Another fuel gauge issue...

No, when I tested the float outside the tank, both sending units have same results with the gauge. I wanted to refurb a cluster anyway (Orange paint on needles, etc...) for $40 at the jy, I figured why not. unfortunately, all same issue. I'm going to check the connectors you'd mentioned earlier.
 
VAcherokee said:
No, when I tested the float outside the tank, both sending units have same results with the gauge. I wanted to refurb a cluster anyway (Orange paint on needles, etc...) for $40 at the jy, I figured why not. unfortunately, all same issue. I'm going to check the connectors you'd mentioned earlier.
Click to expand...

Post #12: Correct. I ran the IC test, it passed.
 
Oh, THAT test. Yes, I ran it and it passed function... I got lazy today but should get into it more tomorrow. Dash is still out and I need to calibrate the Speedo. I was able to pinpoint locations of connectors and spices for the fuel pump harness while digging in the wrecked jeeps.
A little recon at the JY is always fun!
 
UPDATE: Today I took the Cherokee out for a drive... I went to get gas and it took 6gal. The new cluster was at the line just before FULL...

Now that I've verified the gauge does move but incorrectly, where should I start looking now? I've checked out all the plugs by unplugging and reconnecting, still same ol sh...


I wasn't able to document EXACT mpg because I changed clusters in the middle of the diagnosis. I'm currently doing a mileage vs consumption vs indicator test.

Any further ideas or help is much appreciated.
 
Do you get any CEL Codes indicating fuel level problems? Some codes will be stored but not put a CEL on. You'll need a scanner or code reader to see if any codes are stored (pending).

Here's some DTC codes:

P0460 (No CEL) - Fuel Level Unit No Change Over Miles - During Low Fuel.
P0460 (No CEL) - Fuel Level Unit No Change Over Miles - Fuel level sending unit voltage does not change for more than 40 miles.
P0462 (No CEL) - Fuel Level Sending Unit Volts Too Low - Fuel level sensor input below acceptable voltage.
P0462 (CEL On) - Fuel Level sending Unit Voltas Too Low - Open circuit between PCM and fuel gauge sending unit.
P0463 (No CEL) - Fuel Level Sending Unit Volts Too High - Fuel level sensor input above acceptable voltage.
P0463 (CEL On) - Fuel Level Sending Unit Volts Too High - Circuit shorted to voltage between PCM and fuel gauge sending unit.
 
So far, no codes stored or set. I did have a hard fault (light on) After cycling the key with the CPS disconnected along with the 3 connectors on the passenger side of the engine... I reset the PCM (disconnected battery).

The gauge IS moving with the Airtex sending unit but it's not right, YET. Guess it's time to pull the seats and inspect the body harness from the pump to the dash.

I've been a mechanic for 16 years and NEVER have I had my @ss handed to me on a silver platter of this caliber! :-!
 
VAcherokee said:
So far, no codes stored or set. I did have a hard fault (light on) After cycling the key with the CPS disconnected along with the 3 connectors on the passenger side of the engine... I reset the PCM (disconnected battery).

The gauge IS moving with the Airtex sending unit but it's not right, YET. Guess it's time to pull the seats and inspect the body harness from the pump to the dash.

I've been a mechanic for 16 years and NEVER have I had my @ss handed to me on a silver platter of this caliber! :-!
Click to expand...

Don't una$$ your Heep yet.

I generated a reply but did not hit submit reply before jumping back to the forum so I lost it all. After a few beers to calm my nerves I'll regenerate the replay.
 
It's funny... every time I crack into this Damn fuel gauge I manage to find something else to "fix". Today, I find my bad vacuum check valve that's been rendering my CC inop/C to btow from the defrost vents.

Yeah, let me know Whatcha come up with, I'm curious. I suppose it's easier to work on your vehicles when you actually have your tools! Mine are being shipped from CA to my new house in VA. :farmer:
 
Well,

I was wondering if...

You can check your old fuel pump fuel level sender to see if its within specs.

Resistance Specs are:

Full Up - 20 Ohms +/- 5% = 21.0 to 19.0 Ohms
Full Down - 270 Ohms +/- 5% = 283.5 to 256.5 Ohms.

Below is a pic of the fuel pump module connector and a pinout chart of the body harness connector, which shows the pin cavities, wire colors, and functions. The wire colors are the body harness colors, not the pump colors.

FuelPumpModuleConnector_3.jpg


Using your digital Volt/Ohmmeter set at 2K Ohms for the Down reading and at 200 Ohms for the Up readings, back probe (using Safety Pins or other back probes) the pump connector wires for pin cavities 3 and 4. Connect your Ohmmeter to the back probes (see pic) and run the float arm full Up. You should see the Up spec resistance. Switch to 2K Ohms and move the arm Down. You should see the Down Spec resistance (move the decimal point over three places).

FuelLevelBackProbe.jpg


If your old level sender is within specs, disconnect your fuel pump connector and connect your old pump connector to the body harness connector, leaving the back probes in 3 and 4 wire positions. Hook your voltmeter to the back probes. Select 20 Volts DC on your meter. Turn key to RUN. Move the float arm full Down and record the voltage reading. Move the float full Up and record the voltage reading.

You may want someone in the cab to watch the fuel gauge while you're doing this to see how the gauge reacts. The low level light should come on around the 1/8 level (+/- 3 gallons).

I don't know what the voltages are supposed to be right now but I would think that the full Down position would be lower than the full Up position because if the different resistances.

Do this and get back.
 
Ok: Since I ran out of fuel with this OE pump reading 1/4 tank, I was able to emulate it with my meter. I REALLY MISS MY TOOLS AND ALLDATA PRO right now! Thanks for the pictures and pinouts

*2k down reading: 00.0 (If I wiggle test armature, I get 277)

*200 for up reading: 20.02

I'll head out to XJ in a few.
 
Jeep is showing 69.9 ohm... this is parked on somewhat level ground, key off and pinned to the fuel pump module harness (disconnected from body harness)

I'm assuming 270 / 69.9 is 25.89, roughly 1/4 tank used so I'm actually at 3/4 tank? I'll fuel it up and check resistance vs how many gallons it actually took...
 
Last edited:
VAcherokee said:
Jeep is showing 69.9 ohm... this is parked on somewhat level ground, key off and pinned to the fuel pump module harness (disconnected from body harness)

I'm assuming 270 / 69.9 is 25.89, roughly 1/4 tank used so I'm actually at 3/4 tank? I'll fuel it up and check resistance vs how many gallons it actually took...
Click to expand...

Didn't see any voltage readings in the above post. The Ohm data I gave you was just to test your old pump fuel level sensor. The readings you gave in the previous post look good.

Can't figure out how/why you're trying to figure out what the tank is doing using an Ohmmeter.

:dunno:
 
I know my original sending unit is bad, has a huge dead spot at the bottom end (empty). I had to push on it to see what the ohms were. I was simply trying to see how much fuel the current in tank sending unit reported in ohms with direct relation to the gauge. I had to go into town so I didn't have time to get voltage and reported what I could while I remembered. :-)

I'll back probe and get volts in the am.

Thanks!
 
Ok sir, got the volts!
EMPTY IS: 2.95v
MIDDLE IS: 1.68v
FULL IS: 0.46v

I got these numbers using the AIRTEX pump that is installed in the tank... (after I drained the tank, I removed it and took out the pump) I siphoned out all the fuel and monitored it in 5gal increments. I confirmed the following:

When there's 5gal in it, the gauge reads 1/2. When there's 2.5 gal in it, tank is at 1/8 & fuel light comes on. Any less than 2gal the needle is buried in the E.

any suggestions from here? I'm willing to leave the jeep apart at this point to solve the issue.

Thanks!
 
I also wanted to emphasize when I had the OE & AIRTEX pumps side by side the armature on the AIRTEX was up higher than the OE. I performed a mechanical sweep of both sending units and when they were compared and marked at 1/4 tank, the AIRTEX armature float was exactly 1/4 tank higher! SO: If I matched up float levels side by side, the OE would read 1/4 tank and the AIRTEX would read 1/2 tank. Perhaps we're back on AIRTEX SUCKS? If I sound out of it, it's because I am! 2hrs in and around GASOLINE on my back. Lol :puke:
 
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