FUEL GAUGE/SENDING UNIT STARTING TO MALFUNCTION??????

Hello All,

*2005 Avalanche LT/Z71 with "Z" Code (Flex Fuel) 5.3 Liter Engine.
*187K+ Miles

I believe My fuel gauge may be acting up of late, its been reporting lower fuel levels than I actually have intermittently.

The first time this occurred a few months ago I was thinking that somebody may have siphoned fuel out of my tank while the trucks was parked at a friends house overnight.

But yesterday this fuel gauge thing happened again.......

The gauge showed that I had just 1/4 tank of fuel for the first part of the drive, I knew I had more because the night before it was showing 3/4 full when I got home and parked it in the garage overnight.

Then after my first stop and I started the truck up again and the gauge now showed 3/4 full.

As the truck sat in a garage overnight so I know it was not any kind of fuel theft type situation, very interesting I thought.

I did some research on the web to find out that this is a common problem with high mileage GM 1500 trucks and SUV's.

Something about sulfur build up on the fuel level sensor

The remedies ranged from adding fuel additives/changing gas stations to replacing your fuel pump/sending unit. (after total failure)

Now, since I have a flex fuel engine, would it be a good idea to run a full tank of E85 through it instead of an additive?

I hardly ever use E85 in the first place.

And my regular fueling stations are Shell and Costco, I alternate between the two on each fill up.

Might the results be the same

Or should I consider running a full tank of E85 first then follow up with a tank of regular gas with some additive put in.

Would that be overkill?

As always any input is greatly appreciated!

If it were mine I would just add fuel system cleaner

I suspect either a sensor issue as you mention or more likely the motor in the cluster is going bad. If you can scan your truck for fuel level it should become real obvious quickly what the issue is.

I also have an '03 and will be playing around with diagnostic codes for my college project but I am quite a ways from that right now and it wouldn't be very helpful for you now. But the fuel gauge on your cluster is actually a needle connected to a motor that is driven by the computer in the cluster. It pulls its information from the databus which is available to the ODBII scanners but may not be incorporated in most scanners.

Dealership should be able to diagnose this issue in like 5 minutes...

To fix your cluster is not hard if it is indeed the cluster. You can get the part for about $15 and if no problems takes less than an hour to swap out if you are lucky and no other motors break as you disassemble to cluster. (Look on ebay or amazon for them. )

These motors are using in most if not all GM's from 2002-2006 and maybe other years. There were a variety of versions.

Otherwise if it is the sensor in the gas tank your best bet is to find a good quality fuel pump and sender unit and plan to swap them out. This can be an early sign that your fuel pump is about to go out. As our fuel pumps wear out they use more energy to run and this increased energy can tax the wiring. As the wiring is taxed it can show up as low fuel pressure or as a screwy fuel tank level.

My caprice had this happen and it burned the ground wire in one of the connectors when the pump went out as well as the wires in the sending unit.

But regardless find a shop that can pull up the fuel tank level on their scanner and see if it is the motor in the dash or the fuel pump sending unit.

OK, thank you guys for that information!

I also had a thought about the gauge itself being suspect, but the fuel pump also being a possibility is somewhat troubling.

I will most likely need to take the Avalanche to the local Chevy dealer and let them run a quick check to see what is actually misbehaving here.

Then, depending on what it is I'll make the decision whether I will let them repair it, or if its a DIY thing.

I've done some repairs on my truck myself already, (oil pressure sending unit and the water pump) so if its a gauge thing, no problem, but if its the pump, fuel sending unit then I may have to let the dealer do it.

I'll do some research here on what has to be done to replace the fuel pump/fuel sending unit........

Thanks again!!!!!!!!!

Note that if a dealer does this job you will be looking at $500+ regardless of the issue... Maybe $1000 for a fuel pump...

The cluster is a $15 part and an hour or 3 of your time depending on your ability. (Research how to do it.. The Cluster blue LED thread can be very helpful when dealing with the cluster... The motor its self took me about 2 minutes to remove and replace...)

Fuel pump / fuel sending unit... Cost for my caprice was less than $300. No idea on the truck.

To change out the fuel pump it will require you to drop the tank or cut a hole in your floor. In this case since you know about it ahead of time you could easily drop the tank. You just have to pump out all of the fuel out of the tank first. Or most of it anyhow.. Every gallon is about 8lbs so a full tank would be almost 300lbs in just gas. The actual change of the pump should be pretty simple. Should be just removing the unit with a quarter turn twist or something similar, unplugging the old one from the wire harness and the fuel lines and the new one.

You SHOULD be able to do the job yourself for well under $500. As to the cluster it would be the perfect time to upgrade the lighting to LED's and change the overlay if you want if it is the cluster.

But as mentioned the dealer should be able to trouble shoot the issue.

Rodney

I have not heard of anything lately about bad fuel here in So Cal. It has been numbers years since a few stations had issues with water in their tanks.

Sulphur has never been a problem here and Costco & Shell push too much fuel for this to have been building up in your tank.

I'm inclined to think the stepper motor in you Instrument Panel is the most likely place to start. A less strenuous repair than a fuel pump.

If you are only experiencing conflicting gauge readings and nothing with the fuel delivery I'd start there. Then again with your mileage, a pump replacement could be a good thought to consider soon.

Thanks Guys!

I watched some "how to" videos on You Tube about removing the fuel tank and replacing the fuel pump module, its not that difficult to do and I believe I can do this, if it comes to that.

The stepper motor on the fuel gauge, no problem, that will indeed be the first thing I'm going to look into doing if the gauge gets worse,  but its been behaving lately.

I'll have to agree with the statement about So Cal's fuel quality, I'm fairly sure what I'm experiencing is either gauge or fuel pump related.

So does anybody have a link to some step by step gauge motor replacement instructions?

I'll check on You Tube to see if there is anything there........

As always, thanks so much for chiming in and sharing your thoughts and opinions!

D.