Possible fuel pump failure or...?

[The Other Red Baron]

Normally our fuel pressure on the M20E fluctuates between 28-31psi but is generally near 30-31.  We've flown like this for years and my understanding from multiple mechanics is this is just the way these newer fuel pumps operate.  On my flight today after about 30 minutes I noticed the fuel pressure begin to drop down to 23-24psi then creep back up.  At the same time the fuel flow would increase (which seems opposite of what I would expect).  I was cruising at 9.2/gph but it would jump to ~10gph.   When it would get down to ~23psi the engine would make a sound and felt like we temporarily lost some power.  Switched tanks and turned on the boost pump which looked like it helped. 

Landed, stretch legs, etc. went to start back up on the fresh tank and got a big red X on the engine monitor's fuel pressure so I decided to throw in the towel.  Does this sound like a failing engine fuel pump?  I ended up getting a rental car and driving home and started thinking maybe the right tank fuel vent was clogged but I don't think that would explain the X on the fuel pressure engine monitor. Annual was in May and we've flown some fairly long XC since then.

Edited September 11, 2023 by The Other Red Baron

[N201MKTurbo]

I would look at the fuel selector. Did you try both tanks when you had low fuel pressure? It sometimes the fuel selector sucking air.

[The Other Red Baron]

11 hours ago, N201MKTurbo said:

I would look at the fuel selector. Did you try both tanks when you had low fuel pressure? It sometimes the fuel selector sucking air.

I turned the boost pump on and switched to the left tank then landed so not sure if the boost pump was doing the heavy lifting or the issue was with the right tank only. 

[The Other Red Baron]

Loose injector for anyone curious...

[Gary0747]

Was it leaking fuel outside the engine?

[Ragsf15e]

1 hour ago, The Other Red Baron said:

Loose injector for anyone curious...

If it was loose enough to cause that, there should be blue stains everywhere around it.  Probably outside the cowling too.  I suspect you’ll continue to notice fluctuations in fuel pressure from the electronic gages.

[The Other Red Baron]

On 9/17/2023 at 1:21 PM, Gary0747 said:

Was it leaking fuel outside the engine?

The mechanic did see some blue staining around it.  I couldn't find any outside the cowling though.

[The Other Red Baron]

On 9/17/2023 at 1:53 PM, Ragsf15e said:

If it was loose enough to cause that, there should be blue stains everywhere around it.  Probably outside the cowling too.  I suspect you’ll continue to notice fluctuations in fuel pressure from the electronic gages.

The fuel pressure has always bounced between a range of 28-31psi the whole time we've had the plane and the JPI installed. Has always seemed to run OK like that and I don't think any mechanic has brought it up except the gentleman that found the fuel injector loose.