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  #11  
Old 12-08-2017, 07:17 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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Maybe your pressure sensor is bad. Try changing it out.
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  #12  
Old 12-08-2017, 07:35 PM
RFSchaller RFSchaller is offline
 
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I may have misunderstood your last post. Was the drop in pressure present on the mechanical gage too? Have you tried disconnecting all the hoses and blowing them out with air? Any chance the red cube is plugged?
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  #13  
Old 12-09-2017, 09:19 AM
Mich48041 Mich48041 is offline
 
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Electrical fuel pressure sensors are notoriously inaccurate. Mechanical gauges can not be trusted either unless their accuracy has been verified. To check the accuracy of the mechanical gauge, remove it from the airplane and attach clear plastic tubing about 10 feet long. Fill the tubing with water so that the water level is 83.2 inches above the gauge input port. The gauge should read exactly 3 psi.
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  #14  
Old 12-09-2017, 09:45 AM
TS Flightlines TS Flightlines is offline
 
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Rich;
"Put a mechanical gauge in place of psi sensor".
I'm seeing that Ric put the gauge in place of the sender, and not in conjuction with it. Was showing the same 1psi result as what his Dynon was showing. SURE---having the gauge plumbed with a tee just before the sender would allow you to read BOTH the mechanical gauge and the Dynon from the same source to compare the readings. My FLAWED LOGIC says that if they are different with the gauge being higher and possibly more correct, then a faulty sender is a good candidate.
If they read the same, then check the hose and the source location.
If necessary, check it at the pump discharge port to verify the pressures.
IF the pressure is 'normal' at the pump, then there is some sort of anomaly between the pump, through the system to the gauge/sender location where you originally take the pressure readings. If the pump pressure is also low, then check the supply from the gascolator to the pump.
It is NOT beyond the realm of possibility that the supply hoses 'could' be partially collapsing under the suction of the pump, IF they are the rubber hose, and IF the pumps suction is sufficient enough to develop enough force to partially collapse the hose.

Ric didnt say whether or not his test was WITH the boost pump running or not. Since the plans call for the pump to be running all the time, I would assume his test was with the boost pump on. So--again FLAWED LOGIC, you would think that IF the boost pump were producing proper discharge pressure, then the fuel pressure supplied to the mechanical pump would be 2.5-5 psi ( or whatever it is). IF it is NOT ( as measured at the supply port of the mechanical pump) then obviously there is an issue with the supply system. Tank, tank vent, cabin lines, boost pump, flow transducer, gascolator, supply hose. Easiest test would be to open the fuel cap and create a large vent. Rerun the test and see if anything changes. IF everything operates normally, then FLAWED LOGIC would tell me to look at the vent system, and repair/update as necessary and retest.
IF the vent test yielded the same low pressure results, then there is something in the supply side.

IF the measured pressure was with the boost pump OFF----then recheck it with pump ON and see if the pressure rises. IF it doesnt, then check the boost pump pressure. Just because it may be running, doesnt mean it's producing the necessary pressure.

By systematically point by point testing and restesting you will find the problem. YES its time consuming but much less expensive than guessing and throwing a bunch of parts at this and seeing if that fixes the problem. Doing so may in fact 'fix' the problem for a while, but if you havent found the actual culprit, then it will occur again.

OH----I mentioned the rubber hose collapsing under suction. I dont KNOW that this is occurring. I DO KNOW that once in years past it occurred in an automotive application, where the rubber hose looked fine, until you took it off and looked through it. Guy was supposedly street racing and mixing octane booster and it literally eroded the liner to the point where the nylon braid was beginning to show. YEP===lots of debris in the filter. He thought it was bad fuel.

So---sorry for the long explanation, but troubleshooting this shouldnt be as difficult as it seems. YES, by all means, its a pain, and painstaking.

Tom
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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
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  #15  
Old 12-09-2017, 02:04 PM
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Phantom30 Phantom30 is offline
 
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Quote:
Originally Posted by RFSchaller View Post
I may have misunderstood your last post. Was the drop in pressure present on the mechanical gage too? Have you tried disconnecting all the hoses and blowing them out with air? Any chance the red cube is plugged?
Rich....unless iím Completely out to lunch, the flow test @ feed to engine MECH pump which measured @ 1/2 gal=90 secs....which equals 20 gals/hour flow; eliminates issues to that point.

The MECH psi gauge showed same as electrical sensor (just wanted to varify readings).
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Search and Destroy (Can
Tho RVN)
Distinguished Flying Cross Society Member
CH-47 & UH-1H "Driver"
Rotax 9 Series Service IRMT

RV-12 Kit#729 "N312RD" is now a full functioning fun machine!! Thanks Van for fulfilling my dream😎
2018 Dues Paid
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  #16  
Old 12-09-2017, 03:50 PM
Mich48041 Mich48041 is offline
 
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Fuel pressure from the electric pump is dependent on restrictions to flow. Not much restriction results in not much pressure, even though the flow rate might be 30 gallons per hour. The pressure out from the engine driven fuel pump is dependent on the internal spring. If that spring is weak, then pressure will be low. Not saying that is the problem, just explaining how it works.
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  #17  
Old 12-09-2017, 08:31 PM
RFSchaller RFSchaller is offline
 
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Not to steal his thunder, but today at the airport I met a friend who was working on the problem with Ric. The mechanical fuel pump outlet fitting was obstructed by what looked to be shredded plastic or rubber. I suggested taking apart the old fuel pump and seeing if the diaphragm is intact. I hope Ric makes a report to Vanís or ROTAX. Iíd hate to think there is a bad batch of fuel pumps in the fleet.
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  #18  
Old 12-09-2017, 09:32 PM
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Phantom30 Phantom30 is offline
 
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Quote:
Originally Posted by RFSchaller View Post
Not to steal his thunder, but today at the airport I met a friend who was working on the problem with Ric. The mechanical fuel pump outlet fitting was obstructed by what looked to be shredded plastic or rubber. I suggested taking apart the old fuel pump and seeing if the diaphragm is intact. I hope Ric makes a report to Van’s or ROTAX. I’d hate to think there is a bad batch of fuel pumps in the fleet.
Rich..thanks to Julian and Mark, problem found And “Miss Betty-Jeanne” is breaking the sound barrier again��. I am replacing fwf fuel lines/fittings with Aircraft Specalty’s set-up; also, will inspect the fuel pump and fuel lines to find out what the heck the shavings are...really weird where and how they plugged the an fitting....really glad we kept the plane close to field once fuel pressure started acting squirrely. Could have caused an off field landing.

Edit: Findings will be reported to Van’s; and if fuel pump is cause, full reporting to Rotax thru official channels.
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Ric Dickison
307 (CAB) Phantom
Search and Destroy (Can
Tho RVN)
Distinguished Flying Cross Society Member
CH-47 & UH-1H "Driver"
Rotax 9 Series Service IRMT

RV-12 Kit#729 "N312RD" is now a full functioning fun machine!! Thanks Van for fulfilling my dream😎
2018 Dues Paid

Last edited by Phantom30 : 12-09-2017 at 09:37 PM.
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  #19  
Old 12-09-2017, 10:19 PM
RFSchaller RFSchaller is offline
 
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Ric,

Glad you found the problem. The pics Julian showed me were scary. Looked like almost total blockage.

I have the TS Flightlines after market fuel system. If you want to drop by the hangar and take a look before installing drop me a PM. The TS Flightlines instructions are very good, but it never hurts to see one in place.

Rich
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  #20  
Old 12-10-2017, 06:54 AM
TS Flightlines TS Flightlines is offline
 
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NOTE---Since Steve at Aircraft Specialty and I worked on this project together, the hose packages are the same. So if you purchase it from Aircraft Specialty, or TS Flightlines, you are getting the same kit. Believe me its AWESOME to be working with a partner company, than to do it alone. Sharing of data is good for ALL of us!!
Tom
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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
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