Gas gauge problem.

[wtd]

The gas gauge in my 98 chevy K1500 does not work. It usually reads completely full but will sometimes drop down to empty momentarily and than go back to full. The needle also seems to be vibrating.

Is there an easy way to determine if it's the gauge itself or the sender in the fuel pump? Thanks.

 

[RonRonnster]

I have a similar issue with my '98, but it normally reads completely empty. I would also like to know if there is an easy way to test the gauge to determine if it's for sure the gauge or the sending unit/fuel pump. If the needle is vibrating, it's possible the stepper motor is going bad on the gauge, but I think the sending unit in the tank can also cause that issue. Unfortunately, in our '98s the sending unit and fuel pump is a combined unit, and pricey $$. I've been putting this off for a couple years and just filling up every 300 miles.

 

[clinebarger]

Might be a little of both (Gauge & Sender) on a late GMT400, You can hook a Ohm meter to the Gauge Sender Wire & see how erratic the signal is. IIRC....These are 40-250 Ohm sending units.

Temporally installing a fixed resistor that's within the above range is a quick & dirty test for the gauge.

 

[clinebarger]

No stepper motor in these.....They are Analog-Resistive, Just not as good/well built as the earlier GM analog gauges. The PWM Stepper Motor fuel gauges was introduced with the GMT800 platform.

 

[wtd]

Originally Posted by RonRonnster
I have a similar issue with my '98, but it normally reads completely empty. I would also like to know if there is an easy way to test the gauge to determine if it's for sure the gauge or the sending unit/fuel pump. If the needle is vibrating, it's possible the stepper motor is going bad on the gauge, but I think the sending unit in the tank can also cause that issue. Unfortunately, in our '98s the sending unit and fuel pump is a combined unit, and pricey $$. I've been putting this off for a couple years and just filling up every 300 miles.

Mine has not worked for probably five years and I usually fill it up at about the same mileage as yours. I'm just getting tired of it not working so I thought I would ask this question.

I replaced the original fuel pump years ago because it was starting to get very loud and I figured it was going out. The replacement was an AC-Delco pump that probably has about 100,000 miles on it.

 

[wtd]

Originally Posted by clinebarger
No stepper motor in these.....They are Analog-Resistive, Just not as good/well built as the earlier GM analog gauges. The PWM Stepper Motor fuel gauges was introduced with the GMT800 platform.

Thanks, I didn't know if these gauges had stepper motors or not. Is the gauge sender wire at the fuel pump and do you know what color it is?

 

[clinebarger]

GM used Purple or Purple with a White Tracer.

The easiest access point to this circuit is at the PCM.....Pin 13 of the Clear C3 connector.....Purple/White wire. This circuit goes to the tank mounted sending unit.
Pin 9 of the Blue C1 PCM connector is Purple in color & goes directly to the Cluster.

The PCM just reads the resistance on the circuit for EVAP diagnostic purposes, The circuit passes through the PCM unabated.

 

[incognito_2u]

I seem to remember issues with GM fuel level sending units where the contacts would be eaten up by the sulfur in gas. The remedy was to put in a concentrated dose of "Techron" and let it clean up the contact points. Maybe someone else could chime in and confirm?

So I found a Video of Interest.....FF to the 2 minute mark:
Sulfur in old gas impacts fuel Pump

 

[MParr]

Typical problem with this era of GM trucks. Want to fix it? Replace the pump and sensor. Easiest thing to do is ignore it. Just reset your odometer after every fill up. I assume you know how far your truck will go on a tank of gas.

 

[wtd]

Originally Posted by incognito_2u
I seem to remember issues with GM fuel level sending units where the contacts would be eaten up by the sulfur in gas. The remedy was to put in a concentrated dose of "Techron" and let it clean up the contact points. Maybe someone else could chime in and confirm?

So I found a Video of Interest.....FF to the 2 minute mark:
Sulfur in old gas impacts fuel Pump

I use Techron on a fairly regular basis and it has not helped. I also only buy top tier gas.

 

[wtd]

Originally Posted by MParr
Typical problem with this era of GM trucks. Want to fix it? Replace the pump and sensor. Easiest thing to do is ignore it. Just reset your odometer after every fill up. I assume you know how far your truck will go on a tank of gas.

I will probably just live with it like I have been until the truck needs a new fuel pump. Those pump assemblies are not cheap. I fill up anywhere between 270-300 miles on the trip odometer.

 

[Duffyjr]

My 89 GMC gas gauge has similar issues. I was told the same thing to try a cleaner so Techron was my first choice but it didn't work so I had some StarTron and tried it and it worked. If I stop using it it only takes a couple tanks for it to start acting up again so I always put a couple ounces in every time I fill up and no more issues, might be worth a try. If it works get the bigger bottle.

https://smile.amazon.com/gp/product/B00D3IEIY0/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

 

[tiger862]

Shell had a claim number dealer was given and they covered claim. Can't tell you how many we changed under Shell's bill. To much Sulphur in gas.