Wonky Oil Gauge

[Prong]

The specifics: 79K10 350/SM465. Engine has 35K with a hi-vol oil pump installed. I checked resistance in the 3 ground wires that go to instrument cluster--the worst of the three had 3 ohms resistance, so that can be ruled out.

What happens: Fire it up cold and the gauge quickly goes to halfway between the 45 and 60 psi has marks. Give it a bit of throttle and it will go to the 60 or a shade over, but not in a smooth sweep. Acts like it's stuck but then pegs to the higher spot nearly instantly. Let off the gas, it returns to the previous spot in the same way. I've also discovered that with engine off, the needle rests about the 30psi mark (not unusual), but if you turn on the lights (either park or headlights), that needle will drop to near zero. Turn the lights off and the needle rises to near its previous position. I've replaced the headlight switch and added a ground for that, and tried a new oil gauge and sender with no change.
Now would the hi-vol pump cause the sudden jump in the needle from off idle because the gauge isn't really designed for a hi-vol pump? Or am I just thinking crazy?

[VileZambonie]

1st off why did you put in a high volume oil pump? I hope you have at least a 7 quart pan.

Check the basic operation of the gauge, key on engine off pull the wire off the sending unit. Observe the gauge, ground the wire and observe the gauge again. If you want to test it incrimentally hook it up to a potentiometer and see if it changes gradually or if it spikes or jumps. If your connections are good then you have a bad gauge.

You can easily screw in an oil pressure gauge and check your actual oil pressure for peace of mind.

[Prong]

I didn't install the pump. The PO did that during the rebuild and installed a 6qt. pan along with an oil cooler as well.

[red4wd]

I don't understand the big deal with high volume pumps...I have run them forever with a stock pans and never had problems. 

[VileZambonie]

They're not a big deal til you pump your pan dry. It's unecessary for mild applications. If you have a serious engine with a modified sump w high capacity go for it but for a stock pan configuration it's an unecessary risk. So anyone running a stock pan w/ HV oil pump it's not a performance gain.

[red4wd]

I've had them in bone stock to mildly built engines all with stock pans...guess ingorance is bliss egh...

[VileZambonie]

Just be careful if you're running a low (numerically high) gear ratio. A friend of mine made this mistake with a 4:11:1, Th400, 350 combination and at 75 on the highway he started to hear a knock. Failure was oil starvation - we replaced his crankshaft and bearings and replaced the pump with a standard volume. It's still running great 14 years later. I work with 3 machine shops and they all agree - use a standard volume oil pump unless you have a high capacity pan.

[Prong]

If I ground the gauge wire lead with the power on, it should read zero, right? If not, I'm guessing a continuity check of the gauge wire is next?

[VileZambonie]

yeah or try grounding it right at the gauge. either or will give you the same answer.

[gmiles]

Make sure you have the right sender for your gauge...meaning the right range/resistance. I ran into a problem on an aftermarket temp gauge that always read hot on the OEM sender. It needed a Stewart Warner temp sender.

[Prong]

I grounded the lead at the gauge and got a zero reading with key on. So now that the gauge and wire is good, what's the next step? Did I mention I abhor electrical work?

[VileZambonie]

replace the sending unit.

[Prong]

Already did that. New one or the old one has no affect...

[VileZambonie]

If you verified you have good oil pressure, you verified the operation of the gauge, the sending unit is good then you either have a bad gauge or faulty connection/wire