Oil pressure issues

[Petescj]

Coming up a hill by my house I heard the valve train rattle like I was low on oil. I costed home from there since it was only a few blocks away from home. My oil pressure gauge was shot so I put one I knew worked in today. It started at 20 psi and then jumped around sporadically from 0 to 20 to 40 to 0 and so on. I was wondering if the oil pump was a possibility instead of the bearings. It ran fine and had good power all the way up to that point. I have no idea what the mileage is cause it's not the original engine.

I already bought another engine but haven't picked it up yet. I'm sure the guy I bought it from would let me use the money for the engine on something else if I didn't need it. I don't want to throw more money at a bad engine but what does this sound like to everyone? A new pump and pick up from Jegs is $77. Money is tight right now though.

Thanks in advance
Pete

 

[JR74CJ5]

I know mine jumps a lot and drops pretty far at idle, but don't think I have seen it drop all the way to zero...

If this is on the scrambler the AMC 304 pump is driven by the distributor. If the motor still runs, its not the gears (distributor wouldn't rotate). So I would assume mechanically the pump is working fine, but functionally it may be losing some pressure through worn seals etc?

If its the AMC 258 i6 / 4.2l I don't know much about them...

You may want to drop the oil pan and take a look at the bearings while inspecting the pump... Worn Bearings can cause the reduced oil pressure.

Is this the gauge that works on actual oil being sent through the tube or the electronic with pressure sending unit?

 

[jammer1]

Do you have another oil pressure gauge/sending unit. If you have a manual gauge or another gauge connect and check before you go through dropping the pan, etc. Hate to see you do something and find out later it was the oil gauge (I'm on my third in my one work truck in the last yr.). On the work truck I had a working gauge, mechanic installed new rebuilt jasper engine. Gauge was high and pegging on freeway when I get truck back. Replaced sending unit, no difference. Put new gauge and sending unit in and was high and pegging on freeway like other. Went to a different gauge (speedhut) and sending unit, works great. Gauge went bad New gauges and or sending units were bad. Speedhut gauge is gold

 

[Lumpy Grits]

If it's electric. Don't trust it!
Could be a bad sender or gauge. Can also be a bad dash ground.
If mechanical-Buy quality stuff like here.........
Oil Temperature Gauge. Black Dial, Mechanical Oil Temperature Gauge.

How low was the oil level?
LG

 

[Petescj]

It's the AMC 258 i6 / 4.2l and the distributer drives it. The distributer has a screwdriver like end that goes into a slotted shaft with a gear on the end inside the pump. I don't know what holds that gear to the shaft. I was hoping it uses a pin or key way that sheared or backed out. That would explain the erratic readings I'm getting from the gauge.

It is a stock electronic gauge. I know it worked correctly when it was in the Limited and I used that sending unit as well. With being out of work I just don't have the cash to spend on a good mechanical gauge. I will run another ground wire from the gauge to the dash and see if that changes anything. If not I'm going to drop the pan , pull and inspect the pump. Hopefully I find something there. If not I'll pop a couple bearing caps off and check there.

 

[Lumpy Grits]

Remove the sender on the block and clean the threaded area. Do NOT use a Teflon tape etc on the re-install. Clean the electrical contacts on the sender and then coat the contacts with dielectric grease. Make sure the leads on the back of the oil gauge are tight.
Run a dedicated ground lead from the dash panel, to the NEG(-)of the battery.
Clean the battery GND connection to the block and reattach to the top bolt of the starter motor.
Clean your battery posts and connectors.
The OEM oil pressure gauge was well known for erratic/incorrect readings and failure. I had 2 sending units replaced under warranty when I bought my '7' in '85.
I then installed a SW mechanical gauge and never look'd back------
LG

 

[Fastatv]

Pete....be careful. Does not sound like the problem is just the gauge. Hearing lifters or valves rattling means that your low on oil or have an oil pump problem, blockage, or a bearing problem. As Lumpy mentioned, what was the oil level?

 

[Posi]

^^ x2

 

[007]

Agreed. My $ is on the pump given how the issue manifested itself.


Sent from my iPad using Tapatalk

 

[Neuner]

I agree. Appears to be an issue with the engine and not the gauge.

When I had my AMC 258 i6 / 4.2l , my electric oem gauge fluctuated around the 20-40 range but never dropped to zero. Swapping in the 4.0, I installed the sender from the AMC 258 i6 / 4.2l , still used the same gauge and the pressure is now constant so I believe it was the AMC 258 i6 / 4.2l , oil pump, etc.

 

[Lumpy Grits]

Any up dates?
LG

 

[Fastatv]

Any up dates?
LG

Me too LG.. I'm curious. I hope he hasnt experienced an engine failure....that would stink!