I had a stock sending unit and recently installed a spectra premium fg69b, and now the gauge reads way off.

I did replace the in dash regulator with the popular 7805 upgrade long ago but it was working fine with the original sender. The original sender probably read +/- 1/16 tank (compared to how much gas the pump said it gave me, and the known 16 gallon capacity of the tank)

Now, with the spectra sending unit, when I fill the tank its at full, but when I use ~4 gallons, 1/4 capacity, it reads 3/4 empty! yikes, way off.

Before installing the tank, I measured its resistance - full = ~9 ohm (original is ~10 ohm) and empty = ~80 ohm (original ~ 60). I know spec is 10-73 - so the fullend is fine, the stock is below the spec on the low side, whereas the spectra is above.

Its not the car wiring - I ran 2 full lengths of wiring for ground and signal directly to the connector besides the kickpanel and readings were the same.

Did I get a mis-calibrated unit, or is this par for these senders? Anyone get a spectra unit and expereince the same thing? My original unit had one single 5/16" line. Are the units with fuel return line calibrated differently?

Hmm - I tried to take the sending unit back out and bend the arm down. I was hopeful this worked, because it was somewhat accurate for the first 1/4, but then started descending way too fast, by the time it was supposed to read 1/2 it read empty.

The sending unit with the vapor return wasn't used until 75/76 right? My tank was the 2 (3?) year only californa emissions package. The 70-71 parts book shows pictures of the california emisisns system but doesn't metnion a seperate part # for this tanks sender. I know the tank for this system is shaped differently on the inside - wonder if this means the sender for this system/tank is a one off unit that wasn't used again.

There is no difference in senders between ECS and non-ECS senders. The tank shape difference is way up at the top (air dome in the ECS tanks), so doesn't affect how the sender works. I think you got a defective sender, is all.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I have a second spi fg69b unit in my hands. Wiithout installing it in the tank I know it is no where near the original sending unit interms of calibratin because I'm measuring it and the stock one, side by side, at similar float levels and the original one is approximately half the resistance of the new one at various points. I have a feeling the ECS sending unit / tank isn't as documented as one would hope it was....

Is there anyone here that replaced the sending unit in their 70-71 california tank and had their fuel level gauge read the same?

Again: There is no difference between ECS and non-ECS tank senders. That's going by factory parts catalogues and service manuals. The problem sounds like it's on SPI's end.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I know chrysler says theres no differnece but thats just whats in the books, I wouldn't of surprised me of chrysler didn't bother to put a note in the books about a sender that was only used for 2 years....

Anyhow, what other brands are there? I'm looking at picutres of Quanta brand senders - they don't have a sending unit with vent line listed for a duster. They do for a volare but the pictures look different.

Let me broaden the scope of the question - has anyone used spi senders, in any applicaiton and had issues with guage reading?

In the real world, There is. No difference. Between. ECS and. Non-ECS. Senders! Period. And it wouldn't involve a "note in the books". The FPC for '70 has all the ECS and non-ECS part numbers. The '71 US FPC has only the ECS numbers, while the '71 Canadian FPC has the ECS and non-ECS numbers, with the latter being listed as "EXPORT ONLY". Think about it: When the roads were full of 1-to-10-year-old '70-'71 Darts, Valiants, Demons and Dusters, repair parts were needed. There were no super-secret unlisted part numbers for common replacement parts. There have been lots of one-year-only, two-year-only, five-year-only, half-a-year-only parts over the years, every one of them catalogued. You are on the wrong track guessing that there's a special ECS-only fuel gauge sender.

Chrysler will still sell you a genuine Mopar sending unit P/N 4051004 (no return line, if you want one add your own).
Not compatible

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Is that the new superceeded number? The 70-71 book shows 2932960.

It may be a little tricky to get a line added to my original sender, theres not much room on that plate. I may put it back in and tap a line into the fill tube, poke through the trunk and run it that way. Guess I'll have to rig my own return line, there goes an easy solution.

That is indeed the newest number for the sending unit that services all A-bodies starting from '63.

Why do you need a return line? Adding EFI?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I've had efi for a few years now - I used to tee the return line into the pump input instead of dumping into the tank and that has lead to some quirky hot run conditions - pump sucking fumes after the warm fuel boiled.

I have pictures of the setup in my slixers gallery thread and other scatterd posts. If you want to see more pictures just holler.

Yargh... and the tale lives on

I pulled out the spectra sender, and put in the dealer sender after fitting a return line to it - gauge is still off.

Thinking the gauge and/or 7805 retrofit may be at fault, I bought an aftermarket gauge, autometer 2642, rated for ford/chrysler (73 ohms empty, 8-12 ohms full) and it does same thing as stock gauge did.

At 3/4 tank full, it reads proper. After that it speeds up in a hurry, 5 gallons gone it reads 1/2, 6 gallons gone it reads quarter.

I think the aftermarket (spi, dealer) senders may be more linear, whereas stock senders (and stock/aftermarket gauges) are set to do something like expnentialy decay, a little at first (say one or two ohms per the first couple gallons) and more later (say 5 ohms per gallon for the last few).

I may have to get my scrap tank and play around with the senders by filling it up with water and reading at various points. Its hard to compare the senders accuately, externally just with an ohmeter because the pivot points for the arms are different, the stock one pivots at hte front just by the plate, where as the spi and dealer ones pivot about half way down the pickup tube.

Here's what I would do:

Get some various resistors (or a variable resistor) and figure out how much resistance is needed to put the fuel gauge at various positions (E,1/4,1/2,3/4,F).

Then figure out the arm position of the sending unit to match those resistances.

Then figure out how to place the sending unit so that the arm position will match the reading (some bending no doubt involved).

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Its not as straight forward as that... if you bend the arm then you change all positions not just one. You can get one spot acurate, not the others. Just like how I have now, the 3/4 full is accurate, but the rest arent. If I bend the arm to say make the 1/4 full accurate, then the 3/4 will be off.

Besides this is a dealer part bought by part number. Shouldn't have to go through anything to get it to work. Unles I'm missing something major, theres a universal manufacturing flaw amongst the replacment senders.

It sounds to me like there's a problem with your gauge or regulator. At any rate, the most critical reading is when the tank is empty. I don't really care if it doesn't read quite right at full but I sure want to know when it's empty or nearly empty.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

And thats why I did this...
Aftermarket gauges get straight +battery voltage, built in regulator and all, self contained.

The original sender, before this whole mess of adding a return line started, worked fine throughout the entire range.