crabi53263@aol.com

Hi folks

I would like to think i came here for a better reason than help with my Suburban, I love these trucks i have a 96 tahoe and a 01 suburban both very high mileage i have gone through both of them from front to back, not perfect but they ride nice, the 2500 is a little ruff but lol

Ok the point of my post is the fuel gauge prior to both fuel pumps being replaced was on E with the light on and it was out of gas, the line broke by the rear tank so i replaced every fuel line on the truck and all the brake lines with full nickel, put it all back together and the fuel gauge will cycle once then read empty, so i thought it was the main tank sending unit, i dropped the tank again and bench tested the main fuel pump, empty was 38ohms full was around 240 which is within specs, So i replaced the dash cluster with a junk yard one, i saw the fuel gauge work before putting it in my truck, still nothing when actuating the float level arm, so i got another junk yard cluster and the same thing, i reinstalled the original cluster and same thing, then i tested the harness up to c152 plug which is under the fuse panel and when i actuate the float arm i can see the 39ohms empty and around 240 full with no bouncing around, after the c152 plug it goes into the ECM then to the dash, so im stuck, this all leads me to believe the ECM has failed, I have never once seen a ECM fail where only the fuel gauge wouldnt work, I have power and ground at the pump i also have a 5v reference on the sender wires.
Any ideas folks?
If anyone has a wiring schematic for the cluster or how to test the fuel gauge in the cluster that would be great, as a note i have not programmed the dash cluster to this truck, i will also mention the original cluster does the same thing all 3 clusters do, cycles once then goes to empty
Any help would be greatly appreciated, i spent the last 6 months going through this 2500 suburban, i replaced everything in the front end ball joints tie rods hub bearings you name it lol, , the hydro boost lines and ps pump, the ABS module and pump, set of new front window lift motors, front driver seat, its loaded with air ride which i have not dug into yet, but i dont want to put this tank back in until i see the fuel gauge n the dash work.

Thanks in advance for any help with this, I dont enjoy asking for help but i am stuck and i know others have run into this one, i cal tell by just a internet search

repairman54

I use alldatadiy.com for shop manuals. They are the real deal, yeah it's a subscription but I don't trust online freebies.
Use an electronics cleaner / lubricant in all the connectors. PCM has multiple grounds that affect its different functions so the manual is a must to probe the harness.
Check the connectors for pins that may have backed out or are bent also. I've read about pins that were never fully locked into position from the factory and caused issues later on.

crabi53263@aol.com

Thanks for the reply
I have seen some schematics online and kinda figured on the chevy forums someone would have some, i have a bunch for an Nissan i helped a friend with that had a short in the dash harness, that was fun,
having been able to articulate the float arm and visibly seeing the sending unit operate correctly means from that part of harness back is working, its able to send the correct information, from that connector through to the IPC is the question, the IPC has been replaced so that leaves me a short piece of harness and the ECM,
ever seen a ECM lose only the fuel gauge?
it sounds like software not hardware, but i dont recall ever hearing a issue with the gauge that was fixed by a reflash of the ECM

crabi53263@aol.com

Hi folks,

Anyone have the diagnostic path for this fuel gauge testing? i am at c152 plug and have full operation of the fuel sending unit, i could use the rest of the procedure to find out if this is in the ECM or harness, i would also like to test the gauge cluster,, i could use a pin out or some color reference to continue testing,
what does the ecu do with the information from both fuel pumps?
how does the ECU use both fuel pumps to come up with a fuel level,
can i bypass the ecu and go direct to the cluster with the fuel sending unit wires?

Wavelength

I had the same problem with my 2001 Yukon. Make sure there is a good ground coming out of the fuel pump/sensor connector. I cut into the wire at the fuel pump and made a good ground at the chassis by grinding to bare metal with a dremel tool and screwing a ground connector there. I think it would be just as good to cut in at the cluster connector under the dash. Good luck.

repairman54

Since you have 2 gas tanks then tank selector switch could be an issue also since it switches the gauge to the tank being used.
Really need the wiring diagram.

crabi53263@aol.com

Thank you for the response,

I did clean and replace the main grounds on the fuel pump when i installed it, there is 2 grounds i ground to metal then put new ends on and secured, on the frame rail under driver door is the fuel pump ground if i remember right, interesting thing happened today however, as i noted I when i articulate the float arm i can read that from the c152 bulkhead connector with a ohm meter under the fuse panel. today while doing some additional fuse testing, i found a fuse for the trailer wiring blown and replaced it, i had removed the ECM to get the part number in case i need to replace it, i put that all back in place, with the pump still on the ground i had plugged everything back in hooked the battery up and the fuel gauge on the dash was working, i articulated the arm and it worked, it moved slow which was good also, i stuck the pump back in the tank reinstalled it started it up ran great but the fuel gauge is again not working, so i unplugged the c152 bulkhead plug again looking for resistance on the G and K wires and now nothing, so i had it working immediately installed it and now its getting no signal from the ECM, it will run the truck but no readings on the fuel gauge wires now.
maybe bypass all the fuel gauge signal wires outside that look from the c152 plug to the main fuel pump, thhat gets rid of that being a possible issue, im starting to wonder if when i compress the fuel pump during install it loses connection, its an airtex and yeh i know but no one had the delphi or the delco when i tried to get one, it bench tests perfect but i never compressed it during a bench test,
This is getting annoying really, its a damn fuel pump it should not be this much trouble
any ideas?

crabi53263@aol.com

thanks for the reply

This does not have a tank selector its run off the ECM, the rear tank operates on its own to drain it into the center tank, supoosedly the ECM does the math through the 5v reference lines it uses to meter the variable resistor or sending unit in the fuel tank. it does this without intervention.
when i had it on the ground i can see the 5v reference and when tested at the c152 bulkhead connector it tested good, i could articulate the float arm and see it in the ohm readings, but when put back together it all went back out again, and now at the c152 connector i have no ohm readings at all, i should at least get 38ohms,
I may just run my own gauge wires inside a seperate loom from the c152 bulkhead to both pumps, then i know its not wiring, problem is both sending units have two wires used for the gauge, i dont know if they just are spliced together somewhere along the harness or not, the test on the c152 plug has one orange with black stripe wire and one dark blue, the wires at each fuel pump are orange with black stripe and purple, i see 4 in that huge harness along the frame rail when i opened it

any ideas?

crabi53263@aol.com

anyone know if i can just run two wires from the c152 plug to the fuel pump to rule out it being a short?, in the wiring diagram the two sending unit wires from the rear tank also connect to the ECM, do they splice into the two sending unit wires? or is that on a diferent plug?
If anyone has the wiring from the fuel pumps to the ECM that would be awesome, i think i can bypass the harness with a splicing a couple wires running them from that plug all the way to the main pump,
testing today i still have 5v reference, i have 38.6ohms coming from the sending unit the 38ohms would lead me to believe the tank is empty, but i put 5 gallons in, needle didnt move. i noticed one thing ill test again tomorrow is the 12v to the pump, at one point during testing it went to 28mv approx, so who knows
anyone have any insight or some wiring diagrams i would greatly appreciate it

thank you

crabi53263@aol.com

hi again folks

anyone have any ideas?
at the g and k terminals i find 38.6 ohms, which is withing spec considering theres only a few gallons in the main tank, i ran a voltage check across those same terminals and found 12 volts also?, does anyone know what i should be reading on the c152 plug to test the fuel pump and gauge?