fuel guage bouncing

[motox]

I have a 98 yukon I got it about a month ago and the fuel guage isnt working. When I turn the key on the guage jumps to full then back to empty. As im driving it will bounce back and forth. Yesterday I put a brand new pump and sending unit in and fixed the wires properly. My brother is a tech at the GM proving grounds so I know it was done right. Still have the problem. Today I went to the junk yard and got a new insterment cluster and put it in, still the same problem. Can anyone help?Its got a new pump and sending unit, it has good ground, and getting good power to the sending unit. Im lost

 

[SunlitComet]

video of said bouncing please.

 

[motox]

My phone wont let me upload the video. Is there an email i can try sending it to? Like I said I turn the key to the on position it jumps past the full line then drops to empty and sits there. Sometimes as Im driving it will jump to full and a few min latter it will drop back to empty.

 

[domer94]

i have a similar issue in my 96, but just bounces , no wierdness on startup. do our trucks have voltage regulators? when my turn signals are on , my ammeter bouces with the signal as well. i know form tinkering with old british sportscars that strange guage activity was usually the voltage regulator or grounds. my grounds look good as well.

 

[ccapehartusarmyINF.(ret)]

okay you mentioned your brother is a tech at the GM proving grounds? just curious but were is that now? because they closed down the proving grounds here in east valley close by me in gilbert arizona been closed for almost 10 years now i was just wanting to know were there new one was

 

[SunlitComet]

My phone wont let me upload the video. Is there an email i can try sending it to? Like I said I turn the key to the on position it jumps past the full line then drops to empty and sits there. Sometimes as Im driving it will jump to full and a few min latter it will drop back to empty.

your sender goes thru the pcm before it reaches the gauge so if you are up to it disconnect the purple/white wire from socket #13 on the connector on the pcm that is labelled as clear. that will disable the sender for testing of it and the pcm if needed. if after you disconnect the wire the same problem is there then likely your pcm is at fault short of a bust ire somewhere along the way.

 

[domer94]

your sender goes thru the pcm before it reaches the gauge so if you are up to it disconnect the purple/white wire from socket #13 on the connector on the pcm that is labelled as clear. that will disable the sender for testing of it and the pcm if needed. if after you disconnect the wire the same problem is there then likely your pcm is at fault short of a bust ire somewhere along the way.

three questions... first , how common is the pcm to be at fault , second, where is the pcm / what is it? ... something control module? and third where can i locate the position # on the conector ? hanes manual wiring diagrams?

thanks

 

[SunlitComet]

sometimes yes sometimes no. pcm is the black module under hood left side engine compartment. the connectors have a color id cast into the module outer surface and when you dissemble the connector your should have location numbers on it if not let me know. this procedure applies only to 98 or newer only. earlier years go straight from the sender to gauge.

 

[domer94]

sometimes yes sometimes no. pcm is the black module under hood left side engine compartment. the connectors have a color id cast into the module outer surface and when you dissemble the connector your should have location numbers on it if not let me know. this procedure applies only to 98 or newer only. earlier years go straight from the sender to gauge.

ok thanks, guess i dont have to worry about the pcm then.. this issue is on my 96. so its either the guage / or sender at least.

 

[SunlitComet]

electrical resistance of the sender is 0-90ohms your can measure that of the sending or create that resistance to test the gauge.