Electrical Grounds
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Something is a muck for sure. But while both gauges do share a common ground, they are for the most part the same gauge. You could if you wanted, remove the face from one and swap it. The oil pressure would be more responsive to change but it would give you an accurate reading as a fuel gauge.
So my thinking on this is that there are two different problems and based only on the fact that the two gauges are not doing the same thing. If it were a grounding issue I would think both gauges would do the same thing.
If a fuel or oil pressure gauge has a burned resistor or is without one, it will read a steady 1/4 value and it would be steady. It would not fluctuate as illustrated in the video. So we can eliminate that as the problem.
I really think the input ohms wires need to be checked on both gauges as a starting point. IMHO
So my thinking on this is that there are two different problems and based only on the fact that the two gauges are not doing the same thing. If it were a grounding issue I would think both gauges would do the same thing.
If a fuel or oil pressure gauge has a burned resistor or is without one, it will read a steady 1/4 value and it would be steady. It would not fluctuate as illustrated in the video. So we can eliminate that as the problem.
I really think the input ohms wires need to be checked on both gauges as a starting point. IMHO
Should that isulator/resistor be there between the oil pressure gauge mounting points? Does it matter which nuts are used and where?
Anyway to kill power to the fuel meter device to see if the problem stops. Is there a fuse or a wire that can be disconnected at the tank? I bet you the bouncing of the oil pressure gauge will stop if you take the power supply away from the fuel gauge.
Jim
Last edited by jdp6000; Feb 28, 2011 at 12:02 AM.
Thread Starter
Instructor
Joined: Jul 2009
Posts: 213
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From: Jefferson City Missouri
Thats the back of yours right? The missing nuts? You took the pic after you took the nuts off right?
Willcox will probably know the answer to this. The yellow insulator I see on the oil gauge....should that be there? Did you get this flicker before you changed the board? Did the flicker start after something you did or did you get the car that way?
Interesting you get a flicker in the on position. Try this turn the ignition on. Sit in the car and get someone to bounce the rear up and down so the gas in the tank moves around excessively. Does the flicker get worse on the oil gauge? Its tough trying to figure this out via internet. I am only asking you to do the things i would do if i was there.
Jim
Willcox will probably know the answer to this. The yellow insulator I see on the oil gauge....should that be there? Did you get this flicker before you changed the board? Did the flicker start after something you did or did you get the car that way?
Interesting you get a flicker in the on position. Try this turn the ignition on. Sit in the car and get someone to bounce the rear up and down so the gas in the tank moves around excessively. Does the flicker get worse on the oil gauge? Its tough trying to figure this out via internet. I am only asking you to do the things i would do if i was there.
Jim
I will give you suggestion a try but why will the oil gauge flicker more if the gas is sloshing around, or did you mean gas gauge?
Thread Starter
Instructor
Joined: Jul 2009
Posts: 213
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From: Jefferson City Missouri
I think the movement of the oil pressure gauge in the start position is because it is picking up the signal from the fuel metering device. Its the only thing that make sense to me. Current should be constant. The only thing that would change the current value is movement of the fuel metering device when in an stopped position and engine off. If it was anything else like a draw from lights it would beg left or right everytime the a power consuming source was activated.
Should that isulator/resistor be there between the oil pressure gauge mounting points? Does it matter which nuts are used and where?
Anyway to kill power to the fuel meter device to see if the problem stops. Is there a fuse or a wire that can be disconnected at the tank? I bet you the bouncing of the oil pressure gauge will stop if you take the power supply away from the fuel gauge.
Jim
Should that isulator/resistor be there between the oil pressure gauge mounting points? Does it matter which nuts are used and where?
Anyway to kill power to the fuel meter device to see if the problem stops. Is there a fuse or a wire that can be disconnected at the tank? I bet you the bouncing of the oil pressure gauge will stop if you take the power supply away from the fuel gauge.
Jim
Thanks
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Try disconnecting the ground for the gas gauge back at the tank. The gauge should peg and not move. Then see if the oil gauge still flickers.
You can also try leaving the gas gauge ground connected and disconnect the oil pressure gauge. The car shouldn't start with the oil gauge disconnected....at least i don't think so. The purpose of that sensor is to kill the motor if the oil pressure is near zero.
With the key on your oil pressure gauge should be at 0. As you kick the motor over it will climb gradually. This is the proper operation of the sensor and gauge. Oil pressure should be between 20-40.
If you choose to remove the cluster. Play around with it out. Connect it and try it. Maybe the harness plug is shifting when you put it back in or something is touching the back of the board in the "in" position.
Jim
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From: Jefferson City Missouri
The gauges are not moving in unison! I think you have two separate issues and I don't think the issue is in the dash. I'll watch the whole video and look close, with some stops and starts later today. But here is why I say this. The fuel gauge and the oil pressure are darn near twins with the only difference being the dampening fluid.
If this were a ground issue both gauges would be acting the exact same way and your fuel gauge is flickering toward the empty, while your oil pressure is trying to peg.
So.. maybe inspect the oil pressure wire at the sending unit.. see if it's shorting out on something. A shorted input wire will cause the gauge to peg.
I'll check back later tonight.
Willcox
If this were a ground issue both gauges would be acting the exact same way and your fuel gauge is flickering toward the empty, while your oil pressure is trying to peg.
So.. maybe inspect the oil pressure wire at the sending unit.. see if it's shorting out on something. A shorted input wire will cause the gauge to peg.
I'll check back later tonight.
Willcox
I pulled the wire off and found rust on the conncetor, I brushed it off and reconnected it back, no change. I then pull the wire again and started the car thinking I should get a zero reading from the gauge no change also. I hope this helps you.
Thread Starter
Instructor
Joined: Jul 2009
Posts: 213
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From: Jefferson City Missouri
The trick is to isolate each gauge.
Try disconnecting the ground for the gas gauge back at the tank. The gauge should peg and not move. Then see if the oil gauge still flickers.
You can also try leaving the gas gauge ground connected and disconnect the oil pressure gauge. The car shouldn't start with the oil gauge disconnected....at least i don't think so. The purpose of that sensor is to kill the motor if the oil pressure is near zero.
With the key on your oil pressure gauge should be at 0. As you kick the motor over it will climb gradually. This is the proper operation of the sensor and gauge. Oil pressure should be between 20-40.
If you choose to remove the cluster. Play around with it out. Connect it and try it. Maybe the harness plug is shifting when you put it back in or something is touching the back of the board in the "in" position.
Jim
Try disconnecting the ground for the gas gauge back at the tank. The gauge should peg and not move. Then see if the oil gauge still flickers.
You can also try leaving the gas gauge ground connected and disconnect the oil pressure gauge. The car shouldn't start with the oil gauge disconnected....at least i don't think so. The purpose of that sensor is to kill the motor if the oil pressure is near zero.
With the key on your oil pressure gauge should be at 0. As you kick the motor over it will climb gradually. This is the proper operation of the sensor and gauge. Oil pressure should be between 20-40.
If you choose to remove the cluster. Play around with it out. Connect it and try it. Maybe the harness plug is shifting when you put it back in or something is touching the back of the board in the "in" position.
Jim
Thanks
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
The oil pressure sensor is bell shaped and on the driver side at the very back of the engine. If you unplugged the right thing and still getting movement of the needle power is getting to it from somewhere else.
Its actually the pink ohms wire that will be at the neck....disconnect it to disable the gauge.
Jim
Last edited by jdp6000; Feb 28, 2011 at 05:56 PM.
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Ok, back when I got the car I was told that the oil pressure sending unit was on top of the engine under the distributer cover, should have check myself. I looked in my GM 1981 Corvette Shop Manual and it is telling me that it's on the left side just above the oil filter. Is the right?
I pulled the wire off and found rust on the conncetor, I brushed it off and reconnected it back, no change. I then pull the wire again and started the car thinking I should get a zero reading from the gauge no change also. I hope this helps you.
I pulled the wire off and found rust on the conncetor, I brushed it off and reconnected it back, no change. I then pull the wire again and started the car thinking I should get a zero reading from the gauge no change also. I hope this helps you.
It has to be from the gas level sensor in the tank. The reason you get the flicker is because the minute you sit in the car you cause the gas to slosh around. It will slosh around for a long time.
Anyother way to test this theory is by putting your window down. Park the car for about 10 hours. Until the gas has stopped moving around for sure. then reach in carfully without touching the body or the car or rocking the car. Stick the key in and turn it to one. Should be no movement of the gauges because there is no movement of the gas.
See my previous post on disabling the gas level sensor.
Jim
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Melting Slicks
Joined: Aug 2001
Posts: 3,035
Likes: 121
From: Wichita KS
The ground for the fuel meter (sending unit) is located on the underside rear driver's side frame rail by the bumper energy absorber assembly. If you have a GM circuit diagram, the ground is circuit 150 - also shared with the LH&RH side markers/backup lights/tail stop directional lights/license plate light.
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
The ground for the fuel meter (sending unit) is located on the underside rear driver's side frame rail by the bumper energy absorber assembly. If you have a GM circuit diagram, the ground is circuit 150 - also shared with the LH&RH side markers/backup lights/tail stop directional lights/license plate light.
Thats correct but I would still disable the sender at the filler neck. Make sure its off completely.
Willcox's test proceedure link posted here will give you a visual of what to look for.
Thread Starter
Instructor
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From: Jefferson City Missouri
When I pulled the pink wire off the fuel sending unit the oil pressure gauge was still flickering. This weekend I will pull the cluster and look at the conections and see if I can get a meter to do some testing.
Thanks,
Darren
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Ok, I disabled the sender at the filler neck (pink wire) and the gas gauge peged to the 3:00 position then I grounded that wire and then it went to E, just as it should if the gauge is good, (Wilcox's test). So I am thinking the sending unit is going bad, the gauge flickers now only when the car is moving or after I have come to a stop. I backed out of the garage the gauge started to move then I came to a stop and put the car in park and waited for about 5 min and the gauge stoped moving. I did this two more times with the same results.
When I pulled the pink wire off the fuel sending unit the oil pressure gauge was still flickering. This weekend I will pull the cluster and look at the conections and see if I can get a meter to do some testing.
Thanks,
Darren
When I pulled the pink wire off the fuel sending unit the oil pressure gauge was still flickering. This weekend I will pull the cluster and look at the conections and see if I can get a meter to do some testing.
Thanks,
Darren
Jim
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Ok, I disabled the sender at the filler neck (pink wire) and the gas gauge peged to the 3:00 position then I grounded that wire and then it went to E, just as it should if the gauge is good, (Wilcox's test). So I am thinking the sending unit is going bad, the gauge flickers now only when the car is moving or after I have come to a stop. I backed out of the garage the gauge started to move then I came to a stop and put the car in park and waited for about 5 min and the gauge stoped moving. I did this two more times with the same results.
When I pulled the pink wire off the fuel sending unit the oil pressure gauge was still flickering. This weekend I will pull the cluster and look at the conections and see if I can get a meter to do some testing.
Thanks,
Darren
When I pulled the pink wire off the fuel sending unit the oil pressure gauge was still flickering. This weekend I will pull the cluster and look at the conections and see if I can get a meter to do some testing.
Thanks,
Darren
You've made progress then.. and proven that there are in deed two separate issues.
Roger posted on here a long time ago where he took a flasher and attached it to a temperature sending unit wire. (flashers have about 50 ohms resistance) So if you have one laying around you could put this inline on the input wire and see if the fuel gauge reads just past 1/2 a tank.
You could also do the same with the temp sending unit and use this same method. http://forums.corvetteforum.com/c3-t...post1570154949
You have proven that the fuel gauge is working properly though!
and that the cause of this, in my head is issue with input or the sending unit. The way to test this is to purchase a 0-100 linear pot at radio shack or a similar store. I have a link for this http://www.allelectronics.com/make-a...TAPER/-/1.htmlOne thing that crossed my mind after trying to catch up with these post is that you could have a back feed voltage issue. But.. I drew a line through that when you posted again and when thinking about this some more. This isn't the case! If it were again, both gauges would be responding the same way and not opposite.
I'm watching...
Willcox
Last edited by Willcox Corvette; Mar 2, 2011 at 10:08 PM.
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Darren-
You've made progress then.. and proven that there are in deed two separate issues.
Roger posted on here a long time ago where he took a flasher and attached it to a temperature sending unit wire. (flashers have about 50 ohms resistance) So if you have one laying around you could put this inline on the input wire and see if the fuel gauge reads just past 1/2 a tank.
You could also do the same with the temp sending unit and use this same method. http://forums.corvetteforum.com/c3-t...post1570154949
You have proven that the fuel gauge is working properly though! and that the cause of this, in my head is issue with input or the sending unit. The way to test this is to purchase a 0-100 linear pot at radio shack or a similar store. I have a link for this http://www.allelectronics.com/make-a...TAPER/-/1.html
One thing that crossed my mind after trying to catch up with these post is that you could have a back feed voltage issue. But.. I drew a line through that when you posted again and when thinking about this some more. This isn't the case! If it were again, both gauges would be responding the same way and not opposite.
I'm watching...
Willcox
You've made progress then.. and proven that there are in deed two separate issues.
Roger posted on here a long time ago where he took a flasher and attached it to a temperature sending unit wire. (flashers have about 50 ohms resistance) So if you have one laying around you could put this inline on the input wire and see if the fuel gauge reads just past 1/2 a tank.
You could also do the same with the temp sending unit and use this same method. http://forums.corvetteforum.com/c3-t...post1570154949
You have proven that the fuel gauge is working properly though!
and that the cause of this, in my head is issue with input or the sending unit. The way to test this is to purchase a 0-100 linear pot at radio shack or a similar store. I have a link for this http://www.allelectronics.com/make-a...TAPER/-/1.htmlOne thing that crossed my mind after trying to catch up with these post is that you could have a back feed voltage issue. But.. I drew a line through that when you posted again and when thinking about this some more. This isn't the case! If it were again, both gauges would be responding the same way and not opposite.
I'm watching...
Willcox
The oil pressure gauge is bad but the oil sender is good?
Jim
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If you place a flasher or linear pot in line go generate an input ohms reading and the same results, then the issue is on the wire between the sender and the gauge. If the symptoms go away then yes.. you have isolated the issue. It's just a quickie simple test that will tell you where the problem is. 
Your test above where you remove the ohms wire and the gauge pegs full and then ground out that same wire and it reads empty tells me the gauges are working fine.
Willcox
Your test above where you remove the ohms wire and the gauge pegs full and then ground out that same wire and it reads empty tells me the gauges are working fine.
Willcox
Thread Starter
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Joined: Jul 2009
Posts: 213
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From: Jefferson City Missouri
Darren
Thread Starter
Instructor
Joined: Jul 2009
Posts: 213
Likes: 13
From: Jefferson City Missouri
Darren-
You've made progress then.. and proven that there are in deed two separate issues.
Roger posted on here a long time ago where he took a flasher and attached it to a temperature sending unit wire. (flashers have about 50 ohms resistance) So if you have one laying around you could put this inline on the input wire and see if the fuel gauge reads just past 1/2 a tank.
You could also do the same with the temp sending unit and use this same method. http://forums.corvetteforum.com/c3-t...post1570154949
You have proven that the fuel gauge is working properly though! and that the cause of this, in my head is issue with input or the sending unit. The way to test this is to purchase a 0-100 linear pot at radio shack or a similar store. I have a link for this http://www.allelectronics.com/make-a...TAPER/-/1.html
One thing that crossed my mind after trying to catch up with these post is that you could have a back feed voltage issue. But.. I drew a line through that when you posted again and when thinking about this some more. This isn't the case! If it were again, both gauges would be responding the same way and not opposite.
I'm watching...
Willcox
You've made progress then.. and proven that there are in deed two separate issues.
Roger posted on here a long time ago where he took a flasher and attached it to a temperature sending unit wire. (flashers have about 50 ohms resistance) So if you have one laying around you could put this inline on the input wire and see if the fuel gauge reads just past 1/2 a tank.
You could also do the same with the temp sending unit and use this same method. http://forums.corvetteforum.com/c3-t...post1570154949
You have proven that the fuel gauge is working properly though!
and that the cause of this, in my head is issue with input or the sending unit. The way to test this is to purchase a 0-100 linear pot at radio shack or a similar store. I have a link for this http://www.allelectronics.com/make-a...TAPER/-/1.htmlOne thing that crossed my mind after trying to catch up with these post is that you could have a back feed voltage issue. But.. I drew a line through that when you posted again and when thinking about this some more. This isn't the case! If it were again, both gauges would be responding the same way and not opposite.
I'm watching...
Willcox
Thanks
Darren
Thread Starter
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From: Jefferson City Missouri
That's what I am thinking but when I pulled the wire to what I think is the oil sending unit the gauge still flickered. I will check that wire again this weekend to see if the gauge still flickers, I will even take a pic of it and post it to let you all see if I am pulling the oil sending unit wire.
Darren
Darren
Darren
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Ok after some searching around here I found out that the wire I pulled by the oil filter is for the oil temp gauge, and my oil pressure is located by the distributor. So If you have a 1981 Corvette that came from the factory with an oil temp gauge be carefull, My GM Shop Manual does not take that into account or I overlooked it.
Darren
Darren
I wish I was there I could figure this out in less then an hour.
Jim
Thread Starter
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From: Jefferson City Missouri
Me too, My wife keeps asking why I don't call her brother or cousin, but they are always busy so I don't bother.
Darren