Fuel Level Sender - Gauge Reads Backwards

[erniek70]

I just purchased a MkIV roadster. The fuel tank sending unit, and gasket, were both leaking. I ordered a new sender, Dorman Fuel Tank Sending Unit 692-246, which should work for a FI Fox body (in this case '93). I wonder if I ordered the wrong one? With the new sender installed, and the tank full, the gauge reads E. What sender should I have ordered? A SN95 sender? Weird thing, both old, and new sender, show approx, 160 ohms with float at the full position. I cannot imagine the new sender, the float is stuck at E? Gauge wrong? It cannot be as simple as wired backwards?

[i.e.427]

What did the old sender read at the gauge?

[Mastertech5]

The sender is just a variable resistor so polarity shouldn't really matter. The float arm may be stuck. I know that's sucks but... R&R and inspect. Does your gauge have power and ground, that would make it read E.

This bothered me since I posted it. The polarity [U]would[U] matter in this case. Sorry to mislead you. I see you probably have a handle on it now. Good luck.

[Papa]

What is the Ohm range for the new sender? Typical Ford range is 16-158. If the old and new sender are different, you may just need to calibrate the gauge. What gauges do you have?

Speedhut example:

Speedhut - Fuel Level Instructions (2-1/16”) (Settable Warning Light) https://speedhut.com/content/instructions/2in_and_258in_rev_fuel_level_instructions.pdf

[Jeff Kleiner]

Gauge pegged full indicates infinite resistance (an open) between the two sender wires, pegged empty indicates zero resistance (a short) between them. Unplug the sender and turn on the ignition. If it still shows "E" you have a wiring or gauge problem; if it shows "F" you have a sender problem. If you have Speedhuts you wouldn't be the first to have a faulty gauge.

Jeff

[erniek70]

both old sender, and new sender, resistance reads the same. around 160 ohms, full. I saw the sender for 83-86 FI works different. 0 ohms empty 78 ohms full. I am unsure which gauges I have, re: resetting them. I will have to take a look.

[erniek70]

It is pegged to E....but does not do the diagnostic sweep, like the other gauges. needle just jumps a little, then pegs to E.

[erniek70]

I just watched the video. My gauge has no built in button. Is this little plated hole on the back where the remote programming button would plug in? I have no remote button. I bought the car used. The gauges make no mention of the supplier, in the paperwork. From the video in the speedhut PDF QR code link, it appears to be a Speedhut gauge, and I just need to get a programming button. Naturally, the shipping is more than the part.

188432

[Papa]

Those are Speedhut gauges and yes, the port is for a programming button. Check your clock and speedometer to see if one of them has the programming button plugged into it.

[egchewy79]

I just watched the video. My gauge has no built in button. Is this little plated hole on the back where the remote programming button would plug in? I have no remote button. I bought the car used. The gauges make no mention of the supplier, in the paperwork. From the video in the speedhut PDF QR code link, it appears to be a Speedhut gauge, and I just need to get a programming button. Naturally, the shipping is more than the part.

188432

while at it, buy an extra programming button to keep on your clock which perpetually ends up about 15min fast every few weeks.

[Papa]

I bought an extra so I could keep one on the speedometer and clock as both of these should have one attached for normal use. The speedo needs one for accessing and resetting the functions in the digital display and the clock needs one to adjust the time.

[erniek70]

I ordered one this am...will check speedo id button is there.

[erniek70]

rec'd programming button this am. Gauge is fixed! Thanks for everyone's help!

[erniek70]

ok, works...sort of. Only reads accurately if alt is putting put over 14 volts. If I turn on electric cooling fan, headlights, etc., the gauge read low. WHY? Poor quality gauge?

[Papa]

ok, works...sort of. Only reads accurately if alt is putting put over 14 volts. If I turn on electric cooling fan, headlights, etc., the gauge read low. WHY? Poor quality gauge?

The alternator should always be putting out around 14 volts. If powering a fan causes your voltage to drop, something else is going on there.

[Mastertech5]

Is that at idle? Rev it to about 2000 and check. Most alternators will put out less at idle, depends on pulley size and amp rating.

[rich grsc]

Sounds like a 1 wire alternator. :(

[erniek70]

At 2000rpm, electric fan on, voltmeter shows only 12.5V. Dying alternator? Undersized amperage alternator? Still weird that fuel gauge is only accurate at over 14V charging system.

[erniek70]

It is. Do not know the specs...so far cannot find it in the paperwork

[Mastertech5]

Sounds like a bad alternator.

[Nigel Allen]

Underdrive pulleys?

[erniek70]

Ok, it is getting more complicated.


When I have the electric fan on, and headlights, the Speedhut voltmeter reads 12.5V. My multimeter, at the alternator, shows over 14.5V. So, I have a Speedhut voltmeter reading incorrectly, and a fuel gauge inaccuracy that seems to be tied to that erroneous voltage reading?

[mikeinatlanta]

Ok, it is getting more complicated.


When I have the electric fan on, and headlights, the Speedhut voltmeter reads 12.5V. My multimeter, at the alternator, shows over 14.5V. So, I have a Speedhut voltmeter reading incorrectly, and a fuel gauge inaccuracy that seems to be tied to that erroneous voltage reading?

Are the voltage readings coming from the same place? If from same place then maybe bad gage, but the rest of the symptoms are screaming bad connection or grounds.

[erniek70]

Per Factory 5 circuit diagram (MkIV, 2013), alternator feed fan switch, fan switch them feeds voltmeter, and the feed daisy chains the rest of the gauges. See top left of photo.188656

[Mastertech5]

You have a bad connection somewhere or bad gauge ground. Check the voltage at the other end of the charge cable, starter stud maybe, and work back to your fuse box feed. It should be about the same as at the alternator.