Fuel for thought
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Fuel for thought
So I'd like to get some opinions from the group on what is wrong with the fuel gauge on my '82 and how to attack this situation.
symptoms... My fuel gauge goes to full when full and then goes to a little under half then seems to "lock." When driving the gauge "bounces" quite a bit (like a 1/4 tank swing) on the way down then stops in place with no further movement at the half mark. When at idle the gauge settles down and will read accurate and steady (like 3/4) as the sloshing of the tank ceases
The gauge is accurate until the half point as I've filled the tank at half and the amount of fuel added was 12-13 gallons.
Now, the gauge was super accurate until I replaced the stock fuel pump with a higher pressure '85-89 unit on a couple of months ago. It was a straight forward installation with no issues. (BTW for all peeps with an '82 CFI do yourself a HUGE favor and upgrade to the higher pressure model-- you car will completely wake up)
My thought is that the arm may be getting hung up on something, as it has movement (although the bouncing) until the half mark. I'm stuck on what it could get hung up on?
Could this be more electrical or does it sound mechanical?
Thanks!
symptoms... My fuel gauge goes to full when full and then goes to a little under half then seems to "lock." When driving the gauge "bounces" quite a bit (like a 1/4 tank swing) on the way down then stops in place with no further movement at the half mark. When at idle the gauge settles down and will read accurate and steady (like 3/4) as the sloshing of the tank ceases
The gauge is accurate until the half point as I've filled the tank at half and the amount of fuel added was 12-13 gallons.
Now, the gauge was super accurate until I replaced the stock fuel pump with a higher pressure '85-89 unit on a couple of months ago. It was a straight forward installation with no issues. (BTW for all peeps with an '82 CFI do yourself a HUGE favor and upgrade to the higher pressure model-- you car will completely wake up)
My thought is that the arm may be getting hung up on something, as it has movement (although the bouncing) until the half mark. I'm stuck on what it could get hung up on?
Could this be more electrical or does it sound mechanical?
Thanks!
Last edited by billschroeder5842; May 7, 2016 at 02:44 PM.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
I'm guessing that you don't want to pull the pump & sender out to verify? I'd recommend getting something like a borescope/endoscope device to get a better look inside the tank. I bought one on Amazon last year that plugs into my smartphone, and have found it extremely useful several times (but haven't had to use it on the gas tank yet). This could at least tell you if the float is getting physically stuck or not, and it was less than $20...
To find it, do a search on Amazon for 'GCA 5.5mm Diameter USB Waterproof 6 Led Endoscope Borescope Inspection Wire Camera' (I'd post a link, but I don't think Amazon is a supporting vendor).
If the camera end of the cable is not rigid enough, just tape a small piece of stiff wire to it temporarily. And I'm guessing that the camera is not 'gasoline proof', so you'd probably want to run the tank down to less than 1/4 tank first.
To find it, do a search on Amazon for 'GCA 5.5mm Diameter USB Waterproof 6 Led Endoscope Borescope Inspection Wire Camera' (I'd post a link, but I don't think Amazon is a supporting vendor).
If the camera end of the cable is not rigid enough, just tape a small piece of stiff wire to it temporarily. And I'm guessing that the camera is not 'gasoline proof', so you'd probably want to run the tank down to less than 1/4 tank first.
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
I've had the sender out recently to swap out for a new high pressure fuel pump, so really about 15 minutes.
I think I'll pop it out next time the fuel gets down to half and make sure the arm swings freely.
I was hoping to find a few "on car" tests to isolate the problem before I tear it apart.
I think I'll pop it out next time the fuel gets down to half and make sure the arm swings freely.
I was hoping to find a few "on car" tests to isolate the problem before I tear it apart.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
Here is a link to the site Croaker is referring to:
http://repairs.willcoxcorvette.com/w...it-testing.pdf
I'd still concentrate on the sender unit in the tank first, since as you recently had that apart (and taking the gauge cluster apart isn't a 5 minute job either).
http://repairs.willcoxcorvette.com/w...it-testing.pdf
I'd still concentrate on the sender unit in the tank first, since as you recently had that apart (and taking the gauge cluster apart isn't a 5 minute job either).
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Thanks- I appreciate the postings. I read the help document from wilcox, and while real good did not address my symptoms.
I took the glove box out and checked the connections on the instrument cluster-- it seems fine.
If luck hold, I'll take the pump out of the tank tomorrow after work and fiddle with that a bit. maybe when I reinstalled, I screwed something up.
I took the glove box out and checked the connections on the instrument cluster-- it seems fine.
If luck hold, I'll take the pump out of the tank tomorrow after work and fiddle with that a bit. maybe when I reinstalled, I screwed something up.
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
I took the fuel filler and pump out tonight. It was pretty straight forward as it took everything apart a couple of weeks ago to install the new high pressure fuel pump.
I inspected everything and it all seemed great. I got my daughters boyfriend to help me and we tested the float arm-- it worked perfectly. I plugged in the harness and the moved the float up and down and the dash gauge moved right with the float-- super accurate with no bouncing.
I reinstall the filler tube and bounced the car. The gauge moved around some but it to check accuracy. The gauge moved but it seemed normal to the car movement.
Maybe I installed it poorly the first time and a simple re install might do the trick?
Tomorrow is the test as I drive to work!
I inspected everything and it all seemed great. I got my daughters boyfriend to help me and we tested the float arm-- it worked perfectly. I plugged in the harness and the moved the float up and down and the dash gauge moved right with the float-- super accurate with no bouncing.
I reinstall the filler tube and bounced the car. The gauge moved around some but it to check accuracy. The gauge moved but it seemed normal to the car movement.
Maybe I installed it poorly the first time and a simple re install might do the trick?
Tomorrow is the test as I drive to work!
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Racer
Joined: Sep 2009
Posts: 437
Likes: 3
From: Alvin Texas
The tank has a bladder that deforms, it happened on my CE, gauge was correct to 1/4 then it would hang up and not register below 1/4, I pulled the gauge and reformed the float lever to clear the deformation works now.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I'm betting that your problem has nothing to do with the sending unit. I think your grounding wire is either mostly broken near a connecting terminal or the places where it is making contact are corroded so bad the electrical connection is poor. Find the ground wire for the sending unit; remove the connections; clean/wire brush the connectors and contact points on frame/sending unit cover; reassemble and spray some clearcoat over those connections to protect from corrosion.
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
7T1vette, you may have something there...
There is a splice on the ground back in the fuel door close to the harness block. While it looks good, I'll un wrap it and inspect it, fixing whatever needs fixing.
I never worried about it as the gauge seemed to be working.
So,why would the test show a full range of motion and only getting the bounce when driving unless the tank is REAL sloshy? Would the electric fuel pump not work if the filler was not properly grounded?
BTW... I drove the car to work today and the gauge did the typical "bounce" during driving with bumps--- it settle down at a stop.
There is a splice on the ground back in the fuel door close to the harness block. While it looks good, I'll un wrap it and inspect it, fixing whatever needs fixing.
I never worried about it as the gauge seemed to be working.
So,why would the test show a full range of motion and only getting the bounce when driving unless the tank is REAL sloshy? Would the electric fuel pump not work if the filler was not properly grounded?
BTW... I drove the car to work today and the gauge did the typical "bounce" during driving with bumps--- it settle down at a stop.
Drifting
Joined: Mar 2011
Posts: 1,347
Likes: 121
From: Kernersville NC
May be the gauge. Mine started bouncing around shortly after changing the sending unit. I thought the sending unit was bad because I had it on the shelf for a while, but another new one did no good. The sending unit out of the car ohm'ed out perfect and the gauge would move perfectly by moving the float up and down. However, I learned that the gauge is damped by a fluid that prevents the bouncing. The fluid can leak out. I changed the gauge and the problem went away
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
In general, the GM C3 gauges are VERY simple with almost NO moving parts. When a gauge fails, it usually just quits operating (often because a thin connecting wire has broken or melted, due to an external short).
If the gauge works at all, it is unlikely to be defective. Not always true...but almost always true.
Check the wiring..especially the ground wire. Bad connections and/or corrosion will cause the gauge to read erratically.
If the gauge works at all, it is unlikely to be defective. Not always true...but almost always true.
Check the wiring..especially the ground wire. Bad connections and/or corrosion will cause the gauge to read erratically.
Last edited by 7T1vette; May 12, 2016 at 05:30 PM.
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
WEIRD
I was driving yesterday keeping and eye on the gauge- it was doing its "normal" bounce.
At one point I hopped in and started it, and the gauge read on the orange line, just above empty and was "stuck" there-- no movement.
I went and filled the tank, and the gauge was still stuck on orange. I drove it about 4 miles and then suddenly the gauge sprang to life and pegged the full, acting "normal" with the little bounce. I drove it home and it was all normal again. Weird.
I did check the ground repair unravel the harness and found that the black wire ground was good and one of the tan (power?) wires had been spliced. The electric fuel pump is running great so I'm figuring that the repair was solid.
What could explain the weird gauge action? BTW... I ordered another gauge to have on standby if I need it.
Thanks!
I was driving yesterday keeping and eye on the gauge- it was doing its "normal" bounce.
At one point I hopped in and started it, and the gauge read on the orange line, just above empty and was "stuck" there-- no movement.
I went and filled the tank, and the gauge was still stuck on orange. I drove it about 4 miles and then suddenly the gauge sprang to life and pegged the full, acting "normal" with the little bounce. I drove it home and it was all normal again. Weird.
I did check the ground repair unravel the harness and found that the black wire ground was good and one of the tan (power?) wires had been spliced. The electric fuel pump is running great so I'm figuring that the repair was solid.
What could explain the weird gauge action? BTW... I ordered another gauge to have on standby if I need it.
Thanks!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I'll say it just one more time: Either the signal wire or the ground wire is NOT making solid electrical connection. You have to do a little more than LOOK at some patched wires to diagnose the fault properly.