Author Topic: Temp Gauge Pegged Right  (Read 835 times)

allenga

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Temp Gauge Pegged Right
« on: September 05, 2018, 09:36:57 AM »
HI Guys, my temp gauge is pegged to the right.  I cleaned the contact on the sending unit.  No change.  Also, the gauge is pegged right with the sending unit wire or or off the sending unit. Thoughts appreciated.  Thanks!
1977 Trans Am, stock 400 W72, auto.

81Blackbird

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Re: Temp Gauge Pegged Right
« Reply #1 on: September 05, 2018, 10:57:57 AM »
What work did you do before the gauge went hay wire? Sounds like a gnd wire is not connected.

allenga

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Re: Temp Gauge Pegged Right
« Reply #2 on: September 05, 2018, 11:02:57 AM »
Thanks.  I just took air cleaner base off, replaced PCV grommet.  Where is the ground.
1977 Trans Am, stock 400 W72, auto.

81Blackbird

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Re: Temp Gauge Pegged Right
« Reply #3 on: September 05, 2018, 11:28:00 AM »
If I remember correctly the gnd is behind that gauge cluster and is connected to one of the pegs.  But I don't see how that would just come off if you were under the hood.  Check fuse.

Dreamn2

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Re: Temp Gauge Pegged Right
« Reply #4 on: September 05, 2018, 01:17:57 PM »
Wire could have a bare spot grounding to motor somewhere
79 Fire Am
76 Fire Am
79 W72 Formula

Re: Temp Gauge Pegged Right
« Reply #4 on: September 05, 2018, 01:17:57 PM »

Grand73Am

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Re: Temp Gauge Pegged Right
« Reply #5 on: September 05, 2018, 04:20:45 PM »
To check to see if your gauge is working, ground the sender wire straight to the engine, and turn the ignition key on. The needle should peg all the way to the left. If it does, then your gauge is good, and I would suspect that your sender unit is bad. Or if somebody wrapped the sender unit threads with some teflon tape or some other thread sealant, that could be the problem too. The threads of the sender have to make a good ground with the intake manifold, so tape or sealant can interfere with the grounding. So try cleaning the threads on the sender and in the hole of the intake and re-install without any tape or sealant. If that doesn't work, I'd try a new sender unit. 
Steve F.

allenga

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Re: Temp Gauge Pegged Right
« Reply #6 on: September 05, 2018, 07:39:22 PM »
Thanks Guys for the feedback.  Right now, temp gauge pegged right.  Steps: took off wire from sending unit, no change.  Grounded sending unit wire to car, no change.  Disconnected and reconnected battery, no change.  There are no other electrical issues with car at the moment. 

Where should I go next.

Thanks  :?
1977 Trans Am, stock 400 W72, auto.

70RAIV455

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Re: Temp Gauge Pegged Right
« Reply #7 on: September 05, 2018, 07:43:20 PM »
Thanks Guys for the feedback.  Right now, temp gauge pegged right.  Steps: took off wire from sending unit, no change.  Grounded sending unit wire to car, no change.  Disconnected and reconnected battery, no change.  There are no other electrical issues with car at the moment. 

Where should I go next.

Thanks  :?
The Temp gauge is suspect defective.
Pull it and check for 12 vdc to gauge with ignition key on with a DVM volt meter.

allenga

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Re: Temp Gauge Pegged Right
« Reply #8 on: September 05, 2018, 07:46:28 PM »
Thanks.  I need to drive this thing in a day.  I need to just put up a temporary gauge so I can drive without worrying about overheating.  Any thoughts..
1977 Trans Am, stock 400 W72, auto.

70RAIV455

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Re: Temp Gauge Pegged Right
« Reply #9 on: September 05, 2018, 08:13:06 PM »
Thanks.  I need to drive this thing in a day.  I need to just put up a temporary gauge so I can drive without worrying about overheating.  Any thoughts..
Stewert Warner or VDO Temp Gauge.

Autometer my Favorite.

allenga

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Re: Temp Gauge Pegged Right
« Reply #10 on: September 05, 2018, 08:54:50 PM »
Any testing I can do from under dash.  I happen to have my a/c duct work out.  I can see the back of the instrument panel easy.
1977 Trans Am, stock 400 W72, auto.

allenga

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Re: Temp Gauge Pegged Right
« Reply #11 on: September 06, 2018, 05:36:36 PM »
Any thoughts.  I am not ready to pull the dash apart to get the cluster out.  Any testing of gauge I can do from behind dash.  Thanks!
1977 Trans Am, stock 400 W72, auto.

70RAIV455

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Re: Temp Gauge Pegged Right
« Reply #12 on: September 06, 2018, 05:57:56 PM »
Any thoughts.  I am not ready to pull the dash apart to get the cluster out.  Any testing of gauge I can do from behind dash.  Thanks!
Not easily no.

Grand73Am

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Re: Temp Gauge Pegged Right
« Reply #13 on: September 06, 2018, 07:42:06 PM »
Since the gauge remains pegged to the right when you ground the sender wire, it means the gauge isn't getting the ground signal. One small possibility is that the sender wire is cut or broken somewhere between the sender and connector that plugs into the back of the cluster. Or a more likely possibility is the wiring connector isn't making a good connection with the copper strip for the temp gauge on the printed circuit, or the printed circuit is otherwise damaged. Sometimes the copper strip in the hole in back of the cluster can be loose and get out of place, so the connector and copper strip aren't lined up and don't make the connection. Making sure it's lined up when plugging the connector in is the way to ensure the connection. Examine the printed circuit for damage to the circuit going to the temp gauge too. That's about all you can do by partially pulling the cluster out so you can get a look at the connector.
Steve F.

allenga

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Re: Temp Gauge Pegged Right
« Reply #14 on: September 06, 2018, 08:03:49 PM »
Thanks Steve for all the help input. A picture would be helpful if you had one. Thanks
1977 Trans Am, stock 400 W72, auto.

Re: Temp Gauge Pegged Right
« Reply #14 on: September 06, 2018, 08:03:49 PM »



Jack

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Re: Temp Gauge Pegged Right
« Reply #15 on: September 06, 2018, 08:37:37 PM »


Here you go. I created this to show the ground and other circuits.
Steve is right, most likely the hot circuit that feeds both the temp and pressure gauge is broken after the pressure gauge.
You can trace the circuit based on the location of the gauges (top center) and you will see how the temp and pressure gauges are fed.




Regards, Jack

Jack

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Re: Temp Gauge Pegged Right
« Reply #16 on: September 06, 2018, 08:39:37 PM »
For more help check out the "how to convert standard to rally gauges" post.




Regards, Jack

allenga

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Re: Temp Gauge Pegged Right
« Reply #17 on: September 06, 2018, 08:50:26 PM »
Thanks Jack.  Such a great group of guys on this board.
1977 Trans Am, stock 400 W72, auto.

allenga

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Re: Temp Gauge Pegged Right
« Reply #18 on: September 07, 2018, 09:54:21 AM »
darn car. I took it out this morning and after 10 min the guage started working
1977 Trans Am, stock 400 W72, auto.

81Blackbird

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Re: Temp Gauge Pegged Right
« Reply #19 on: September 07, 2018, 11:23:19 AM »
Did ya hit a speed hump or pot hole?  :P

allenga

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Re: Temp Gauge Pegged Right
« Reply #20 on: September 07, 2018, 11:56:53 AM »
Flat open road. No bumps. ????
1977 Trans Am, stock 400 W72, auto.

Jack

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  • 1971 Esprit TA Clone W72 1972 Formula 68 350 HO
Re: Temp Gauge Pegged Right
« Reply #21 on: September 07, 2018, 12:08:52 PM »
Since it's working I would do the open and short circuit test to rule out the sending unit. I still think the issue is with the printed circuit and the gauge not getting power (especially since the oil pressure was always working). The circuit board is very thin copper that can develop cracks over time, once I fixed mine by adding a jumper but they sell paint on copper/repair kit, I would order one and fix it once it does it again.




Regards, Jack

allenga

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Re: Temp Gauge Pegged Right
« Reply #22 on: September 07, 2018, 12:16:26 PM »
Will
Do and report back. Thanks ????
1977 Trans Am, stock 400 W72, auto.

allenga

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Re: Temp Gauge Pegged Right
« Reply #23 on: September 14, 2018, 07:50:17 PM »
Update.  So I have driven the car 4 times.  Each time the gauge starts out pegged right, then after 10 minutes, starts working.  After I shut off the car and turn on, pegs right.   :???:

I am not ready to pull the cluster, but I tried to get a socket up behind to tighen the bolts for the guage and I cant contort myself enough.  I already have the duct work out of the car too.

Sigh..
1977 Trans Am, stock 400 W72, auto.

81Blackbird

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Re: Temp Gauge Pegged Right
« Reply #24 on: September 15, 2018, 05:08:25 AM »
If you remove the speedo cable you can move the cluster out of its position just enough to get your hand back there.  Easy it forward slightly then bring the left side out so you can get your hand back there.  Use just your fingers at this time to see if one of the small nuts are loose.  Use a mirror first just to inspect.  Battery disconnected before work.
Also, follow the temp lead all the way back to the firewall.  The ten minute lag is perplexing. Previous posts mentioned Teflon tape and a clean threads.  Could a faulty sending unit be your issue.  I would spend a few dollars and change that out before pulling the cluster.

allenga

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Re: Temp Gauge Pegged Right
« Reply #25 on: September 15, 2018, 06:32:07 AM »
Thanks Blackbird.  This is my task for today.
1977 Trans Am, stock 400 W72, auto.

Aus78Formula

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Re: Temp Gauge Pegged Right
« Reply #26 on: September 15, 2018, 06:53:31 AM »
wonder if it's a fault in the sender that is grounded until engine warms up, also check if it's a 60 or 80 unit.

allenga

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Re: Temp Gauge Pegged Right
« Reply #27 on: September 15, 2018, 10:53:47 AM »
Update.  I inspected the sender wire all the way to firewall.  No issues.  Took the car for a drive, after 10 minutes temp gage started working as usual.  This time I pulled over while car running, unplugged wire from sender and gage went to 100, pegged left like it should.
1977 Trans Am, stock 400 W72, auto.

Re: Temp Gauge Pegged Right
« Reply #27 on: September 15, 2018, 10:53:47 AM »
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