Another fuel gauge topic

[2000tahoeZ71]

I know we have all seen a thousand of them, but I have yet to see any definitive fix. I have a 2000 Z71 obs and mine has always humminbirded, but always read correctly(as possible) until the other day. I was sitting in traffic and my needle went from 3/4 to buried at E. It then popped back up and since has read off. Filled it up and it started and E and gradually crept to full where it remained for 200 miles. I know it could be the sending unit, the actual gauge motor, or the PCM. I replaced my pump about 4 years ago with a parts store special and haven't had a lick of trouble with it. I can get a new delphi module for 109, but should I just replace the pump and sending unit first? I have seen that you can check the ohms from the purple and white wire where it plugs into the PCM, but I dont really want to unwrap that bundle of wires and start to fooling with it just yet. Thanks for any help.

 

[ccapehartusarmyINF.(ret)]

mines worse ever since i replaced the entire evap emissions parts and replaced my fuel pump my guage up front only reads just above a 1/4 tank when i runs completely outta gas

 

[SunlitComet]

getting that wire off the pcm may be the only way to test the actual sender. de-pin is best but also maybe cut wire upstream of pcm then splice back together. and while testing the disconnected sending unit see if the gauge acts goofy. if it does really bounce around weird then the pcm is goofed.

 

[2000tahoeZ71]

I disconnected the connector to the pcm and cut the key on and the gauge pegged at flat to the right past full. I tested pin 9 (counting from the right of the connector facing it as it plugs into the pcm) using the 200 ohm range on my meter and showed no connectivity. I tested to what I thought were good grounds(firewall bolts and master cylinder). Any suggestions?

 

[SunlitComet]

it see's it as an open circuit as you did and by design the fuel gauge moved to full as the pcm sees no resistance on the wire that is not connected. for reference when the tank is empty the sender should give out 40 ohms and when full 250 ohms. try the negative battery post for ground. if that fails try cleaning up the pump module ground terminal on the left frame rail along side tank. Hell it might help the pump as well if corroded. if still no reading from the sender then it may be safe to assume the circuit is dead. Can you get your hands on a potentiometer in the 40 -250 range to hook up to the pcm that would test its function. or some good resistors from radio shack.

 

[2000tahoeZ71]

I knew with no connectivity it would read as if no resistance and therefore a pegged out gauge. Is it safe to say that my stepper motor is working correctly? I didn't have any resistors or a pot on hand to test, and I didn't have any wire to go to battery ground. Thinking at this point I may just go ahead and put a pump in it as its only 100 bucks and will buy me peace of mind, and I've got a leak when I fill it up so thinking the top vent is leaking or something.

 

[SunlitComet]

If the gauge was not ******* against an internal stop and not vibrating then yeah the gauge could be fine and likely the pcm. If you do the pump and have a 4 door get the Delphi fg0089. The best you can get $110 at amazon right now. It is the redesigned one with new connector pigtail as well.

 

[2000tahoeZ71]

That's the one I'm looking at sunlit. I figured for 110 bucks for a Delphi then what the hell. I've made it 4 years with a spectra that I bought when I had to have one ASAP. I don't plan on getting rid of it so I guess I'll just bite the bullet and replace it and see what happens. I know a lot of people send their pcms off to get retuned by blackbear etc. If it was the pcm is it an internal error or something a retune could fix possibly? As for the gauge, when it was disconnected and pegged, I didn't notice any vibration but then again didn't really look for any either. I'll try again tomorrow with a good ground and a pot hopefully. The pin I'm
Going to is pin nine counting from the right and the one I'm pretty sure the purple and white wire is going to

 

[SunlitComet]

correct wire i think when i checked the manual. i think when you test this circuit like you did you will maybe lock in a dtc code. likely will be hidden and not activate the ses light. in fact look for any set codes at all while messing with it. wipe it clean of codes afterwards. retuning can change just about any thing but is just a band-aid solution for a broken sender. if it decides to get worst guess what you do again.

 

[2000tahoeZ71]

I tried again today with a known ground, and every time I touched the pin with the meter I heard what sounded like a faint static coming from the engine bay somewhere. Almost sounded like it was on top of the intake. When I reconnected the pcm the gauge pegged at below E. I rocked the truck and the gauge shot back to full. Started to really lean towards the sending unit. New pump will be here Friday so we will see what happens.