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RV-10 IO540 Fuel pressure loss on climb

C

CopterJohn

Active Member
I've seen this issue posted other locations, but never heard of any solutions.
On extended, full tank 120kt climbouts to 9-11kft, the fuel pressure bleeds down from 24 to around 8 psi unless the boost pump is left on. Of course, the AFS "check fuel pressure" alarm goes off. Engine continues to run fine, but turning boost pump on returns pressure to normal values. Previous owner dealt with this and changed out pumps, which obviously was not a solution.
I've heard theories of venting issues with the tanks, vaporization near the pump, etc. Has anyone else successfully dealt with this? Lines are firesleeved but no additional cooling on fuel pump.
 
Adding a blast tube on the mechanical pump seems to help, but the best solution is to leave the boost pump on 5-10 mins after you level off. Several "spam cans" require this procedure also.
 
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It might be a sender issue. Senders are vented to the atmosphere, but (usually) being of automotive nature, the venting isn't adequate for the climb and descent rates an RV can generate. This causes the reference pressure in the sender to be incorrect and creates false low readings during a climb and false high readings during a descent.

It is something like what you'd see from your altimeter if your static system was clogged.

Check to see if your pressure seems artifically high on descent and that will (probably) tell you if you're chasing a real problem or a sender issue.
 
If you have a fuel -water drain under the cowling, my money is on it as the gasolater. I once had a commander 114B that had the same problem. After much money and time, a very smart A&P felt the gasolator was sucking air at hjgh altitudes and replaced the O-rings. Problem solved. Who would have thunk it.

Sam Butler
RV-7A
 
We ran into a similar problem after doing the annual condition inspection on my buddies Cozy MKIV with an IO-360. After lots of head scratching we traced it down to the fuel filter element. The plane has an Airflow Performance fuel pump and filter. We replaced the filter element with a new one from AS&S and the new element's screening was so fine,,,it could not keep up with the demand at WOT on climb-out. We ended up cleaning the old element and putting it back in. Problem solved.
 
I solved this problem by mounting the fuel sensor low on the firewall. My theory is that when the system is hot vapour collects in the line if the sensor is mounted higher then the main fuel pump. I have not had a bad fuel pressure reading in six or seven years, on multiple aircraft, since moving the sensor.
 
This is also a common problem with the Rockets using the same engine. I just left the electric fuel pump on for a few minutes after leveling off. My alarm used to go off all the time too, of course I was making 2500 FPM climbs!;)
 
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