gas gauge trouble

**wolfmoon98** · 06-19-2009, 05:30 AM

Gas gauge troubles
Hey, I have a 98 TA and have started having gas gauge troubles. I wish for some consensus on where the trouble is. Here are the symptoms. Was driving one day and made a stop and switched ign off. Started back up later and the gas gauge was reading empty. Tank was full or nearly so. After driving several miles, gauge gradually returned to accurate indication. Stopped and switched ign off and back on. Gauge read empty. Again, a gradual return to accuracy after driving a while. This condition continued for several weeks, but now it seldom indicates at all, staying on empty (except for a momentary full indication when the ign switch is turned on), but when it does read correctly, switching the ign off and back on causes it to lay over on empty. When this happens, the needle moves to full upon switch on, but then goes to empty. Note that the car is a weekend driver and the tank has been kept full or above 3 quarters full. There is no erratic movement such as would be indicated by a loose wire, and the symptom seems unrelated to road conditions such as bumps. I changed the dash to try another gauge, but the replacement operated the same way. It would seem that the tank sender is not at fault, because when the gauge is indicating accurately, even sitting still, simply switching the ign off and back on causes it to return to empty immediately after momentarily indicating full upon switching back on. Is it the PCM? I understand the tank sender sends a signal to the PCM and the PCM then regulates the gauge. Opinions/experience? Thanks

**pajeff02** · 06-19-2009, 05:59 AM

Gauge senders can malfunction due to the crappy gas we have to run in our cars -- the sulfer content affects the gauge. Before tearing in to anything, try running two (2) tanks with Chevron Techron.

With the tank almost empty (good luck figuring that out) add the Techron and then about 10 gallons of fuel. Next time you are almost empty (again, good luck) do it one more time. This is only assuming you have no wiring or dash gauge issues -- as you car is now 10 plus years old, this is the easiest thing to try.

I think Sarge also recommends an oil change after running the fuel system cleaner as gunk can get down into the oil during the process. Good luck.

**chiller2484** · 06-19-2009, 06:07 AM

he could always reset the trip meter on the odometer to guess about how much gas he has. (ie- if you know you can go 250 miles before you need to fill up, then fill it up and count miles until you think it's about empty)

**blackcar** · 06-19-2009, 07:27 AM

Don't konw where your problem is but I do know our gas gauge moves slow. If I fill my car up with it running, when I get in after putting up the nozzle and putting the cap back on it will show about 1/4 a tank on the gauge. As I drive around it will slowly move its way up to the full mark.

**pajeff02** · 06-19-2009, 10:26 AM

Originally Posted by blackcar

Don't konw where your problem is but I do know our gas gauge moves slow. If I fill my car up with it running, when I get in after putting up the nozzle and putting the cap back on it will show about 1/4 a tank on the gauge. As I drive around it will slowly move its way up to the full mark.

This could be a symptom of a gummed up sender. Ours will read full by the time I get my debit card receipt and am back in the driver seat.

**blackcar** · 06-19-2009, 12:34 PM

Originally Posted by pajeff02

This could be a symptom of a gummed up sender. Ours will read full by the time I get my debit card receipt and am back in the driver seat.

Do you leave it running while you fill it up or kill it? If I kill it while I fill it up, when I turn it back on it will show full. If I leave it running it takes a while to show full. Its done it since day 1. I bought it new. I just assumed the pcm controlled how fast it would move to keep the needle from moving around while driving.

**pajeff02** · 06-19-2009, 05:05 PM

Originally Posted by blackcar

Do you leave it running while you fill it up or kill it? If I kill it while I fill it up, when I turn it back on it will show full. If I leave it running it takes a while to show full. Its done it since day 1. I bought it new. I just assumed the pcm controlled how fast it would move to keep the needle from moving around while driving.

Good question -- our gauge works fine so I never noticied if there was any difference between running and not running.

**JROBINSON1016** · 06-19-2009, 06:49 PM

sounds like a sender issue to me,if it's actin crazy & erratic,most of the time it's the sender,they just tend to wear out over time,like most things do,unfortunately you know where it's located,might as well do a pump as well while you're there,save ya a lot of trouble.i've seen these problems on many kinds of vehicles,9 times out of 10 it's the sending unit. would be my guess.
i put a pump in a 86 iroc for a guy just a few months ago,car had like 16k actual on it,pump was froze up,told the guy you probably should put in a sending unit too,well...savin a few bucks,now says his hand doesn't read right, i mean go figure,car hadn't run in like 10 years,pump was bad from sludge & corrosion,well the sending unit was dealing with the same thing,bunks in the same room as the pump.

**wolfmoon98** · 06-22-2009, 07:55 AM

OK thanks

**wolfmoon98** · 06-22-2009, 07:55 AM

OK Thanks.

**wolfmoon98** · 06-22-2009, 07:58 AM

OK Thanks

**0rion** · 06-22-2009, 08:41 AM

you can start by checking the ohms coming out of the tank. The sender is the purple and black/white wires. Empty is 40 ohms and full is 259 ohms. Fill the tank and check the ohms across those wires at the plug coming out of the tank. That should at least tell you if it's a sender issue or forward of the sender. I would imagine that sender is just gunked up like everyone has said but I would still check the ohms and trouble shoot it correctly. If it ohms out correctly you can then check it at the pcm. Here are the pinouts for the 98's
98 pcm pinouts

**silverWS6** · 06-23-2009, 10:00 AM

Originally Posted by blackcar

Don't konw where your problem is but I do know our gas gauge moves slow. If I fill my car up with it running, when I get in after putting up the nozzle and putting the cap back on it will show about 1/4 a tank on the gauge. As I drive around it will slowly move its way up to the full mark.

Isnt it bad to fill up a car while ts running?

**pajeff02** · 06-23-2009, 10:28 AM

Originally Posted by silverWS.6

Isnt it bad to fill up a car while ts running?

Probably, but I can't tell you why exactly.

**blackcar** · 06-23-2009, 11:02 AM

Originally Posted by silverWS.6

Isnt it bad to fill up a car while ts running?

Hope not. I fill my Camaro and other cars up while running almost all the time.

The only thing I can think of is: if you had trash in the btm of your tank it would get stirred up while the gas was pumping. But its not like all the trash would settle back down by the time you quit pumping gas and started the car.

Has anyone else filled their car while running? Jst courios if my gage is the only one that does that.

To the op did you get your prob solved.

**0rion** · 06-23-2009, 11:03 AM

most places it's against the law to leave the car running while filling it up. Not sure how it cold be hard on the car to do that though.

**pajeff02** · 06-23-2009, 11:09 AM

Originally Posted by 0rion

most places it's against the law to leave the car running while filling it up. Not sure how it cold be hard on the car to do that though.

On start up most cars pressure test the fuel vapor system and an open gas cap will trigger a CEL. Other than that I know you are supposed to shut your car off at the pumps just for safety. I bet static electricity actually causes more problems than a running vehicle. Anyone ever see those vids? Pretty scary.

**blackcar** · 06-23-2009, 11:21 AM

Yeah I always thought it was a safety thing. But your car is running when you pull up to the pump and when you pull away

I very rarely get in the car while it is pumping to keep from building up static elect. And always touch the side of the car and/or the pump to discharge b4 I touch the pump.

**pajeff02** · 06-23-2009, 04:54 PM

Just for giggles, I left our car running at the pump this evening and filled it. The gauge was at 1/4 when I started and rose steadily as I fueled the car - no hesitation or delay whatsoever.