High fuel pressure (52 PSI) on a Lyc IO-360. Normally 27 PSI. Any ideas to why?

[ao.frog]

Today was the 11th flight with my new -7, tach was around 19 hrs when it happened.

Until today, the fuel pressure has been steady at 27 PSI during flight.

About an hour into todays flight, (2:30 mins planned) I noticed that the fuel press was 32 PSI.
I kept an eye on it and about 10 mins later it was 35.
5 mins later it was 40.

The increase where slowly, so I assumed this probably wasn't an indicator malfunction. (No "jumpy" indications)

I decided to turn towards the homebase and during the turn it slowly climbed to 52 PSI.
I climbed to 8000' on course for home.

During the climb, the fuelpress decreased to 40 PSI.
After about 5 mins cruise at 8000' the fuel press decreased to 32 PSI

Here a pic:





A few minutes later, it climbed back up to 40:





When reducing power for landing, it climbed back up to 51 PSI.
I turned on the boost pump and it jumped to 55 PSI, so I quickly turned the boostpump off again.

When taxing in, the fuel press stayed at 51 PSI.

I pulled the cowls after shutdown and no leaks or blue stains anywhere.
Tomorrow I'll check the fuel filter.

I'll also check for good grounding at the fuel pressure sensor.

On my first -7 (Extreem IO-360 engine) the fuel press has been 30 PSI since the first flight.
On this -7, I've been satisfied with 27 since it has been steady.

The mechanical fuel pump was installed by Lycoming when I got the engine, so I haven't done anything with it.

Does anyone have an idea to what can be the cause of this?
To me, it looked like there really was a high fuel pressure and not an indicatotion problem, since the indications where so gradual.

Any ideas anyone?

[dougweil]

Had a similar issue on my IO-375 with AFS instrumentation although the readings never got quite that high. Fixed with a new fuel pressure transducer.

[UnPossible]

I had an issue in Phase 1 with my Oil pressure spiking rapidly (which really got my attention) - turned out to be a bad ground on the transducer - might be something to check.

[alpinelakespilot2000]

Have had the fluctuating fuel pressure twice with my Dynon transducer over the first 150 hours. Both times I fixed it by bleeding the line by pulling the transducer off the manifold and then pumping a bit a fuel through before screwing the transducer back on. On the second time I also added an extra ground write to make sure I kept a good ground. Hope this helps... I know it can be frustrating chasing these kinds of issues.

[BCP Boys]

Alf, I had similar issues several years ago on my twin with IO470s.... After almost a month of searching, rebuilding the fuel pump, cleaning and/or replacing injectors, etc. I was ready to throw in the towel and give up.... I was putting the cowling back on when I found the needle in a hay stack! The body of the fuel injector (looks like a spider) there is a very small pin hole that allows air into the injector. There was a bug inside of this hole and was blocking the air from getting into the body of the injector. I am by no means a mechanic but thought I would share my experience .... We (my A&P and I ) cleaned it and it immediately fixed the issue. I spent over $1000 trying to fix it and it turned out to be a stupid bug building a mud nest (we call them dirt dauber) in the injector body. You may want to make sure the injectors and the body are all clean.
Good luck.

[scsmith]

I had this happen on my Dynon last year. When I called to order a replacement I found that they are supplying a different, higher-quality sensor now. It took a different excitation voltage so it was a bit of a pain to re-wire, but I did the oil pressure sensor at the same time, so they are both the newer, better style.

[Kahuna]

Originally Posted by ao.frog

The increase where slowly, so I assumed this probably wasn't an indicator malfunction. (No "jumpy" indications)

This is where you went wrong.

[molson309]

I don't think the mechanical pump is capable of doing this - the pressure is developed by the spring tension inside the pump on the return stroke of the pump lever. Rather, I believe it has to do with the transducer used by AFS for the fuel pressure sender. If it's like the ones on the 2 planes I have with AFS units, it is a VDO pressure-to-resistance unit and is sensitive to grounding issues and other mechanical factors. The one supplied by AFS is grounded through the pipe fitting which makes it possible to have an unreliable ground - VDO makes one that has a separate ground terminal with otherwise the same pressure and resistance ratings as the original, which makes it easier to connect a secure ground to it. I don't have the part number handy but will see if I can find it today.

The upside is that these VDO sensors aren't horribly expensive - that's a good thing because they have a limited life and eventually fail. I replaced one on the RV when it started to intermittently show either zero or off-the-scale high pressure. Really got my attention when it suddenly showed zero while I was over rather rugged terrain on a cross country flight...

[molson309]

http://www.vdo-instruments.com/senso...7npt-32-1.html

80 PSI, 10-180 ohm with ground terminal.

[spinomaly]

We had 2 VDO sensors go bad. First one after 200 Hobbs. Second one immediately after install. Third one working fine with 20-30 Hobbs. I took the first one apart. The wiper had worn through most of the resistive coiled wire at one location. Probably from the wiper vibrating around the constant fuel pressure point.

The symptoms on the first one was the pressure would go max because the wiper would go past the worn through resistive wire which would then be an open circuit to the EFIS. The second one was just intermittent. It would be fine around 25-27 psi, then would creep up to 40. Then back down.

Apparently there is another type of sensor that is recommended. We have not gone that route yet.

Good luck.