Guage problem

[SnackPack]

Hey all, I've been reading up in here about oil pressure guages and the problems that people have had, but I can't seem to figure out mine.

No matter what I do, my oil pressure guage goes off the scale (about the 3 o'clock position) when I turn on the key. This is even with the sensor wire disconnected at the instrument panel. For example, I can connect the positive and ground on the back of the guage and it does this.

Is this a problem with the guage itself, or is this supposed to happen when the sensor wire is not connected?

I don't see what I could have done to the guage since it worked last (before my engine rebuild), as I didn't touch any of the instrument cluster until now.

Thanks,
Adam

 

[5kerblaz]

Adam,

Try this site: http://members.cox.net/vipir14/gmgauges.html.

The Chevy service manual describes the testing procedure for the gauge but doesn't provide detail for the testing tool. The above site describes the tool AND the testing procedure.

When an oil-pressure gauge isn’t working, or any gauge really, most of the time it’s a faulty sending unit or severed or grounded lead to the sender. A peged needle indicates a short to ground somewhere in the cirecuit.

 

[SnackPack]

So it's normal to have the needle pegged at 3 0'clock (prolly 100psi?) when it's not connected to the sending unit, or connected to a faulty one?

 

[gn4u2c]

bad gauge or it is grounded out, thats the only 2 possible anwsers period,

 

[alec78]

Ummm, I'm sorry but I have to correct you on that. The test procedure is reasonably correct in describing how to test a 0 - 90 ohm based gauge circuit.

(Although it would be easier to buy 1 pkg of 2 or more 180 ohm resisters instead of the 220 and 150. It will yield the same resistance (90 ohms) but you only have to buy one package of resistors instead of two.)

...but that's not my point...

First off I do not know for sure if the oil gauge is on the same 0 - 90 scale that a fuel gauge is on. Actually I'm pretty sure it doesn't. I do know that the temp gauge absolutely does NOT work on that scale.

Also the "short to ground is causing the problem" that 5kerblaz and gn4u2c discuss is also totally wrong and backwords.

IF the oil gauge does work on the 0 - 90 ohm scale (0 ohms being 0 psi and 90 ohms being whatever the top of your gauge is) then reading the 3 o'clock position would be an open not a short to ground. Likewise as a short to ground would be no resistance (0 ohms) then a short to ground would read 0 psi.

SnackPack, I'm up in your neck of the woods frequently (actually its kinda my back yard) I'll come help you if you want. Shoot me a PM!

 

[SnackPack]

Hmmm,

So I got a new gauge, hooked it up, turned the key to start the motor, and nothing... in fact, the whole gauge cluster went out with all the systems that run when the key is on. I checked all the fuses on the fuse block and everything checks out.

Is there a fuse for the whole system somewhere that I'm missing? Argh, I went from a nicely running new motor with only an oil pressure gauge problem to a vehicle that now doesn't even turn "on".

The headlights work though.

Adam

 

[alec78]

Everything died? Hmmm..... If you mean a fuse to everything, there are fusable links on the starter that most of your powwer goes through. Of course this depends on previous owner changes and mistakes.

Did I understand that you installed the new gauge and THEN you lost all your power?

I'll be looking for you post.

 

[SnackPack]

Well, I had the instrument cluster exposed with the old gauge removed. Then I hooked up my new one loosely to make sure it was functional. In fact, I only had + and - wired into the instrument cluster when I hit the starter. Then everything went out. I don't think it's related to the gauge since there's always been quirks with my wiring.

Do you know physically where this inline fuse would be? I see there's one on the diagram in my Haynes manual.

 

[alec78]

I'll study my diagrams also, but the one's I mentioned earlier are on the starter solenoid. They are actually fuseable links and are usually they are orange or red in color.


To "test" them you basically give them a hard pull. Yes I know, that was a crappy description. Let me describe like this: A fuseable link is a wire that works like a fuse in that it burns up when too much amperage go through it. They are two wire gauges larger than the main wire and due to the fact that they are normally aluminum, they are crimped on. Sometimes you can look at the insulation and tell that they are spent. Usually you pull on them hard enough to tear the insulation as the core is no longer in tack. If it is spent it will tear. if not it won't. They are found on the main post (the one with the battery cable) of the starter solenoid and are about six inches long.

let me know if you need more help.

 

[SnackPack]

Welp, I wish I found the problem, but it's not the fusible links. I found them on mine, but they're not quite like you describe. One's right off the alternator and the other is on the red wire from the start up the back of the engine. They're about 2-3 inches long, and they're black.


Anyhow, like I said about wishing I found the problem... I probed around, checked a few things, and tried it once more... everything lit up and I heard the fuel pump start up... so I gave it a crank and it worked like a charm.

I also found the problem with the gauge... it's not the gauge or the sending unit, but apparently a severed sending wire somewhere. I routed a new wire from the back of the intrument panel to the sending unit and all is well.

Thanks for your help... I'll keep you in mind in case I ever need a hand, alec. Where are you from?

Adam