fuel sending unit

Topic: fuel sending unit (Read 2676 times) previous topic - next topic

fuel sending unit

Reply #30 – January 06, 2009, 06:58:35 PM

can you jump the wires off the sender connector with the paperclip, and see if it pegs the gauge too?

fuel sending unit

Reply #31 – January 06, 2009, 07:00:21 PM

What do you mean? If i jump the connectors on the sender end only its not connected to the wiring going to the gauge nothing is going to happen.

fuel sending unit

Reply #32 – January 06, 2009, 07:04:00 PM

I thought it was connected to the gauge

fuel sending unit

Reply #33 – January 06, 2009, 07:48:46 PM

I think he meant "unplug the sender, take the harness plug, jumper the wires, and look inside the car and see what happens", which it appears you've done.

Either that, or he meant plug the sender back in and jumper the wires with the sender connected (jumper between where the wire is soldered to the board and the "wiper") to eliminate the possibility of a short or poor connection in the sender itself...

Mitchell OnDemand's advice for testing the gauge itself:

Quote

To test gauge for open windings, remove gauge from cluster. Connect gauge to ohmmeter and read resistance.
A reading of 10-15 ohms is normal because current increases temperature of gauge coil windings. If ohmmeter
reads below 10 ohms or above 15 ohms, replace gauge.

fuel sending unit

Reply #34 – January 09, 2009, 03:05:26 PM

What do you mean plug the sender in and jumper the wires with the sender connected? How is that possible?

fuel sending unit

Reply #35 – January 09, 2009, 03:16:32 PM

Let's just start from the beginning so we can keep track of what we tested.......
Did you use the paper clip in this connector to try and peg the gauge?
This one plugs into the tank sender under the car.

fuel sending unit

Reply #36 – January 09, 2009, 07:14:32 PM

no. I did it from the connector in the trunk. I'll have to drop the tank again to do that. I was hoping it might be something else.

I'm begining to think the aftermarket tank might have something to do with it. All jumping the circuit does is tell us that the gauge will go to full right? Because didn't i accomplish that by jumping the circuit in the trunk? I'm just wondering.

fuel sending unit

Reply #37 – January 09, 2009, 07:58:28 PM

If you pegged the gauge from the trunk, the wiring is more then likely ok from that point to the dash.
If the gauge doesn't peg from the connector in the pic, you have a wiring problem between the tank and the trunk.
if you peg the gauge from that connector in the pic, then we'll recheck the sender, and go from there.

Sorry, I wish there was an easier way to check this, but there isn't unless you cut a access door in the bottom of your trunk like what was discussed in a recent thread.

Jerry

fuel sending unit

Reply #38 – January 10, 2009, 12:26:05 AM

all of the above sounds good to me. but................

If you decide to read from the trunk connector again, the only way to get the sender float to move is to pump gas out.

To do that, you go to the eec self test connector and ground the tan / light green wire prior to turning on your ign switch.

This will run your fuel pump full time. Disconnect the fuel rail feed and rig up a hose from your fuel feed to an empty gas jug.

With a meter already placed on the trunk connnector set to ohms,
your key on and the tan / light green wire grounded and fuel emptying into a gas jug, you should see the resistance change as the fuel level drops.

fuel sending unit

Reply #39 – January 10, 2009, 12:49:40 AM

Quote from: jpc647;250507

The gauge pegged. Way beyone full. What does this mean? .

What this means is you did follow the instructions but technically, you needed to jumper the yellow and white wire with a 8-10ohm resistor.

That would properly simulate ............
Full- for an buttstuffog cluster and sender
Empty for a digital cluster and sender

Using the resistor would prevent the full peg effect. Its covered in my diy link by the way.

fuel sending unit

Reply #40 – January 10, 2009, 02:05:43 AM

ok, lets think about one other variable that has already been suggested.
We have to remember that it takes very very little change in resistance to have a drastic effect on the cluster needle reading. The sender can read anywhere from 8 (full)- 90(empty) ohms on an buttstuffog sender. 8-15 extra ohms can force the buttstuffog cluster to read more empty sooner than full if the yellow wire has high resistance. Its a ratio thing and it makes sense.

Remember ,, an buttstuffog cluster's sender reads opposite from what you would logically think is correct. An buttstuffog sending unit empty resistance is high. Any additional resistance along the yellow wire will cause it to read "more empty" than what it normally would. (ie-higher resistance back at the sender / wiring = higher voltage drop along that path, thus less voltage delivered across the guage showing less fuel than what really is there.

-go to the yellow wire under the car as close to the tank sender as possible.
-penetrate that wire with a stick pin
-go to the yellow white wire up at the cluster (yes remove cluster again)
-insert your meter into pin 4 (yellow/white) of main cluster connector C285.
-jumper from the stick pin up to your other meter lead with as short of a wire as possible.
-read resistance

for whatever its worth, reading from the actual connector as mentioned would have yielded the most accurate resistance reading because that physical connector is pr0ne to corrosion and the like. All of this equals high resistance. remember, your symptoms are appearing like your sender is reading higher resistance than you think it should. Any additional resistance from the output of the guage to the ground side of the sender would cause faulty readings on the guage.
*******report back

Next,
I would check something new that i have pondered for you off and on. IN the EVTM, page 129, there is a resistance wire called out on pin 7 (black / light green)of cluster connecter C285.
The reason i bring this up is because you also mentioned you were having cooling needle issues as well.
We would all think the one thing in common is the cluster but you have swapped these with no change in your symptoms. We have to look now at what feeds the IVR (ie-pin 7 of C285 black / light green).

I have never ever had to check this wire so its up to you.
-locate the black/light green wire at both ends from the ignition switch to cluster c285 pin 7 black / light green.
-read the reisistance of that wire.
>jot down value
-increase the temp of this wire via a hair dryer (simulate heat produced by the dash being loaded with current in the form of watts.
>jot down value
*******report back
The resistance wire should hold at approx 8ohms.
I have not idea what the purpose of the "bare copper wire" is other than it may be a heat sync.
If it is a heat sync, then perhaps its not connected at one end and thus it is not pulling the heat off your resistance wire.

To improve the copper wires capability to remove heat from this wire, skin you up a bare copper wire and wrap this black / light green wire with it. connect the copper wire to a good chassis ground connection somewhere.

-reheat resistance wire and read resistance of approx 8 ohms.

If for any reason you think this wire is fubar (fuggered up beyond recognition), you can replace it with a solid wire making sure to insert an 8ohm resister in line with it.

-----------------------------------------------------------
Next....

with your cluster in, tell us how many volts you have appearing on the input to the fuel guage. You must have approx 5volts. there is more to this but I will leave it at that for now.

------------------------------------------------
look at the diagram below.
current travels through the igntion switch,
then through the reistance wire with (assumed heat sync)
then into the IVR (metal little box on back of cluster)
then out of IVR to branch feed 5v to three guages.
then through the fuel guage
then through the sender
then to ground.

Basically its a series circuit for this specific feature.

When the reistance of the sender is high (ie-low fuel level), the majority of the 5v is lost across the rheostate in the sender. this leaves very little voltage drop across the guage thus reading low.

When the reistance of the sender is low (ie-full fuel level), less voltage is dropped across the rheostate on the sender. This leaves a large proportion of the voltage drop across the guage thus reading high.

so,,,,,, to more easily understand this, please remember that the higher the resistance of the sender , the more voltage drop it gets and thus leaves very little for the guage to feel thus reading low.

compare the above to a digi sender and you will see that the dash LED indicator will be configured backwards but still opperates on the same premis.
However, by simply opening up the digi sender and relocating the blackwire to the other end of the rheostate, you inherit an buttstuffog sender.
another option would be to flip the guage wiring to compensate but I dont think thats a good "long term" idea because you might sell the car and no one is gonna know what the hell is going on.

perhaps your dealing with this now and you dont even know it:flip:
------------------------------------

Last but not least,, perhaps your sender(s) have bent arms where they are suppose to be 110deg as stated on the midway down bend? if thats the case, your float is not reacting in a calibrated way with relation to fuel level.

fuel sending unit

Reply #41 – January 10, 2009, 08:08:31 AM

and if your looking for the angles of the float rod. I listed them in post #18 I believe.

fuel sending unit

Reply #42 – January 10, 2009, 08:49:16 AM

Quote from: jcassity;251004

all of the above sounds good to me. but................

If you decide to read from the trunk connector again, the only way to get the sender float to move is to pump gas out.

To do that, you go to the eec self test connector and ground the tan / light green wire prior to turning on your ign switch.

This will run your fuel pump full time. Disconnect the fuel rail feed and rig up a hose from your fuel feed to an empty gas jug.

With a meter already placed on the trunk connnector set to ohms,
your key on and the tan / light green wire grounded and fuel emptying into a gas jug, you should see the resistance change as the fuel level drops.

Just remember to connect the meter to the connector that goes to the tank not the dash. (you may need alligator clips) If there's no change or signal, then you'll be draining the tank anyway to be able to drop it, and get to the wiring to do the rest of your testing.

fuel sending unit

Reply #43 – January 10, 2009, 02:01:09 PM

this certainly does not look like a wanted/for sale thread. I almost continued this up in its original thread.

fuel sending unit

Reply #44 – January 10, 2009, 02:06:38 PM

LOL.
it got taken over.
I didn't even realize it was in the wanted section.