2001 Blazer LS, 4.3l, when fuel level gets below half tank, the gauge goes crazy jumping sometimes to full tank but usually shows below empty then as I go along, it will finally start registering acurately. If tank is full or above half a tank, no problems at all. Fuel pump was replaced 2 years ago. Faulty sending unit or electrical? Hate to have to drop the tank again. Been tracking mileage to validate readings but it's getting to be a pain. Thanks in advance for any input.

 

I would say you have a problem with the sender. Yes a tank pull is in the cards if that is what is wrong.

 

I have the same vehicle ,and apparently this is one of many VERY common problems. I had to change the fuel pump/sending unit. To the best of my knowledge, you cannot get the sending unit seperately, it comes as a fuel pump/sending unit assy.
I have a '99 Sonoma with the same problem, but it is just a "utility" vehicle, so there is no urgency to change it out,but I suspect the sending unit is gone in it as well.

 

Mine just went out a week ago and that is what it is looking like for me now. Im probley just going to deal with it unless anyone knows where to get one cheap

 

Just changed filter on '99 Blazer hoping I had a blockage in the filter, but that wasn't it. Am wondering if I can just unscrew the 16mm fitting at the intake of the fuel filter and crank the engine to see if the pump is working, or does it have to have the system pressurized for the pump to work.? Thanks!

 

You can purchase the sending unit separately.

This post may be helpful in getting to the root of your problem:
98+ Fuel Gauge Diagnosis

terbates, this post is discussing the fuel level sending unit. Please ask your question in a new thread if a quick search or two doesn't turn up the results you are looking for. The Tech Article (DIY) Index link in my signature may prove to be quite helpful as well!

 

my fuel gauge just jumps from full to empty. like ill be at a light and it would jump to empty then as soon i give my truck gas to go it would jump up to full. or sometimes when im parked it jump down to empty then ill put in gear and as soon i start moving it would jump back to full. wth is it a short or a bad sending unit.

 

Did you read through the link I posted?

 

Well I have a 98 and the same problem. Been told by several GM mechanics that it is the sending unit, unfortunately you cant just change out the sending unit unless it has been done before because there is a new adapter plug for the pumps and sending unit and a new one wont work with the old pump. However what I have found is that even the high dollar units fail just as easily as the aftermarket ones so don't waste your money on a 400 dollar unit. Get a 60 to 200 dollar unit of ebay or rock auto and save your money for other things.

 

Or if you know what you get for mileage, just keep track with the trip meter