I know it's been covered 17 million times but I've never been able to find a definitive answer. My 2000 model 2 door 4x4's fuel gauge stays pegged at full (actually a little over) and I've looked and looked only to find everyone says it's a ground. Well I found where that stuff is grounded (called sp423 I believe) I cleaned the wires and wire brushed the cross member it was attached to and it didn't help anything and by anything I mean it didn't fix the fuel gauge OR the sputtering and misfiring (a problem I didn't mention before but read 2 threads that people fixed their misfires with this). Maybe I didn't clean the cross member good enough, maybe this isn't the problem for either issue. The Blazer has a hard time getting up to 55mph and going up a small hill it'll drop down to 35mph easily, it definitely feels like it's running on 5 cylinders. What would be YOUR next step? Plugs are new btw. Thanks for taking the time!

 

If there is an open circuit anywhere from the instrument cluster to the level sender, or from the level sender to ground, or the level sender itself is open, the dash gauge will indicate overfull when the ignition is in the RUN position.

SP423 is a ground splice pack located behind the rear bumper and is subjected to water, salt, etc etc and can be a problem area. The fuel pump ground goes through SP423 and grounds at the left rear corner of the frame. The level sender ground also goes through SP423 but it is not connected to the pump ground. The level sender ground goes from SP423 directly to S102, (no connectors in between) which is located about 4" from the underhood fuse panel and grounds to the engine block. If you probe each wire at SP423, it should have less than 5 ohms resistance to ground. At the fuel pump module connector, both black wires must show less than 5 ohms to ground.

EDIT: It would be best to start another thread for your driveability issue to avoid confusion.

 

Mine used to do the same thing at less than 1/2 tank it would jump around wildly and sometimes settle on over full reading or under empty. It turns out the rheostat pickup for the sending unit inside the tank had corroded and was missing pickup contacts. I noticed this when I replaced my fuel pump that came with the sending unit. It may still be an external electrical issue but based on your other symptoms you may need a new fuel pump/sending unit. Troubleshoot with this article for fuel pressure issues. https://blazerforum.com/forum/tech-a...agnosis-23038/

 

Thanks for the info, guys. I'm thinking/hoping that when I cleaned the sp423 the other day maybe I didn't wire brush it good enough. I'm going in again and taking a drenel tool this time. Oh and my Dad will be there with his electrical ohm checker thing.

 

I got back into it and cleaned those grounds and the frame with a flat file and a wire brush and they look like they did when they were new only to find out that this is NOT the problem. I don't know the difference between the grounds under the hood but I found 2 one behind the battery and one on the driver side up against the firewall kind of right under the driver wiper assembly and they both looked great. What's the most logical step from here? I have spent too much time and money on this I'm now down to having <20 bucks to spend to fix this which is why I'm struggling to fix it at home. Not to mention, it needs a lower tie rod end and lower ball joint! I have full coverage and I live in the mountains of southwestern Virginia, this thing better not push me any farther...

 

I'm not sure if you've seen this thread or not, but it runs down through the steps to determine the cause of fuel gauge problems to a 'T': 98+ Fuel Gauge Diagnosis

Try not to let inanimate objects get the better of you. It is NEVER better to toss it all away because you have full coverage. You will always get boned on your premiums later on in life.

 

The first step is check all of the ground wires in SP423 by probing with an ohm meter. As I mentioned in post #2, the fuel level sender does not ground to the frame in back, only the fuel pump grounds there. The fuel level sender grounds to the rear of one of the cylinder heads. There are grounds on both heads, so check both of them.

 

Oh I wouldn't do that I was just exaggerating. Thanks to everyone for the help and I actually DID NOT know about those grounds on the heads but I'll check them, thanks. I'd imagine they look good being under the hood and all because my engine is really clean but you always have to check just in case. I'll report back in case anyone is interested.

 

I talked to a local mechanic and he says that more often then not it's the sending unit but it doesn't so much tear up as it just gets faulty. He said what happens is these little tongs lose connection to the other piece of metal that sends the current. I know what he's talking about so I'm gonna get in there and look at it tomorrow. He said the piece that holds it together is plastic and it gets loose and wobbly that I'd see how to fix it when I got in there that it's hard to explain.

 

The first sentence in post #2..... "If there is an open circuit anywhere from the instrument cluster to the level sender, or from the level sender to ground, or the level sender itself is open, the dash gauge will indicate overfull when the ignition is in the RUN position."

Pull the module out of the tank, you'll see exactly what he's talking about. The pivot for the float arm is pretty cheezy and you might be able to tighten it up. Sometimes the wiper arm will lose contact with the windings, which causes the gauge to go to full. You can carefully bend the wiper arm to increase the tension on the windings. If the windings are worn or broken, you can replace the level sender separately, you don't have to replace the entire module.