I have been watching the treads on fuel gauge issues mine seem to be a little bit different the what other people have been seeing. Mine the gauge show full all the time until the tank is about half full and the goes to empty and low fuel light comes on, I have seen 3/4 or 1/2 tank indications it full or nothing, sitting still it will bounce around full and then empty but as soon as you start it it goes to full unless it around a half a tank then it reads empty. I have as near as I tell good 5volts or at least when I do the testing. I think I might have other problem (maybe fuel level sensor buffer or something) I have checked the connections underneath and ground wires they seem to be fine.

I just got a new sending unit this week but I need to use up some of the fuel before dropping the tank.

I my doubts that the sending unit will fix it, I would change the gauge in the dash but again I don't think it will solve it either with the behavior it has. it really weird.

 

Sounds like two problems with the fuel level sender. The business about dropping to empty sounds like a problem with the rheostat, (variable resistor) and the bouncing around is without a doubt, the buffer in the level sender. Both of these problems are usually associated with an aftermarket fuel pump module. Don't make the same mistake as the last guy, use an AC Delco level sender.

 

I'll second what the captain has to say. Also, if you don't have an ac delco pump, take it back and get an ac delco. I can't stress this enough!!!! also, I replaced mine last year. I took lots of pics and have been meaning to write up a detailed how to but I haven't yet.....when you go to pull the tank out make sure you disconnect the evap tube(s) from the top of the tank toward the front...if you don't and damage the tank, you will be buying a new tank too!

 

Seeing a trend here...
Everyone now seems to forget Delphi is the OEM.
Ac Delco should be the same. It isnt likely to be better.
There IS NO EXTERNAL {to VCM} BUFFER on a 99. I assume 98 up to 2002, at least, are same.

The signal near as I can tell.. because alldata left it out, or I cant find it... goes to and from the VCM, the crossmember gnd is not involved. The VCM drives the dash gauge.

Someone else provided this.. If you have contrary info please post publicly. I am not the authority on this, I'm a fact-checker.



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or DelphiJonboy, I did that and cracked that nipple.. It can be fixed. Search 'hit bump fuel pump dies' and my handle. Has direction to fix, cheap. Will work even if nipple is totally broken off. You can use my stuff for write-up.

https://blazerforum.com/forum/2nd-ge...s-fixed-63397/

 

I hope to be able to put mine on the lift this weekend and pull the tank and see. I got a OEM sending unit I just hope it fits the pump that is in the tank. so far this this week I have drove about 140 miles so I should be close to a half tank or less.

 

Dano.. if the fault isnt obvious when you pull the pump, short the purple and small black w white stripe at the pump. disconnect VCM clear -C3- connector and ohm between pins 13 and 19. Purple and black.
See diag above
Should read 0 ohms or close to it.

Alt: Read 5 v internal to sender with resistor opened. Not as good or reliable test, could read 5v and still ohm higher resistance

 

I will check that when I get the tank out, I have some reasons to believe there might be other issues like you described in your post. here might be another clue to my problem. sometimes the gauge goes nuts sitting in park, but goes to full when in drive. sometime when it is park and goes to empty and the low fuel light come on then if i back out of the drive in reverse and while in reverse the gauge bounces around until you put it in drive. some times it bounces in park but normally in reverse.

any clues there?

 

Two different connectors: C3 pin 19 & C4 pin 13

Two black wires, (no tracer) at the module connector: one is ground for the pump, and one is ground for the level sensor. Make sure you jump to the correct one or your results could be skewed as the level sensor grounds through the PCM and the fuel pump grounds to the frame. Resistance from C4 pin 13 & battery negative, should be less than 5 ohms. The fact that the gauge failure is so predictable, the wiring is probably not the problem.

 

Nope. See that little dotted line between the two. Means 'on same connectors'. Go figger

Hey.. I thought so too.

 

the pump in the tank is about 3 years old, it came from O'Reilly auto parts about 3 years ago and has worked with no problems, then last year we changed out the transmission last spring and everything was OK until last fall, then the gauge become possess by demons some time it worked OK and sometime it was full all the time, then about Christmas it got worst and started the dropping to empty and bouncing up and down thing. I got my wife a newer vehicle this month and now I have a hunting and fishing buggy (1999 blazer) to play with. now trying to get all the bugs worked out of before I start off on 500 mile trip with it. in the last 2 weeks I just about got everything back working or fixed (note: working doesn't always means fixed).

its had installed just lately:
new brakes
new shocks
new idler arm
new lower ball joints
new fuel filter (5 months ago)
tested the fuel pressure (63 psi and only drops 5 psi down to 56+ or - in 15 minutes)
new timing cover seal
new serpentine belt
new idler pulley
new belt tensionor
new radiator (4 months ago)
new rad hoses upper and lower (4 months ago)
new vacuum lines (6 months ago)
new front drive shaft (8 month or so ago)
new right side wheel bearing and drive axle
new stabilizer bushings

so I have crawled all over this thing thinking during all this I might find a loose connector or bad wire or loose or pinched wire. in about 3 weeks I am going to put a new heater core in so I will have the dash apart then. Is there anything in the dash that might be part of my problems to the fuel gauge I should check?