Need Advice On Oil Pressure Problem

[kurtdirt1]

When I bought my truck the oil pressure would read 15psi @ idle and around 17 on the freeway. I replaced the sending unit (the big cylinder looking thing) and got the same readings, figured the engine was worn as the truck shows that it was used alot.


Well a few months after buying the truck the engine gave up on me so I replaced it with a re-manufactured engine from autozone with a 3yr warranty. My oil pressure is still reading 15psi & 17psi so now I'm thinking that something must be wrong with my gauge.


So I got a gauge from a donor truck and it shows the same thing. What else should I consider? What is the other thing by the cylinder sending unit. I think it has two wires that go to it, what's that thing do?


I haven't hooked up a mechanical gauge to it but I suspect that somethings going on with my stock gauge system, being that both engines read the same exact psi. What do you guys think?



Truck is an 86 Silverado Qjet 305, all stock

[VileZambonie]

How about a little more info on your truck...year make model engine....

Checking it with a mechanical gauge is what you need to do to know what your pressure really is.

[kurtdirt1]

Do you know what that other thing is by the "cylinder unit" at the rear of the engine. The one I'm talking about has two wires going to it I believe

[Jim Rockford]

The two bladed switch is for the choke heater and oil pressure light.

the one for the gauge is a large canister looking one with one wire....

[kurtdirt1]

The two bladed switch is for the choke heater and oil pressure light.

the one for the gauge is a large canister looking one with one wire....

Okay I have both of those on my engine, does everyone else have those two? My truck is an 86 SWB 2wd Silverado 5.0 Is it necessary to have the two prong unit at the back of my block?


So I'm assuming I have some kind of grounding issue that is causing my stock gauge not to read right? The reason I believe this is that I bought a new oil sending unit (the big round one) and had two stock gauges that both read the same after the new unit. So what's my next move?



I would really like to have my stock gauge working again and have the mech gauge installed under the hood to check every now and again as a reference to the functionality of my stock gauge. (It irritates the crap outta me having to look down at my feet to see my oil psi)



EDIT: Forgot to say that I installed a mech gauge and my pressure is 55@idle and 65 cruising fully warm (melling 55hv with 20/50w, will be dropping to 10/30 next week to balance out my psi)

[kurtdirt1]

Okay so I did some searching and found that the two prong switch acuates my choke heater and choke light inside (not oil pressure light) When I start my truck my choke light NEVER comes on nor has ever since I've owned it, nor does my truck idle high when cold or when first started.



So lets say this switch isn't working on my truck. Why does my choke still pull open and why wont it idle high? Would the switch malfunctioning cause it to not idle high or is something else wrong? Perhaps my carb needs adjusting or something?



I apologize for kinda going off topic here. Figured we could kill two birds with one thread. Thanks in advance everyone.

[VileZambonie]

The oil pressure switch closes with oil pressure. If the choke light doesn't work check the bulb. Do you have an oil pressure gauge or just a lamp?

[kurtdirt1]

I have an actual gauge that I'd like to troubleshoot. I meant the choke light never comes on when I first start it, just when I turn the key to the second click when everythings buzzing. I read a thread on another forum and the way the guy wrote it sounded like it should be on when it's running? lol

[VileZambonie]

No the choke light should go off when you start it. AS far as fast idle goes, close the choke flap and hold it shut while you snap the throttle. It should land you on the fast idle cam. If it does just adjust the fast idle screw. This is a factory oil pressure gauge you are trouble shooting correct? What does the gauge read Key on engine off and engine running?

[kurtdirt1]

Yes I am trying to troubleshoot the stock gauge. I disconnected it yesterday when I installed the mech gauge. But it was reading zero with key on but engine not running and it would read around 15lbs at idle and 20ish cruising but my mechanical gauge shows 55idle and 65cruising. I installed a melling hv pump (now I wish i would have bought the mech gauge first)



EDIT: I already changed out the sending unit and tried two different stock oil gauges. All gave the same readings

[VileZambonie]

If you replaced the sending unit with the same results I would suspect a faulty gauge.

[kurtdirt1]

Is there a way I can check the gauge with an ohm meter? I doubt both of the gauges were broke being that they read EXACTLY the same. but what do i know *shrugs shoulders*

[kurtdirt1]

Can somebody else chime in? I'd like to get my stock gauge working again. So here's all the information.


I have check my oil psi with a mech gauge and it reads 55idle and 65cruising

I have replaced my oil sending unit THE RIGHT ONE the big cylinder

My stock gauge reads 15idle and around 20cruising (swapped gauge and same EXACT READINGS)


So what's my next move Vile stated that my gauge sounded broke but I find it hard to believe that both gauges are broke being that they both read Exactly the same. I may be wrong but what would my next move be in troubleshooting?


Like I said above it irritates the crap outta me looking down at my feet to check my oil psi. Thanks in advance

[choptop]

If you have already replaced the gauge and the sending unit, then the problem is in the wiring. I would replace the terminal at the sending unit, and see what happens from there. It should just be a spade type terminal available at any automotive store. If that doesnt work, then you'll have to ohm out the wiring from the sending unit to the gauge. It could be something as simple as a dirty connection at the bulkhead connector on the fire wall. If I remember correctly, you should be able to ground out the wire at the sending unit, and the gauge should peg high. If it does, you may not be getting a good ground through the sending unit base. If you put alot of teflon tape on the sending unit before you installed it, then there is a good chance its not getting a good ground.

[zieg85]

It wouldn't surprise me that the circuit board on back of the gauge cluster couldn't be the cause of your problem.  Just a suggestion...