EIS bizarre fuel readings

I have an EIS 4000 and standard floats in the wings. I have checked the resistance with a volt/ohmeter and each float moves correctly between 240 and 30 ohms when adding fuel, one gallon at a time. On one tank, it stops at 30 ohms with 17 gallons in the tank (float is at the top of its travel and 4 more gallons simply won't appear on the gauge) and on the other side this occurs at 16 gallons. Fine. As expected. No problemo...

But...

When I look at the EIS instrument fuel levels and the Horizon EFIS fuel levels, when I start pumping fuel out of the full tank, using the boost pump with the main fuel line disconnected at the fuel servo and pumping into the other tank, the fuel level on the gauge starts dropping IMMEDIATELY! As in, within 1/2 gallon from the top of the tank! This is after verifying that the float doesn't move until either 4 or 5 gallons are drained...

I have verified that there is a good ground path between the float sender and the surrounding tank by reading a dead short on the volt/ohmeter. I have done this with a battery charger both on and off the battery (worried about dipping voltage while running the pump for 20 minutes at a time). Checked the wiring from sender to the pin that goes in the EIS. And finally, got a loaner unit from Grand Rapids to compare. Both units do the same thing.

Other ideas? I'm soooo close I can taste it but don't want to start rushing things now.

Jeremy Constant

There are two ways fuel is displayed on the GRT EFIS on the engine page.

There is a set of bar graphs (one per tank) that reads the floats and displays that data. There is a translation table (in the EFIS engine page setup) for the float value vs. actual level to account for the wing dihedral.

There is also a fuel flow bar graph which is independent of the others and uses fuel flow to compute the fuel used/remaining. There is an EIS parameter called FloCal that you have to adjust to calibrate.

Bob
RV-10 N442PM

tank levels indications...

drop on both the left hand set (left/right) on the EFIS, but more importantly on the EIS itself. As I understand it the EIS is only reading the resistance from the senders and then applying the scale factor and offset that has been adjusted in the calibration stage, in addition to the settings for decimal or integer and the +/- setting. Interestingly, in my set up session, the +/- setting changed the indication from full = 66 gallons to full = the correct 18 gallons. It did not reverse the sensing as I expected...but I digress.

I've been doing the set-up based on the EIS readings, and just glancing at the EFIS to see what I would need to be changing once I got the EIS set up.
I will look into the flocal setting, but the fuel flow readings on the eis and efis are dead bang on the money!

Thanks for the response...any other ideas

Jeremy

The setting is "-" and you have to re-do calibration numbers after changing that... so just write 'em down (every 2 gal is fine)

Worst case, just post the numbers you wrote down (after you had it in correct direction) and we can maybe see if there's something wrong with them or help you come up with the AuxSF and AuxOff

PS I find it hard to belive you can get that float to indicate as high as 17 gal on an 18-gal tank. I have a 21-gal tank and they stop right at 16...

update tomorrow with numbers

I'll get to the hangar tommorow and try a coupla things. If it doesn't work, I'll post the numbers and settings I'm using and tap the brain trust here...

Thanks

Jeremy

Are you looking at fuel tank level or at total fuel remaining? The former uses float sender signals and the later is calculated from the fuel on board and the fuel flow sensor.

On my RV-8 the EIS does not show any fuel level decrease until about 5.5 gallons has been burned off.

no explanation, but

on the advice of others in the hangar who were scratching their heads, they suggested that I simply use scale factors and offsets based on 21 gallons readable in each tank. Did it and sure enough, they each read just above 21 gallons and started decreasing within 1 gallon of draining! One stopped at 2 gallons when empty, the other at -1, so a little tweaking to go, but much closer.

I have NO IDEA how it's possible to show decreasing fuel levels when the floats aren't moving but they do. I've now attached independent ground wires to the float bases, going to my single point ground, to eliminate the possibility of some kind of ground loop phenomenon. The only thing is if there is some sort of interconnect between fuel flow and float readings, but it still would not explain how, based on fuel flow, it knows WHICH TANK it's draining from. (Would be a cool feature though...set the floats up to read correctly fom where they start moving and set the fuel flow to show decreasing level in each tank from full until the floats take over and then read the floats levels)

This morning I will drain the tanks through the sump, rather than pumping through the fuel flow transucer and check to see what happens. I'll report back....

Jeremy

sorry Bubblehead...

didn't see your response...
No, I'm reading the levels from each tank on the EIS. I'm only using the totalizer to determine how close I am to running the tank dry and to compare indicated levels remaining with the amounts of fuel pumped. The totalizer is wonderfully accurate.

Just to clarify my first post, the very first thing I did to begin the troubleshooting process was disconect the sender wire from the sender, put a volt/ohmeter into the hole for the sender wire screw, put the other lead to the skin of the fueselage, add fuel in measured 1 gallon increments and measure the float sender resistance readings. My big fear was that I had installed the floats incorrectly and was going to have to rip into 2 beautifully sealed tanks. It turns out that the floats, based on their resistances, were behaving exactly as we all expect...starts to show a change in resistance from 1 gallon from empty and on one tank stops changing at 15 gallons and on the other 17. The good news is I don't have to rip open my tanks. The bad news is I STILL don't understand what's going on, even if the readings are now "right-ish". (new word for Stephen Colbert!)

I've now spend a week trying to get this right. I'll be calling GRT today but is this one of those things that won't hurt anything if I leave it, or am I rushing when I really should chase this down? Builder fatigue is setting in.

Jeremy

No problem Jeremy. The questions I asked were basic and I was pretty sure you had them covered.

I agree that the totalizer is the best thing ever to come along. I don't even pay much attention to the fuel levels anymore. I just use them as a backup and a double check.

I'll be interested to hear what else you learn on this issue. I'm still learning about the EIS but it sure is a lot better than the old round gages that used to be in my plane.

One last question that you may have already covered. Is your plane a "A" model or a taildragger?

success!

Well, after WAY too many hours we got it. It was a combination of things wrong, starting with needing to attach redundant grounds going to my single point ground, the offset numbers needing to be tweeked BEFORE the scale factors get monkeyed with, the offset numbers needing to be adjusted in a very different manner than GRT says, and finally, realizing that when switching between my EIS and the loaner EIS that GRT send, the fuel tank indications SWITCHED SIDES!

Ultimately, the numbers I got from GRT for offsets were in the 65 to 105 range, depending on how many gallons I wanted to indicate as full. The actually numbers that work are 795 and 827, so I suspect that there is a decimal/integer issue at work.

Thanks for the ideas and if anyone wants the actual numbers I'll try to remember to get them from the hangar, although I tried using other's numbers and between flailing with numbers, grounds and reversed tank indications, it is hard to tell how helpful other's numbers were...

Jeremy

It's an

A model. As the Brits say, I'm playing for the A team

With all the fuss people put up over the A model tip overs, it may be time to claim that "real men fly nose draggers"!

Jeremy