Indicating low fuel pressure - RV-6A O-320

Will Bentley · #1 12-26-2008, 05:09 PM

Folks,

At our airport here in NW Arkansas there are two of us that have 6A's that are curious about why we are seeing (at cruise flight) fuel pressures indicating anywhere from "0" psi to about 1.5 psi. When we activate the boost pump pressure seems to come up to 5psi or more.

My POH says .5 to 1.0 psi is normal at cruise. Have we a problem with our fuel pumps or is this typical? Neither of us built our 6A's...

Thanks,
Bill

hughfi · #2 12-26-2008, 05:18 PM

I have a 6 with an 0-320 and found my fuel pressure dropping often during a climb up through 6k etc. I replaced lines, fuel pump, added a cooling shroud and verified I had not leaks in the system. I was determined to fix the problem. I left one thing to the end which cost me dearly because I was told that the pressure sensors 'never go'. I was told that the either work or do not... Well thats BS.

After replacing the pump, lines etc. I still had the problem.

I replaced the pressure sensor 60hrs ago and its been rock solid since then. I would advise doing this and verifying you have not getting leaks around the sensor etc. You should have rock solid pressure after this assuming your pump is fine.

I can't explain why the secondary pump brings it up even to this day.

Hugh.

Will Bentley · #3 12-26-2008, 05:26 PM

Hugh,

Thanks for your input. Certainly seems reasonable. Will see what else
comes in as a response to our delima, but I'll bet you are right on.

Thanks
Bill

Sam Buchanan · #4 12-26-2008, 06:40 PM

Quote:

Originally Posted by Will Bentley

Folks,

At our airport here in NW Arkansas there are two of us that have 6A's that are curious about why we are seeing (at cruise flight) fuel pressures indicating anywhere from "0" psi to about 1.5 psi. When we activate the boost pump pressure seems to come up to 5psi or more.

My POH says .5 to 1.0 psi is normal at cruise. Have we a problem with our fuel pumps or is this typical? Neither of us built our 6A's...

Thanks,
Bill

The low fuel pressure indication in carbed RV's has been discussed heatedly since.....well....probably since the first RV-6's in the mid-80's. This forum has seen several threads devoted to this issue, here are a couple the search feature brought up:

http://www.vansairforce.com/communit...+fuel+pressure

http://www.vansairforce.com/communit...+fuel+pressure

I'm not going to tell you that there is no problem with your fuel system, but read the referenced threads and others you can search then decide how you want to approach this matter.

Will Bentley · #5 12-26-2008, 07:12 PM

Sam,

As far as I'm concerned (with my particular situation) you are right on the money! I have seen this "0" fuel pressure, with no engine problem, for
about two years. That, to me, indicates something other than a pumping problem. Reading the archives you made available to us absolutely confirms that I shouldn't be losing an engine because of this. Unquestionably, it is mysterious, but I sure get that warm & fuzzy feeling knowing this has been an ongoing RV situation for years. I'll do as I have been doing....I'll watch it closely but not panic. If things begin to add up that a mechanical issue is at hand I'll handle it accordingly. But, from what I've been seeing, it just doesn't seem to be an issue that requires any major mechanical modifications.

And, Sam, I'm sure I can speak for many of us, I've appreciated your input on many, many issues throughout the years. You've been spot-on regarding a variety of aircraft subjects. I've just sort of hidden in the shadows and enjoyed the benefits of reading a number of your suggestions. This, in no way, takes away from the tremendous amount of information we have all gleened from all the other "above average" meticulous builders and gifted aeronatical experts out there helping the "average" RV drivers keep their aircraft safe to fly another day... Thanks for being there for us.

Bill (Will) Bentley

Bob Martin · #6 12-26-2008, 07:47 PM

I too had the low fuel pressure readings on my 0-360.
I read the threads and lived with it for awhile but then figured I should keep trying to find it.
It was a bad fuel sender.
Some are better quality than others, I suspect.
Once it was replaced, I got normal pressure readings.
Keep looking for the problem!!
What good is a pressure indicator if you can't trust it to tell you when you are having a problem.
I can't tell you how good it feels to see normal fuel pressure reading in my scan while flying. Keep after it!

RVONE · #7 03-04-2009, 06:57 PM

Hey everyone, We've been searching the databases for info that may help us figure out our little fuel pressure issue. Any input would be much appreciated.

We run a 6 with a carberated 360. We use the Grand Rapids EIS 4000 engine monitor and have been getting an intermittent HIGH fuel pressure reading. We have the warn limits in the EIS set for low of 5 psi and High of 8. In discussing the issue with Grand Rapids Tech, they said it may be a failing fuel pressure sending unit so we ordered a new one. We switched that out but still have the same problem. Any suggestions?

Anyone else use different warn limit settings in thier EIS?

If it isn't a sending unit problem and the fuel pressure is actually intermittently higher, any ideas what may be causing it?

Anyone with similar setup mind sharing thier average fuel pressures and settings?

Any ideas would be greatly appreciated.

Greg Arehart · #8 03-05-2009, 10:11 PM

RVONE,

I have been seeing a similar issue in my 9A. Different engine (IO-360) and electronics (Dynon). My fuel pressure generally ran around 24 psi (normal for injected) but has been creeping up of late, and now is at 27. It also is reading much noisier than in the past and occasionally spikes to 33-35 (35 is the supposed upper limit for my engine). Boost pump seems to smooth out the fluctuations but I haven't experimented extensively. I posted a thread here a couple weeks ago and it was suggested perhaps air in the fuel pressure line and harmonics being set up. Haven't had a chance to do anything about it yet, but I plan to add a flow restrictor in the line (rivet with a tiny hole in it) and see if that helps. Maybe its just something about Reno....

greg

RVONE · #9 03-05-2009, 10:46 PM

Greg,

I appreciate the ideas, I'll have to look into them. Air in the fuel pressure line is an interesting theory.

It could just be Reno.....

Thanks,

Chris

kiwipete · #10 03-06-2009, 02:33 AM

I've noticed the same thing but haven't yet investigated. I seem to get a high spike every now and again without the fuel pump on. Thinking about it I have never tried to bleed the air out of the line to the firewall transducer. I'll try that first.

Superior IO360 Dynon DEK180

Peter