GRT EIS - Van's 60 PSI sensor

My fuel pressure sensor feeding my GRT EIS never has worked correctly. I discovered the builder incorrectly wired the 301 ohm resistor on the lead that is fed by 4.8v line from the EIS. I checked the wiring using the approach outlined in the EIS trouble shooting guide and based on that guide my sensor is now correctly wired up. Here is my problem.

GRT instructions for their HPS-02 (80 psi) sensor says the aux SF should be set at 91 and aux OFF at 15. Those settings gave me very bad fuel pressure readings (idle = 14, climb/ cruise 54-58 psi, decent -2 psi). I then tried the aux SF and OFF settings for the 150 psi sensor and the readings were even worse. When I bought the airplane the EIS settings for the fuel pressure sensor were SF=19 / OFF = 30. This gave me a good cruise fuel pressure reading of ~ 24 to 26 psi but really high psi readings at idle or when I pulled the power back.

Searching Aircraft Spruce for fuel pressure sensors I discovered they sell a 60 psi sensor and when I looked at the sensor instructions on line I noticed they were Van's instructions. This makes me think my installed sensor is the Van's 60 psi VDO sensor. Using the recommended GRT settings for the 80 and 150 psi sensor and extrapolating from them a reading for a 60 psi sensor I compute a SF = 51 and OFF = 11. I haven't tried these new settings yet because the airport where I'm hangared is a one hour drive.

My question is: does anyone else have a 60 psi sensor for fuel pressure setup with their GRT EIS? If so, what do you use use for aux SF and OFF settings? What psi readings do you normally see? (Assuming you also have a IO-360 with Airflow Performance injection.)

Tankerpilot75.

I have an IO-360 with AFP Fuel Injection and the GRT EIS. I am using the GRT HPS-SS-01 pressure sensor (0 to 100 psi). I set the AuxSF and Aux Offset to the GRT recommended values for integer display of fuel pressure. Initiallly, I tried using the decimal readout SF and Offset but didn't like have to mentally adjust the displayed reading by X10 to get the actual value.

My fuel pressure is steady during all phases of flight. From memory it is about 29 or 30 psi on the mechanical engine pump and increases to around 31 psi when the elec boost pump is on. I have the limits set at 14 psi min and 45 psi max.

If your considering getting a replacement pressure sensor I would recommend getting the GRT HPS-SS-01. Be advised that it does require using the 12Vdc excitation output of the EIS rather than the 4.8 Vdc that you currently have wired with your existing pressure sensor but you don't need the external reistor.

If you use a pressure sensor that GRT hasn't defined the AuxSF and Aux Offset for, you are on your own to calculate the AuxSF and Aux Offset for that specific sensor. There is a MSWord document on GRT_EFIS, Yahoo Groups that details how to go about calculating the parameters for a generic sensor. The name of the document is "EIS Aux Input Config.doc"

https://groups.yahoo.com/neo/groups/GRT_EFIS/files

Originally, I was the using GRT 0-80psi sender. At times it would become sporadic in reporting and would self correct. I've gone through 3 until I replaced it with the GRT HPS-SS-01. It's a much better designed sender. The 80psi membrane was prone to introducing erratic behavior due to its sensitivity & exposure.
It was worth the extra money.

Fuel Pressure Location

Tankerpilot75 said:

My fuel pressure sensor feeding my GRT EIS never has worked correctly. I discovered the builder incorrectly wired the 301 ohm resistor on the lead that is fed by 4.8v line from the EIS. I checked the wiring using the approach outlined in the EIS trouble shooting guide and based on that guide my sensor is now correctly wired up. Here is my problem.

GRT instructions for their HPS-02 (80 psi) sensor says the aux SF should be set at 91 and aux OFF at 15. Those settings gave me very bad fuel pressure readings (idle = 14, climb/ cruise 54-58 psi, decent -2 psi). I then tried the aux SF and OFF settings for the 150 psi sensor and the readings were even worse. When I bought the airplane the EIS settings for the fuel pressure sensor were SF=19 / OFF = 30. This gave me a good cruise fuel pressure reading of ~ 24 to 26 psi but really high psi readings at idle or when I pulled the power back.

Searching Aircraft Spruce for fuel pressure sensors I discovered they sell a 60 psi sensor and when I looked at the sensor instructions on line I noticed they were Van's instructions. This makes me think my installed sensor is the Van's 60 psi VDO sensor. Using the recommended GRT settings for the 80 and 150 psi sensor and extrapolating from them a reading for a 60 psi sensor I compute a SF = 51 and OFF = 11. I haven't tried these new settings yet because the airport where I'm hangared is a one hour drive.

My question is: does anyone else have a 60 psi sensor for fuel pressure setup with their GRT EIS? If so, what do you use use for aux SF and OFF settings? What psi readings do you normally see? (Assuming you also have a IO-360 with Airflow Performance injection.)

Click to expand...

So your post has me wondering where you are actually measuring the fuel pressure from. I have an IO-360 and I've found that my fuel pressure tends to be a fairly constant 24-26 psi regardless of the flight regime. I am using the deluxe 100 psi sender with my EIS and I verified the EIS readings against a mechanical pressure gauge and variable pressure source when I built the plane. Nevertheless, if you're measuring the fuel pressure at the mechanical pump outlet you should have pretty constant pressure readings even if the values are incorrect due to using the wrong Scale Factor (SF) and Offset (OFF) values for the sender. Also, since the VDO sender that you're using is a single wire sender, you need to verify that the body of the sender has a good electrical ground path.

Skylor
RV-8

First, I would suggest checking your sensor and installation. Remove it from the fuel system but keep it connected electrically to your EIS (signal and ground). Pressurize it and see what the reading on the EIS is. A easy way to pressurize is to use oxygen from a welding torch. With the regulator you can change the pressure and the torch will have a gauge on it. Be sure the sensor is grounded to the same ground as your EIS - the sensor uses the threads for a ground.

If the sensor is working and changes with the oxygen pressure but the calibration is wrong, it could be a SF, OFF setting. On the sensor there should be stamped numbers (usually on the wrench flats by the threads). Post them here and I will calculate SF and OFF for you. I wrote the document mentioned in post 2.

I fly a Rotax so I don't know much about IO-360, but Skylor's post has a good question, are you measuring the correct place?

Hope this helps.

Jim Butcher

h&jeuropa said:

First, I would suggest checking your sensor and installation. Remove it from the fuel system but keep it connected electrically to your EIS (signal and ground). Pressurize it and see what the reading on the EIS is. A easy way to pressurize is to use oxygen from a welding torch. With the regulator you can change the pressure and the torch will have a gauge on it.

Hope this helps.

Jim Butcher

Click to expand...

Oxygen? You can't be serious.

Never allow oil, grease or fuel to come into
contact with oxygen under pressure. Even a small amount of hydrocarbon can be hazardous in the presence of high oxygen concentrations. Any organic matter in contact with oxygen
under pressure could have a violent reaction.

I think regulated shop air with calibrated gage would be my choice.

Oops, you are correct Wayne. Do not use oxygen, use shop air.

Jim Butcher

I'm pig headed

h&jeuropa said:

First, I would suggest checking your sensor and installation. Remove it from the fuel system but keep it connected electrically to your EIS (signal and ground). Pressurize it and see what the reading on the EIS is. A easy way to pressurize is to use oxygen from a welding torch. With the regulator you can change the pressure and the torch will have a gauge on it. Be sure the sensor is grounded to the same ground as your EIS - the sensor uses the threads for a ground.

If the sensor is working and changes with the oxygen pressure but the calibration is wrong, it could be a SF, OFF setting. On the sensor there should be stamped numbers (usually on the wrench flats by the threads). Post them here and I will calculate SF and OFF for you. I wrote the document mentioned in post 2.

I fly a Rotax so I don't know much about IO-360, but Skylor's post has a good question, are you measuring the correct place?

Hope this helps.

Jim Butcher

Click to expand...

Jim,
The easy approach for me would be to just replace the "da-n" sensor with the HP-SS-O1. However since I've been living with this problem for almost two years as I've worked through a long list of "builder" issues it's become a bit of an obsession to try and figure out. I'm getting near the end of my "squawk list" so this sensor problem is a major milestone or "millstone" to figure out.

I will go to the airport either Monday or Tuesday and take the sensor off, try to do a pressure check using my air compressor, and identify the numbers on the thread nut. I will either pm you or post them here. I know the sensor does work because I've done enough work with it to figure that out. Now whether it's working correctly or not that is what I'm trying to identify.

I'm almost positive it's a non-standard VDO 60 psi sensor that was initially purchased by the builder from Van's. If that's correct, based upon other web searches I've done this week, the 0 psi ohm reading should be 10 ohms and the 60 psi reading 156 ohms. Maybe using this data you can compute a "trial" SF and OFF setting for me.

I really appreciate the VAF community for helping me on a number of issues over the last two years. Since I wasn't the builder and have never owned or built an aircraft before; this forum has been invaluable. I can honestly say I would now put my RV up against almost any out there and believe it would compare vary favorably.

That wasn't the situation when I bought it and had I gotten a better prebuy by a "knowledgeable inspector" and not been so enamored by the airplane's panel and paint job I'd had moved on to a different RV. But that's water under the bridge and now no longer the situation.

My advice to anyone looking to purchase a used RV is to get a "knowledgeable inspector" to evaluate the aircraft. That's not to say an RV with "squawks" shouldn't be bought but buyers should at least have a better idea of what their looking at so a "fair" price can be identified with all parties aware of significant defects. Caveat Emptor!

I've had a vdo 0-80psi sensor fail and the symptoms were a little weird. I have 2 electric fuel pumps and when running on pump 1 at normal power settings everything seemed fine, then at high power (full power climb) then sensor would jump from 35 to over 100 and fluctuate anywhere in between. When I switched to pump2 to the readings would stabilize again. Reading over 100 on an 80psi sender was not possible, and nothing noticeable in engine performance. This had me looking at my pumps, wiring, the resistor, actual fuel pressure with mechanical gauge, and the ESI settings.

After a while i would get sporadic readings no matter what pump or power settings I was using.

I replaced the sensor with a new one and everything is normal again. The initial settings from GRT for the SF and offset were close, but I used another gauge to fine tune the readings.

The documents from VDO specifically state that the sensors should not be used with fuel:
----
Warning Notice: VDO pressure senders are not to be used with any type of fuel application. VDO pressure senders may not be used in automotive braking systems. VDO pressure senders are not suitable for use in aircraft.
----
I have the other type (HPS-ss-01) that is installed, just not wired up. I'll start using that one as soon as the VDO fails again. I wonder if my use of 91 pump gas with ethanol caused its short useful life?

Hi Jim,

My VDO catalog doesn't list any 60 psi senders. There are lots of 100 psi and lots of 80 psi. If it is 80, and 1/8 npt, it should be stamped 29/4. If is 80 and 1/4 npt it should be stamped 29/8.

Lets assume it is 80 psi. The GRT datasheet is here: http://www.grtavionics.com/documents/EIS/VDO 80 and 150 Pressure Sender Aux Input.pdf

GRT assume you use the 4.8 volt output of the EIS and a 301 ohm resistor and I did my calculations assuming this too.

I calculate SF=76 and OFF=7 for that case. GRT specs SF=91 and OFF=15 and states that there will be 2-4 psi error over 40 psi.

If indeed your sensor is 10 ohm, 0 psi and 156 ohm, 60 psi, I calculate SF=103 and OFF= 15.

I hope this helps. Give it a try and post your results.

Jim Butcher

Thanks Jim

I will use your "trial" Aux settings and let you know. If they don't work I'll admit defeat and buy the HP-SS-01 sensor from GRT. This has been an interesting exercise in trouble shooting something relative simple (or so I thought) . I appreciate everyone's inputs and will post my results by mid week.

I accept defeat

Jim,

Today I went to the airport and tried four different EIS aux SF / OFF settings and even a few "wild idea" EIS settings. None worked. Ordered new sender (HPS-SS-01) from GRT. I appreciate everyone's input and thoughtful assistance.

Jim Harris

Jim,

Did you notice the numbers stamped on the sender?

You did try it using the 4.8 volt source from you EIS not 12 volt, correct?

Jim Butcher

Didn't pull cowling

Jim

I didn't pull the cowling today to better examine the sensor. Last week I did put on a Hobbs oil pressure switch and tried to look closely at the fuel pressure sensor when I was working in the area but my eyes couldn't read the number stamped on the sensor nut. The only way I was going to be able to get a better look would be to remove it and if I'm going to do that I'll replace it. Therefore I went ahead and ordered a new one.

Last week when I did my trouble shooting of the sensor I did re-wire the resistor placement and checked both the voltage and resistor values. They were as they should be (300 ohms, 4.8v).

Like I said earlier, I was pretty sure the sensor worked based on these earlier efforts but wasn't sure if it was working correctly. Now I'm pretty sure the senor is messed up and the best and longest lasting fix is to just replace it.

Based on what Eric at GRT said, and some other commentators, I'm pretty sure every avenue has been explored and it's now time to go with a better, more reliable sensor (HPS-SS-01).

I really appreciate your assistance.