fuel gauage stopped working - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Electrical
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-23-2010, 12:45 PM
watchdude1's Avatar
Registered User
 
Last photo:
Join Date: May 2009
Location: hillsborough,nj
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
fuel gauage stopped working

I have a 1988 Toyota pickup, my fuel gauage stopped working, I unplugged the wire connection and checked the wires, the 2 side wires have no power and the middle wire has power, but it does no go to the other side of the connection, so I bought and installed a new sending unit. still not working,followed the wires to the computer, then I removed the dash but it is a circuit board, went back to the tank and ran a ground lead from the tank to the frame it wil not work, what else can I do?
why are there 3wires with power in the middle wire and then only 2 wires on the sending unit?
Attached Thumbnails
Click image for larger version

Name:	gauge.jpg
Views:	66
Size:	25.1 KB
ID:	45777   Click image for larger version

Name:	plug.jpg
Views:	77
Size:	35.4 KB
ID:	45778   Click image for larger version

Name:	plug2.jpg
Views:	90
Size:	20.1 KB
ID:	45779   Click image for larger version

Name:	plug3.jpg
Views:	81
Size:	15.0 KB
ID:	45780   Click image for larger version

Name:	fuel.jpg
Views:	113
Size:	60.2 KB
ID:	45781  


    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-24-2010, 09:50 PM
Barry.M's Avatar
Old Phart
 
Last wiki edit: How to identify a Ford V8
Last journal entry: 27 T Roadster project: Underway cont.
Last photo:
Join Date: Apr 2002
Location: S.A.Australia
Age: 55
Posts: 132
Wiki Edits: 3

Thanks: 0
Thanked 0 Times in 0 Posts
Generally speaking fuel gauges work as follows but original equipment manufactured (OEM) made gauges by companies do strange things.

The power wire (12V middle wire in your case) supplies power to the gauge (wire 1). One wire from the gauge goes to the sender unit (wire 2) in your fuel tank, sometimes via the computer if a late model vehicle. The other wire from the gauge will go to a "ground" (wire 3).

To make matters confusing, many OEM gauges (i.e.factory installed) take the power from a little voltage regulator (not the voltage regulator on the alternator) situated behind the dash somewhere or in the computer box and the other "ground wire" goes back to this voltage regulator also but on the "ground" /negative side. These gauges operate at 8-10V or less. They do this knowing that modern vehicles often operate at lower than 12V battery condition i.e. Aircon on, stereo on, lights on etc. etc.. This is why some gauges fluctuate up and down a bit for no particular reason.

OEM gauges are made like this (thermostatic principle) as they are cheaper to make than aftermarket gauges which generally are of the "balancing coil" type. But I digress.

Now back to your gauge. Once power is supplied to the gauge one wire as discussed goes back to the fuel tank sender and either the sender unit earths out through the tank or a "ground" wire supplies the earth. That is why you have three(3) wires on the gauge and two(2) wires on the tank. The fuel tank sender is in fact a type of Rheostat that "earths out" the gauge.

Checking which one is working or not requires a multi-meter or a known good gauge. Without a multi-meter you are very limited with what you can check. The fact that you've got power at the gauge is step one. Now it's time to buy a multi-meter, they are cheap and very useful if you don't have one. If you don't have one buy a LED display unit. A Good basic one for Automotive work is an 830B sold by many companies under there own brand and you should be able to pick one up for $10-$20.00.

Hope this helps........Barry.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 05-25-2010, 02:11 PM
watchdude1's Avatar
Registered User
 
Last photo:
Join Date: May 2009
Location: hillsborough,nj
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Barry:
I have a multi meter the problem is what to do with it,How do I check the fuel gauage when it is a circuit board were do you check, i traced the wires they go into the computer then to the sending unit, I tested the two wires coming out of the sending unit with a tester the light does not light up on either wire one is white with red and other is white with black the ground I suppose,I dont want to put any 12volt source onto these wires going to the sending unit it might blow up the gas tank so what or how do I check there is no power going to the 2 wires on the sending unit. maybe I need to find the voltage regulator ,the truck is pretty rusty and the ground on the tank is rusted out but I ran a ground wire to the tank to the frame with a ala-gator clips it still did not work, so confused what the.
Thanks Tom

Last edited by watchdude1; 05-25-2010 at 02:17 PM.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 06-19-2010, 07:31 PM
watchdude1's Avatar
Registered User
 
Last photo:
Join Date: May 2009
Location: hillsborough,nj
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
ok, I removed the instrument panel I checkd the fuel gauage it has 3 bolts, there is a marking which says 7v and ing and fu ,I put my volt meter on the ing and there is 9.50 volts the two other ones have no voltage don't know what they go too I'm thinking one to the computer then too sending unit and other to a ground?
I also ground the metal around one of the bolts on the fuel tank and ran a ground wire to the frame,thinking that the tank might not be grounded good still my fuel gauage is not working,can't seem to find a reguato runder the dash to check, any ideas on what else I can do.
Attached Thumbnails
Click image for larger version

Name:	gauage.jpg
Views:	99
Size:	67.2 KB
ID:	46297   Click image for larger version

Name:	gauage2.jpg
Views:	81
Size:	63.1 KB
ID:	46298  
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 06-20-2010, 08:19 AM
Barry.M's Avatar
Old Phart
 
Last wiki edit: How to identify a Ford V8
Last journal entry: 27 T Roadster project: Underway cont.
Last photo:
Join Date: Apr 2002
Location: S.A.Australia
Age: 55
Posts: 132
Wiki Edits: 3

Thanks: 0
Thanked 0 Times in 0 Posts
G'day Watchdude,

OK there are a couple of more things you can check with your multimeter. Unfortunately as I don't have an electrical schematic or vehicle to reference to, it is pretty much guesswork from my seat. The fact that you've got 9.5 Volts to the IGN pole is a good sign. The 7V lead is probably the regulated supply we talked about previously. The FU is probably the sending unit lead. The last unidentified lead could be a ground or may go to the computer to complete that circuit.

Now for some more tests. Switch your multimeter to Ohms something in the 500u to 2000u range. These next tests will determine if you've got a circuit or not and therefore do not require power to be turned on to the gauge or sender. You will be testing what resistance there is in the circuit. No resistance at all, not even a poofteenth means an open circuit or broken circuit.

Disconnect the sender unit wire at the sender. Now place the red lead on the terminal and the other lead to the sender unit mounting plate. You should get a reading of some sort ?. May only be small like 5, 10, 20, 30 ohms or less or as much as 500-600 ?. Yes/No ?. If you get a reading of any kind you've got a circuit, this is good. No reading at all, no circuit, means dud sender. Pull the sender and check over, repair or replace.

If Yes go to next step. Repeat the above except this time place the black lead to a good earth on the chassic. Resistance should now be greater than before ? Yes/No ?. If yes, this is good, how much extra resistance could be a problem, but one step at a time. If No then the ground wire from the tank to earth is broken.

Next step assuming Yes to all tests so far. Switch you multimeter back to a setting that will read 12V. Switch on the Ignition and test for voltage coming down to the tank sender via the sending unit wire. Once again, red lead on the sender wire, black lead to the chassic for a good ground. Got voltage Yes/No ?. Anywhere from 3-10 Volts probably. Yes is good, No means the problem is either the sender wire or further up. Switch Ignition off again.

To test the sender wire, find a long piece of auto electrical wire of similar size to the sender. Switch your multimeter back to Ohms. Check the test wire and note the resistance value. Now attach that test wire to the sender wire, you are making a big loop circuit. Now at the gauge end place the red lead of the MM on the FU terminal and the black lead on your test wire, Any reading ? Yes/No ?. If yes we guessed correctly that the FU terminal is the sender wire and that circuit is good. If Yes, is the reading similar to the tank reading less the noted resistance in your test wire ?. If the reading is MUCH, MUCH higher than before then there is a problem with dodgy connections or frayed wires. This needs to be investigated.

If NO, move the red MM lead to the 7V terminal any reading ?. Yes/No. If Yes then this lead MAY be the sender unit lead. If No, move the red MM lead to the unidentified terminal. Any reading ? Yes/No ?. Ditto previous comments.

If Yes to these tests then the problem is at the gauge end. You can do some similar resistance tests to the gauge but without a wiring diagram you (and I) are flying blind. But what you can test is the resistance of the printed circuits from terminals to the plug where the gauge cluster attaches to the wiring loom.

But at least after these tests you should be able to determine where the fault lies. i.e. at the tank, sender wire, ground, or at the gauge.

I hope this doen't sound too comfusing but once you've done a few tests it will become second nature and will be good experience for future troubleshooting.

Post again with results and maybe I or somebody else will be able to suggest more test options.

Good luck..........Barry.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 06-20-2010, 04:04 PM
watchdude1's Avatar
Registered User
 
Last photo:
Join Date: May 2009
Location: hillsborough,nj
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thanks, Barry
I will give it a shot next weekend, if i have time
thanks again for your time.
Reply With Quote Quick reply to this message

Recent Electrical posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Aftermarket EFI ? x007 Engine 61 02-08-2012 10:38 AM
Pinging on 03 Chevy 5.3 Engine in Suburban bry21317 Engine 42 10-02-2011 07:35 PM
Nitrous fuel supply ??? 67 Deuce 4 Me Engine 7 11-11-2007 09:30 AM
new fuel pump not working 53LEDSLED Engine 4 08-30-2005 06:48 PM
Hydraulic Jack has stopped working?? HotRodMan Engine 3 06-06-2003 03:55 AM


All times are GMT -6. The time now is 06:03 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.