I know you all have seen this atleast 50 times before... I searched the board and looked closely and didnt see anything that describes my problem, but I know you all can help. So here it goes:

1986 305 TransAm 4bbl
5w30 Oil - Full Synthetic

First Start Engine Cold: 0 PSI Oil Pressure
Wait a few seconds and rev the engine a little (slight smoke) and the oil pressure becomes 30-40psi.

Few times when I stop, 0 Psi (continous) no knock or clicking in the engine, runs and idles fine.

I drive and 30-50PSI depending on RPMs and sometimes high accelleration takes pressure down instead of up.

Oil is new replaced with filter, no leaks.

I do not have a mechanical oil pressure gauge and the shops in my small town want 120$ to hook one up, .... theifs....

I am not fully mechanically inclined but can do anything instructed to me, I am great with electronics and the gauge inside is fine....

My guess is the Oil Sending Unit or the Pick-Up Screen.

If the odds are the sending unit, is there a tech DIY page on how to replace and check it?

Thanks.

 

Your oil pressure switch should be a single or triple wire bell-shaped object located at the rear of the intake, just behind the distributor.



The 2 gold cylinders at the rear, up against the firewall, are oil senders. The one on the right is what the factory unit looks like.



That's what the component looks like.

As for checking, you really don't. The check test is called replacement. To replace it, as you can see, there is a hex on the spade end. Unplug it, set the wire off to the side, fit a deep socket over it (sorry, don't know off hand what size) and remove it. Installation being reverse of removal.

 

I appreciate the pics, as for understanding, only one question, you said the two gold are oil senders, do I replace both? or just the right hand side one.

Will I have to remove the distributor and carb etc to reach this?
(Its raining and night or id go look myself)

Will I have to test the pressure with the new replacement or is it stock set to specs?

Do you have part numbers by chance?

 

I took the bird out tonight, its almost freezing here, it had pressure from the start and stayed 28-60psi the whole time, its about 39* or so outside, vehicle went from 180-205* during the ride, but no pressure problems, seems to only be on hot or warm enough days for the engine to reach nice hot temps for riding, never about 230*.

Any ideas?

 

I've had a very similar problem, and I was preparing for the worst, but then decided to replace my sending unit and it cleared everything up instantly.
Another idea is to get an inexpensive mechanical gauge and connect that to the 1/8npt hole that is just to the rear of the water pump above the timing cover. On my 305 that hole is plugged, but can be easily accessed. And an oil press reading can be taken there.
It's especially handy if you already have a mech ga and you just want to us it as an aux fitting for a quick double check if your factory ga is acting suspiciously.

 

A mechanical gauge will eliminate any fault with an electrical sending unit or gauge. You don't even need to drive around to use it. Get the oil hot, install the gauge and check pressure. It should be close to what the gauge on the dash says. If the mechanical gauge says 30 psi and the dash says zero then I'd say there's probably a sending unit problem.

Pull the oil filter off and cut it open. Take a section of filter media and squish it in a vise to get all the oil out. Open up the media and check for any metal.

I was having a problem last fall. Engine temperature was running hot and an alcohol engine should never run hot. Everything else was fine. I couldn't hear any knocking and engine power was only down slightly. One day, oil pressure dropped dramatically when at an idle. Enough for my oil warning light to come on. Engine still ran and pressure came up when I brought the rpms up.

I pulled the pan off to find the bottom covered with bearing material. I spun a main bearing. You won't hear any knocking from a main bearing. The extra heat created from a failed bearing was enough for the engine to run hot.

I'm not saying this is your problem but you need to track down the loss of oil pressure. Maybe you'll get lucky and only have a sending unit problem.

 

The oil has absolutely no metel in it, I cut the filter open and squished it, so im lucky for now....

I plan to buy a sending unit soon and put it on, If that doesnt fix it I am going to remove the pan and check to see if there is a magnent in it for shavings also. I am also going to check the pick-up unit, but the sending unit will be first then.

any suggestions on the sending unit or just a GM OEM Replacement?

Thanks

 

I as well have a similar problem. I have a new sending unit and switch, but my pressure will sometimes be all the way maxed, sometimes in the middle, etc. I have no leaks, and all the seals are new. I just stopped looking at the gauge, as I have no idea what to do

 

I had the same problem you are describing some time ago.
Heres my post & how it got solved:
https://www.thirdgen.org/techbb2/sho...hreadid=265114
hope it helps.