Problem with JPI EDM930 fuel indications

[PilotDAR]

I completely lucked through a rather alarming event with a C182 project I'm flying these days. It includes a complete redo of the entire panel, with an STC'd JPI EDM930 among other avionics. This instrument includes primary (and only) fuel quantity indication, and fuel flow and totalizer information. It is brand new, installed in the aircraft by STC, and was programed correctly by an experience AME, in my presence.

I taxiied the plane for fuel, with about 3/8 fuel quantity indicating in each tank, which seemed about right for the flying I had previously done. No one else flies or runs the plane. I planned three hours of flying, so I specified 170 liters total between the two tanks, which was fuelled. The fuel as found was to be my reserve. (the nature of the flying did not permit a "fill r up"). After this fuelling, the qty indicated full on both tanks, and I thought to myself, I had goofed, and ordered too much fuel.

And no, before you correctly and wisely ask, I did not dip the tanks. It's a brand new fuel quantity indicating system, STC installed into that plane 33 flying hours ago, which had been checked, and appeared to be operating properly.

I did my three hours of flight testing, and landed "safely" - I found out the next day, I had landed on fumes. It was independently confirmed that I had 3/8 tanks indicating before I fuelled, and again as I landed following the three hours of flying. So how could I have been on fumes?

The plane was then fuelled with 293 liters, with a uselable quantity of 284, and a total capacity of 302. That pucker factor went waaaay up! What had happened?

So, with confirmed full fuel, I flew again. I watched the EDM930 very carefully. I saw wandering fuel quantity information during the flight, but nothing wildly out of what should be normal for the first hour. But as the flight went along, I saw this:



So the useable that instrument should indicate would total to 284L. According to the certification rules, the unuseable fuel should not indicate in level flight. (When the useable fuel is exhausted, the quantity should read zero).

In the photo, it can be seen that the quantity indicators think the plane is carrying (142+135) = 277 liters - but I am 1.7 hours into my flight, and the totalizer is saying that I have burned 101 Liters so far. That totals to 378 liters, or 94 liters more than the useable amount, or 75 liters more than the absolute capacity of the tanks. The EDM930 is way out.

So I'm getting a dipstick. I'm also drafting a report to support a complaint to JPI, and I'll be filing an SDR. I'm thinking that a $6000 engine instrument, newly STC installed should be more accurate than this, or else come with a huge disclaimer. It is a certainty that accuracy like this does not meet the requirements for certification - which it has.

But, at the very least, one would think that this wizard instrument, which is factory programmed for this aircraft, would sum the fuel it reports is aboard, and the fuel it reports as burned, at pop up a red flag if it thinks the sum of those exceeds the total capacity of the aircraft (or, more properly, the total useable fuel).

The client now wants the original Cessna fuel indicators reinstalled. I can't blame him!

So, I am again a little wiser, and feeling rather stupid, which is not the first time. I have flown with suspect fuel quantity indication in other aircraft, but at least the indication led you to be suspect, and then I did check and dip. I guess we don't even trust the most expensive fuel indicators available for this plane! I got it wrong, and nearly very wrong - learn here from my mistake...

[willow burner]

Good post. I already have a dipstick. Cost .99 cents, heh, heh.

But seriously, its a good reminder for all of us to not rely entirely on the guages, no matter how supposedly precise they are. I ve had similar experiences with capaticence type indicators. They re the only indication you have in some planes, other than a watch, and still not that infailable.

[Airtids]

While I am not familiar with the JPI system (I have an EI), I would suggest there is a problem with the calibration or initial setup. What has JPI Tech Services had to say on the matter? They should be pretty good at trouble-shooting the problem.

[pdw]

I taxiied the plane for fuel, with about 3/8 fuel quantity indicating in each tank, ..... I planned three hours of flying, so I specified 170 liters total between the two tanks ..... After this fuelling, the qty indicated full on both tanks, and I thought to myself, I had goofed, and ordered too much fuel.

The potentiometers were sending FULL information when not full ?

(This can be a relatively minor glitch during that type of hookup procedure)

So how could I have been on fumes?

If the fuel you requested was actually LESS than ordered ?

Any chance 170lbs was fuelled instead of 170 liters by mistake due to a potential miscommunication in among all the testing discussion ? That would be roughly 90lbs less fuel available (if it was lbs mistaken for liters) so that in either case 170 of either would still have read full with the potentiometer(s) out of line (are reading FULL regardless of the above-half precise level).

It sounds like the fuel was in there despite the measuring being off ... unless I'm reading that incorrectly

Understandable how frustration would be over the top for the owner (expectations not met) due to a tiny wire ... or its ground.
Might want to give troubleshooting a chance after reading the positive vibes in favour of the Fuel Totalizer, as discussed on this site only recently.

[pdw]

Around 3/8 to start is 50 liters per side = 100 ... of which 40litres is reserve and 60 liters extra / legal-usable. So 3/8 ("seemed about right") is over 100 liters in the tanks to start. Correct ?

For the 3 hours of flying 170 liters was ordered.

After 1.7 hours where 101 liters (155lbs) is burned, another 1.3hours were flown on the remaining fuel supply.

How much was left for the 1.3 hours ?

If the "170" was lbs then there's only 15lbs (170-155) plus the "60 liters initial legal-usable " remaining in the tanks for those last 1.3 hours of flying, plus the 40 liters of reserve.

Fuel flow is given as 61liters per hour, so it's "60liters initial legal-usable"/ 1-hour plus .3 (20L) which consumed everything and into about half of the reserve.

Unless fuel was lost some other way ...

Seeing 80-90% of the original total fuel level had disappeared plus a ballpark 170lbs, had the whole intended 170 liters actually been added, the indicated fuel level could'nt have burned down below quarter in 3 hours ... at least not into "fumes".

[Big Pistons Forever]

When the unit was installed were the tanks drained to unusable fuel and then the unit checked to ensure the quantity was indicating zero ?

[pdw]

I found out the next day, I had landed on fumes.

You had 33 hours on the install already ... hmm

Somebody siphon out fuel overnight? (Is it too late to check fuel caps for extra fingerprints or ask "the client" who had access ?)

Let's say that happened ... a theft ... of what would then be approx three or four 5-gal jerry cans; how would the JPI calibrate that kind of consumption ?

Furthermore, would you have had a chance to actually check those gauges again before that complete "293 liters" refuelling took place that next morning ? My understanding of this, the normal procedure with a "fill r up", makes me guess you ordered that refuel the next morning by phone / text or in person.

For that reason there would have been no need for actually going out to the aircraft to confirm a precise gauge indication as you have to do for the partial fuelings, so in that case (if theft happened) we can't know for certain that those gauges were/weren't reading EMPTY "the next day".

[PilotDAR]

The photo shows the indications I witnessed after about an hour and a half of flying from tanks which were filled to brimming. This was done following the suspicion of an indication error. There is zero chance of fuel theft, or misfuelling (liters to pounds), and I am a witness to all fuelling, and the only pilot to fly the plan so far.

The indication system, wiring, tanks and senders are all brand new, and from certified origin - no half measures. They were all installed in accordance with their instructions, and I witnessed the set up of the indicators, from zero fuel to full fuel, in accordance with those instructions. Nothing about this installation is "not right".

For those things which remain unconfirmed at this point, I am certain that it should not be possible for fuel on board, and fuel used to sum to more than the plane can hold. Something does not add up....

[black hole]

Any chance that the fuel tank vents are plugged an that the fuel bladders are collapsing and causing the inaccurate readings

BH

[PilotDAR]

Yeah, vents and collapsed bladders were considered and checked. Both okay. These are a real risk, though in this installation, there is more chance of a false low quantity, than a false high quantity. If the ceiling of the bladder released, and moved down with the consumed fuel, it would push the quantity sender float down. It would not be possible for the bottom of the bladder to unclip, and lift up with the weight of the fuel in it, to move the sender float erroneously up for a false high fuel quantity.

But, keep the ideas coming, it keeps me thinking. I do want to have all the angles covered when I make my reports, the ideas help me to be thorough - thanks!

[higherthenakite]

I have flown a C185 in the past with the JPI EDM930 installed. I still used a dip stick every time I went flying. It never lies. I always noticed would that EDM in the plane anything over 30 gallons it would read full on the gages.

Also if the tanks were filled up to 40 gallons a side and entered it into the EDM that it would say "TOP OFF 74 gallons" the tanks had 3 unusable a side. So this plane would have the unusable showing on the gage.

When the tanks were filled up I could fly for at least 20 minutes and I still had not burned any fuel according to the fuel gages, but the EDM would tell me I had burned approximately 6 gallons.

I always wondered why this expensive piece of equipment would ask how much fuel is onboard when it also shows how much fuel I have. It doesn't even trust it's self. It has and electronic fuel gages that are supposedly accurate then when the system is turned on it asks how much fuel I put on, kinda weird to me.

One time I was flying around and I will say it was kinda turbulent. I had the fuel selector to the right tank as it would show a higher burn rate out of the left tank. I was co-ordinated it always did this. Anyway I wasn't paying a close attention as I should of been I was talking to the guy next to me and the engine sputtered I did everything mixture fuel boost and both tanks and we were fine. the right tank read 8 gallons that is roughly 30 liters or so.

After about a week of flying it I stopped programming it how much fuel I had and had it tell me I had used over 4000 gallons. It would tell me I was low on fuel and had no time left cause I had burned all my fuel even though I had just filled it and I just never told it that I had.

So over all I don't trust the fuel gages even on something bigger like a caravan and the computer doesn't trust the gages either.

Kinda winded but that is my experience with the system.

[cgzro]

Software problem of some kind? If you are going to trust your life to it , and not manually check, you really should have two independent systems, that goes triple for software based systems.

[Big Pistons Forever]

I would go back to the senders in the fuel tanks. The little wipers get old and could start sending spurious voltages to the EDM. The irony is wobbly voltages that would just cause the OEM primitive fuel gauges to just wiggle a bit could really screw up a modern electronic system.

Also is the K factor set right ? That is are you getting the right fuel flows and fuel used numbers ?

[ragbagflyer]

I would say to use this unit the manual needs a good reading.

Normally a stand-alone fuel computer counts the pulses from the flow transducer to calculate how much fuel you've actually used and subtracts that value from the user entered fuel quantity to come up with fuel remaining. These fuel computers leave the original gauges and fuel tank sensors alone.

This unit however is not calculating fuel remaining by simply subtracting fuel used from your original fuel quantity. It's taking data directly from the sensors in the tank and the original calibration is critical and involves filling the tanks incrementally from a metered source to obtain several calibration points.

https://www.jpinstruments.com/wp-conten ... 12-jfp.pdf

This process is detailed in the above link starting on page 47 of the manual (page 52 of the entire pdf document). Based on your description of the problem I'd start there assuming all your other numbers (flow, pressure, fuel used) seem correct.

[GyvAir]

ragbagflyer: Give Section 6 of the Pilot's Guide that you posted a read.

On the problem itself.. I have no specific experience with this exact instrument, but my first thoughts, in order of likelihood are: Finger trouble, either in the initial calibration or in the operation of the unit; faulty or somehow incompatible qty senders/wiring; software/firmware problem.

Another question that came to mind after looking at the installation manual again was: How many calibration points were used in setting up fuel qty calibration? I see it allows you to choose from 2 (full and empty) to 5 (F and E, plus 3 points in between). Leads me to wonder if particularly non-linear reading senders would be able to give you the erroneous fuel quantity readings you're observing, yet still give you "correct" readings when the tanks are full and empty, especially if only the 2 points were used at calibration.

Edit: Just remembered you specifically said 3/8 tanks indicated when on fumes, which basically negates the above theory. I take it that it never indicates empty now?

[ragbagflyer]

Yeah exactly. This unit does the same thing but it doesn't derive the remaining fuel by subtracting fuel used from the initial quantity.

The calibration procedure is what I think mighty me the problem.

[GyvAir]

ragbagflyer: I misunderstood what you were saying. I thought you were implying that the unit was getting all of its fuel information from the tank senders alone.

[Rookie50]

I would go back to the senders in the fuel tanks. The little wipers get old and could start sending spurious voltages to the EDM. The irony is wobbly voltages that would just cause the OEM primitive fuel gauges to just wiggle a bit could really screw up a modern electronic system.

Also is the K factor set right ? That is are you getting the right fuel flows and fuel used numbers ?

I have a new Edm 830, non primary with no fuel gauges just a totalizer. After 40 hrs flying its apparent it works fine but the k factor is incorrect. It's reading about 1 gph higher burn than actual, so I may just leave it for the insurance that builds in.

Btw, and mine is also a 182, the ships sending units are seriously over-reading at each fuel level. We've charted the over-read but are discussing how to proceed. They are Borg senders and not the most accessible. This does not affect the JPI but the ships fuel guages. I am flying using the totalizer and dipping tanks.

[Heliian]

Step 1: Confirm calibration of the EDM in the a/c

Step 2: If you can't calibrate it properly, check the a/c wiring and fuel senders individually for proper output/resistance
(you may find that one of the senders is erratic or has dead spots)

Step 3: Replace EDM with a known functioning one.

I have seen this issue on many conversions, the old fuel senders and gauge systems were never meant to be that accurate, even converting capacitance type probes to digital gauges can produce erroneous readings. Your analog gauges have increments that are quite large and give you a good estimate of what's left, now it's trying to "guess" how many litres are there, which without a precise measuring system in the tank is next to impossible.

[pdw]

... the old fuel senders ...

So that is saying then these could be fifty year old senders, left in there from the previous system ... feeding this new device

[pdw]

If it's the existing level sensors producing the error, .. imagine it would be a fair amount of AME-time to change them all.

[GyvAir]

Achieving any resolution to this problem, PilotDAR?

[pdw]

If its a software issue, the programmers should be onto it quickly, how to figure out a glitch like this .... something as serious as an aircraft's fuel quantity showing 'adequate' mixed-up with 'empty'. The install definitely needs the disclaimer in view for fueling ... ' dip tanks for accurracy until sure of calibration "'

[chu me]

Not trying to be an "A" hole here, but this senario just backs up the old adage " never trust your fuel gauges. When I flew in the bush I always checked, either by looking in to see the fuel or by dipping. Now that I have been in the "jet age" for awhile I can no longer do this......or I would. Just remember, had you actually run out of fuel ( god forbid ) the first question the lawyers would ask at the finger pointing ceremony would be..... DID YOU DIP THE TANKS !!!!!! I am glad to hear that your trip ended safely, hope you get it figured out.

Sincerely

Chu me

[PilotDAR]

Reports are submitted, but no resolution yet. I've been working out of Canada for the last two weeks, so I'm letting things settle. I'll start in on it when I return.

Yes, I can stand to be told I should have dipped the tanks. But, for all intents and purposes, this is a completely new fuel indication system, which complies with the latest, and all prevailing design standards for the aircraft. None of those standards, nor the manuals for the aircraft or EDM930 state that you should or must determine the fuel quantity manually before flight. It's supposed to work. If you bought a brand new Cessna, and the fuel quantity was showing a 1/3 error, you'd take it back for warranty! You would not just accept it "'cause fuel indicators aren't reliable".

The design requirements require that a system must work in an aircraft, and specifically fuel quantity indications. If I am to put my name behind this modified aircraft, and present it to my client as airworthy and finished, it's got to do what it says on the box, without manual double checking. My client (the aircraft owner) saw the faulty indications first hand, and is every bit as alarmed as I am. He wants the old pointer type indicators put back in!

Yes, I can dip the tanks, but no lawyer could stand in front of me in court, and state that I failed in my piloting duties, which do not state anywhere (except a century of wisdom) that dipping is required before flight. I flew the aircraft in accordance with the approved instructions. Yes, I got lulled into laziness, and darn near went gliding, and I am totally lucky, that you lot are not ridiculing my accident, reported one sub forum away. But, even if I had dipped the tanks and found the error before I flew, I would still be here saying that if it is approved to a standard which says it's gotta work - its gotta work!

I only get to stand on a tiny soap box on this one, 'cause I was careless, but the facts are the same. I will present the progress here, as I am able... I do appreciate the interest....