No oil pressure light....me two!!

cosmo · 05-25-2004, 11:56 AM

I'am just starting the "after rebuild" first start up proceedures, after hooking op the battery and turning the key I have no oil pressure light and the pressure guage pegs to the top. I cranked the engine just a bit and nothing changed, I have tested the bulb and and also tried disconnecting both the sender and guage unit but nothing changes. The yellow alt. light comes on as it should. HELP!!!!!
71 911 E all stock 2.2E

dtw · 05-25-2004, 12:00 PM

If the gauge pegs, it is a wiring/component issue. Check your grounds, sounds like the circuit is open (which causes the gauge to peg as it is designed to do).

There is NO oil light that I'm aware of. I believe that top light on the gauge deals with the brake failure switch and the e-brake switch - nothing more.

cosmo · 05-25-2004, 12:53 PM

Well I have a sending unit on top of the case near the breather that looks like a guage type sender and also a sender near the rear by the chain houseing smaller that looks like a light type of sender??? What gives?
Thanks

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by cosmo
Well I have a sending unit on top of the case near the breather that looks like a guage type sender and also a sender near the rear by the chain houseing smaller that looks like a light type of sender??? What gives?
Thanks

The pressure switch at the flywheel end of the motor near the breather is what you should be concerned about. If you think that the switch is broken, replace it (they are less than $10). To check too, you can remove it and see if oil comes out. You can also crank the engine with this sensor removed (have an assistant crank, while you watch, armed with a roll of paper towels). If oil squirts out of the hole, then you're sender is probably bad.

You can also check the continuity of the switch. I forget whether it's supposed to be open or closed when the engine is off, but the state of the switch should change when there is oil pressure.

Hope this helps,

Wayne

dtw · 05-25-2004, 01:24 PM

Wayne, on the early cars there is no switch back there. There's just the sender, which is more expensive to replace ($50). Cosmo, the smaller sender in the case by right-side chain box wouldbe the temperature sender. I agree with your sanity-check of removing the sender and checking for squirtage while cranking (trying a mechanical gauge would be a bit more elegant but $ for that mechanical gauge of course...).

With Cosmo's gauge pegging though, it sounds like there is no signal from the sender.

cosmo · 05-25-2004, 02:08 PM

Ok, I pulled the sending unit off and the good news is there was plenty of oil up there. In checking the unit (it's brand new) there is continuity between the houseing and the contact pin so the wire is grounded is this normal or do I have a bad sender??
Thanks

jgparker · jgparker's Garage

Cosmo,

The sender should be grounded with no pressure. This is normal. It sounds like you may have an open between the sender and the gauge. Ground the wire that is connected to the sender and the guage should read 0 PSI. Leave it disconnected and the guage should go full-scale. If it doesn't, the problem is with the wire or the gauge.

Good luck,

JP

ischmitz · ischmitz's Garage

Did you install the ground strap between the transmission and the chasis. If not there is your problem.

Wayne 962 · Wayne 962's Garage

Get a multimeter and watch the resistance values as you crank...

-Wayne

cosmo · 05-27-2004, 01:11 PM

It ended up being a bad pin connection at the harness plug on the rear fuse relay panel. The guage works properly now but after turning the engine over for 30sec and then about 15 sec's I still have no o/p reading on the guage. I'am thinking it's not turning fast enough to build pressure, I pulled the sending unit off on top and their was oil there,I also pulled the temp sender off next to the chain box and their was plenty of oil there as well. So I will assume there is o/p, I think I will start it for a couple of secounds and watch the guage.