Anybody have any experience with fuel fluctuations in a C180? My new to me 1954 180 with an O470 and the fuel analyzer is doing a goofy periodic jump in fuel flow. At any cruise setting it will be rolling along and wandering between a few tenths on the flow and then will periodically jump up about a gallon or so then drop back. the interval is about one or two minutes. Fuel level doesn't appear to matter. It sort of looks like it's pulling a slight vacuum on the bladder, gurgling air in then repeating the process but the vent appears free and clear. I now have about 1 1/2 hours of Cessna 180 time so am definitely a Skywagon retard. Any thoughts? (on the fuel flow part, not the retard part). Thanks BCPs.
FZ

Does the engine sound or feel different when the fuel flow changes? RPM or MP differ?

Gump

My JPI does the same thing periodically. Just a tenth or so either way. What's more important is that if you fly it and the totalizer says you used 35.? or so gallons and you top it off how close is it to the 35.? gallons. in other words how accurate is the totalizer?

I'm not a mechanic but I fly a couple of airplanes with fuel totalizers (one being a '55 C180) and participated with the install and set up on both and I know that the transducer needs to be installed properly so that air bubbles do not interfere with the flow readings. I'm not sure if what you are describing reflects that or not but it might be something to look at and consider. Congrats on the Skywagon! Awesome airplane!

CW

Engine is not changing, MP, tach and EGT are steady but the higher flow periods are pretty short, like a few seconds. So, it's running between 9.2 and 9.6 for about a minute or two, then goes to 11.5 for a few seconds and then back to the 9.2 to 9.6. The totalizer function looks perfect. It indicated that we had used 11.2 and we topped off at 11.4 today. I don't have a CHT and the EGT is single channel.

And, thanks. I am really loving the Skywagon! I miss the limo room of the 206 but am very glad it's draining somebody elses fuel budget!
FZ

9.6 to 11.5 is pretty extreme shouldn't be that much. Is this a JPI? And I'd rather it said I used 11.4 and I put in 11.2. If it's a JPI I'd call them and to calibrate they will walk you through the process.

Yup, JPI 450.

There is a setting in the JPI FS-450 which allows you to smooth the fluctuations with a carbureated engine. There are three settings, and in my 57' 182 I ended up on the #2 setting. It should say CARB F=1,2,or 3. 3 is the highest smoothing level. Check the Pilot's Guide....it's in there under setup mode. The trick is remembering that to get to the setup mode, you must go one layer deeper than the "program" mode to access it. Hope this helps.

Also make sure the wires on the transducer are pointing up...I accidentally put one in upside down once, and the readings were low and it fluctuated wildly.

JC

Um, 9.6 gph is very low fuel flow for an O470. Not crazy low, but....

I'd suspect the flow transducer as well. Either installation or it may be failing.

Again, at the end of a flight, does the "Fuel Used" equal or close to the amount of fuel you meter into the tanks??

MTV

MTV, Out of the one time I have topped off, the fuel I added was .2 off of what the analyzer said we'd used. I assume that is easily within differences of exactly where I topped to?
If nobody here is totally creeped out by thee swings in the flow, I think I'll keep flying for a bit, over hospitable ground, and keep monitoring, then move to the resetting suggestions?

flyingzebra wrote:....If nobody here is totally creeped out by thee swings in the flow, I think I'll keep flying for a bit, over hospitable ground, and keep monitoring, then move to the resetting suggestions?

I'm definitely no totalizer guru, but if all the other indications (tach,MP,sound,feel) are within parameters then I'd say it's the instrument with a glitch-- not the airplane.

I'd bet the fuel flow transducer has some kind of a problem.....either improperly installed (they do have a specific manner in which they MUST be installed) or it's got some contaminants in it. More than likely the latter. I'd get a competent mechanic to check it out, and send it back to JPI if necessary. If it's got junk in it, it probably isn't going to get better.

Give JPI a call and see what they have to say. My experience with them has been pretty positive, and they're the ones that made it.
ANd, let us know what you find out.

MTV

flyingzebra wrote:MTV, Out of the one time I have topped off, the fuel I added was .2 off of what the analyzer said we'd used. I assume that is easily within differences of exactly where I topped to?
If nobody here is totally creeped out by thee swings in the flow, I think I'll keep flying for a bit, over hospitable ground, and keep monitoring, then move to the resetting suggestions?

That extra .2 gallons could be the jumps in fuel flow adding up. If it lasts more than a fraction of a second, you can bet the totaliser is counting it.

Sounds like it could be an electrical problem internal to the transducer?
Or perhaps an occasional slug of turbulent flow shedding passing through - the transducer needs at least 6" of straight line each side to smooth out turbulent fuel flow - but that doesn't necessary explain the periodicity of your problem.

Don't trust / rely on it. Dip the tanks.

I have an Electronics International fuel flow meter in my P172D. Once in awhile, when I'm on a long cross country and switch between tanks, there will be a fuel flow fluctuation for a few seconds, which I've always attributed to a burble of air in the line--hardly something to be concerned about.

All of the manufacturers were using the same transducer, made by Floscan, which is the pioneer in fuel flow meters. They don't make the entire kit, just the transducer (although they make the whole thing, including the meters, for boats, trucks, etc.). I can't say whether Floscan is still supplying all of the various manufacturers. But the transducers all work on the same principal, fuel flow spins a little paddle-wheel which interrupts a light beam, and the rotations are converted electronically to either a digital or analog read-out. I don't know how the JPI is adjusted, but the EI comes with clear instructions on how to narrow the gallons used reading to the actual gallons used. Of course, it's better if there has to be an error, that the meter reads that more was used than actual. In my case, it took about 3 fill-ups to narrow it down so that now if I fill up with say 35 gallons, the meter may say I burned 35.2 at the worst.

Incidentally, I stick my tanks, too. Trust but verify!

Cary