trouble shooting aftermarket fuel level guage

[CUDA JAS]

I instaled an aftermarket fuel level guage (for mopar applications) the other day and I am not sure it is working right.

My bet is that the sending unit (not that old) is not working correctly.

I have a multimeter, but I am not sure how to use all the functions.    Can some one please explain where to put the pos and neg leads to check the resitiance coming from the sending unit.

Thanks,

Jason

[Supercuda]

On the ohms scale (resistance), set for the lowest range, or for 0-infinity. The red lead goes on the sender post, the black lead to the sender body (ground). At low or empty, it should have about 90 ohms of resistance. At full, it should show about 12 ohms, but a low resistance is the important thing to remember. To check the gauge, turn the key on with the sender unplugged. Grounding the sender wire momentarily should shoot it straight to full. I use a remote starter switch to do this by myself. Just clip one wire of the switch to ground, and the other to the sender wire, and hit the button when you can see the gauge.

[Strawdawg]

I instaled an aftermarket fuel level guage (for mopar applications) the other day and I am not sure it is working right.

My bet is that the sending unit (not that old) is not working correctly.

I have a multimeter, but I am not sure how to use all the functions.    Can some one please explain where to put the pos and neg leads to check the resitiance coming from the sending unit.

Thanks,

Jason

Do you recall which brand of sending unit you have in the car...or where you bought it?

[CUDA JAS]

On the ohms scale (resistance), set for the lowest range, or for 0-infinity. The red lead goes on the sender post, the black lead to the sender body (ground). At low or empty, it should have about 90 ohms of resistance. At full, it should show about 12 ohms, but a low resistance is the important thing to remember. To check the gauge, turn the key on with the sender unplugged. Grounding the sender wire momentarily should shoot it straight to full. I use a remote starter switch to do this by myself. Just clip one wire of the switch to ground, and the other to the sender wire, and hit the button when you can see the gauge.

Hmmm....well with all the wires conected (properly I think) my meeter reads no resistance across the sender and ground.

I unhook the ground wire and it reads 188 ohms (the gauge now reads just below full, which should be about right).

When I ground the sender wire the gauge shoots right to ground, so it seems to ok...but now I am confused as hell!!!

Thoughts?

[CUDA JAS]

Do you recall which brand of sending unit you have in the car...or where you bought it?

Not sure, had for a couple of years.  Probably bought it at rock auto..I am thinking that it is a Specter unit...maybe.

[Strawdawg]

I ask because I am having problems as well...with a Sprectra from Rock.

When I stuck it in, I checked for a smooth transition in ohms from empty to full...something like 70-10 which is right.  What I did not check was the actual ohms at say half tank....I assumed that it would be linear...but after Googling, I am under the impression that empty should be about 70 ohms, half tank should be around 23 or so, and full should be about 10.....in other words, a non linear resistance with movement.  I have not mapped out the arc to see if that makes sense

Now, with about half a tank of gas, I am seeing closer to 40 ohms when I remove the wire from the gauge to the sender and read the post coming out of the sender to ground.  In a linear sense, this would be about half way between 10 and 70...but, if my searching is correct, it should be around 23.

At any rate, I am seeing empty on the gauge.  If I take a couple of resistors and make up ~23 ohms, I am seeing half on the gauge.  I am trying to figure out if the sending unit is not wound correctly, or if the arm just needs to be bent up a bit to read  closer to 23.....

It is not unusual for these things to have three or four gals left when they drop to E, but, not half a tank

[Supercuda]

Sounds like the wiper contact on the arm is not hitting the windings properly. I guess that means that you try to"adjust" this one, or find a better-built sender.

[Strawdawg]

Sounds like the wiper contact on the arm is not hitting the windings properly. I guess that means that you try to"adjust" this one, or find a better-built sender.

that would be my guess.  Given the arc traversed, it would not take much to throw it completely out of whack

[shadango]

I cant get over at how much an issue these damn things are. 

I went the rock auto route....went thru two or three, each having adifferent reading......then tried the better built ones (2 of them...got mine from Roseville) and while they are DEFINATELY better looking units, I have had almost as much trouble.

At this point i was able to tweak the thing enough so that at full it reads REALLY full, and at half tank it is really a half tank (8 gallons).......below that it gets goofy......dead spots, drops to empty, etc.  Sometimes, after filling a near empty tank, the gauge reads empty until i drive a bit and shake things up and then it jumps up to full and is fine.

There has to be some sort of design issue.   I know people say the gauges were not that accurate back in the day, but this is ridiculous.

And before anyone suggests it, I have tried running separate wires and ground wires...no luck.

Someone on Moparts (I think) had said he tried soldering a wire from the sending unit's float arm to the body of the unit. That seems to have made the difference for him. Seems that the arm makes the connection to ground through the actual pivot point....which (at least on these repops) seems to be very sloppy and loose.....

That is on my list to try next at some point.  I picked up the special wrench to make removing/installing the lock ring easier.....have to find a GOOD lock ring too...the one that shipped with the spectre and the Roseville ones seem to be a might undersized so you have to be very careful not to get it off center, which will result in a huge leak.....ask me how I know THAT.  LOL