Inconsistent oil pressure

[SuperTramp]

‘98 k2500 5.7 4x4: once the engine warms up, there are times when I’m completely stopped, in DRIVE, with the truck idling, and the oil pressure drops so low that the truck wants to stall. It doesn’t stall, but the engine starts to shudder enough to shake the cab. I’ll put it in neutral and the idle increases a bit on its own and engine quits shuddering. Typically There is a strange, burning-type smell coming from exhaust. Then, for the past two days, no problem whatsoever. 3weeks ago I changed oil and filter and the oil stick is reading the proper level. The first picture is of the oil pressure gauge needle sitting between the 6th and 7th mark from the left. When I’m experiencing problems, stopped, in gear and idling, needle is around the first mark. .

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Thank you in advance for your responses.


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[stutaeng]

Are you sure the shuddering is related to the oil pressure? How low does it go? If it goes on the orange you'll get a "check gauges" light also. Does that light up?

Any codes stored? The oil pressure gauge is only a "relative" reading, meaning, it's not accurate at all as one would think. You need to hook up a mechanical gauge. I had to so this one my Silverado 4.3 that has low oil pressure. Sort of paint to get back there. I was near the orange mark and the mechanical gauge showed 6 psi...No knocks or anything, and certainly no stalling problems. It's my daily driver, so I'm monitoring oil pressure...

Sounds like you are burning oil? Maybe your O2 sensors (or spark plugs) are fouled up. You might want to check for stored codes.

 

[andy396]

I had a similar situation when the trans input speed sensor was bad on my transmission, however that eventually threw code. It will also do it if the trans cooler line flow is restricted or the trans line pressure is pegged at 100%. Basically what happens in scenario is there’s not enough pressure going to the TCC to keep it released. Usually in my case it always eventually stalled.

 

[SuperTramp]

CHECK ENGINE light comes on once oil pressure gauge needle drops down to the first tick mark. This is when the cab begins to shudder. No, I’m not sure if the engine is causing the shudder but what else could it be? Burning smell isn’t noticeable other than when idling at stop light, when the needle drops. I’ll check for saved codes and use a mechanical oil pressure gauge ASAP. While it’s important to resolve this issue, once it starts doing it again, truck isn’t my daily driver. I couldn’t afford 10 MPG. Thanks for your input!


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[stutaeng]

I switched to 10W-50 oil, and that bought me a few higher oil pressure pounds. It's not ideal, but it's working okay.

I'm not ready to do a rebuild or engine swap financially. As the weather cools down and into the winter I'll switch back to the specified oil...

 

[Schurkey]

the oil pressure drops so low that the truck wants to stall. It doesn’t stall, but the engine starts to shudder enough to shake the cab.

I suspect you're exactly backwards.

The low oil pressure is not causing engine stalling and shaking.

The engine nearly stalling, and shaking, is causing low oil pressure.

Fix the way the engine runs, I bet the oil pressure takes care of itself.

 

[Hipster]

Check the oil pressure sending unit/cut-off. Maybe it's not holding pressure or leaking.

 

[94_Z71]

These engines always have fluctuations in oil pressure, but not usually that bad. Is it idling fine when stopped, or does the idle drop? If so, there's a little torx screw on the front of the throttle body that adjusts the blade. Turn it clockwise until it holds idle around 750 or so.

 

[Schurkey]

Idle speed should be controlled by the IAC. The "screw" sets the base idle, and should not need to be dicked-with.

Assure all cylinders run at idle.

Assure the IAC works

Look at the data stream for anomalies that could cause or be caused by idle misfire.

Fix the way the engine idles, and the oil pressure is likely going to be fine.

 

[94_Z71]

It depends on the modifications to the truck. That little screw can come in handy. But you're right, you don't wanna use it if you don't have to. In my case, I had to. Even with a Black Bear tune, the stock computer just doesn't know what to do with a 383 stroker.