low fuel pressure

funflying · #1 07-31-2013, 09:50 PM

I think I am on the right track but I am looking for some opinions.

On my first (and only so far) flight the fuel pressure was 1.9 - 2.0 which put it in the yellow. I followed this up with a disconnect of the hose to the sender to check for any obstruction. The fuel that came out looked a little thick and had an orange tint. I flushed the line with fresh fuel, removed the sender, and checked the fitting. Everything clear and clean not.

This evening I checked the system again. Electric pump only 3.2psi, with engine running at 2100rpm it dropped to 2.1, and if I pulled the fuse to the electric pump it dropped to 0.5psi and wasn't running well.

Fuse back in and warmed up I ran it up to 4000 and the pressure stayed low at 2.0psi, pulled the fuse and again down to 0.5psi. I have a new fuel pump on order and plan to follow SB 912 063UL to replace the fuel pump. I should try and see if it might be covered on warrant since it was only 3 hrs. on it.

Comments please.

rvbuilder2002 · #2 07-31-2013, 10:45 PM

It could very well be a bad engine driven pump, but one thing you should also check is the filter screen in the gascolator.
This should actually be done by everyone after about the first 5 hours.
No matter how careful you are, there will always be contaminates in the fuel tank system (some more than others), that gets flushed out in the first few hours. A restricted filter screen will cause lower fuel pressure.

N223JH · #3 08-01-2013, 03:35 AM

Patrick, your experience mirrors mine in 2011 with the old style fuel pump. Replacement pump solved the problem.

Rotax may have changed the policy on warranty replacement of the old style pumps but just in case they haven't, be sure your notation on it includes an observation of fuel leakage at the pump. Prior to the switch to new pumps, it was verboten for the pumps to fail without a leak.

Jim

Tom Delaney · #4 08-01-2013, 07:34 AM

I had the same problem but at the other end of the spectrum...fuel pressure was too high at over 7.5 psi. I also had the thick string of contaminant at the fuel sensor connection.

Once you check the gascolator screen you might consider placing a mechanical gauge into the clamp block on the compensating tube as a final check that the cockpit instrumentation is true.

Passing this information on to Lockwood quickly confirmed the diagnosis and a warranty form was emailed to me.

Hope you don't have to wait long for the new pump.

Catbird · #5 08-01-2013, 09:49 AM

As for the fuel in the pressure indicator (PI) line looking a little thick with an orange tint, it may be because that line deadheads at the PI. There is no recirculation of the fuel in the PI line. I found the same thing in mine after 100 hours.

funflying · #6 08-01-2013, 11:32 AM

Catbird,

Where you experiencing low pressure readings or did something else cause you to check that line? Also..nice paint job!

Tom, so have you replaced your fuel pump already? I have read where some have experienced high reads with the new pump and changed the limits in their Skyview to silence the alarm.

Thanks to all for your input.

aerofurb · #7 08-01-2013, 02:05 PM

I would initially remove and physically check the fuel pump.

We had a brand new Tecnam P2006T twin lose a mechanical pump on the delivery flight. I removed the pump and found the plunger spring had broken and coil bound itself holding the plunger almost right way from the prop driveshaft cam.

Changed the pump for a new one. Initial ground run was fine. Released the aircraft for flight but it came back with low fuel pressure again. Given that the pump was brand new, looked at everything else before removing the pump.

Another broken, coil bound spring....

Pleased that there is a new fuel pump now!

PS And never trust those Honeywell oil pressure senders. Changed quite a few of those, too.

Tom Delaney · #8 08-01-2013, 03:15 PM

Patrick,

I replaced my fuel pump prior to the first flight. My conversation with Dean at Lockwood and this forum made me aware of the higher pressure being encountered with the new pumps. However, Dean said that at 7.5 psi output I needed a new one.

The new one puts out almost the same pressure but dropped to 5.8 during the first flight. So I probably did not need a new one but since I had not flown yet I wanted it taken care of before I jumped in and headed skyward.

Catbird · #9 08-01-2013, 03:20 PM

Patrick,

Although I'm wandering from the original subject of this thread, the reason I removed the PI line and found what appeared to be stale gas was because I'm in the process of replacing all of the Rotax fuel lines. In a recent thread on the subject of fuel pump upgrades, I came across Aircraft Specialties' offering of teflon lined braided hose kits for the RV-12. The main reason I jumped on this opportunity was to get rid of the seemingly fragile Rotax banjo bolt at the clamp block between the carbs.

On Van's Kit Assembly Instructions Page 46-09, Figure 5, the nefarious Banjo Bolt M8X1X17 appears with instructions to remove the pilot jet and retorque the bolt to 90 in-lbs. Well...two of these bolts snapped off before reaching the specified torque. Upon inspection, I noticed that with all of the holes in that bolt, there's very little metal left in the shank. I got the third bolt (and these things arenn't cheap) to hold at something less than 90 in-lbs and have worried through 100 hours of flying that if that bolt snaps off in flight or comes loose from being under-torqued, than raw gasoline will be puming onto the hot engine during flight.

Aircraft Specialties' kit uses AN fittings and gets rid of the Rotax clamp block and associated banjo bolts altogether. Down the road, these new hoses will last much longer than the 5-year life span of the Rotax fuel lines.

There - I've said my 2-cents worth.

rvbuilder2002 · #10 08-01-2013, 03:24 PM

Quote:

Originally Posted by Tom Delaney

Patrick,

I replaced my fuel pump prior to the first flight. My conversation with Dean at Lockwood and this forum made me aware of the higher pressure being encountered with the new pumps. However, Dean said that at 7.5 psi output I needed a new one.

The new one puts out almost the same pressure but dropped to 5.8 during the first flight. So I probably did not need a new one but since I had not flown yet I wanted it taken care of before I jumped in and headed skyward.

Some of the early delivered new style pumps had excessive pressure. Rotax exchanged them.

Rotax specified an increase in max. operating pressure for the new style pump.
If you install the new pump you should adjust the pressure limit in the SV-1000 to 7.2 PSI