gas gauge issues

[Kozworth]

Wow, I really lucked out when I got the 'new' gas tank for my car, I didnt even know that just the facelift year of 88 had such an impact.

I might just try inplugging one and seeing how it affects my gas needle.

[nando]

Im almost sure one is for the fuel guage, and one is for the empty light at 2 gallons.

seperate.

does a 318 not have an empty light? even if it does, it goes from the same sender obviously.

no, it's two level sensors. one does have the reserve light built into it, but they both function as level sensors.

and yes, a 318 has a reserve light.

[stamar]

no, it's two level sensors. one does have the reserve light built into it, but they both function as level sensors.

and yes, a 318 has a reserve light.

Thanks.

[Kozworth]

why is there two though? So what would be some symptoms if one sender was bad, and the other was good?

[stamar]

why is there two though? So what would be some symptoms if one sender was bad, and the other was good?

x2

I have one sensor that i know works because the light works. one sensor that might work or the gauge is wrong.

what happens if one sensor works and one doesnt? Does the needle go to the middle then by chance?

or is one going to the obc?

[nando]

why is there two though? So what would be some symptoms if one sender was bad, and the other was good?

because if you're cornering hard or at an angle, it will still read the correct level even though the fuel is sloshed to one side of the tank. a single sensor on the passenger side will read low when cornering right, and high when cornering left.

if one sensor went bad - well it depends. it could always read from full to half, or it would read half to empty. Or it would simply read full or emtpy. they're wired in series so it depends how one of them failed.

the operation from the light is actually seperate from the sensor. it's built into the housing - but it's really just a switch, it's not dependent of the resistance curve of the senders. It even has it's own wires.

[ev87]

I've had a very similar issue. Here's how you diagnose an 88+ with the two senders, and some general info:

I'll refer to the two sender units as passenger and driver side just to make it easier. One has three pins, and the other two. The empty bulb is driven off the passenger's side one, and is indeed the third pin on that sender unit. My understanding is that the empty indicator can still function even if the level sensor is broken.

To diagnose, look at the data sheet. The passenger's is part# 224-817-022-006Z and the driver's is 224-802-033-001Z. Specifically, what's interesting here are the empty and full values for resistance. The sensors function as a variable resistor, the more empty the tank, the more resistance.

The procedure I used involved taking a multimeter in resistance (ohm) mode, and measuring both sensors at various points of tank full-ness. To measure the driver's side, place the two leads on the two terminals. For passenger's side, place them on the left and middle terminal if looking at the plug head-on.

Practically, grab a piece of paper, and draw a table with columns for estimated fuel level, passenger's resistance measurement, and driver's measurement. Then, fill up to the top of the tank. Write down your measurements. Drive around a bit. Take a measurement. Keep driving. Take another. Keep driving. Take some more measurements. Finally, take one last measurement when the empty indicator comes on. Compare the values you see to the ones in the data sheet. It should become obvious from looking at these which fuel level sender is broken.

Hope that helps!

[stamar]

I've had a very similar issue. Here's how you diagnose an 88+ with the two senders, and some general info:

I'll refer to the two sender units as passenger and driver side just to make it easier. One has three pins, and the other two. The empty bulb is driven off the passenger's side one, and is indeed the third pin on that sender unit. My understanding is that the empty indicator can still function even if the level sensor is broken.

To diagnose, look at the data sheet. The passenger's is part# 224-817-022-006Z and the driver's is 224-802-033-001Z. Specifically, what's interesting here are the empty and full values for resistance. The sensors function as a variable resistor, the more empty the tank, the more resistance.

The procedure I used involved taking a multimeter in resistance (ohm) mode, and measuring both sensors at various points of tank full-ness. To measure the driver's side, place the two leads on the two terminals. For passenger's side, place them on the left and middle terminal if looking at the plug head-on.

Practically, grab a piece of paper, and draw a table with columns for estimated fuel level, passenger's resistance measurement, and driver's measurement. Then, fill up to the top of the tank. Write down your measurements. Drive around a bit. Take a measurement. Keep driving. Take another. Keep driving. Take some more measurements. Finally, take one last measurement when the empty indicator comes on. Compare the values you see to the ones in the data sheet. It should become obvious from looking at these which fuel level sender is broken.

Hope that helps!

where did you hook up the ohm meter for each sensor, you mean inside the tank? where in the car?

what was your symptoms, and what were the readings like?

what was wrong with yours?

[nando]

To diagnose, look at the data sheet. The passenger's is part# 224-817-022-006Z and the driver's is 224-802-033-001Z. Specifically, what's interesting here are the empty and full values for resistance. The sensors function as a variable resistor, the more empty the tank, the more resistance.

got a working link? 404 not found..

this is a model I built of the 2-sensor gauge:

Voltage divider formula:
vout = r2/r1+r2*vin
Vin: ~13.5v
R2: ~136 ohms (the gauge is ~68 ohms, and an on-board resistor is also ~68 ohms).

(R1; ohms per sender)
Empty 40.0
1/8 36.1
1/4 32.3
3/8 28.4
1/2 24.5
5/8 19.0
3/4 13.5
7/8 8.0
Full 2.5

(volts)
Empty 5
1/8 4.7
1/4 4.3
3/8 4.0
1/2 3.6
5/8 2.9
3/4 2.2
7/8 1.4
Full 0.5

being a model, they're not exact values.

[ev87]

got a working link? 404 not found..

this is a model I built of the 2-sensor gauge:

Voltage divider formula:
vout = r2/r1+r2*vin
Vin: ~13.5v
R2: ~136 ohms (the gauge is ~68 ohms, and an on-board resistor is also ~68 ohms).

(R1; ohms per sender)
Empty 40.0
1/8 36.1
1/4 32.3
3/8 28.4
1/2 24.5
5/8 19.0
3/4 13.5
7/8 8.0
Full 2.5

(volts)
Empty 5
1/8 4.7
1/4 4.3
3/8 4.0
1/2 3.6
5/8 2.9
3/4 2.2
7/8 1.4
Full 0.5

being a model, they're not exact values.

I uploaded a mirror here.

When I say hook up the multimeter, I mean to the sensor itself. There are access ports under the rear seat. Just pull the bottom cushion of the rear seat up, and It'll come right out. Then, lift the carpet, and you'll see two metal covers that'll give you access to the sensors.

My driver's side sensor was shot (the resistance values it put out in no way corresponded to the actual fuel level in the tank).

[Kozworth]

Epic, thank you for putting up the explination to the sending units and the correct values for the correct ohm resistance.

Its wierd, i filled my tank (first time woo)! And for the 1st 100 miles the needle hardly moved an 1/8th.. then doing the next 100 it moved down to about a half.. then the next 30 miles it dropped a little more then a quarter. Atleast i know how to diagnose this now!!

[stamar]

that rules . Doin it word problem style didnt sound exciting although i admire you did that definitely. Particularly since I no longer have anything but an estimate of what half a tank is gonna be like anymore. I just need that top reading.

btw, someone pmed me and asked me to post the youtube video

http://www.youtube.com/watch?v=HwdBXIITqBs

This is for the grounding nut problem.

I think between that and a list to check the ohms and volts of each sensor thats all you need. I didnt even understand how that could work until i saw the list.

Id say fill it up, hit each one you should know the answer right away. smack the dashboard and see if it moves.

[nando]

To diagnose, look at the data sheet. The passenger's is part# 224-817-022-006Z and the driver's is 224-802-033-001Z. Specifically, what's interesting here are the empty and full values for resistance. The sensors function as a variable resistor, the more empty the tank, the more resistance.

according to VDO, the E30 sender for the passenger side is 224-817-022-007Z. 224-817-022-006Z is for the E12, E23, E24, & E28.
(page 25)

http://www.vdo.com/generator/www/com/en/vdo/main/hidden/downloads/replacement_parts/fuel_systems/flc_catalogue_fuelsystems_v_7_0_en.pdf?redirect=false

[nando]

updated my model to reflect better data:
Ohms (total)
Empty 124.9
1/8 110.1
1/4 95.3
3/8 80.5
1/2 65.7
5/8 50.8
3/4 36.0
7/8 21.2
Full 6.4

Volts
Empty 6.5
1/8 6.1
1/4 5.6
3/8 5.1
1/2 4.5
5/8 3.7
3/4 2.9
7/8 1.9
Full 0.6

fortunately the difference between my first pass doesn't affect what I'm trying to do. The volts at empty are pretty much what I saw measuring in the car, too.