnants of an O ring? It could not have gotten in through the screen! Screen is clean. Bowl was cleaned 5 hours ago at annual!! There is a small O ring on the end of the spring loaded (drain) shaft. It seats in the nut that is on the bottom of bowl. I can see that it could be possible to damage it if probed with a drain cup!

Bob

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Bob,

if you can post a picture of what you collected (black gob) it may be helpful to see if somebody recognizes it...

Chunks on the back side of the screen can't be a good sign...

Best regards,

-a-

 

Edited by carusoam
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One easy way to check the engine pump:

1. Open throttle and mixture

2. Turn electric fuel pump on

3. Close mixture and throttle

4. Turn electric fuel pump off

5. Check fuel pressure

A good pump with no line leaks will hold pressure for over 5 minutes.

If the pressure drops in less than a minute suspect a line leak or a perforated pump diaphragm.

José

 

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10 hours ago, Piloto said:

One easy way to check the engine pump:

1. Open throttle and mixture

2. Turn electric fuel pump on

3. Close mixture and throttle

4. Turn electric fuel pump off

5. Check fuel pressure

A good pump with no line leaks will hold pressure for over 5 minutes.

If the pressure drops in less than a minute suspect a line leak or a perforated pump diaphragm.

José

 

Thanks Jose, will try it!

Bob

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14 hours ago, carusoam said:

Bob,

if you can post a picture of what you collected (black gob) it may be helpful to see if somebody recognizes it...

Chunks on the back side of the screen can't be a good sign...

Best regards,

-a-

 

Sorry, I did not take any pictures. It was a small black gob next to one of the ports on the bottom of the stem. I am thinking it came from the outside as It was sticky enough that I don't think it would have been able to flow from the tank! The port that it was next to is immediately above the O ring on the stem drain. I found that the previous owner had used a very sticky "fuel proof" grease when he re-assembled it, to prevent leaks. The drain O ring was covered with this sticky stuff, and had lots of dirt stuck to it. A reply on another subject had this problem. The sticky grease prevented the drain from leaking, but it let air in! (I may be grasping at Straws)!! But,,, I have cleaned it up and re-installed. Am waiting to make sure it doesn't leak. Then will move on! Do another run up and see if there is any change.

Bob

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On ‎3‎/‎22‎/‎2017 at 9:59 AM, Robert A. Reed said:

Thanks Jose, will try it!

Bob

I tried your test today! Some throttle, mixture in, boost pump on! Fuel pressure jumped to 25 lbs.(Good)! Pulled mixture and throttle. turned off boost pump. Pressure held at 25 for about 3 minutes, then slowly dropped to 14 after 5 minutes. I turned the key, started the engine, the pressure immediately dropped to 8 lbs! Activated the boost pump, and it went up to about 10 lbs? Increased RPM. No change in pressure? WTH?? Engine Pops every so often, like too much Air? HELP!

Bob

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On ‎3‎/‎21‎/‎2017 at 8:35 AM, GregF said:

Hello, just checking back in with the symptoms (or lack of) with my J fuel pressure issues. 

I have a fuel flow meter, it's indications are rock solid under all conditions. 

I have had no evidence of any fuel leaks around the selector, gascolator, or anywhere else. All of these systems were rebuilt or new since 2009. 

I'm a few weeks away from a mechanical fuel pump replacement as a next step in solving my falling fuel pressure issue. I will report back if I learn anything  

Greg

Greg, I put new O rings in the sump drain. Ran it up. Still had the problem! Did a full power check. Fuel Flow was solid, but fuel pressure did not improve! About 10psi.

I put it back in the hanger! My mechanic told me it probably needs a new Fuel pump, or the servo needs overhaul! I pulled the old fuel pressure transducer (probably original), it had small grains of Something coming out of it! I put on new transducer! Checked for leaks. Ran it up! It held 24-25 psi just fine!! I think the problem is solved! I will check it again when I get the cowling on and fly it!

Bob

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