The computer definitely makes electrical problems a challenge.
Hands on is soooooo much easier.

 

Hey Roger,

You know these cars inside and out. I am at a bit of a disadvantage here. I don't have an 81 wiring diagram but do have an 82. The 82 is different the oil pressure sensor actually provides a function and is intertwined with the fuel pump relay and ECM.

On the 81 its just there to provide a reading I take it? One wire from it to the guage. If that wire is disconnected there should be no signal to the gauge. I thing the gauge is powered through the circuit board, brown wire second from the bottom on the left. So if that gauge moves with the sensor disconnected something must be sporadicly grounding of providing a signal.

Darren still has to try it with the sender disconnected. But i am curious.

Jim

 

Hi Jim,
Your correct the 81 just provides an oil pressure reading and doesn't tie into the ECM.
Your correct again in that if the tan sender wire is pulled off the sender the needle should be still (and at full or high oil pressure with key on)and not flickering around.

I'll take a quick read over the thread and see if I can shed any light.

OMG I see Ernie has been posting ,you guys know after 8pm he's probably snookered ! Just kidding !

edit- OK read over most of the posts and watched the movie, I agree with Ernie,the gauges sound as if they are fine.
I would be leaning towards a bad fuel sending unit or one that has a bad ground.
On the oil pressure - we need to wait until Darren finds the correct oil sender and pulls the wire but from watching the vid I would lean towards a bad oil sender or a very poor connection or a broken tan sender wire or the tan wire circuit is making and breaking connection.

 

Snookering starts at 10 Roger..

How do I use the linear pot to test the fuel sending unit and input?

you remove the input wire from the sender.. and connect it to the pot. Then ground the pot. You should then be able to adjust the ohms input to the gauge just as the if the sending unit were doing it.

Willcox

 

Thats what I was thinking, I will run to Radio Shack and see if I can pick one up. The link you posted that has them is sold out.

 

Thanks Roger, I will work on it tomorrow and or Sunday.

 

Just do a search on their site for linear pot.. with a range of 0 - 100 or 0-200 ohms.

Get a dozen or so if you plan on working on these cars in the future. I'm sure Roger will attest as to how helpful they are. They will never go to waste.... especially if you build Frankenmeters like me all the time.. I'm always smoking one every now and then testing things I have no business testing..

 

I have some good news, today I pulled the wire off the oil pressure sending unit and with the ignition on I got a reading of 80 psi, when I grounded the wire and got 0 psi. I reconected the wire and pushed on the conection at the wiring harness started the car and now it works with no flickering So I am thinking the short wire form the sending unit to the harness could be bad at the worst. I will put the distributor cover back on and hope it will work there after.

Now with the fuel sending unit I could not find a 100 ohm pot at our two local Radio Shacks and the music gear shop. There is one other place I will check but it will have to wait, they are closed on the weekends. If the sending unit does turn out to be bad can it be removed threw the fuel filler opening?

Thanks to all that have put up with me trying to help, you have been great and saved me a good deal of money, you guys

 

I have been suffering this problem with the oil pressue gauge on my 77 for a couple of years now, I was hoping you were going to be the one to solve it.
Mine tends to sit high when the fault is present by about 20psi but isn't fully pegged and fluctuates extremely fast. I originally suspected the connection you have rectified which seemed to cure it for a short while, eventually I got a new sender which fixed it for around a month, since then 2 or 3 senders have been fitted but I have now gone back to the original as it's no where near as bad with the genuine one fitted. I hope you now have yours sorted, I currently have my cluster out so I can carry out some tests. If I do get to the bottom of mine I will let you know - in the mean time I installed a much more accurate capilary gage so I know what it's actually doing.
Lester

 

You can always just use fixed resistors from Radio Shack to make up what you need.
They also have a 25 ohm pot,solder in a fixed resistor of your choice and you can then vary by 25 ohms.
Or put several 25s in series, 4 would get you 100 ohms.
I think if I remember right you have already established your fuel gauge does the full swing (grounding and ungrounding)so if you buy a 25 pot and connect it between the pink and ground at the fuel tank , turn the pot to 25 ,pointer should be around 1/4 tank,if there is no flicker you have proven the pink wire circuit and gauge are good. Then you only have the tank unit,the pink connection and the ground of the tank unit as suspects.
( Its early and I know others have probably said what I just said but I just finished a whole pot of coffee. )

 

It should all come out through the hole. No need to drop the tank. Remove the gas lid. Tap around the edges so you don't damage your paint. Remove the 6, 7 or 8 bolts...can't remember how many and lift it out. Have a new gasket available.

Make sure your disconnect the battery....just in case.

It will be interesting to see what it looks like. Could be as simple as most of the float being deteriorated.

Jim

 

Lester,

You sure its not the gauge itself thats gone or the resistor on the board?

Jim

 

You can remove the sending unit through the filler???

 

To remove the sender on the 1978-1982 cars, the tank must be pulled.

 

Lester-

If you use the fuel gauge help page I have on the site.. and the link posted above.. you can do the exact same test on the dash gauge.

But in most cases intermittent issues are not the gauge or the sender but rather an issue between the two.

On your oil pressure gauge... same as with Fuel. If the resistor is burned on the back of the gauge the most it will read is 1/4 at best. Even when the input is 90 ohms.

so if it passes the ground out test, and the missing ohms test, the odds are that the issue is else where.

Three sending units are not going to be defective.. or should I say the odds of this are highly unlikely. Now the sending unit grounding.. if you coat the threads extra thick with Teflon tape there is a chance the tape is not allowing the sender to ground. May don't realize it but the teflon tape on any thread is meant as a lubricant for seating the threads and not a sealant. So just like with a temperature sending unit, only the first few threads should be tapped.

Now you may want to check the printed circuit for a fault in your dash as well. Make sure to check the fingers where the center connector plugs in to make sure one is not touching or almost touching another finger.

Vetteman.. glad you have one nailed down.. one to go!

 

What ? I've been wondering why I always have so much trouble getting it out through that little hole.

 

Thats not so. I have an 82. The whole thing came up through the hole and I even have the fuel pump in there on mine. Seems like it won't but and you lift and turn it comes out with ease.

Jim

 

Willcox/Jim, thanks for the response, I didn't intend to hijack the thread. I have carried out the gage tests, checked the printed circuit, tested the wiring for high resistance/short to ground, I have also tried the sender with and without tape.... Previously the fault was there before I even started the engine and the gage would flicker around the 20psi range with just ignition feed, now it zero's perfect but after driving for a while starts to play around. It's got me stumped.... I have had the gage cluster out so will see if the fault continues when I get it back on the road in the next month or so.

 

I'm clumsy.. guess I'm worried about bending the float or scratching the paint.

 

That may explain why my gas gauge has never read right! It does get hung up from time to time.

It probably would probably be better to drop the tank. A lot of twisting and turning to get it out thorugh the hole. I figure since the 81 does not have the pump in the tank it may come out easier.

Jim