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  #1  
Old 10-30-2020, 09:54 AM
f14av8r's Avatar
f14av8r f14av8r is offline
 
Join Date: Apr 2012
Location: Tampa (Wimauma actually)
Posts: 433
Default Fuel Pressure unreliable

Hello All,
Looking for some help troubleshooting a fuel pressure issue. My RV-8 has an IO-360 being monitored by my EFIS, an Advanced Flight Systems 3400s with the AF-3400 Engine Monitor Package AF-3400-EM-4.

I acquired the airplane in May of 2019. The fuel pressure readout has been a constant issue and I'm trying to focus on getting it fixed.

Here's the problem. The fuel pressure reading is accurate and reliable when I'm running just the engine driven pump, or just the boost pump (on the ground obviously) but when I have both operating, such as for takeoff and landing, the fuel pressure readout goes haywire. It runs into the triple digits, then back down to zero and, eventually, the indication gets XXXed out.

I have the standard VDO sensor installed. I've replaced the sensor. No difference. I've checked the wiring. All good. I've checked the EMS setup. All good. I've checked that the reducer is installed in the line from the pump to the sensor manifold.

I'm considering replacing the VDO with the AFS/Dynon Kavlico pressure sensor. I would have already tried this but it the Kavlico requires +5v which I'll have to run from the EMS. That's a lot of work and the opportunity for maintenance induced failures are always high anytime one starts mucking around behind the panel!

What other troubleshooting steps would you take? Any thoughts / ideas much appreciated.

Thanks,
Randy
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Tampa (Wimauma), Florida
RV-4 N212CS (sold)
RV-8 N184RK (flying)
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  #2  
Old 10-30-2020, 10:30 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by f14av8r View Post
What other troubleshooting steps would you take? Any thoughts / ideas much appreciated.

Thanks,
Randy
Be sure that the FP line to the sender is coming from a point downstream of the engine fuel pump. I wouldn't be surprised to see this behavior if plumbed between the two pumps.

Larry
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  #3  
Old 10-30-2020, 10:40 AM
Ralph Inkster Ralph Inkster is offline
 
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Location: Calgary, Alberta
Posts: 1,244
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My first thought too. But I can't imagine getting a mechanical pressure (normal engine running without boost) reading if the sender feed is before it.

Can you describe where the press sensor is mounted & where the line is T'd into the main fuel line?
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Last edited by Ralph Inkster : 10-30-2020 at 10:43 AM.
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  #4  
Old 10-30-2020, 10:41 AM
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f14av8r f14av8r is offline
 
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Hi guys, the sender line is coming directly off of the engine driven pump, straight to the manifold.
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Tampa (Wimauma), Florida
RV-4 N212CS (sold)
RV-8 N184RK (flying)
Flying an A320 to pay the bills
Exempt and gladly donating anyway - Current through March 2025
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  #5  
Old 10-30-2020, 10:46 AM
Ralph Inkster Ralph Inkster is offline
 
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Through a -03 line about 18" long?

Also review what sensor profile is used in the EFIS setup.
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  #6  
Old 10-31-2020, 03:59 AM
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f14av8r f14av8r is offline
 
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Quote:
Originally Posted by Ralph Inkster View Post
Through a -03 line about 18" long?

Also review what sensor profile is used in the EFIS setup.
Hi Ralph,
Yes, that's the line. And, I have reviewed the EFIS setup and it is correct. I even tried other settings to see if that made a difference. Using other settings did not produce acceptable results, even when the pumps were running individually - wrong sensor type.
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Tampa (Wimauma), Florida
RV-4 N212CS (sold)
RV-8 N184RK (flying)
Flying an A320 to pay the bills
Exempt and gladly donating anyway - Current through March 2025
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  #7  
Old 10-31-2020, 04:42 AM
74-07 74-07 is online now
 
Join Date: Dec 2016
Location: Greenville, SC
Posts: 550
Default Fuel Pressure

Is the boost pump the AFP boost pump type setup? Are the fuel lines run as depicted in the plans? I'm asking because our recently acquired 8 (built around the same time) had a non-standard boost pump/fuel line/check valve system that produced weird pump pressure readouts and had other operational characteristics that I didn't like at all. In doing some research, I discovered that there was apparently a magazine article published in the early 2000s that described this "low cost" alternative and several were built and flown this way. Once we got ours home, it all came out and the airplane is now plumbed and pumped according to plans. All is good. I know it's a long shot but thought I'd mention it.

Last edited by 74-07 : 10-31-2020 at 04:46 AM.
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  #8  
Old 10-31-2020, 05:20 AM
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f14av8r f14av8r is offline
 
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Quote:
Originally Posted by 74-07 View Post
Is the boost pump the AFP boost pump type setup? Are the fuel lines run as depicted in the plans? I'm asking because our recently acquired 8 (built around the same time) had a non-standard boost pump/fuel line/check valve system that produced weird pump pressure readouts and had other operational characteristics that I didn't like at all. In doing some research, I discovered that there was apparently a magazine article published in the early 2000s that described this "low cost" alternative and several were built and flown this way. Once we got ours home, it all came out and the airplane is now plumbed and pumped according to plans. All is good. I know it's a long shot but thought I'd mention it.
Were your pressure readings weird all the time, or like my case, only when BOTH pumps were running?
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Randy King
Tampa (Wimauma), Florida
RV-4 N212CS (sold)
RV-8 N184RK (flying)
Flying an A320 to pay the bills
Exempt and gladly donating anyway - Current through March 2025
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  #9  
Old 10-31-2020, 06:54 AM
74-07 74-07 is online now
 
Join Date: Dec 2016
Location: Greenville, SC
Posts: 550
Default Fuel pressure

Randy,

Rather than suggesting I had the exact same problem, I was really suggesting that any deviation from the standard install can introduce both indication problems and operational issues.

In our case, I noticed on the first pre-buy run that there was no pressure indication with just the boost pump on. We knew it had a non-standard boost pump install so we checked the pump pressure later and it was working so we figured it was an indication problem. Got it home and dove into it. It had essentially two firewall forward fuel delivery systems from the firewall penetration. It had one line that went to the mechanical pump and then to the throttle body AND another line that went to the Holley pump then to the throttle body. The two systems were separated by one-way check valves. The fuel pressure was taken only from the mechanical side SO you never, ever knew if the boost pump was really working. We ripped it all out, installed a new AFP pump IAW the current drawings, installed new T&S fuel lines and fittings, put everything back the way it should be and all works perfect now.

So, I was only suggesting that you get the drawings and go through everything and make certain you are starting your investigation from a known point. You may just find a surprise somewhere!
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  #10  
Old 10-31-2020, 10:42 AM
TS Flightlines TS Flightlines is offline
 
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Location: Ridgeland, SC
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Randy, you are getting the variation only when the boost pump is on? And it goes haywire? Quite probably an electrical ground. A couple of things:
1) how long, has this been going on; anything changed that brought this on?
2) have you verified the fuel pressure with a mechanical gauge?

Since things seem to be fine in ground tests, I feel that there is an electrical issue, maybe ground, maybe power at the sender. MIght also be that in flight there is enough movement in the pressure manifold to distrupt any additional grounding of the sender. Try this---short piece of grouning wire, clamped to the sender, and terminated on one of the mounting bolts on the pressure manifold. Probably a long shot, and its probably a sender issue itself, but worth the 10 minutes to find out.

UH---any other electrical anomalies in flight?
Tom
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