VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 07-04-2018, 02:11 AM
High_Flyer's Avatar
High_Flyer High_Flyer is offline
 
Join Date: Sep 2010
Location: Saint-Jorioz, France.
Posts: 189
Default Fuel pressure drop

Hi,

I have a RV-7 with a Aerosport IO-375-M1S engine.
Lately I noticed that my fuel pressure drops erratically when above about 8-9000 Ft. I saw as low as 10 Psi. When I switch the boost pump on fuel press goes back to normal, boost pump off fuel press drops again erratically.
This happens much frequently on hot days...
Here is a graph of the fuel press agains Pressure alt:


The positive peaks are when switching the boost pump on.

I suspect vapor lock, but I'd like more opinion.
What could be done to avoid this?

Thanks,
Alain.
__________________
Location: France
RV7 (F-PRVZ), Tip Up, Aerosport IO-375, Dynon Skyview, VP-X, Day VFR.

Flying since June 2017.
Reply With Quote
  #2  
Old 07-04-2018, 09:02 AM
TS Flightlines TS Flightlines is offline
 
Join Date: Apr 2010
Location: Ridgeland, SC
Posts: 2,110
Default

Alain---as with most of these issues, its generally an instrumentation/sender/wiring connection issue. You are taking fuel pressure and converting it to an electronic signal so the EFIS can read it. As we ask most of our clients that ask us about this, we ask them How do they KNOW its a real pressure issue, or instrumentation? We have them plumb in a mechanical pressure gauge along with the electrical sender to read BOTH gauges at the same time.
If they read the same, then obviously there is a real delivery issue. If the mechanical gauge reads normal pressure, then suspect the sender or the connections. It may take some extra time and effort to verify, but sure beats banging your head against the wall when you spend a bunch of $$ on a new pump or other components and find that you have the same problem.
Test---dont guess.

Tom
__________________
Tom Swearengen, TS Flightlines LLC
Teflon Hose Assemblies for Experimentals
Proud Vendor for RV1, Donator to VAF
RV7 Tail Kit Completed, Fuse started-Pay as I go Plan
Ridgeland, SC
www.tsflightlines.com
Reply With Quote
  #3  
Old 07-04-2018, 09:46 AM
AirbusPilot AirbusPilot is offline
 
Join Date: Jul 2007
Location: Santiago, Chile
Posts: 446
Default

Quote:
Originally Posted by High_Flyer View Post
Hi,

I have a RV-7 with a Aerosport IO-375-M1S engine.
Lately I noticed that my fuel pressure drops erratically when above about 8-9000 Ft. I saw as low as 10 Psi. When I switch the boost pump on fuel press goes back to normal, boost pump off fuel press drops again erratically.
This happens much frequently on hot days...
Here is a graph of the fuel press agains Pressure alt:


The positive peaks are when switching the boost pump on.

I suspect vapor lock, but I'd like more opinion.
What could be done to avoid this?

Thanks,
Alain.
i have been flying my RV-8 for almost 9 years and I got same indications as yours, pretty sure is vapor lock. Anyway I stoped turning on the electrical pump every time the pressure drops, specially because I have enough altitude when this happens, but I always have an eye over fuel pressure during cruise
__________________
Fernando Abasolo
Santiago Chile
SubSonex waiting for tailkit to arrive
Flying phase II RV-8 (SCSE) Serial Number 83290, Tail Number CC-AJC
Flying RV-8 (SCTB) Phase II 600 hours and counting since February 22nd 2010
Serial Number 82727, Tail Number CC-PXG
Lyc. IO-360, Hartzell Prop
VAF #2056
EAA Member 774981
Reply With Quote
  #4  
Old 07-05-2018, 10:24 AM
High_Flyer's Avatar
High_Flyer High_Flyer is offline
 
Join Date: Sep 2010
Location: Saint-Jorioz, France.
Posts: 189
Default

Thanks for the replies.

Quote:
Originally Posted by TS Flightlines View Post
Alain---as with most of these issues, its generally an instrumentation/sender/wiring connection issue. You are taking fuel pressure and converting it to an electronic signal so the EFIS can read it. As we ask most of our clients that ask us about this, we ask them How do they KNOW its a real pressure issue, or instrumentation? We have them plumb in a mechanical pressure gauge along with the electrical sender to read BOTH gauges at the same time.
If they read the same, then obviously there is a real delivery issue. If the mechanical gauge reads normal pressure, then suspect the sender or the connections. It may take some extra time and effort to verify, but sure beats banging your head against the wall when you spend a bunch of $$ on a new pump or other components and find that you have the same problem.
Test---dont guess.

Tom
I don't think it's only an indication/sensor problem because on the most extreme fuel pressure drops, which is not in the graph I posted here, the engine RPM drops slightly as well, and the EGT/CHT also changes (less fuel flow), and as soon as I siwtch the boost pump ON everything, including the indication, gets back to normal.

As with AirbusPilot another RV-8 owner here in France told me he has the same problem above 5000 Ft, although much worse than me with his engine almost quitting when the fuel pressure drops... Boost pump ON and all back to normal.

I'll keep monitoring and troubleshooting. Maybe if gets worse I'll do the mechanical pressure gage test.

Thanks
__________________
Location: France
RV7 (F-PRVZ), Tip Up, Aerosport IO-375, Dynon Skyview, VP-X, Day VFR.

Flying since June 2017.
Reply With Quote
  #5  
Old 07-05-2018, 11:25 AM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 629
Default Fuel System Restrictions

Quote:
Originally Posted by High_Flyer View Post
Thanks for the replies.



I don't think it's only an indication/sensor problem because on the most extreme fuel pressure drops, which is not in the graph I posted here, the engine RPM drops slightly as well, and the EGT/CHT also changes (less fuel flow), and as soon as I siwtch the boost pump ON everything, including the indication, gets back to normal.

As with AirbusPilot another RV-8 owner here in France told me he has the same problem above 5000 Ft, although much worse than me with his engine almost quitting when the fuel pressure drops... Boost pump ON and all back to normal.

I'll keep monitoring and troubleshooting. Maybe if gets worse I'll do the mechanical pressure gage test.

Thanks
There are a number of things that could contribute to this behavior. If you can answer several questions below, it might help identify the root cause and possible solutions.

1. What kind of fuel are you using?
2. Do you have a fuel flow meter in your system, and if so where is it located in relation to the mechanical and electric fuel pumps?
3. Are your fuel lines insulated and protected from exhaust manifold heat?
4. Do you have a cooling shroud on your mechanical fuel pump?
5. Have you checked for evidence of very small leaks upstream of the mechanical fuel pump (these can draw in small amounts of air when the engine is running)?

Skylor
RV-8
Reply With Quote
  #6  
Old 07-05-2018, 01:27 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 4,258
Default

Check you fuel filters - if you have one partially plugged up, this behavior will get worse.
__________________
Greg Niehues - VAF 2018 dues paid
Garden City, TX
N16GN flying! http://websites.expercraft.com/airguy/
Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 03:06 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.