High fuel pressure with new fuel pump

[MooneyBob]

On my few last flight I noticed that my fuel pressure fluctuated between 24 - 17 psi specially in higher altitudes. It was all good with the electric pump on. The fuel selector switching didn't do any difference. So I decided to get the new fuel pump and swapped it today with my mechanic. Testing on the ground now shows the fuel pressure over 30 psi at idle and lower RPMs which puts me in the red on the fuel gauge ( CGR30P) and around 29 psi ( top of the green ) at full throttle. My fuel pressure used to be around 24 psi before swap.  Whithout engine running the boost pump only gives me around 25 psi which is what I remember before the swap. 

We have attached mechanical pressure gauge to check the pressure just in case the transducer is bad but we got same results.

Any pointer here? I am pretty confident I got right pump. It is Tempest AF15473. It even says on the box 25-30 psi. 

My engine is  A3B6. 

Thank you. 

[amillet]

First run up of factory re-built IO360A3B6 today went great except that fuel pressure gauge pegged at top.  Gauge appears to be working when boost pump is run.  I also would like to know how to resolve it.  Hope to fly two hour break in flight tomorrow.

[KSMooniac]

I'm using the same tempest on my overhaul, and it is behaving just like yours. I'm about 9 hours in and the pressure has come down a little to 27-28 in cruise. I'm just keeping an eye on it for now.

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[MooneyBob]

I like the higher pressure more than low one for sure. I just hope it is not an indication of some other troubles. And that red warning light scare the sh**t of me.  

[Yetti]

Did you clean the screen on the fuel servo?

[MooneyBob]

51 minutes ago, Yetti said:

Did you clean the screen on the fuel servo?

Not yet but I am about to check and clean it together with other components and fuel filter. 

Thanks. 

[Yetti]

This is what came out of mine....

[MooneyBob]

1 hour ago, Yetti said:

This is what came out of mine....

Did it cause the higher fuel pressure readings?

thanks 

[Yetti]

Not sure but it caused higher blood pressure as screens are fuel screens are something on the Mooney Check list for Annuals.   The last annual was before I owned it.   lots of things were missed.

[takair]

Older topic, but I just ran into this today.  Installed a new Lycoming pump as a precaution and my fuel pressure is at 35 with the new pump (limit is 30).  The old pump was consistently in the mid 20s and the electric pump alone is mid 20s.  Was there any resolution for those on this thread?  Will see if I can verify that the gauge is correct, but I suspect that it is.  So much for being proactive, this is cutting it close for making Oshkosh.  Pump is not fun to change.

[carusoam]

What would be the source of extra fuel pressure?  

- increased volume of flow..?

- increased restriction in the line..?

 

Since the lines haven't changed, the back pressure caused by restriction probably hasn't changed...

what would cause more flow for a new fuel pump?  Bladders and springs or other parts internal to the pump...

 

Now would be a good time to verify the pumps model number details...

PP thoughts only, Good luck getting to the details on this one...

Best regards,

-a-

[takair]

1 minute ago, carusoam said:

What would be the source of extra fuel pressure?  

- increased volume of flow..?

- increased restriction in the line..?

 

Since the lines haven't changed, the back pressure caused by restriction probably hasn't changed...

what would cause more flow for a new fuel pump?  Bladders and springs or other parts internal to the pump...

 

Now would be a good time to verify the pumps model number details...

PP thoughts only, Good luck getting to the details on this one...

Best regards,

-a-

I'm afraid it may be the pump.  I verified the part number of the pump again.  The pressure jumps high the moment I turn over the engine.  The pump is supposed to essentially self regulate.  In theory, one should be able to block the outlet line and the pump should not go over 30 psi.   I found a lot of threads on this subject.  In many cases it is the indication, but there are a number where it was not indication, but I can't find alternate resolution.  I would hate to pull pump again.  Going back to airport with another gauge to verify pressure.

[RLCarter]

I replaced the mechanical fuel pump last year, with the new pump my fuel pressure is at 27~28 psi as well. Talked to several A&P's and posted it on MS as well, didn't seem to bother anyone so I don't worry about it, will be interesting to see what results you get get

[Fly Boomer]

For anyone flying with "higher" pressure, does it affect your fuel flow?  Does the engine run richer with extra pressure?

[takair]

3 hours ago, RLCarter said:

I replaced the mechanical fuel pump last year, with the new pump my fuel pressure is at 27~28 psi as well. Talked to several A&P's and posted it on MS as well, didn't seem to bother anyone so I don't worry about it, will be interesting to see what results you get get

Just checked my gauge with a calibrated gauge and it is dead on. I would not mind seeing 29psi, which is below red line, but I'm seeing over 35. Unless I managed to find a new way of screwing this up,I think I got a faulty pump. Will call Lycoming Monday. 

[RLCarter]

Just now, takair said:

Just checked my gauge with a calibrated gauge and it is dead on. I would not mind seeing 29psi, which is below red line, but I'm seeing over 35. Unless I managed to find a new way of screwing this up,I think I got a faulty pump. Will call Lycoming Monday. 

With the boost pump on it's really hard to see an increase, but it does go up slightly. Be sure to post what Lycoming has to say. They had a recall on my old pump for engine oil getting into the fuel, which mine was doing but mine was outside of the range or what ever, only thing I remember was having to reach in my pocket

[Guest]

A blocked crankcase breather will raise your fuel pressure.  I've seen it happen once, it took some effort to figure out.

Clarence

[takair]

8 minutes ago, M20Doc said:

A blocked crankcase breather will raise your fuel pressure.  I've seen it happen once, it took some effort to figure out.

Clarence

Thanks Clarence.  I did have the line off and I'm pretty sure it is clear, but I will check it one more time.  I'm curious, how was the line plugged?  Was it kinked?

[Guest]

20 hours ago, takair said:

Thanks Clarence.  I did have the line off and I'm pretty sure it is clear, but I will check it one more time.  I'm curious, how was the line plugged?  Was it kinked?

A plastic cap inserted in the hose while the engine was out, ended up migrating down the rubber hose, un-noticed.  On run up the crankcase pressure rose as did the fuel pressure.

Clarence

[Yetti]

in the year and half of a new pump, It seems to have come down a bit.   When new it was really close/on the redline

[takair]

15 hours ago, M20Doc said:

A plastic cap inserted in the hose while the engine was out, ended up migrating down the rubber hose, in noticed.  On run up the crankcase pressure rose as did the fuel pressure.

Clarence

Pulled the vent line and it is clear.  I was suspicious because I had plugged the line when I had it out.  Think I'm back to the pump.    Interestingly the Lycoming TCDS seems to indicate that the pressure could be as high as 35....but it is not entirely clear if they mean inlet or outlet pressure.  i would put the old pump back on, but the actuator arm moves too freely and has a bit of a catch to  it....wonder if that was on its way out too.  Guess I will see what Lycoming says.  Wonder what their AOG warranty service is like?

[takair]

Getting toward the bottom of this.  I had ordered a LW-15473 pump, but was told that the new replacement pump is a 62B26931. I verified this via Lycoming SL L255A (https://www.lycoming.com/sites/default/files/SL255A Approved Diaphragm-Type Fuel Pump.pdf).  Today I called Lycoming tech support and the rep said that the new 62B26931 pumps tend to run at a higher pressure than the 15473 and that 35 psi is not unusual.  He pointed out that our engines are certified for an input pressure of 45 psi at the servo and 35 psi into the fuel pump (I assume that this is for the boost pump.  The dilemma comes down to the airframe, which limits us to 30 psi.  I have a call into Mooney, but have not heard back.  I suspect that they won't be able to tell me much more than to get the lower pressure pump.  The problem is, as others have seen, is that the pumps can run high, because Lycoming allows it.  I also have a call into Spruce, who actually understood the dilemma, but needs to make some calls.  Long story short, it looks like the 62B26931 is NOT a perfect drop in (form, fit, function) replacement for the LW-15473, in spite of what Lycoming SL L255A says.  Will post once I have further resolution, but unless Mooney has something that lets me bump up the pressure, it looks like it will be another pump replacement...and likely missed Oshkosh...

[Yetti]

Replaced mine with a 41234 Tempest Pump

https://www.aircraftspruce.com/catalog/eppages/TEMPESTfuelpumpLYC.php

[takair]

Just to try to close out my previous post regarding 62B26931 pump.  I ended up purchasing a new LW-15473 and my troubles are behind.  It puts out about 28psi and just bumps up to redline of 30psi with the boost pump on.  I have written Lycoming to try to get reimbursed and to notify them of this issue.  I don't know if I will get my money back, so if anybody needs a higher pressure pump for their Piper I will let it go for a slightly reduced price if I can't get the warranty. 

[Hillard]

Despite this issue having been around for at least six months, mooney and lycoming appear to have done nothing to resolve it.  We have just discovered this issue after starting up an overhauled A3B6 engine last week.  Everything was fine except the fuel pressure gauge is hard over to the right.  No response yet from mooney or lycoming.    

Despite it being listed on the type certificate and marketed for the 20J, the engine supplied by lycoming is incompatible with the airframe in three respects:

a) fuel pressure higher than mooney limit

b( prop oil line supplied interferes with engine mount and has to be replaced at your cost (usd500)

c) extra parts required from mooney to rig prop control cable (another usd500)

Did lycoming tell me any of this when they supplied the engine? - no.  I’ve only discovered it from mooneyspace.  

The engine supplied is not “fit for purpose” and lycoming appear to care not a jot.  I treat their statements about “customer care” as utter garbage.