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Fuel flow or other problem?

T

tomagin

Active Member
I now have 6.5 hours flying my RV-8. The engine is an XIO-360M1B with the silverhawk fuel injection servo.

The fuel system is per plans --- tank to selector, through gear tower to the filter [mounted vertically on the tower on the firewall side], to the airflow performance pump then thru the firewall, the flow transducer and on to the servo.

The vertical fuel filter is not unique to my installation but probably most have it laying on the floor ahead of the selector valve. I am suspicious of this being a possible cause of the symptom.

I cold start the engine as follows:

Mixture rich
Throttle full
2 seconds of prime with the elec pump then pump off
Throttle cracked
mags on [LASAR ignition]
crank the starter and it usually fires in a blade or two.

It runs perfectly for 5-10 seconds and then just about quits --- semingly for lack of fuel ---- and then picks up and runs normally.

If I kick on the elec pump just after it starts it minimizes this. Hot starts can have a similar dead spot but some vapor lock is more likely.

Once it's running everything is normal with just the engine driven pump. In flight the fuel pressure is solid at 29 psi with the mech pump. Runs perfect.

Question: Anyone else have this happen? I have thought maybe the vertical filter drains after shutdown and creates a dead spot that needs to be filled before the fuel flow stabilizes. There is no eveidence of fuel leaks or conversely air leaks and it doesn't matter which fuel tank.
 
tomagin said:
I now have 6.5 hours flying my RV-8. The engine is an XIO-360M1B with the silverhawk fuel injection servo.

The fuel system is per plans --- tank to selector, through gear tower to the filter [mounted vertically on the tower on the firewall side], to the airflow performance pump then thru the firewall, the flow transducer and on to the servo.

The vertical fuel filter is not unique to my installation but probably most have it laying on the floor ahead of the selector valve. I am suspicious of this being a possible cause of the symptom.

I cold start the engine as follows:

Mixture rich
Throttle full
2 seconds of prime with the elec pump then pump off
Throttle cracked
mags on [LASAR ignition]
crank the starter and it usually fires in a blade or two.

It runs perfectly for 5-10 seconds and then just about quits --- semingly for lack of fuel ---- and then picks up and runs normally.

If I kick on the elec pump just after it starts it minimizes this. Hot starts can have a similar dead spot but some vapor lock is more likely.

Once it's running everything is normal with just the engine driven pump. In flight the fuel pressure is solid at 29 psi with the mech pump. Runs perfect.

Question: Anyone else have this happen? I have thought maybe the vertical filter drains after shutdown and creates a dead spot that needs to be filled before the fuel flow stabilizes. There is no eveidence of fuel leaks or conversely air leaks and it doesn't matter which fuel tank.
Click to expand...

I would try running the electric fuel pump longer than 2 seconds....What is your fuel pressure, before cranking engine, after shutting off fuel pump?
 
Hi Tom.

We have an almost identical set-up except that I am using an Andair gascolator as the fuel filter - tho it is on the forward side of the left gear tower, same place as your filter. My engine is a Superior IO-360 with Silver Hawk fuel servo. Pump is the AFP pump supplied by Vans.

I initially used 5 seconds of prime and the engine did not always start - I now use 8 seconds and there are no problems. Fuel pressure post-prime, before cranking the engine is 30psi.

Apart from this issue, are you having fun?

Chris

RV-8 G-GIGZ flying
 
Purge the vapor

With the Silverhawk fuel injection system there is no vapor return. So on a restart the vapor that is in the engine driven pump, hoses, fuel control, etc. must be purged out. The only place for the vapor to go is through the fuel system and into the engine. So even on a cold start the vapor must be displaced from the previous hot shut down. A longer prime period may help. But without a way to purge the vapor from the system is, you just have to deal with it, that is unless you want to install a purge valve.:)

Don
 
What Prop?

Just a curious side note, my similar set up does the same as does one of my neighbors, but only on a hot start. Cold starts fire right up. However on a hot start mine still catches as it winds down and usually I do not have to crank again. My neighbor has to always crank twice. The difference we noticed and assumed is that his composite light weight prop and my heavy Hartzell make enough momentum difference that the extra blade or two that mine makes is just enough to catch where his does not.
This is a total assumption but seems to make sense.
 
I keep the pump on for a count of 5 for a cold start, then turn it off, return throttle to idle and then start the engine. Seems to work good.
 
On our flying club's two 2002 C-172SP's (IO-360) there is no primer pump, and the Cessna checklist has you turn on the electric fuel pump then apply just enough mixture to have the fuel flow guage show some fuel flow, then back to idle-cutoff. If your problem is low fuel in your filter, this might ensure that your lines are full. Here is an excerpt (I don't know if this works for Silverhawk):

9. Master Switch (ALT & BAT) .............ON
Prime Engine (omit if engine is warm)
10. Throttle.................................OPEN (IN)
11. Fuel Pump .......................................ON
12. Mixture ................................FULL RICH
until stable fuel flow is indicated (3 to 5
seconds), then set to LEAN CUTOFF
13. Fuel Pump .....................................OFF
14. Throttle..........CLOSE THEN ?? OPEN
15. Propeller Area........................... CLEAR
16. Ignition Switch........................... START
17. Mixture ...... ADVANCE as engine starts
NOTE: If engine is primed too much
(flooded), place the mixture control in the
LEAN CUTOFF position, open the throttle
halfway, and engage the starter. When the
engine starts, advance the mixture to
appropriate setting for smooth engine
running and retard the throttle promptly.
18. Throttle................................. 1000 RPM
 
thanks for the various replies!

I now have 19 hours on the engine. As some of you have suggested I am priming it a bit more for both cold and hot starts. I usually flip the fuel pump on after it starts and this help minimize any vapor lock effect.

Other than getting used to the starting cold and at various invervals after shutdown the engine runs great. I have LASAR ignition which so far I'm happy with --- if a mag or controller goes in the near future I trash it as it is now too expensive to fix given the other options. It does make it start easier.

Fuel pressure sometimes dips to16-17psi after starting if I don't come in with the electric pump. Once the lines are full of fuel it is rock solid on the mechanical pump at 29 psi. With the electric pump it settles at 31psi.

As many of you know "the grin" only gets bigger with each flight!
 
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