Fuel Pressure

[Jim Peace]

We thought my problem was the gascolator gasket because air was getting into the bowl. Spent a lot of labor checking and replacing it more than once. Check the fuel line mentioned in my previous post as it can mimic a bad gasket.

I will have it all checked out........

 

Thank you

[N601RX]

I had a problem with a fuel and brake line rubbing. The way it was positioned, it wasn't obvious that it was rubbing.

http://mooneyspace.com/topic/5456-brake-and-fuel-line-rubbing/?hl=%2Bfuel+%2Bline+%2Brubbed

[mooney_man]

OK.

 

Here is a video of my fuel pressure as soon as I turned off the electric pump and then you will notice when I turn it back on then off again.  Is this what other people see?  This was during climbing after the engine was cold.

 

http://youtu.be/Z4NqYTXpskU

 

Why is it that I have flow about 15 legs in this airplane recently and this is the first time it is happening?  

 

reminder, at cruise all is well with fuel pressure not to far below what the electric pump would provide and it is stable.

Saw your video, I have the exact same issue on my 1962 M20C. So what was the resolution? what did you find. I have already replaced, both pumps, opened the accessory case to see the idealer gear cam and the pump plunger. they all look fine. What else can I check.

[Jim Peace]

My plane is going to go down for annual in a couple of weeks. It will be addressed then. I am going to check everything that has been mentioned in this thread.

The former owner said it has been doing this for decades and it is normal. Other M20c drivers report the same.

I will know more in a few weeks.

Jim

[jrwilson]

Saw your video, I have the exact same issue on my 1962 M20C. So what was the resolution? what did you find. I have already replaced, both pumps, opened the accessory case to see the idealer gear cam and the pump plunger. they all look fine. What else can I check.

My plane is going to go down for annual in a couple of weeks. It will be addressed then. I am going to check everything that has been mentioned in this thread.

The former owner said it has been doing this for decades and it is normal. Other M20c drivers report the same.

I will know more in a few weeks.

Jim

I literally spent thousands on this "problem" guys... New boost and engine pump, overhauled carb, fuel lines traced/tightened/re routed and replaced, overhauled gauge...still does it... Granted, it was intermittently dropping below 1pound, sometimes below 1/2 pound, and there certainly was an issue which has IMPROVED, but Cs do this. I think checking gaskets can help the OP reduce some gauge jitter but there is a green arc and you're in it and you're int the climb green arc too...like I've said, it seems to be a function of low wings and o360 combination...

[mooney_man]

Experiencing the same problem on my 1962 c model. Fuel pressure drops down to 1.5 psi and The gauge starts to bounce. Turn the electric pump on and it gets stable at about 3.5 psi. Engine gets rough at 1.5 but ok at 3.5. Have replaced engine driven pump and electric pump but the problem still remains. Now trying to get the carb checked. Checked the lines by vacuuming, it holds vacuum so no leaks. Really confused. I had this airplane for 6 years and suddenly it started doing this. Any ideas?

[Andy95W]

Check out all the things that Don Maxwell told Jim in post #24.

I think your problem is something more significant than just a gauge/indication problem, since your engine runs rough at 1.5 psi and turning on the electric boost pump smooths it out, and since it came on so suddenly.

When you checked your lines by vacuum, did that include the gascolator and switching valve assembly?

How long ago was the carburetor overhauled?

It is rare, but I have seen engine driven fuel pumps go out for overhaul and come back bad. I would leave that for last, however, as less likely than other things.

[jrwilson]

Experiencing the same problem on my 1962 c model. Fuel pressure drops down to 1.5 psi and The gauge starts to bounce. Turn the electric pump on and it gets stable at about 3.5 psi. Engine gets rough at 1.5 but ok at 3.5. Have replaced engine driven pump and electric pump but the problem still remains. Now trying to get the carb checked. Checked the lines by vacuuming, it holds vacuum so no leaks. Really confused. I had this airplane for 6 years and suddenly it started doing this. Any ideas?

Yeah 1.5 is solid in the green and the engine shouldn't be rough. Assuming gauge is accurate and your 1.5 isn't actually lower , there must be something going weird.

[jkhirsch]

I'm going to throw a bump on this thread, just to see if anyone ever came to a resolution.

[Jim Peace]

I'm going to throw a bump on this thread, just to see if anyone ever came to a resolution.

My plane is still down and I will have a report on it I hope in a few weeks....

[DXB]

Ok first time flying my '68C without my transition instructor, and I notice a very similar problem.   Traits are as follows:

-On ground, boost pump on before takeoff: pressure reads high, just above red line

-Initial climb, boost pump on: needle in upper green arc

->1000 AGL pump turned off, WOT climb: steady drop in pressure.  Initially I think no big deal, but then it drops below 1. I'm having a heart attack.  No drop in RPM though, and engine sounds fine.

-turned boost pump back on:  pressure back to high in green arc, my chest pain abates.

-pump off after entering cruise at 23(sq): minimal pressure drop.

 

Given my inexperience, this freaked me out.  The fuel line to the gauge was replaced after my pre-buy last year. I think the gauge is original, and I have plans for a JPI900 later this year.  From reading discussion above, I'm not clear if I should dig deeper until after the new gauge is in.  Has anyone actually had a real indication of a real drop in fuel flow or engine problem when this happens?

[Jim Peace]

I changed some fuel lines and was going to update this thread today,,,the winds were to strong at VNY a few days ago for a test flight.  My plane will be flown tomorrow by a friend of mine for the first time in 4 months.  

 

Should have more info this week

 

Jim

[jrwilson]

Ok first time flying my '68C without my transition instructor, and I notice a very similar problem.   Traits are as follows:

-On ground, boost pump on before takeoff: pressure reads high, just above red line

-Initial climb, boost pump on: needle in upper green arc

->1000 AGL pump turned off, WOT climb: steady drop in pressure.  Initially I think no big deal, but then it drops below 1. I'm having a heart attack.  No drop in RPM though, and engine sounds fine.

-turned boost pump back on:  pressure back to high in green arc, my chest pain abates.

-pump off after entering cruise at 23(sq): minimal pressure drop.

 

Given my inexperience, this freaked me out.  The fuel line to the gauge was replaced after my pre-buy last year. I think the gauge is original, and I have plans for a JPI900 later this year.  From reading discussion above, I'm not clear if I should dig deeper until after the new gauge is in.  Has anyone actually had a real indication of a real drop in fuel flow or engine problem when this happens?

Yes, my engine quit after a similar situation, dropped down below .5 lbs. The carb float was sticking. Replaced the carb and that was solved. My pressure still drops in climb but is well within the green arc.

[mike20papa]

O-360 fuel systems....

 

1. DESIGN fuel pressure is the sole function of the integral pressure regulators built into the fuel pumps.  This pressure is specified by Lycoming as 2 - 5psi at the carb inlet.  Mooney green arks on the gauges are based on this spec.  The original & replacement fuel pumps are also mfg. to this spec.  The carb has a special port for attachment of the pressure gauge line at the inlet to monitor this spec. PSI.

 

2.  The float type carberator has no way of influencing the fuel pressure outside of the spec. PSI.  Period.  The fuel pumps are designed to supply the required amount of fuel within the spec. PSI regardless of the float needle valve opening.  The carb has a dumb float level actuated "on/off" valve at the fuel line inlet.  To think otherwise is like believing the float valve in your bathroom toilet tank can significantly  effect the water pressure in the water main down town...IF it is effecting the PSI, you have a dangerous - "hazardous to your health" - restriction in either the supply or vent piping.

 

3.  Fuel flows from the tanks, to the selector valve, to the aux. fuel pump, thru the gascolator and then to the engine driven pump then to the carb via the float valve into the float then metered into the engine intake.

 

4.  There are 3 filters that the fuel passes thru (actually 4 on my A model - if you count the coase finger screens in the tanks.  The other three filter screens are very fine - the first is in the elec. pump, under the cap at the end of the pump (Bendix/Faucet type).  ALL fuel first hits this screen and Mooney put out a SB decades ago recommending checking these every 50 hr.s  If I had old slosh sealer in my fuel tanks (which the A models do NOT) - I'd do this religiously!  The second filter screen is in the gascolator - but seriously doubt anything would get past the first screen in the electric pump, but it's there.  Then of course the sediment bowl in the gascolator, FINALLY there is a very fine finger screen inside the carb inlet - suppose to be checked at annual.  Requires a special locking ring to secure the fitting - AC Spruse sells them.

 

5. Inhibited fuel flow will not show a pressure drop unless there is a high demand for fuel flow from the engine. Fuel flow and therefore pressure..can be inhibited by clogged screens or lines on the pressure side - AND just as important - clogged VENT lines can inhibit fuel flow and pressure.  It's rather doubtful that all vent lines should clog at the same time, so fuel selector valve switching during runup should analize this problem. 

 

6.  IF you don't have 2 - 5 psi at run up with the aux. fuel pump OFF or ON - do NOT go flying.  Things won't improve after you leave the ground.  Get a knowledgeable dude to look things over and turn the wrenches on those delicate alumn. fittings.  Fuel is your life blood - you should know the system.  And it will help keep our Mooney insurance rates low/affordable, too!

[DXB]

O-360 fuel systems....

 

1. DESIGN fuel pressure is the sole function of the integral pressure regulators built into the fuel pumps.  This pressure is specified by Lycoming as 2 - 5psi at the carb inlet.  Mooney green arks on the gauges are based on this spec.  The original & replacement fuel pumps are also mfg. to this spec.  The carb has a special port for attachment of the pressure gauge line at the inlet to monitor this spec. PSI.

 

2.  The float type carberator has no way of influencing the fuel pressure outside of the spec. PSI.  Period.  The fuel pumps are designed to supply the required amount of fuel within the spec. PSI regardless of the float needle valve opening.  The carb has a dumb float level actuated "on/off" valve at the fuel line inlet.  To think otherwise is like believing the float valve in your bathroom toilet tank can significantly  effect the water pressure in the water main down town...IF it is effecting the PSI, you have a dangerous - "hazardous to your health" - restriction in either the supply or vent piping.

 

3.  Fuel flows from the tanks, to the selector valve, to the aux. fuel pump, thru the gascolator and then to the engine driven pump then to the carb via the float valve into the float then metered into the engine intake.

 

4.  There are 3 filters that the fuel passes thru (actually 4 on my A model - if you count the coase finger screens in the tanks.  The other three filter screens are very fine - the first is in the elec. pump, under the cap at the end of the pump (Bendix/Faucet type).  ALL fuel first hits this screen and Mooney put out a SB decades ago recommending checking these every 50 hr.s  If I had old slosh sealer in my fuel tanks (which the A models do NOT) - I'd do this religiously!  The second filter screen is in the gascolator - but seriously doubt anything would get past the first screen in the electric pump, but it's there.  Then of course the sediment bowl in the gascolator, FINALLY there is a very fine finger screen inside the carb inlet - suppose to be checked at annual.  Requires a special locking ring to secure the fitting - AC Spruse sells them.

 

5. Inhibited fuel flow will not show a pressure drop unless there is a high demand for fuel flow from the engine. Fuel flow and therefore pressure..can be inhibited by clogged screens or lines on the pressure side - AND just as important - clogged VENT lines can inhibit fuel flow and pressure.  It's rather doubtful that all vent lines should clog at the same time, so fuel selector valve switching during runup should analize this problem. 

 

6.  IF you don't have 2 - 5 psi at run up with the aux. fuel pump OFF or ON - do NOT go flying.  Things won't improve after you leave the ground.  Get a knowledgeable dude to look things over and turn the wrenches on those delicate alumn. fittings.  Fuel is your life blood - you should know the system.  And it will help keep our Mooney insurance rates low/affordable, too!

Thanks, great info on relation of fuel pressure transducer line to carb.   My M20C POH specifies fuel pressure "Green Arc- Wide(normal operating range)" as 2.5-3.5 psi and "Green Arc - Narrow (operating range)" as 0.5 to 6 psi.   I'm not sure how to use the two different ranges for real world operation.  I'm trying to figure out if the 1psi reading I observed during a 100mph climb at WOT throttle (only after turning electric pump off above 1000agl) is cause for immediate concern. This would still seem to be in the "operating range" but was still uncomfortable to observe even with engine running fine, lest the pressure drop lower.   I've had no other concerning pressure indications with boost pump off or on, excepting pressures slightly >6psi with pump on at lowest rpms on the ground.   

[carusoam]

You will also see a pressure change from climb attitude to leveling off...

Experience from my 65C,

-a-