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ajshns
Samba Member
Joined: June 29, 2012
Posts: 6
Location: North East Illinios
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 Posted: Tue Aug 13, 2019 3:36 pm Post subject: Fuel Gauge improper reading only with engine running |
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I'm working on a 67 bus. Its 12v and has a new fuel gauge and sender. With the key on engine off the gauge reads properly all the time. When the engine is started the gauge will flop all over from empty to whatever the fuel level is and anywhere in between. Ive checked voltage, ground and ran a new wire from the sender to the gauge. I also took the gauge and sender out and ran wires to battery + battery - and the sender and the gauge still does the same thing. Here's the weird part... I took that set up with the sender to another car and the gauge works perfectly engine off and engine running. So.....something in this bus is feeding into the fuel gauge circuit and causing the gauge to flop. I did disconnect the alternator and its the sane result so its not electrical feedback from that. Maybe ignition? It has an empi electronic distributor with a bosch blue coil.
Any ideas would be greatly appreciated |
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BarryL 
Samba Member
Joined: November 01, 2004
Posts: 14269
Location: Casa de Oro, California
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| Posted: Tue Aug 13, 2019 6:58 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| Make sure the bracket that holds the gauge is digging into the metal of the dash as that is its ground. Make sure the sender is grounded to the body. Make sure you don't have the internal light wire and the power wire mixed up. |
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ajshns
Samba Member
Joined: June 29, 2012
Posts: 6
Location: North East Illinios
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| Posted: Wed Aug 14, 2019 8:19 am Post subject: Re: Fuel Gauge improper reading only with engine running |
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| BarryL wrote: |
| Make sure the bracket that holds the gauge is digging into the metal of the dash as that is its ground. Make sure the sender is grounded to the body. Make sure you don't have the internal light wire and the power wire mixed up. |
The gauge has a ground terminal on it that is grounded to the dash shelf mounting bolt. The sender is grounded to the body and I have run jumper wires from both gauge and sender to the ground strap on the battery. I have also ran jumper cables from the battery - to the engine block so I know grounds are good. |
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ToolBox
Samba Member
Joined: January 27, 2004
Posts: 3439
Location: Detroit, where they don't jack parts off my ride in the parking lot of the 7-11
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| Posted: Wed Aug 14, 2019 8:52 am Post subject: Re: Fuel Gauge improper reading only with engine running |
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| Check the charging system. Could be a faulty regulator causing spikes. |
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ajshns
Samba Member
Joined: June 29, 2012
Posts: 6
Location: North East Illinios
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| Posted: Wed Aug 14, 2019 9:03 am Post subject: Re: Fuel Gauge improper reading only with engine running |
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| ToolBox wrote: |
| Check the charging system. Could be a faulty regulator causing spikes. |
It has an internally regulated alternator and it does the same thing with the alt hooked up and disconnected. I've checked voltage at the gauge and it stays steady while the gauge is freaking out. Also today I swapped out the empi electronic distributor and put in an old points distributor and still same thing on the gauge. |
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BarryL
Samba Member
Joined: November 01, 2004
Posts: 14269
Location: Casa de Oro, California
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| Posted: Wed Aug 14, 2019 6:49 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| ajshns wrote: |
| The gauge has a ground terminal on it that is grounded to the dash shelf mounting bolt. |
Aftermarket gauge? |
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ajshns
Samba Member
Joined: June 29, 2012
Posts: 6
Location: North East Illinios
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| Posted: Thu Aug 15, 2019 5:23 am Post subject: Re: Fuel Gauge improper reading only with engine running |
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| BarryL wrote: |
| ajshns wrote: |
| The gauge has a ground terminal on it that is grounded to the dash shelf mounting bolt. |
Aftermarket gauge? |
Yes |
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Bruce Amacker
Samba Member
Joined: December 26, 2007
Posts: 1786
Location: Cleveland, Ohio
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| Posted: Thu Aug 15, 2019 6:39 am Post subject: Re: Fuel Gauge improper reading only with engine running |
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| ajshns wrote: |
| ToolBox wrote: |
| Check the charging system. Could be a faulty regulator causing spikes. |
It has an internally regulated alternator and it does the same thing with the alt hooked up and disconnected. I've checked voltage at the gauge and it stays steady while the gauge is freaking out. Also today I swapped out the empi electronic distributor and put in an old points distributor and still same thing on the gauge. |
TB is right- did you disconnect ALL of the alt wires? I've seen some where the alt still charges with the small wires disconnected. Spikes would not show up on a DVOM, only on a scope. I've seen several defective alternators cause really weird problems in late model vehicles but still keep the battery up.
_________________
'66 Deluxe Bus
'65 Standard Bus
Build threads:
'66- http://www.leakoil.net/forum/viewtopic.php?f=23&t=2888&sid=54d8dedfb3822f99c7f2ea430cb4e856
'65- http://leakoil.net/forum/viewtopic.php?f=23&t=4263 |
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ajshns
Samba Member
Joined: June 29, 2012
Posts: 6
Location: North East Illinios
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| Posted: Thu Aug 15, 2019 2:43 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| Bruce Amacker wrote: |
| ajshns wrote: |
| ToolBox wrote: |
| Check the charging system. Could be a faulty regulator causing spikes. |
It has an internally regulated alternator and it does the same thing with the alt hooked up and disconnected. I've checked voltage at the gauge and it stays steady while the gauge is freaking out. Also today I swapped out the empi electronic distributor and put in an old points distributor and still same thing on the gauge. |
TB is right- did you disconnect ALL of the alt wires? I've seen some where the alt still charges with the small wires disconnected. Spikes would not show up on a DVOM, only on a scope. I've seen several defective alternators cause really weird problems in late model vehicles but still keep the battery up. |
Yes all wires and even ran it without the belt so the alt was not spinning at all. Still same. |
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BarryL
Samba Member
Joined: November 01, 2004
Posts: 14269
Location: Casa de Oro, California
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| Posted: Thu Aug 15, 2019 6:45 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| Too late to post pictures of the sender and front and back of gauge? It is a weirdass phenomenon you got going on there. |
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western auto
Samba Member
Joined: July 20, 2013
Posts: 293
Location: yuma,az
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| Posted: Thu Aug 15, 2019 6:48 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| solid core plug wires arcing to any electrical wires? |
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ajshns
Samba Member
Joined: June 29, 2012
Posts: 6
Location: North East Illinios
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| Posted: Thu Aug 15, 2019 9:56 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| BarryL wrote: |
| Too late to post pictures of the sender and front and back of gauge? It is a weirdass phenomenon you got going on there. |
I can in the morning when I get to the shop. |
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BarryL
Samba Member
Joined: November 01, 2004
Posts: 14269
Location: Casa de Oro, California
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| Posted: Fri Aug 16, 2019 12:00 pm Post subject: Re: Fuel Gauge improper reading only with engine running |
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| western auto wrote: |
| solid core plug wires arcing to any electrical wires? |
Completely valid theory. ^^^^. It would be interesting to unplug the points wire and crank it and see if the gauge flip-flops. Also what if the coil or distributor were shorting and stealing the voltage in the system which made the gauge respond. |
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