Bouncy Fuel gauge

[mach1mustang351]

I need a sanity check on this one.  My fuel gauge bounces around in my 87 Wagon.  I have been trying to come up with a solution on replacing the sender but then I got to thinking maybe it has something to do with being fuel injected now... I don't think this matters but I need a sanity check here.  Thanks.

[ammachine390]

I believe the reason they bounce so much is because they did not use baffles in the tank to keep it from sloshing so much. Mine really only bounces a lot once it gets below 1/4 full. New cars also use the ECM to send an average reading to the gauge, so that when the gas sloshes around, the gauge doesn't bounce like the ones in our cars do.

[DaemonForce]

Mine has been doing that for a while now. I haven't had reason to address this as it hasn't been an issue until this week. Somewhere in the month I'll drop the tank, replace the sending unit with a modified float and try again. If I'm lucky I'll finally get rid of this Carter garbage and pick a nice Motorcraft carb. I would go with fuel injection but I have enough problems as is and I don't need something else that can strand me when this car dies every 3 miles.

[txjeeptx]

Check gauge ground wire AND the tank sender ground wire.

[GRONK]

X2 on grounding

[BenM]

There should be a capacitor as part of the gauge wiring to dampen the fluctuations. If the gauge is accurate, but moves quickly in a small range with the sloshing then it's the capacitor.

Depending on the type they can burn out internally or they'll swell up and the connection will open.

Edit: I might be wrong on this...

[brentsydlik]

where would i find this capacitor?

[BenM]

Ok, I might be wrong on that. I've never pulled one apart myself.

After more research the Eagle probably uses a grease or mineral oil in the gauge that dries out. The capacitor would be inside the gauge itself and require disassembly, and so would replacing the grease.

Those are the four basic ways to dampen gauges. Some sending units have enclosed floats with little holes to prevent fuel sloshing around the float. Others like ours have the lever style we have there is no practical way to dampen the sending unit, so it has to be in the gauge. There's the capacitor method to even out the electric signal, and some new cars just use the computer to even it out.

If you want to build your own, then I'm seeing a 2,000 mf between the sender line and a ground being recommended. A capacitor is in essence a small storage device and a big one like that will even out the signal by charging and discharging. I haven't done electric component math since college, so I'm not going to claim I verified that.

There are two kinds of gauges, one that's heated by a bi-metallic spring and another that uses two opposing magnetic coils. The spring style needs no dampening because of the rate it heats and cools. The magnetic style moves quickly on its own unless dampened, and can vibrate if the voltage regulator (CVR) on the cluster is bad.

There is definitely some kind of dampening involved, but it's apparently something they don't want you to know about. I can't even find that mentioned in my TSMs. They go from the CVR vibration, which can be slower then you think, to the "Fuel gauge wavers over rough road" as a "normal condition", which is way on the other side of the problem.

If you have what I have, that the fuel gauge continues to seek around the actual level due to sloshing after a stop, or quick movement, but not noticeably on level highway or when the car hasn't moved for a few minutes, its the dampening in the gauge. I just want to clear that up in case I might be misinterpreting your symptoms.

[mudkicker715]

No visible capacitor just wire wrapped around who knows what. here is the gauge itself doesn' really show alot.
 
 

My gauge can bounce on one of mine sitting still right after getting started in park when its under 1/2 tank.

[mach1mustang351]

If you have what I have, that the fuel gauge continues to seek around the actual level due to sloshing after a stop, or quick movement, but not noticeably on level highway or when the car hasn't moved for a few minutes, its the dampening in the gauge. I just want to clear that up in case I might be misinterpreting your symptoms.

This is exactly what mine is doing.  It bounces all the time for me because I drive in town and stop and go and turn and all that so it is constantly jumping and it had started to irritate me enough to ask...

[carguy87]

Check the grounds for your clusters.  I just took the time to correct this same problem on mine as it finally hit that last nerve.  On our clusters, the ground for the fuel and engine temp gauges are linked to the ground for the turn signal indicator lights.  In my case, which sounds probably like what yours is doing, when the turn signals were turned on, the fuel and temp gauges would accordingly bounce up higher and higher from the lights seeking a ground and fall when the signal canceled.  The problem stems from the way the circuit boards are connected to the electrical wiring.  On the back of your cluster you will find a bunch of little metal pins, in a striaght row behind the fuel and temp, and circle between the fuel and speedo.  These metal pins are pushed in through the printed circuit and merely split on the other side and spread apart like the back side of a rosebud rivet.  As age would indicate, they weaken and come loose and cause this problem or cause your indicator lights to dim over time.  In order to fix this, you simply need to get a small screwdriver and scratch some of the protective film off the circuit going to the loose pin right by the base of the pin, hold the pin in the poper position, and solder accordingly.  I even put a little solder on the still tight pins so I wouldn't have to go back in the future.  After reassembly my lights are back to being bright and all gauges and indicators work like new and my fuel gauge only dips or rises when taking hard turns again.  I also took the liberty to clean my clear cluster lens while I was at it, well worth the time.