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  #21  
Old 01-24-2016, 10:07 PM
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GLPalinkas GLPalinkas is offline
 
Join Date: Jan 2005
Location: Venice, Fl
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Kyle, thanks for the update. Seems like a very complex problem. I hope your new sender cures the problem.

Hopefully, someone else will chime in with ideas. I have none.
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  #22  
Old 01-25-2016, 08:21 AM
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DanH DanH is offline
 
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Location: 08A
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Quote:
Originally Posted by Kyle Boatright View Post

I suspect I have an intermittent measurement problem. Funny enough, if you look at GRT's online troubleshooting guide, it mentions that their VDO senders often fail and become erratic at 200-500 hours, particularly on carbureted engines.
Kyle, I have the VDO sender for fuel injection pressures, but it did indeed get funky at around 400 hours, over east Arkansas on the way home from Petit Jean 2014. The indication would drift downward in cruise from its typical 23 or so to 18, which would trip my alarm preset. The boost pump (an old-school AFP) would push it back up above 20.

I almost always check instrumentation first. In this case I pulled the sender, which is oriented nipple-up as you see in the photo....



....and holding it nipple-down, squirted the restricted liquid passage with a quick, gentle squirt from an air nozzle. The idea is to "milk" the internals without breaking them. Sure enough, the return spring pushed out some black gunk. After repeating a few times, I reinstalled the sender, and it was fine for another 115 hours.

Recently I've had the airplane grounded for an annual and some updates. After sitting about 6 weeks, I fired it up and right away got a low fuel pressure indication, about 14 psi. Again, the boost pump would bring it right up. So, I repeated the "clean-out and full range cycling" process with the air hose, and bingo, all is normal again.

I don't know if any of this will transfer to the low pressure VDO sender. Heck, I don't even know why it works, not in detail; I plan to cut the sender open the first time it does not respond to the air hose treatment. But, it might be an interesting experiment worth trying, in particular if you plan to ditch the old sender anyway...doesn't matter if you break it.
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  #23  
Old 01-25-2016, 09:25 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
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I did go ahead and order a new sender today. Should arrive later in the week for a quick replacement. Pulled the cowl (again) instead of eating lunch today, retorqued the prop, and put myself in good position for a quick return to service when the sender arrives.

It would be nice to find a more robust sensor that would work work with the GRT EFIS. I know I used a Rochester fuel pressure gauge for the first 10+ years, and never had a problem. I guess I need to dig through my stuff and see if I can find that old sender to see what it is and perhaps compare its resistance curve against the VDO unit.
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  #24  
Old 01-26-2016, 06:32 AM
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caryr caryr is offline
 
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Location: northwest georgia
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Kyle

I have replaced several of the VDO senders.

I have the GRT box also.

Last summer I relocated the transducer via flex hose to the engine mount rather than the engine itself.

I believe its a vibration problem that kills the transducers.

No problems since.
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  #25  
Old 01-26-2016, 06:35 AM
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caryr caryr is offline
 
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Oh .. another thing.

The packaging it rather funny on the sender unit when you get it.

something to the effect " Do not use on any airplane, ever"

The product is not intended for any use and should not be used for that purpose.
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  #26  
Old 01-28-2016, 01:23 PM
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Doug Doug is offline
 
Join Date: Dec 2005
Location: Sydney, Australia
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Kyle,
I have the same EIS4000.

I have just read through the posts here and on HA and I am a little confused with the mechanical fuel gauge measurement agreement with the EIS. Did the mechanical gauge read 5-6psi with the boost pump on and off during an engine run unlike the EIS? If so it certainly seems like an electrical issue.

Recall the f/p sender uses the 4.8V output from the EIS plus a series resistor. More than normal possible failure points.

May I suggest disconnecting the sender and checking the voltage on the ring terminal for 4.8V with and without the fuel boost pump on.

Also try wiring a fixed resistor in place of the sensor (not sure of the value) again check with the fuel pump on and off. This will at least zero in on the wiring.

You might also want to measure the resistance across the transducer terminals (with the sensor completely disconnected from the electrical system) using a good multimeter under similar conditions.

I can't think of how the boost pump on/off would alter the reading other than if the sensor supply wiring (4.8V) was shorted to the pump supply somehow. I do think a faulty sensor is a long shot, but I have had my own VDO sensor failure.

Good Luck,
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  #27  
Old 03-05-2016, 06:43 PM
Kyle Boatright Kyle Boatright is offline
 
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Location: Atlanta, GA
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The new sender didn't help things. I still had intermittent low fuel pressure readings. Only, they weren't intermittent - I finally noticed that pitch attitude (not climb or descent rate) was driving the pressure indication. Low pressure in a nose up attitude, normal pressure in other attitudes.

What could cause that? Differences in fuel "head" pressure due to the airplane's attitude! Yeah, I know, the math doesn't show much of a "head", but it certainly drove fuel pressure differences in my airplane.

So, I replaced the fuel pump a couple of weeks ago and have been flying around with my fingers crossed (and good fuel pressure) since then.

A hint from a different thread about using safety wire around the fuel pump plunger to put it in a bind so it would stay "up" while I replaced the fuel pump came in very handy. It only took an hour or so to remove some obstructions (fuel lines, breather, a piece of SCAT), pull the old pump, retract and bind the fuel pump plunger, and install the new pump. Even safetying the new one wasn't bad.

Thanks to all for the suggestions in the thread. Maybe it'll help someone in the future.
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  #28  
Old 03-06-2016, 07:49 AM
FLY6 FLY6 is offline
 
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Location: Burlington On. Ca
Posts: 151
Default Fuel Pump

Kyle, please keep us posted if anything changes. I was following your thread but it really got my attention when you mentioned GRT EIS 4000. Same one I have and I too am experiencing fuel pressure fluctuations. Mine started with the right tank only, would go to normal when I would switch tanks or turn on the boost pump. I suspected blockage in right tank plumbing. Made sure lines were clear all the way to boost pump. I have since got low readings on both tanks but they always come back up with the boost pump. Had them on ground and in air but never had any engine roughness. Have not found any material in lines or in my gascolator screen. I may try sender but don't see how it would not work for the mechanical pump yet does with the boost pump on. Like you I may be forced to go the expense of changing out the mechanical fuel pump. Thanks again for posting such details.
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  #29  
Old 11-12-2016, 06:41 PM
jay.pearlman jay.pearlman is offline
 
Join Date: Jan 2010
Location: Port Angeles WA
Posts: 250
Default Fuel pressure challenge

About 7 hours ago, I began to notice that the fuel pressure at times would oscillate between 24 and 28 psi with the engine mechanical pump. I have an IO360. The fuel flow seemed oK. I looked to see if the voltage or current was fluctuating and it did not. Today, the fuel pressure gauge was fine and then went off scale on the high side. I have a Dynon 180. The engine was running fine. I turned on the electric pump and the pressure came back to about 32 psi and no longer had a red indication on the Dynon. I turned the electric pump off and the gauge started to fluctuate again. repeated the same cycle again.
Is this a sender problem or a mechanical pump problem as the failure is a fluctuating reading and an intermittent very high pressure reading?
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