Where did the oil pressure go on my 308 GT4

Unplug the wire from the pressure sender and touch it to ground with the key "on" -- if the gauge is working, the needle should swing to the "max" side when that wire is grounded (to the engine).

What year/version 308GT4? -- I believe the oil pressure switch (and its corresponding red warning light in the gauge) was not introduced until the later years.

 

The red warning light should be "on" when the key is "on" and the engine is not running. If the red light stays "on" when the engine is running, that would be a sign that you really don't have any oil pressure, and would need to look at things like broken/blocked oil pressure regulator, blocked oil filter, you forgot to add oil , etc. -- does the red light go "off" when the engine is running? If it does, it's almost a certainty that the (new) oil pressure sender is bad (as you've already proved that the gauge works, and would give a reading if the pressure sender resistance went down as the oil pressure went up, as it should). If the red light doesn't go off when the engine is running, that's a much more serious issue (and shut off the engine immediately until resolved).

 

If you truly believe you have oil pressure in the engine and it is either the gauge or the sender that is bad, then by all means continue with trouble shooting.

If you are not sure if you even have oil pressure in the engine, then make sure there is adequate oil pressure before you go on. When the engine is all brand spanking new and there is no oil in the oil circuit, you have to prime the oil pump before it can even pump out anything. I don't know what else you did to your engine so I can't say.

 

If you still have the old unit available swap it back in and test.

 

The "open" (i.e., infinite resistance) on the new sender corresponds well with your problem of having no motion of the needle in the gauge, but the 12 ohms for the old sender (at zero pressure or at a normal operating pressure) seems much too low compared to this good data previously posted by RJay (Bob):

http://ferrarichat.com/forum/showthread.php?t=103015

 

With no oil pressure, engine off my sender measures approx 9K ohms or 9000 ohms to ground.

 

Did you disconnect all the wiring before you make the measurement?

 

Check the REAL oil pressure first with a mechanical gauge OR just remove the sender and hand someone crank the engine. The latter will be messy but it will tell you if you have oil pressure. THEN fool around with troubleshooting from that point. THe most important thing to know is IF you have oil pressure. Checking sending units and gauges doesn't tell you a darned thing about the most important item...do you have oil pressure?

 

Another way you can check if there's oil pressure is to remove the oil filler cap, have someone start it up and watch the cam caps you can see through the filler hole. You should see oil coming out from under the cam caps as the cam spins.

 

There have been cases where the wrong sender is in the box. Take the sender out and see if there is a hole in the bottom. If not, it is a temperature sender, not a pressure sender.

BTDT,

Gerrit
http://dino308gt4.com

 

I think you should find out what your actual pressure is with a mechanical guage before you adjust the pressure relief valve. I believe adding shims to the spring will raise the maximum pressure. Removing those shims and adding copper washers to the cap will lower maximum pressure. Remember that the pressure relief valve only controls your maximum pressure, not the minimum.