DualRatedFlyer Posted May 17, 2018 Report Posted May 17, 2018 On the way back from vacation last week I noticed my fuel pressure gauge fluctuating. Like a good MSer, I took out my phone and took a video of the fluctuations with the intent of posting it on a thread asking the group for their input. Unfortunately, somehow between uploading them off my phone to google photos and clicking the "free up space", the clips have been lost to the dark web (sigh). Anyway, perhaps a good description will produce the same effect. Cruising at 9k, I noticed my fuel pressure gauge fluctuating between 18 and 25. The fluctuations were very rhythmic, in that the pressure would hit 25 and stay there for about 5 seconds before dropping to 18 and then slowly working itself back up to 25. In total this rhythm takes place over around 20 seconds and then starts over (working up to 25, dropping to 18/19 or 20, slowly climbing back to 25, holding for a few seconds, dropping again.) Hitting the boost pump resulted in a pressure increase to a rock solid 26/27. Turning off the fuel pressure dropped slightly back to 25, but the pressure would stay solid for several minutes thereafter until repeating the cycle described above. I did notice that while running LOP, my EGT would lose/gain a red bar (insight GEM 602) in what would appear to be correlations with the pressure fluctuations. The aircraft is fairly new to me, but I dont recall normally seeing any EGT movement once stabilized in cruise and LOP. Soon thereafter I was asked to descent to 7k in the DC area. I dont recall noticing it happening at 7k, but that doesn't mean it wasn't. Probably noteworthy that most of my flying is in 6-7k range <2hr hops, and that may be why I haven't noticed the fluctuations, assuming they do indeed only happen above 7k. More observations over the next couple flights will help narrow this down. Has anyone else experienced anything similar? All fluctuations are within the green arc, but I dont imagine that makes it ok? Any input is appreciated.
Bob_Belville Posted May 17, 2018 Report Posted May 17, 2018 Yep, same symptoms. I think that at higher altitudes for us, 9000 +/-, it is likely that air bubbles form in the fuel line where the line gets hot. In the case of my E, there's an ell fitting low on the firewall, downstream of the electric pump, that is not insulated. I wrapped mine with fire sleeve and it definitely helped the problem. You might be able to find a thread here from approx. last summer... 1
DualRatedFlyer Posted May 17, 2018 Author Report Posted May 17, 2018 I figured out where my video went. The video timestamp indicated December 31, 1969, which from what I've read is indicative of a dead timekeeping battery on the logic board. The video was placed in the very beginning of my photos history instead of at the end. Anyway, here is the video of the (poorly) described scenario above. Sorry for the fancy camera work, my ipad was on the yoke and I was trying to navigate around it. https://photos.app.goo.gl/BpoDSmdb7z9JjNlJ3
DualRatedFlyer Posted May 17, 2018 Author Report Posted May 17, 2018 Interesting @Bob_Belville. So in your case the fire sleeve helped reduce the issue, but did not eliminate it? I just want to make sure this is not indicative of an early fuel pump failure other other issue that I need to track down. You believe this is just bubble ingestion?
mike_elliott Posted May 17, 2018 Report Posted May 17, 2018 I had this issue about 15 years ago in my F. It turned out it was a small pinhole in the mechanical pump diaphragm. New pump = all good
Bob_Belville Posted May 17, 2018 Report Posted May 17, 2018 4 minutes ago, DualRatedFlyer said: Interesting @Bob_Belville. So in your case the fire sleeve helped reduce the issue, but did not eliminate it? I just want to make sure this is not indicative of an early fuel pump failure other other issue that I need to track down. You believe this is just bubble ingestion? That's my recollection. @kortopatesand @AGL Aviation were involved. Paul help me analyze the data and Lynn provided the fire sleeve and the clamps as well as the advice. I recall that while I was working on it Lynn had an Arrow in the shop. Piper went to some effort to provide cooling air to the fuel line right where I added the sleeve. They have the ell boxed in and louvers in the cowl to direct outside air around the fitting.
DualRatedFlyer Posted May 17, 2018 Author Report Posted May 17, 2018 10 minutes ago, mike_elliott said: I had this issue about 15 years ago in my F. It turned out it was a small pinhole in the mechanical pump diaphragm. New pump = all good @mike_elliott Was this discovered during a pump overhaul, or did you take the pump apart looking for an issue? After the new pump is your fuel pressure completely solid, or does it wander any?
mike_elliott Posted May 17, 2018 Report Posted May 17, 2018 11 minutes ago, DualRatedFlyer said: @mike_elliott Was this discovered during a pump overhaul, or did you take the pump apart looking for an issue? After the new pump is your fuel pressure completely solid, or does it wander any? THe pinhole was discovered by the IA who replaced the pump who predicted that was the problem after checking for "tightness" of the fuel delivery system. The symptom went completely away with a new pump. He was right. Dont ask me his name, I dont even know if he is still alive. He worked for Dan Montgomery at Indy Executive. 1
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