Fuel pressure and flow fluctuations

[PTK]

Of course not!

However, if you're about to jump into an airplane that you know it's non-airworthy would you anyway? Would you?

The father should be nailed but certainly the son had responsibility to say no! He knew full well what he was about to do and didn't need any A&P to tell him. Unless his father forced him at gunpoint!

This is not a case of an innocent pilot owner who is depending on the A&P for advice. He knew full well the status of  the airplane and what he was doing.

Hopefully we can agree on that! But if we can't, we can agree to disagree!

Edited September 29, 2015 by PTK

[jeffdoran]

I had a very similar problem on my 1982 M20J. After months of fluctuating fuel pressures, that would go strong and steady with boost pump on, we finally tracked it down to a pin hole air leak on the head end of the electric boost pump. 

[Joe Larussa]

How did you find a pinhole air leak? I'm thinking of trying a new fuel pump. Although mine is new with 60 hours on it. 

[romair]

Joe - I have been chasing a fuel pressure and fuel flow fluctuation for almost 1 year, without being able to find the cause. If the fuel pressure fluctuates on the ground, then it makes diagnostics a bit easier. 

Things to try that I have tried, although all this work has not helped me so far.

1. Do the fluctuations happen on one tank only? - easy to do.

2. If not, take a fuel hose and run it from the line from one tank (disconnect it from the attach point into the fuel selector and attach it to your hose there), and connect the other end of the hose past the electric fuel pump - a bit harder to do, may need some help from a mechanic for this. you will rule out the fuel selector and the electric fuel pump as a cause.

3. If that does not work, see if you can find an electric pump that you can borrow for a bit. Then disconnect the fuel line after the engine fuel pump (usually just before the fuel flow sensor). Connect a hose going from the stand alone electric fuel pump to the fuel line, and another hose going into a bucked that has fuel in it (make sure the bucket was clean, etc, etc). With someone's help start the engine using the stand alone electric fuel and see if you have fluctuations. This will rule out the engine driven fuel pump. If possible, try to find an electric fuel pump that puts out 24psi.

4. If all that still does not work, then the problem could be with the fuel injection system (had mine overhauled twice just to be sure, did not help). Also, according to the guy to overhauled my injection system if there is an induction leak it could cause these fluctuations, but I have not been able to find a leak so far.

5. Finally, it may not be a real fluctuation. Using a voltmeter see if you can connect to the fuel pressure connectors and see if you see fluctuations on the voltmeter. This is what I'm talking about:

Hope this helps

Best,

Stefan

[N201MKTurbo]

Handheld volt meters all use some version of the ICL7106 chip. It is a dual slope integrating A/D converter. It will filter out most fast transients. The A/D converters used in the panel instruments are very fast and can respond to noise that will not be seen by the handheld meter.

What I'm saying is that you have noise on the sensor. I would check the grounding of the sensor. If the sensor is grounded to the engine I would check the engine grounding.

[Joe Larussa]

Okay so here is the latest. Yesterday I tried what a few have suggested. I drained the fuel from the fuel pressure gauge line and from the firewall to the fuel servo. Started up and the needle was as still as can be. A major improvement from when I tried bleeding air out of the line. What I did notice is the following:

Fuel pressure was higher from idle to climb. When I finally leveled off at 8,500 the pressure seemed a pound or two lower than I was used to seeing. I was still seeing pressure fluctuations but at least the needle was not freaking out! A little more comforting. On descent pressure increased to about 26 lbs. The lower I got the higher the fuel pressure seemed to be. So riddle me this Batman. If there is now air in the line instead of fuel does the fuel pressure rise and drop with altitude? Yet more to ponder!

For that matter does the fuel pump always put out the same pressure no matter what the altitude?

[carusoam]

Joe,

You may want to update your avatar to include what version of Mooney you are flying.

Fuel pressure in some of our planes is much lower than others.  Of course, it doesn't even get measured in some planes.

This will help the older memories help you.

Best regards,

-a-

Edited October 3, 2015 by carusoam

[Andy95W]

Just gonna hazard a guess:  26 psi so it must be fuel injected.  (If it's not an IO-360, he has other problems at 26 psi!)

 Picture shows a short window, so a 1965-1969 M20E?

[KSMooniac]

He has a 77 J, IO-360-A3B6D.

Sent from my VS985 4G using Tapatalk

[Joe Larussa]

I'm flying  a 77 M20J with a IO-360-A1B6D. Any thoughts on my last post about the air in the pressure line?