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Fuel gauge problems?

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Old 10-11-2018, 06:25 AM
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Red face Fuel gauge problems?

Is anybody else having a fuel gauge problem? My '08 LaCrosse gauge goes nuts when I get drive about 200 miles starting with a full tank. It can do anything from telling me I'm completely empty to simply being grossly inaccurate. A friend's wife has an '04 Buick (forget the model) which has a broken fuel gauge. There's a guy in town currently trying to sell an '08 Lucerne in " Really good condition inside and out except gas gauge doesn't work." I Google for "Buick fuel gauge problems and found out that GM cars in general have a problem because the MoCo got a bad supplier of "stepper motors", whatever they are. If you've been having a problem with your fuel gauge, what was the cause and how did you fix it? TIA.
 
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Old 10-11-2018, 10:53 AM
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Good question, good start. Can't vouch for '08's but fuel gauges used to be a rheostat or potentiometer. This was grounded in the fuel tank and as the resistance varied would change reading of the gauge. May of coarse be going from analog to digital with newer cars but the principal would be similiar.

Sounds like the ground may be intermittent at the tank sender unit, may have access to it through trunk bottom (or not). Don't know what stepper motor is either, hopefully more answers to follow.

https://en.m.wikipedia.org/wiki/Stepper_motor Here it is, I'd call it a servo motor though. Never had need to know about or ever troubleshoot.... Until now maybe lol.

https://en.m.wikipedia.org/wiki/Servomotor So if no one knows, make up your own answer I guess.
 

Last edited by Rich B.; 10-12-2018 at 11:46 AM.
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Old 10-14-2018, 06:49 AM
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https://www.ebay.com/sch/i.html?_nkw...+stepper+motor Learning curve here, suppose these correspond with digital display, more accurate. Don't really notice any gauge flutter these days lol.
 
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Old 10-14-2018, 07:52 AM
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Originally Posted by Rich B. View Post
https://www.ebay.com/sch/i.html?_nkw...+stepper+motor Learning curve here, suppose these correspond with digital display, more accurate. Don't really notice any gauge flutter these days lol.
Thanks for replying! Yes, I've been looking at aftermarket stepper motors. I may have to go this route eventually. Nice to know it worked well for you! That increases my confidence level in doing the replacement.
 
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Old 10-14-2018, 07:57 AM
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Originally Posted by Rich B. View Post
Good question, good start. Can't vouch for '08's but fuel gauges used to be a rheostat or potentiometer. This was grounded in the fuel tank and as the resistance varied would change reading of the gauge. May of coarse be going from analog to digital with newer cars but the principal would be similiar.

Sounds like the ground may be intermittent at the tank sender unit, may have access to it through trunk bottom (or not). Don't know what stepper motor is either, hopefully more answers to follow.

https://en.m.wikipedia.org/wiki/Stepper_motor Here it is, I'd call it a servo motor though. Never had need to know about or ever troubleshoot.... Until now maybe lol.

https://en.m.wikipedia.org/wiki/Servomotor So if no one knows, make up your own answer I guess.
Thanks very much for replying! Yeah, I remember the old sending units too. Planned obsolescence (certainly not increased reliability, given all the problems newer Buicks have with their fuel gauges) is probably responsible for going away from that system. I'm concerned that the ECM unit will shut my car down on the freeway if it detects an erroneous "low fuel" or even "empty" signal from a defective sending unit or gauge. I'll read that Wikipedia article carefully. Thanks for the link!
 
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Old 10-14-2018, 07:27 PM
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I could be way off base here, but a motor is just that , a motor. Before going off the deep end it might be a good idea to confirm the sending unit in the tank is operating correctly.. Once you know what you are dealing with , you can go from there.
Stepper motors are used to control HVAC and idle speed/ air control functions. They are controlled some electrically and others electronically.
I would still start with the sending unit and all the connections to and from it.
Even the latest "Fuel Modules" still use a float to provide the signal regarding how high or low the level is in the tank.

I would not be concerned with the PCM shutting down your engine due to the lack of fuel. If it quits it's because you are out of fuel or the fuel pump circuit has died and there is no fuel pressure.
 

Last edited by hanky; 10-14-2018 at 07:31 PM.
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Old 10-15-2018, 04:31 AM
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Originally Posted by hanky View Post
I could be way off base here, but a motor is just that , a motor. Before going off the deep end it might be a good idea to confirm the sending unit in the tank is operating correctly.. Once you know what you are dealing with , you can go from there.
Stepper motors are used to control HVAC and idle speed/ air control functions. They are controlled some electrically and others electronically.
I would still start with the sending unit and all the connections to and from it.
Even the latest "Fuel Modules" still use a float to provide the signal regarding how high or low the level is in the tank.

I would not be concerned with the PCM shutting down your engine due to the lack of fuel. If it quits it's because you are out of fuel or the fuel pump circuit has died and there is no fuel pressure.
Well, in order to avoid "going off the deep end", one of the things I did was to create an account and post my original message to this forum in order to determine what the most likely cause is for the malfunction. In the OP, I originally was asking for people with the same problem to post what they've done to correct it successfully. I've also done *hours* of Googling the problem, so it's not as if I'm avoiding due diligence. From what I've seen by Googling, the most common cause seems to be the bad stepper motor supply problem (Google for "gm bad stepper motors".) Frankly too, having to work on the sending unit is probably going to be the biggest pain to do. If the cause is something else, I'd far rather know that this is the case before digging into my fuel tank.

Thanks for the info about the PCM and when it would shut down the engine. I guess if it would shut down the engine based on the fuel gauge reading, that would have resulted in a massive recall.

Thanks for replying!
 
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Old 10-15-2018, 02:37 PM
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I don't blame you for trying to determine the easiest to correct possible cause, let's face it , the less we need to do the better.

Unfortunately , not all similar problems have the same solution. What I have suggested is based on years of experience learned, some from GM Factory Service Training and some from the school of hard knocks.
The better way to tackle a problem like this is to start at the source and work your way to the gauge itself. Even if it means to get access to the sending unit and verify it is working correctly , it doesn't make much sense to start in the middle and hope you went in the right direction.
 
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Old 10-16-2018, 06:59 AM
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Originally Posted by hanky View Post
I don't blame you for trying to determine the easiest to correct possible cause, let's face it , the less we need to do the better.

Unfortunately , not all similar problems have the same solution. What I have suggested is based on years of experience learned, some from GM Factory Service Training and some from the school of hard knocks.
The better way to tackle a problem like this is to start at the source and work your way to the gauge itself. Even if it means to get access to the sending unit and verify it is working correctly , it doesn't make much sense to start in the middle and hope you went in the right direction.
And I was a Launcher Technician on a nuclear submarine carrying Poseidon C-3 missiles. My tactics for approaching a problem are always well thought out, are force of habit for me. Thanks for your advice, but I will continue to monitor this discussion for how other people solved the malfunctioning fuel gauge problem.
 
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Old 10-16-2018, 04:27 PM
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Roger that JB on the Boomer SS SIlent Service, Jr. was on a few also (son). The one I recall was the Rhode Island and a few others. Doesn't talk about it much, I don't ask. He was a cook and made E8 recruiting his last few years (retired). Beat me out, I was only a E7 and retired Army(R). Also served in Navy on destroyers in the early 60's, was an ETR. I started Navy and ended Army, he started Army and ended Navy, hmm.

And thank you for your service also.
 
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