The tale of two fuel gauges........

Dave81 · Post by **Dave81** » Mon Jul 13, 15 1:40 pm

The fuel system is next on my (s)hit list. I'd already purchased a replacement Specta Premium tank and sending unit from Rockauto over 12 months ago.

Decided to go and check it out yesterday.

Bodge #112:
Whoever in the states had it before, thought it would be easier to drill through the trunk floor, into the tank and fit a vertical sender rather to replaced the knackered horizontal stock jobbie.

It weeps, it stinks and the car has always had the eau de petrol ect

The Bodge sender was hooked upto an aftermarket gauge on the dash. This, i though, would be as the original tank gauge had given up the ghost long ago..........Not so.

To my surprise they had literally abandoned the stock sender and wiring setup. Upon removing the original wire and hooking it up to the new sender, the gauge actually works.........Result.

Now the interesting bit (all done with the engine off).

Testing the stock wiring, stock gauge and new SP sender:
At the float down position it reads on the E, rather than off the gauge when the car is off. Good!
Move the float upto 50% full........its not moving really. Move it upto 75% and its showing circa 1/4 tank. Move into up/full position and the gauge very slowly climbs upto the F. Also good.
So for 75-80% of the float movement the needle isn't moving then its on the go.......

Testing aftermarket gauge and newer installed wiring and SP sender:

At float down position it reads circa 25-30% full (quarter tank). Moving it up the gauge seems to be better calibrated than stock and moves generally well through the sweep and stops when I stop. At 75% on the float range the gauge is reading full. At max high float its off the gauge past F.
By looking at the float position it seems that the gauge is calibrated around 25% off where it should be?

The aftermarket gauge though works fine with the bodged sending unit in the tank.
I didn't have a chance to check the resistance as I'd only popped out for 5 to get a paint brush, and lost an hour in the trunk!

I believe for stock gauges, it should be:
Empty = 73.7 ohms?
1/2 Tank = 23.0 ohms?
Full = 10.2 ohms?

Not a clue about aftermarket ranges.

In short...The stock under-reads and the aftermarket over-reads????

Thoughts and help please?

Edit: Preference is to be able to dump the aftermarket and clean up the dash asthetics!

Pete · Post by **Pete** » Mon Jul 13, 15 1:51 pm

Often you have to calibrate the sender by bending the tag but they are never accurate anyway, I would not trust one.....

Blue · Post by **Blue** » Mon Jul 13, 15 5:39 pm

Other manufacturers and the aftermarket use various ohm ranges, the Mopar range isn't that popular so finding an aftermarket sender to match the stock gauge or an aftermarket gauge to work with the stock sender isn't easy. To answer your question, I would just bend the arm on the sender so it just reads empty with 2 gallons of fuel in the tank and leave it at that. As Pete says the stock set up isn't especially accurate and all you really need to know is if you are about to run out of fuel or not.

ScottyDave · Post by **ScottyDave** » Mon Jul 13, 15 5:48 pm

Blue wrote: I would just bend the arm on the sender so it just reads empty with 2 gallons of fuel in the tank and leave it at that. As Pete says the stock set up isn't especially accurate and all you really need to know is if you are about to run out of fuel or not.

That sounds like a good plan

Dave81 · Post by **Dave81** » Mon Jul 13, 15 8:09 pm

Thanks chaps.........I'll check the ohms anyway to be sure, then mod and bend to get the gauge to read right.....ish!

Dave81 · Post by **Dave81** » Thu Jul 16, 15 10:31 pm

So I checked the sender.
73 ohms at empty peg and 3 ohms at full peg......great its in the chrysler range.

So went and got an autometer fuel gauge that runs 70/10.

Hooked it all up tonight but just earthed the sender body to the dash via a screw.........used the newer wiring for power and checked....Bananarama! it's doing the same as the 42 year old gauge in the dash...

It's a lot more steady than the stock gauge, but the float arm movement doesn't show a linear increment of the gauge. Empty is empty, full is full, but what I would call the middle of float range is showing 1/4 of a tank or less.

So more checking. If I disconnect and check the sender on its jack, it does seem to show a nice steady increment in ohms.

Hook the gauge back up but leave off the earth on the sender. The ohms empty and full is as you would expect. Only issue is without grounding it, the gauge won't work.

Hook up the earth and??????

Empty is 24 ohms (that should be 1/2 full), and it slowly drops to full showing 3 ohms.

I'm lost. As if that was true the fuel gauge would only ever read between 1/2 and full.

I would like supercharger like readings.....nice and steady through the range. I'm getting old school turbo....nothing nothing, then all at once!

Sender is new. Gauge is new. All the test wiring was new bar the power feed which tested at 11 volts..........again this was all done on battery power (engine not running).

Errr Help?

autofetish · Post by **autofetish** » Thu Jul 16, 15 10:54 pm

Well some thing not right

Take gauge sender and battery put all on bench and use new wires.

Also wire up up any gauge lighting pin correctly on the gauge

Keep it simple on bench

If it works then you know it's not the equipment on bench.

Sounds like a high resistance earth / feed or the garage lighting system that you didn't wire up is causing issues

autofetish · Post by **autofetish** » Thu Jul 16, 15 11:02 pm

<a href="http://s73.photobucket.com/user/autofet ... 6.png.html" target="_blank"><img src="http://i73.photobucket.com/albums/i205/ ... mp3rp6.png" border="0" alt=" photo 82A7D6D0-33BF-440A-BF02-D62069813E1A_zpsopmp3rp6.png"></a>

Just had a look it's a bulb holder not LED so don't thing it's anything light related

Dave81 · Post by **Dave81** » Fri Jul 17, 15 12:47 pm

Thanks Will.

Deffo not the light as I didn't even hook it up. It'll also only be piggybacked of the power feed and earth on the gauge anyway, so that shouldn't have an affect.

I put the stock gauge issues down to 43 year old wiring.
I put the original aftermarket gauge down to the fact the gauge did not conform to the ohms range of the new Chrysler style sender.....hence it read from 1/3 tank up.

This should work........I cant see what is wrong or miss wired/earthed. Again I cant see it but my only hope is that its due to the engine not running its showing low voltage to the gauge (but I'm only talking 1-2V). Everything works until I ground out the sender then the readings are just not as I expected.

As I said it shows full and shows empty, and more importantly its shows empty when the float arm is a good inch + above the inlet sock, so I shouldn't ever run out (it'll read below E with at least a 1/5 to 1/4 of a tank left).

Just frustrating really. I expect 100 miles and it wont budge the needle then in the next 30 it'll drop down to E from Full........

autofetish · Post by **autofetish** » Fri Jul 17, 15 12:56 pm

Bench battery gauge sender

Dave81 · Post by **Dave81** » Fri Jul 17, 15 1:35 pm

autofetish wrote:Bench battery gauge sender

Will do. If it persists i'll do a video of the readings for you to look at!!!

Dave999 · Post by **Dave999** » Fri Jul 17, 15 3:19 pm

do darts use 5 volt or 12 volt for the gauge?

Aussie cars used 12 volt and had 4 different ohm ranges through the years. US cars might have had changes year to year as well

I thought US cars used a regulated 5 volt off the back of the cluster to power all gauges

or is that just B bodies?

5 volt used because someone got their knickers in a twist about the sender sparking.

which makes no sense anyway the vapour in the tank is so dense that ignition is nigh on impossible.

Dave

Dave81 · Post by **Dave81** » Fri Jul 17, 15 9:03 pm

Dave999 wrote:do darts use 5 volt or 12 volt for the gauge?

Aussie cars used 12 volt and had 4 different ohm ranges through the years. US cars might have had changes year to year as well

I thought US cars used a regulated 5 volt off the back of the cluster to power all gauges

or is that just B bodies?

5 volt used because someone got their knickers in a twist about the sender sparking.

which makes no sense anyway the vapour in the tank is so dense that ignition is nigh on impossible.

Dave

I think you correct Dave, they do drop down to 5 at the rear of the cluster.........I tested the aftermarket gauge power feed and it was showing 11v......this is what the new Autometer gauge was hooked upto.