Erratic fuel gauges - Page 2

stackj · #16 09-11-06, 12:25 AM

I agree with Pete. It appears to be a resistor. It is higher wattage than others on the board. This is evidenced by its larger size.

However, don't try to replace it with a resistor based on the value you measure with a volt-ohm meter. You will measure it's current value which is likely to be much higher than its original value. (It may even be totally open - though it is rare, it may be intermittently open - this usually only happens with wire wound resistors).

This resistor is not marked with color bands indicating its value. You may possibly be able to read its value based on numbers printed on it. The burned area may prevent this, but you may be able to get some information from the side of the resistor closest to the circuit board.

Good luck. Hope Pete can find some information from other documentation.

Ernie Martin · #17 10-13-06, 11:40 AM

On my erratic fuel gauges, we've made some progress but some problems persist. The earlier thought that it might be due to the discolored (burnt?) resistor found in the signal-conditioning box has been abandoned after further testing and the fact that sometimes one gauge will work and the other one won't. Connectors on both the signal-conditioning box and at the wing root seem fine.

We now believe that it's poor conductance in the long connector behind the gauge. After disconnecting and cleaning both male and female sides, there was an improvement but we can't get a consistent signal. We tested and all was well. Did it again and no signal on either gauge. Jiggled it and we get a signal. We then lightly sanded the circuit-board male side and re-cleaned it, and now we have consistent reading of the right tank, with the left tank reading depending on jiggling the connector.

Incidentally, let me note that the design supplies a low voltage to the gauge, especially for low fuel quantities (for a 1/4 full tank it is a fraction of one volt). Anyhow, we're considering replacing the female connector but, because that connector looks good, we're concerned that the problem is really the circuit-board male side, where the copper strips seem worn and may be causing the bad connection. Has anyone run into this? Kim, Pete or anyone else, is there a way of "refurbishing" the circuit-board male side in situ? Any other thoughts?

BTW, day before yesterday, when I went to the airport to work on this, I found that the airplane had been hit by some vehicle (e.g., motorcycle, golf cart) along the front-left side, roughly from below the center of the front-engine left cowling to a point below where the circuit-breakers panel sits. While there is no structural damage, there is considerable skin damage. Oh, did I mention that I have no insurance and the culprit ran away? Anyhow, my attention has shifted to getting this repaired -- getting labor quotes and finding the necessary parts. I will be posting some pictures on a separate thread but, on the matter of parts, let me mention how fortunate we all are that Don Nieser of Commodore Aerospace exists. My thanks to him.

Ernie

Pete Somers · #18 10-13-06, 12:09 PM

Hi Ernie
Thanks for the info.
I had to remove the whole cluster to clean one up, also found that the connections to the various indicators from the printed ciruit not very good and had to remove and clean these. The cluster does come out easy once the pipes are removed.

Pete

edasmus · #19 03-02-09, 08:55 PM

Hi Pete,

My name is Ed Asmus and after reading this thread it sounds like the problem I have in my C337G 1973 model. Erratic fuel guage readings began on my last flight last week and my shop is 99% certain the problem is in the "Fuel Control Monitor" also known as the "Signal Conditioner" part number C668004-0102. My mechanic re-soldered the female plug that connects to the control monitor with no improvment. Is it possible to re-solder the pins on the male plug that is attached to the control monitor board? My mechanic thought it could be done seeing as overhauled ones can be purchased so somebody knows how to do this. It looks like to replace the entire control monitor unit would be $1200+ which would make me sad knowing that somewhere there is a simple lose connection. How do you remove the male plug from the control monitor board? Any suggestions?

Thanks Ed

Ernie Martin · #20 03-02-09, 11:20 PM

If you read my post above Pete's you'll see that I've also been struggling with the problem. My best advise to you is to make certain that it's the box before you spend the big bucks. Because of the small voltages, the system is sensitive to the aging effects of corrosion and wear on the connectors, resulting in increased impedance and erratic readings. It would not be inaccurate to say that I've kind of given up on the problem, and I now get good readings if it's mostly full and erratic ones under 1/2 full. So I never take off without climbing on the wings and doing a visual check.

Ernie

JeffAxel · #21 03-02-09, 11:50 PM

Ernie,
Aero-Mach Labs in Wichita can fix these things. They fixed mine and it works great now.

www.aeromach.com

edasmus · #22 03-03-09, 12:01 AM

Thanks Ernie...I did read the entire thread and I was aware of your heartache over this issue. I agree that I certainly do not require super accurate readings to know how much fuel is on board but it does make for a nice cross check. I suppose more importantly, fuel gages would be my only line of defense should I spring a leak during flight and fuel was exiting the wings without going through the engines. My problem appears to be in the aforementioned fuel control monitor, C668004-0102. My gages indicate quite accurately when they receive electricity but it seems to be an all or nothing affair. If you wiggle the connection on the box, the gages come back to life. Jeff Axel has given me a lead on a possible repair facility to fix my existing box so I'll see where that leads in the morning. Thanks! Ed

Pete Somers · #23 03-03-09, 02:24 AM

Ed
I have replaced that connector, but you need to know what you are doing. You need a proper desoldering rig to do it. As I have said on this thread, the only way to fault find and calibrate this system is with a capacitance test box, it makes the job so easy, saving you time and money at the end of the day. Once calibrated this system is very accurate

Pete

edasmus · #24 03-03-09, 08:45 AM

Thanks Pete....I'm going to contact Aeromach today and hope for the best! Thanks!

edasmus · #25 03-17-09, 08:14 PM

HI GJ,

I was reading your thread on your erratic fuel gage problem in your 73 C337. I also have a 73 with the exact problem you were describing. The gages bounce up and down together mirroring each other exactly. Sometimes they do read zero and sometimes they work fine but what ever they are indicating, they always do it together. They look like wind shield wipers going back and fourth. Did you ever actually find the problem and if so what was it? I have had my signal conditioner repaired by Aero Mach labs in Wichita but I think I need to send it back because I think the problem is in that 9 pin plug on the conditioner. I'm certain we have the same problem. I'm mostly curious if you solved it!!!

Thanks Ed Asmus

gkey · #26 03-17-09, 08:59 PM

GJ,

Same problem here. Been to the shop, more times than I can remember. Replaced each part of that system at least once. Still no hope. Now I ignore the needles and fly by weight/amount of fuel alone. Never less than 3 hrs worth in the tanks for contingency.

So, I am waiting for the AuRACLE CRM 2120 to be released (it is a primary replacement - yahoo!!), and then install it. Good riddens to Cessna fuel gauges.

n9121x@aol.com · #27 03-18-09, 09:48 PM

a simple solution and very accurate instrument.....buy a Shadin FF guage

Ernie Martin · #28 03-18-09, 10:51 PM

Simple and accurate -- but expensive.

Ernie

JeffAxel · #29 03-19-09, 02:31 PM

expensive, and won't give you any clue if you have a fuel leak. All a fuel flow tells you is what you have burned, not what you have left. I like having both a fuel flow and working fuel guages. If they agree, great, if not, you'd better figure out why....before you have a very quiet Skymaster!!

edasmus · #30 03-20-09, 09:11 AM

I have started to give thought to alternate means of determining fuel quantity but I am not ready to give up yet on the Cessna gauges. Mine have worked very well until about 3 weeks ago and we are still working the problem. I will have an update in a few days. I do agree with Jeff in that knowing the quantity or at least close to it is important. I have an expectation when I fly as to what the gauges should say and if I see something different, I want to know why. Especially if one gauge is dropping quickly. I feel it is the only way to know that fuel is not exiting the airplane through a hole in the wing. As for knowing precise fuel flow, I am not ready to make that leap yet. As long as I can "guesstimate" within a 2 or 3 gallons at the pump what the airplane should take erroring on the side of caution and confirm that fuel is not leaving the wing through a hole, I feel that is an acceptable level of safety. Thank you for the input.