Rebuilt 4.0 SOHC - Bad Oil Pressure

[Adam Robert]

I recently pulled my 4.0 motor and completely redid all of the chains and guides. I even put in a new water pump and oil pump. Finally got it all together and back in the truck. Everything seems great, except I am now having an oil pressure issue….

Now I understand the gauge is largely worthless, but it’s clearly working along with the sensor, and I am clearly not getting enough pressure. When I start it up, the gauge is a little bouncy and when the idle levels out, it goes flat. I can tell I am at least getting some pressure by looking in the oil filler and hitting the throttle.

Does anyone have any idea what this could be caused by? I cleaned out all of the broken cassette pieces I could find in it. It was almost completely tore down, and rotated multiple times while it was on the stand. I’d think if there was a small piece in a galley somewhere, it would’ve passed through and if it was a large piece, it would’ve fallen out. Any help would be appreciated.

 

[donalds]

Test the oil pressure with a gauge spec is 40-60 psi @ 2000rpm
On a warm engine
The oil pressure switch is just a switch it most likely is just bad
I had to replace mine

 

[Adam Robert]

Teat the oil pressure with a gauge spec is 40-60 psi @ 2000rpm
On a warm engine
The oil pressure switch is just a switch it most likely is just bad
I had to replace mine

I appreciate the reply, but that wasn’t helpful. It’s a new switch, I know it’s good, I know the gauge is a dummy gauge, but I can also tell the pressure is legitimately bad, without a real gauge. I’m hoping someone give me ideas on how to resolve my problem, not more ways to confirm it.

 

[donalds]

Well what is the pressure now ??
Did you actually check it ?
Lots of stuff going on between your engine pressure switch and the dash !
I was gonna walk you through the process one step at a time but your negative comments turn me off .
Good luck

 

[Adam Robert]

Well what is the pressure now ??
Did you actually check it ?
Lots of stuff going on between your engine pressure switch and the dash !
I was gonna walk you through the process one step at a time but your negative comments turn me off .
Good lu

Well what is the pressure now ??
Did you actually check it ?
Lots of stuff going on between your engine pressure switch and the dash !
I was gonna walk you through the process one step at a time but your negative comments turn me off .
Good luck

I wasn’t trying to be negative and I’m sorry I’ve upset you, but simply put, the oil pressure being low is a confirmed problem. I’m hoping to get advice on possible causes and solutions, not more ways to confirm what I know.

Now, if you must know the specific PSI, it is 5 at idle and goes as high as 30 with throttle.

 

[donalds]

5 is To low for idle
30 psi Kinda normal for worn engine under throttle
10 psi per 1000 rpm is the norm in most engines
Is the oil pickup tube plastic or metal
Plastic can crack

It may be clogged again
Worth a look imo

 

[Adam Robert]

5 is To low for idle
30 psi Kinda normal for worn engine under throttle
10 psi per 1000 rpm is the norm in most engines
Is the oil pickup tube plastic or metal
Plastic can crack

It may be clogged again
Worth a look imo

It’s a plastic pickup tube. Prior to the rebuild, the screen was certainly clogged, but it was thoroughly cleaned and didn’t not appear to have and cracks or weak points on instal

 

[Adam Robert]

It’s a plastic pickup tube. Prior to the rebuild, the screen was certainly clogged, but it was thoroughly cleaned and didn’t not appear to have and cracks or weak points on instal

This is the best picture I took before the pans were put back on. This is missing the screen, of course, but that was installed after I put the upper pan on.

 

[donalds]

That's the first place I'd look pickup tube I've seen threads that show them hairline crack or a o ring may have rolled over

 

[donalds]

DiD you remove the balance shaft

 

[Adam Robert]

DiD you remove the balance shaft

I did not

 

[BenDT]

Did you clean the oil restrict or rod on the head and it’s orifice. Pretty tight in there.

 

[imp]

I recently pulled my 4.0 motor and completely redid all of the chains and guides. I even put in a new water pump and oil pump. Finally got it all together and back in the truck. Everything seems great, except I am now having an oil pressure issue….

Now I understand the gauge is largely worthless, but it’s clearly working along with the sensor, and I am clearly not getting enough pressure. When I start it up, the gauge is a little bouncy and when the idle levels out, it goes flat. I can tell I am at least getting some pressure by looking in the oil filler and hitting the throttle.

Does anyone have any idea what this could be caused by? I cleaned out all of the broken cassette pieces I could find in it. It was almost completely tore down, and rotated multiple times while it was on the stand. I’d think if there was a small piece in a galley somewhere, it would’ve passed through and if it was a large piece, it would’ve fallen out. Any help would be appreciated.

Stuck open/malfunctioning oil pump relief valve? Could have been faulty coming with the new pump. If stuck open or missing altogether, most all of the pump output volume dumps back into the oil pan.

 

[Adam Robert]

Did you clean the oil restrict or rod on the head and it’s orifice. Pretty tight in there.

Did not clean, but did replace.

 

[Adam Robert]

Stuck open/malfunctioning oil pump relief valve? Could have been faulty coming with the new pump. If stuck open or missing altogether, most all of the pump output volume dumps back into the oil pan.

Certainly hope not as that would mean I’d have to take the whole engine out again. It is getting oil to the sensor and what I understand is that’s near the end of the line for the oil path. I can get it to 30psi if I go up to 3000 rpms and I’m told that’s satisfactory.

I just let it run for like 20 minutes and it started to sound better at idle, just a little more noisy than I remember with throttle.

another concern I have now is the tranny. I noticed the dipstick tube was loose when I took the engine out and it had been spilling fluid for some time. The dipstick now reads no fluid at all when hot. I’m wondering if the lack of fluid is putting increased resistance on the engine, causing lower idle and thus lower pressure at idle. Im flushing that and swapping the filter and gasket tonight. Will report back.

 

[imp]

Certainly hope not as that would mean I’d have to take the whole engine out again. It is getting oil to the sensor and what I understand is that’s near the end of the line for the oil path. I can get it to 30psi if I go up to 3000 rpms and I’m told that’s satisfactory.

I just let it run for like 20 minutes and it started to sound better at idle, just a little more noisy than I remember with throttle.

another concern I have now is the tranny. I noticed the dipstick tube was loose when I took the engine out and it had been spilling fluid for some time. The dipstick now reads no fluid at all when hot. I’m wondering if the lack of fluid is putting increased resistance on the engine, causing lower idle and thus lower pressure at idle. Im flushing that and swapping the filter and gasket tonight. Will report back.

A transmission low on fluid will not affect the engine adversely, especially since most analysis considering is done with the transmission in neutral or park. To check the oil pump, pan removal should be all that's necessary, not removal of the entire engine.

 

[Adam Robert]

A transmission low on fluid will not affect the engine adversely, especially since most analysis considering is done with the transmission in neutral or park. To check the oil pump, pan removal should be all that's necessary, not removal of the entire engine.

It’d be a heck of a task to get to the oil pump without taking the engine out. I’d have to remove the lower pan, then some bell housing bolts, the starter, then the upper pan. I’m pretty sure it just has to come out to do that.

 

[eevox]

It’d be a heck of a task to get to the oil pump without taking the engine out. I’d have to remove the lower pan, then some bell housing bolts, the starter, then the upper pan. I’m pretty sure it just has to come out to do that.

Yeah, it has to come out. Or at least I couldn't do it without taking it out.

 

[imp]

It’d be a heck of a task to get to the oil pump without taking the engine out. I’d have to remove the lower pan, then some bell housing bolts, the starter, then the upper pan. I’m pretty sure it just has to come out to do that.

Geez, back in the day I had to be careful removing oilpans that they didn't fall on my face! Mustangs were easiest.

 

[eevox]

OP, you said you rebuilt the motor.

But when I read your post, you only mention the timing cassettes, oil pump, water pump, and gaskets. Did you do anything else while you had the motor out? Because no offense, if you just did that, what you are describing isn't a rebuild.

Please understand I'm not trying to be an A._s H__l_ I'm just trying to understand what you might have gone through when you had the engine out.