#1  
Old 01-19-2021, 05:13 PM
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Default Oil Pressure gauge test?

Issue: Oil Pressure gauge registers pegged to the right. I installed a new oil pressure sending unit 60 days ago and the gauge worked properly until yesterday. Car sat for 2-3 weeks and when I started engine, the gauge goes all the way to the right and does not go back to "zero" until engine is turned off. Since the blue wire was tightly connected to the sending unit I suspected the unit went bad. Got another new unit under warranty from Napa but no change. Is there a test I can do before replacing the O.P. gauge in the cluster? I really hate that job and it seems weird that the gauge would just go bad with no warning. This is on my bone stock 70 T/A. Also, the engine wiring harness is about 90 days old and the blue wire is not frayed or damaged. Thanks.

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  #2  
Old 01-19-2021, 07:49 PM
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Decent video from American Autowire that might help.

https://www.youtube.com/watch?v=puNKAW5Nurc

  #3  
Old 01-19-2021, 10:21 PM
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There is a small ceramic resistor that goes across the two posts on the back of the gauge, if those connections from the posts to the pads of the resistor are not good, meaning loose or corroded you will get behavior like this. I'd pull the gauge cluster and check the tightness of those nuts for the oil pressure gauge, if they are not loose, take them off and clean the contacts. Do not get too aggressive though, that ceramic is brittle and the pads can be easily damaged.

Forgot to add that the printed circuit could be bad too, if it is the original they can delaminate and the copper traces lift then snap. The nuts that hold this to the post also get loose or dirty and cause the same issues. The gauge moving with the on and off of they key would make me think the actual meter or movement is ok and working, it is just the connections and or the resistor that are failing.

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Last edited by fbody_mike; 01-19-2021 at 10:26 PM.
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Old 01-19-2021, 10:39 PM
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Default Trans Am; gauges: Oil pressure & coolant temperature

Those 2 pads post # 3 refers to are actually silver. Those turn black over time & will get to the point where it is just as if there were no resister in there at all! (Open circuit.) About once per every 25 or 30 years the resistors in behind those gauges need to be removed & cleaned also all of the attaching hardware that holds those in-place cleaned-replated and/or replaced.


On 2nd Gen Trans Am series cars there are a total of 4 resistors. One per each mounted in behind the gauges for: Oil pressure, coolant temperature, volts and fuel level. In order to access the resistor(s) that are for the oil pressure or coolant temperature gauge(s) the main instrument cluster housing needs to be removed from the dash. After that the printed circuit taken off of the backside to access the light blue plastic access panel. It is actually easier to remove the whole "twin" gauge section out of the center circle of that cluster to best clean and inspect those two.


Those can easily cause problems with the gauges if the touch pads are not clean enough to make contact. It is not common for those resistors to actually go bad but I have see a few that are open. Measure with an ohmmeter but not installed. (Remove from backside of gauge, then measure.)
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Last edited by Peter Serio; 01-19-2021 at 10:57 PM. Reason: add photos
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  #5  
Old 01-20-2021, 10:11 AM
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Great information gentlemen. I will work on removing the cluster and the gauge in the next few days and will report back. Thanks.

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  #6  
Old 01-20-2021, 10:53 AM
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Quote:
Originally Posted by Peter Serio View Post
Those 2 pads post # 3 refers to are actually silver. Those turn black over time & will get to the point where it is just as if there were no resister in there at all! (Open circuit.) About once per every 25 or 30 years the resistors in behind those gauges need to be removed & cleaned also all of the attaching hardware that holds those in-place cleaned-replated and/or replaced.


On 2nd Gen Trans Am series cars there are a total of 4 resistors. One per each mounted in behind the gauges for: Oil pressure, coolant temperature, volts and fuel level. In order to access the resistor(s) that are for the oil pressure or coolant temperature gauge(s) the main instrument cluster housing needs to be removed from the dash. After that the printed circuit taken off of the backside to access the light blue plastic access panel. It is actually easier to remove the whole "twin" gauge section out of the center circle of that cluster to best clean and inspect those two.


Those can easily cause problems with the gauges if the touch pads are not clean enough to make contact. It is not common for those resistors to actually go bad but I have see a few that are open. Measure with an ohmmeter but not installed. (Remove from backside of gauge, then measure.)
I agree 100%, and I will add that an "open circuit" will result in a pegged gauge meter .

  #7  
Old 01-20-2021, 02:19 PM
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Just a thought while you have the cluster out, check the condition of the printed circuit board. Those peel apart when they get old and that could also be the case of an oil pressure or temperature gauge problem.

Thankfully all of the versions of 2nd Gen Trans Am printed circuits are available to buy as a new reproduction part from Ames Performance.

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  #8  
Old 01-20-2021, 05:22 PM
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Thanks again all.

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  #9  
Old 02-05-2021, 04:22 PM
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Default Update

Before pulling the cluster and all of that hassle, I purchased a BWD brand sending unit from Advance and now my gauge behaves correctly. So the first Napa unit (Echlin) worked for several months and then crapped out. The replacement Napa unit did not work at all but after two weeks the BWD works well. Hopefully it holds up long term! Just glad I did not have to get in to the cluster. Thanks.

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