Fuel Gauge and other problems

[k2500]

I recently bought a 1999 Sierra z71 and each time I fill the tank, the gas gauge drops to empty and the slowly recovers. From things I have read this seems to be a fairly regular occurrence and is a symptom of the fuel sending unit going out. However, in addition to the gauge dropping to empty, I have also experienced what feels like a miss and a dimming of the instrument lights at the same time. If I shift into park, the lights become brighter and the engine miss becomes less. I have only filled up 3 times since buying the truck and 2 of the times the lights and miss have occurred.

I have a few questions-

1. What causes the sender to malfunction after filling up? Is the gas shorting something out or is the fact the float is high causing the problem.

2. Could the dimming light/miss be related?

3. If related, what is the mechanism at work that causes the dimming/miss and why does shifting into park help?

Thanks in advance for any help.

 

Jay

[mkayler]

The gauge is an issue with sulfur build up on the sensor in the tank if i remember right. I had this issue once before and ran Techron Plus in the tank a couple times back to back and helped clear this up. But it must be Techron Plus since this is the only Techron that has the additive for the sulfur build up.

 

Hope this helps.

[jwh463]

This happened on my 2005 Envoy XL, it is the fuel level sensor. They drop the tank and replace the sensor. I replaced mine in July to the tune if almost $500. Most of that was labor for dropping the fuel tank...BUT GMC sent a letter in Septemeber recognizing a problem with the sensor and offering to pay for 50% of the repair. I recvd a check 2 weeks ago from GM for $236

[k2500]

Thanks for the input guys. I was guessing I needed to be changing out the sender and fuel pump, but want to make sure that will take care of the problem. I had read about the sulfur issue, but have not been able to understand how that would cause a problem only after fill up. Maybe an internal short in the sender that causes the line to go directly to ground when the float is all the way up? If that happens, maybe that is what is causing the dimming of the lights?

JWH463,

Thanks for the info on the possibility of GM helping with the cost. Since mine is a 1999 and I am not the original owner, I am guessing I am on my own, but it is worth checking into.

Next question, What is the best source (ie quality unit but least amount of $$) for the fuel pump/sender ass'y? I have read the Delphi units are the best ones to buy, but am hoping for on line options that are better than my local dealer pricing.

Jay

[jwh463]

I used an independent shop that uses NAPA stuff

 

this probably 'helped' GM do the right thing

http://www.insideline.com/chevrolet/trailblazer/feds-investigate-865000-gm-suvs-for-defective-fuel-gauges.html

[k2500]

jwh463,

Thanks for the link, it was an interesting read. Also, do you know who made the NAPA fuel pump?

Jay

[RockySierra]

The problem goes back prior to 99. Mid-90s GM SUVs/Trucks have had the fuel gauge issue. Fact of the matter is that the parts GM used are crap, and give out easily. Sulfur build up or other issues. I had the problem on my 99. Had the entire fuel sending unit replaced since my pump went bad also. That fixed the issue.

 

Try this: When the gauge is acting up, shift the truck in to neutral and see if it does anything with the fuel gauge.

 

Replace the entire sending unit in the tank. Pump and module that contains the gauge level floatie thingie. You will be glad you did. Most GM fuel pumps on the GMT-800s did not last more than 100,000 miles, if lucky. Typical wear and tear item.

[k2500]

Rockysierra,

The last time this happened, I shifted into Park and I believe the fuel gauge came up. This is one of the things that has me confused. Why would park or neutral cause everything to work correctly? I realize everything is now electric, but this particular symptom has me baffled. Since there is 83K on the truck I am planning on changing the pump/sender, but I always try to understand what is going on prior to changing things.

 

Jay

[=v8-only=]

http://www.naioa.com/v2/modules.php?name=Forums&file=viewtopic&t=37605&highlight=fuel+level+fix

 

http://impalahq.naioa.com/HowTo/GasTankSender.html

 

heres information from an impala, but its the same process.

 

On the fuel level sensor switch there are little "teeth" that slide on a plate that transfers to your gauge. If the switch becomes loose or if the teeth do not touch the plate properly your gauge reads incorrectly.

 

hope this helps.

[67Olds442]

I had a 2000 Serria. My problem was the ground and wire pack off the sending unit.

A local garage repaired it in about 15 minutes (and $20.00), it worked till I sold it

[k2500]

Thanks Guys,

All good stuff, especially the pics in the links. I have a better understanding of the design and will be dropping the tank to check everything out after I get it down to ~1/4 tank. No reason to make it tougher than it needs to be.

 

Jay

[RockySierra]

Let us know how it goes, Jay.

[CoffeyLover]

Maybe I'm just missing something, but can somebody please explain to me the relation between the fuel gauge and an engine miss?

 

My motor has been missing a tiny bit lately, only when on constant throttle. I have had the entire motor gone over (its a new crate motor too) and replaced the plugs and wires. I have been thinking my problem is my fuel pump, and my fuel gauge acts a little weird. It fills fine, but the last 1/4 tank seems to disappear extremely fast. Could a pump and sending unit solve my problem?

 

Sorry to hijack the thread.. Thanks.

[Toadz]

Bump. Good read here..also hoping some of these questions are answered as I'm having the same issue.

[k2500]

Here is an update on the problems I have been having. I have been driving my old '94 until it sells so I have not used up the gas in the '99 tank so I can drop it and replace the sender. However, yesterday I did drive the '99 and it stalled as I was pulling out of its parking place, It started back up but had the same miss I had experienced the last time I filled up, then stalled again and was completely dead. It finally turned over again and ran (still missing), and I drove it 100 yds to where I could pull over safely. I popped the hood and checked the battery cables and both were slightly loose. I tightened both cables and it fired right up and ran great. I am now wondering if the cables were loose, and that was the cause of the miss, and the miss is unrelated to the gauge issue. I still need to drive it more to see if the miss is gone for good, but so far no more electrical gremlins. I'll be driving it more over the next week and see what happens

DRT_RUNR,

The last 3 Chevy/GMC trucks I have owned all had gas gauges that dropped faster after hitting the halfway mark so I would bet yours is fine.

Jay