Fuel Pressure Issue

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rv6ejguy

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The VDO senders have caused multiple worries for the Subaru guys, figuring that had a FP issue and it was always a sender issue. I've seen at least 6 of them on one forum alone over about a 5 year period.
 

SVSUSteve

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Kyle Boatright said:
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.
A wise old A&P once told me: "Upgrades should be done because you got tired of replacing something and not because it nearly got you killed". If there is a well known problem with their senders- which it sounds like it is- and there's not an option to use another manufacturer's device nor is the company appearing to do anything about it other than selling replacements, it might be time to look at moving away from GRT.
 

kent Ashton

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Early in this thread you said you didn't think this was a ground-loop problem but you haven't described where the instrument and the sender are grounded. Unless they are on the same ground point, I would rewire them to the same ground point and see what happens. Instrument ground loops will cause some strange, variable indications that inexplicably change.
 

Kyle Boatright

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Early in this thread you said you didn't think this was a ground-loop problem but you haven't described where the instrument and the sender are grounded. Unless they are on the same ground point, I would rewire them to the same ground point and see what happens. Instrument ground loops will cause some strange, variable indications that inexplicably change.
All of the grounds in the aircraft (including the sender in question and the GRT EIS) go to a "forest of tabs" on the firewall. The exceptions are a handful of lights that are locally grounded.
 

Doug2233

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Hey Kyle,
It certainly sounds like an electrical problem to me. Please note I have not gone through all the suggestions here and at VAF so I may be duplicating.
I have the same EIS4000 on a Carbed O-320. Same aircraft too!
I recall the f/p sender uses the 4.8V output from the EIS and requires 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 boot pump on. Also try wiring a fixed resistor in place of the sensor (not sure of the value) and checking 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 sensor terminals (with the sensor completely disconnected from the electrical system) with a good multimeter with the engine running with and without the fuel boost pump.
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.
Good luck,

edit: I have just read through the posts here and on VAF 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? If so then this is the basis for my response.
Also, I should say I have had a failure with the VDO oil pressure gauge requiring replacement. No such problems with the fuel pressure transducer in 300 hours.
 
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Dan Thomas

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All of the grounds in the aircraft (including the sender in question and the GRT EIS) go to a "forest of tabs" on the firewall. The exceptions are a handful of lights that are locally grounded.
Standard practice is a max of four grounds per ground stud. Too many and you start getting some ground loops. AC43.13 has some good advice in Para. 11-186.
 

Dan Thomas

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All of the grounds in the aircraft (including the sender in question and the GRT EIS) go to a "forest of tabs" on the firewall. The exceptions are a handful of lights that are locally grounded.
Standard practice is a max of four grounds per ground stud. Too many and you start getting some ground loops or phony indications. AC43.13 has some good advice in Para. 11-186.
 

bmcj

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Standard practice is a max of four grounds per ground stud. Too many and you start getting some ground loops. AC43.13 has some good advice in Para. 11-186.
Standard practice is a max of four grounds per ground stud. Too many and you start getting some ground loops or phony indications. AC43.13 has some good advice in Para. 11-186.
Double post... I think you're caught in a ground loop time loop. ;)
 
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