Help! Need advice on feul sending unit
Thread Starter
Instructor
Joined: Mar 2003
Posts: 173
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From: Janesville WI
Help! Need advice on feul sending unit
This morning the fuel gauge on my 94 LT-1 started reading full even though I know it is only about 3/4 full. Mechanic says the sending unit is bad and it will cost $550 to replace!!!!!
I had the fuel pump replaced only 3000 miles ago, but they claim this failure has nothing to do with that. Can I get some imput from you guys on the situation? Is it possible the fuel pump replacement caused this? Is $550 totally out of hand for this replacement? Sure seems like the "corvette tax" has gotten out of hand here!
:mad
I had the fuel pump replaced only 3000 miles ago, but they claim this failure has nothing to do with that. Can I get some imput from you guys on the situation? Is it possible the fuel pump replacement caused this? Is $550 totally out of hand for this replacement? Sure seems like the "corvette tax" has gotten out of hand here!
:mad
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
Re: Help! Need advice on feul sending unit (PIN DR)
If I remember correctly, if the wire to the sending unit is open, the gauge will read full scale. If the wire to the sending unit is shorted to ground, the gauge will read empty.
The first thing I would do is connect the wire that goes to the gauge sending unit (make sure you don't get a fuel pump wire) to ground to see what the gauge does.
My guess is when the pump was replaced, the connections to the fuel gauge sending unit were loosened and it just took this long to show up.
You could also connect an ohmmeter to the gauge sending unit wire and see if it is open.
Tom Piper
[Modified by Tom Piper, 2:35 PM 8/13/2003]
The first thing I would do is connect the wire that goes to the gauge sending unit (make sure you don't get a fuel pump wire) to ground to see what the gauge does.
My guess is when the pump was replaced, the connections to the fuel gauge sending unit were loosened and it just took this long to show up.
You could also connect an ohmmeter to the gauge sending unit wire and see if it is open.
Tom Piper
[Modified by Tom Piper, 2:35 PM 8/13/2003]
Thread Starter
Instructor
Joined: Mar 2003
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From: Janesville WI
Re: Help! Need advice on feul sending unit (Tom Piper)
[QUOTE]If I remember correctly, if the wire to the sending unit is open, the gauge will read full scale. If the wire to the sending unit is shorted to ground, the gauge will read empty.
The first thing I would do is connect the wire that goes to the gauge sending unit (make sure you don't get a fuel pump wire) to ground to see what the gauge does.
My guess is when the pump was replaced, the connections to the fuel gauge sending unit were loosened and it just took this long to show up.
You could also connect an ohmmeter to the gauge sending unit wire and see if it is open.
Unfortunately the wiring is fine as is the digital dash unit, so the sending unit is definately bad. Is this what these things really cost?
The first thing I would do is connect the wire that goes to the gauge sending unit (make sure you don't get a fuel pump wire) to ground to see what the gauge does.
My guess is when the pump was replaced, the connections to the fuel gauge sending unit were loosened and it just took this long to show up.
You could also connect an ohmmeter to the gauge sending unit wire and see if it is open.
Unfortunately the wiring is fine as is the digital dash unit, so the sending unit is definately bad. Is this what these things really cost?
Drifting
Joined: May 1999
Posts: 1,478
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From: Sacramento, CA Money can't buy happiness - but it's more comfortable to cry in a Corvette than a Yugo.
Re: Help! Need advice on feul sending unit (PIN DR)
I agree with what Tom Piper says. Double check the connection going to the sending unit. The guage displays the amount of fuel in the tank based upon the voltage/resistance reading of the potentiometer hooked to the sending unit float arm. If there is unnecesary resistance due to even the slightest corrosion or looseness in the connection it will throw the reading off. If the sending unit were bad it should probably be way off and show empty when full or full when empty and not off by 1/4 tank. Either there is corrosion or a poor connection at the wire connected to the sending unit , or there is corrosion on the windings of the potentiameter.
The sending unit in my 88 was reading off by 50% due to corrosion in the sending unit float/potentiometer from moisture in the tank. I pulled the whole unit out and bent the retaining tabs back so I could get inside and wipe clean the wire windings with WD-40. I let it dry, put everything back together and reinstalled in the fuel tank. Works perfectly now. Saved $ over buying a new one.
Pulling the sending unit is easy on the C4. It is a 30~40 minute job. If you have never done it before you should be able to do it yourself in an hour or two being very carefull.
The sending unit in my 88 was reading off by 50% due to corrosion in the sending unit float/potentiometer from moisture in the tank. I pulled the whole unit out and bent the retaining tabs back so I could get inside and wipe clean the wire windings with WD-40. I let it dry, put everything back together and reinstalled in the fuel tank. Works perfectly now. Saved $ over buying a new one.
Pulling the sending unit is easy on the C4. It is a 30~40 minute job. If you have never done it before you should be able to do it yourself in an hour or two being very carefull.
Melting Slicks
Joined: May 2001
Posts: 3,270
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From: Winchester VA
Cruise-In V Veteran
Re: Help! Need advice on feul sending unit (PIN DR)
When I worked for Land Rover, we used to clean the contacts for the sending unit with a pencil eraser. So MIKE, has you on the right track.
On a Corvette, it is certainly worth a try. With a few basic hand tools, the sending unit comes out easily (at least on an 85). It may be a good idea to go to a parts outlet and inquire about the "module to tank" gasket. Maybe the original is reusable, I don't know, but it wouldn't hurt to have one on standby. (if you can get it seperately)
On a Corvette, it is certainly worth a try. With a few basic hand tools, the sending unit comes out easily (at least on an 85). It may be a good idea to go to a parts outlet and inquire about the "module to tank" gasket. Maybe the original is reusable, I don't know, but it wouldn't hurt to have one on standby. (if you can get it seperately)
Heel & Toe
Joined: Jun 2010
Posts: 23
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Hi - I am new to this forum and just purchased an 89 Corvette. The fuel gauge was indicating full when not and partially full otherwise but never empty. Today it died at the gas station and sound like a fuel/pump issue maybe. Are irratic fule gaug reading a prelude to the eventual failure of the full pump and if so are docs available for replacement?
Kind Regards,
Kind Regards,
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
Hi - I am new to this forum and just purchased an 89 Corvette. The fuel gauge was indicating full when not and partially full otherwise but never empty. Today it died at the gas station and sound like a fuel/pump issue maybe. Are irratic fule gaug reading a prelude to the eventual failure of the full pump and if so are docs available for replacement?
Kind Regards,
Kind Regards,
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Heel & Toe
Joined: Jun 2010
Posts: 23
Likes: 0
Well - what I have done is sprayed the ground at the feul fill connect area with Aero Kroil spray chemical, which cleans/disolves rust like you wouldn't believe, and VAROOM it started. I think I'll replace it next weekend.
Thanks for your support -
Thanks for your support -
Heel & Toe
Joined: Jun 2010
Posts: 23
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Well I replaced the fuel sending unit and the pump. Quite an easy replacement!
Anyhow that resolved the fuel gadge issue but it has not resolved the strating issue.
After the car reaches 180+ and I turn it off it will not start until its cold again - starts for work and after work but will not start in between. Any suggestions - is the fuel pressure regulator a possibilty or is that an on/off condition?
Thanks for your help!
Anyhow that resolved the fuel gadge issue but it has not resolved the strating issue.
After the car reaches 180+ and I turn it off it will not start until its cold again - starts for work and after work but will not start in between. Any suggestions - is the fuel pressure regulator a possibilty or is that an on/off condition?
Thanks for your help!
Le Mans Master
Joined: Jun 2006
Posts: 5,642
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From: One day you're a Comet...the next day you're dust... Arkansas
Heel & Toe
Joined: Jun 2010
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Hi - I hope you are still willing to offer some advice. I bought a scanner and it flashes 12 but no other code. According to the diag manual it could be an ECM. The symptom is it will not re-start once it reaches 110 degrees - so I can drive it to and from work. Have you ever encountered an issue like this?
Kind Regards
Kind Regards
Race Director
Joined: Aug 2000
Posts: 14,130
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Cruise-In II Veteran
Flu, It may be a bad starter too.When the car is HOT,the starter gets heat soaked.Can you hear a "click" when you turn the key to ON but it wont start until it cools off?The click means the starter relay is working but if theres no cranking over,the starter needs repair or replaced.
Burning Brakes
Joined: Apr 2010
Posts: 1,018
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From: Winston Ga.
you really need to invest in some basic tools. get a FSM, a fuel pressure gauge, noid light, multimeter and start troubleshooting.
they really only need a few things to run, fuel, air, spark. The gauge will tell you if the fuel is good, the noid will tell you if the plugs are getting fire and a meter will help you track down electrical gremlins.
these are must have items to work on a car in addition to a mech tool set.
I think the starter is a good guess but thats all it is since you have given us no info. tell us what the fuel pressure is when the key is turned on and how long it retains pressure after it is off.
Put a noid on the plugs and see if they are getting fire. if not there is an entire troubleshooting tree for that including ECM failure.
they really only need a few things to run, fuel, air, spark. The gauge will tell you if the fuel is good, the noid will tell you if the plugs are getting fire and a meter will help you track down electrical gremlins.
these are must have items to work on a car in addition to a mech tool set.
I think the starter is a good guess but thats all it is since you have given us no info. tell us what the fuel pressure is when the key is turned on and how long it retains pressure after it is off.
Put a noid on the plugs and see if they are getting fire. if not there is an entire troubleshooting tree for that including ECM failure.
