High Fuel Pressure

[zehutiman]

Apologies for a subject that’s been raised several times, but I couldn’t find answers to my situation.  I have a 1980 M20J Missile that recently had an avionics upgrade, to include a GI 275 engine monitor.  I also got CiES fuel senders.  The sender’s performance, along with fuel flow, has been totally underwhelming, and I realize that may be due to “other factors.”  The other day, I descended from 11000’ and began getting a high fuel pressure warning; the maximum allowed is 28psi.  The pressure fluctuated between 26 and 29 — never steady.  That particular day, I flew the airplane on 2 legs, for a total of about 5 hrs flight time, and I did notice the pressure fluctuating a lot, between 11 and 13 psi.  I think it got my attention even before the warning because of the fluctuations.  The high pressure continued until landing — about 20 minutes — but stopped during taxi.  Any ideas?  I’m 500 miles from home base, so one of my biggest concerns is safety of flight, regarding engine failure.  TIA.

[A64Pilot]

Just about any of the warnings associated with electronic sensors should in my opinion first be verified with an old fashioned crude direct reading instrument, sure they don’t display digitally but you don’t need that.

Very often there is no problem with the aircraft, it’s the sensor, wiring or the electronic gauge / panel etc, even old fashioned gauges fail, but I have seen much money spent trying to fix an engine problem that was just the gauge. One I remember well, oil temp on a turbine, he has changed everything, even cut additional holes in the cowling to let heat out etc. I told him to not run the aircraft that I would fly over and look, well I jumped in turned the battery on, oil temp read 70C or something and I looked at him and said Jerry I thought I asked you to not run it, he said I didn’t. I pointed at the gauge and told him I think I’ve found your problem, took two min to change the gauge as I had brought one with me.

He had spent thousands chasing an oil temp problem that he didn’t have.

In other words I would temporarily plumb in a direct pressure gauge and verify your have an actual pressure and not instrument problem before you do anything else.

[Fly Boomer]

10 minutes ago, zehutiman said:

Apologies for a subject that’s been raised several times, but I couldn’t find answers to my situation.  I have a 1980 M20J Missile that recently had an avionics upgrade, to include a GI 275 engine monitor.  I also got CiES fuel senders.  The sender’s performance, along with fuel flow, has been totally underwhelming, and I realize that may be due to “other factors.”  The other day, I descended from 11000’ and began getting a high fuel pressure warning; the maximum allowed is 28psi.  The pressure fluctuated between 26 and 29 — never steady.  That particular day, I flew the airplane on 2 legs, for a total of about 5 hrs flight time, and I did notice the pressure fluctuating a lot, between 11 and 13 psi.  I think it got my attention even before the warning because of the fluctuations.  The high pressure continued until landing — about 20 minutes — but stopped during taxi.  Any ideas?  I’m 500 miles from home base, so one of my biggest concerns is safety of flight, regarding engine failure.  TIA.

Not sure about the "too high" but many here have noticed that their new-fangled digital instruments jump around a lot.  It may be that the pressure was jumping around before the new instrument, but you just couldn't see it.  Some have calmed the readings down using a snubber.

[A64Pilot]

2 minutes ago, Fly Boomer said:

Not sure about the "too high" but many here have noticed that their new-fangled digital instruments jump around a lot.  It may be that the pressure was jumping around before the new instrument, but you just couldn't see it.  Some have calmed the readings down using a snubber.

EI I know uses an algorithm if I use the word correctly to “smooth” out the readings, and I was told by our Power Plant DER that the instruments on Pipers turbines have a “snap” function, that is when the numbers get close to what they are supposed to be, they snap to one fixed reading and stay there until they exceed some parameter, otherwise at least the last digit is an 8 as nothing in an engine is stable to the .1% or .1 temp etc.

[LANCECASPER]

2 hours ago, A64Pilot said:

Just about any of the warnings associated with electronic sensors should in my opinion first be verified with an old fashioned crude direct reading instrument, sure they don’t display digitally but you don’t need that.

Very often there is no problem with the aircraft, it’s the sensor, wiring or the electronic gauge / panel etc, even old fashioned gauges fail, but I have seen much money spent trying to fix an engine problem that was just the gauge. One I remember well, oil temp on a turbine, he has changed everything, even cut additional holes in the cowling to let heat out etc. I told him to not run the aircraft that I would fly over and look, well I jumped in turned the battery on, oil temp read 70C or something and I looked at him and said Jerry I thought I asked you to not run it, he said I didn’t. I pointed at the gauge and told him I think I’ve found your problem, took two min to change the gauge as I had brought one with me.

He had spent thousands chasing an oil temp problem that he didn’t have.

In other words I would temporarily plumb in a direct pressure gauge and verify your have an actual pressure and not instrument problem before you do anything else.

As @Fly Boomer mentions I would bet that a snubber would take care of this.

[zehutiman]

So, the avionics shop said the Continental IO 550A manual states a maximum fuel pressure of 36psi at 2700 rpm.  He’s not sure if the Missile STC changed that.  I wrote in my notes that the max was 28psi, but I can’t remember where I got that from, and I’m away from home, so I can’t double check.  I think I got it from the POH’s STC addendum . The POH is in the airplane.  Any Missile owners out there who could comment on the max fuel pressure?

[LANCECASPER]

4 hours ago, zehutiman said:

Any Missile owners out there who could comment on the max fuel pressure?

@Seth ??

[UteM20F]

I agree with the others that I'd first make sure the readings are correct.  We got all new Garmin instruments, including the G3X engine analyzer, and immediately the oil pressure was going red occasionally.  A new pressure transducer fixed the indication problem.  We are still seeing a bit of weirdness, like CHT instantly jumps by 40-60 degrees when there is large electric load (gear, fuel pump, etc) then just as instantly drops down to normal when the load is ended.  We have since been told that this is a problem of 1967 wires being in the same bundle as the new wires, and that they should be separated.  

[Seth]

I'm pretty sure it's 36 per the STC. The original M20J is less. Hence the setup by the shop making 28 the max allowable. They set it up for a standard M20J fuel pressure with a Lycoming IO360 with 200 HP.

The STC with the Missile and the Continental IO-550 max is 36 PSI. You're fine!

That's what my former Missile used to be (former as of earlier this afternoon ;(

 

-Seth

[zehutiman]

On 9/15/2023 at 11:08 PM, Seth said:

I'm pretty sure it's 36 per the STC. The original M20J is less. Hence the setup by the shop making 28 the max allowable. They set it up for a standard M20J fuel pressure with a Lycoming IO360 with 200 HP.

The STC with the Missile and the Continental IO-550 max is 36 PSI. You're fine!

That's what my former Missile used to be (former as of earlier this afternoon ;(

 

-Seth

Can I change the limitation from 28 to 36, or does that have to be done by the avionics installer?

[Seth]

If you know how to work the maintenance menus inside of the GI275 (guessing) you likely can change it yourself. That said, whoever installed it set it up incorrectly so you can likely reach out to them and either have them walk it through it for you how to do it on the phone, or you can fly back to the shop, sit there while they fix the software setting, and then fly out, at no charge since they set up the equipment incorrectly. And I'm sure it's a common issue. They set it up to a 201 standard. We have the STC. Trust me, I had issues when I sent my former engine into Continental for Overhaul - they sent me back a stock engine missing all the STC Rocket Engineering parts (and couldn't find them so Continental paid Rocket Engineering to reproduce some of the parts).

The GI275 should have been properly set up to your aircraft, and you have STC modifications that change what the limits are for fuel pressure.

-Seth

[201Mooniac]

It is an easy change to make but technically it must be done by an approved person (according to Garmin).  Since this is an EIS, any A&P is also an approved person to make the change as they are allowed to install them.  The install manual for the EIS is available online as it is an over the counter sales unit, not a dealer only unit.