Jeep 4.0 Oil Pressure

[mbryson]

I'd shoot for the junkyard motor if it's got that many miles on it. It's a unibody, can't last a WHOLE lot longer......the 40K-110K motor would probably be a great match for the body.

'91 to like '99 4.0Ls are very similar in build (whenever the go to the multiple coil thing). I think '93 to '96 even use the same engine management computer (I know '91-'93 ones do).

 

[mowlasley]

Tried different gauges or tried new oil pressure sending units? Gauge won't make a difference if the sending unit is bad

Put in two different mechanical gauges in place of the sending unit.

 

[Jeromy]

suggest an SBC swap!

Their you go! solution found!

 

[Herzog]

Just a long shot, but you could always check your oil pressure sending unit to see if it's failing. Mine would always read low when they started getting gummed up.

I concur.

 

[Brett]

Put in two different mechanical gauges in place of the sending unit.

So, you ran a oil line and everything to a mechanical gauge?

 

[mowlasley]

We just unscrewed the current sending unit above the oil filter and screwed in a gauge. Is that not an accurate way to measure?

 

[Brett]

We just unscrewed the current sending unit above the oil filter and screwed in a gauge. Is that not an accurate way to measure?

I would guess that it would work the same way as running a line to a gauge

 

[mowlasley]

I would guess that it would work the same way as running a line to a gauge

Darn, I was hoping that you would say that method is guaranteed to be 25 psi low.

 

[anvil]

The oil pressure at low RPM's isn't too important. 5 psi is plenty for idling. As long as it comes up with your RPM's don't worry about it. I noticed a pressure drop when I ran a cheap Fram filter. When I switched filters the oil pressure came up a few PSI.

 

[mowlasley]

The oil pressure at low RPM's isn't too important. 5 psi is plenty for idling. As long as it comes up with your RPM's don't worry about it. I noticed a pressure drop when I ran a cheap Fram filter. When I switched filters the oil pressure came up a few PSI.

I like the sound of that. Is there a concensus from the group on this view?

 

[Brett]

I like the sound of that. Is there a concensus from the group on this view?

I dunno......my Cherokee 4.0 runs at 20 lbs idling when it's hot. 1500-2000 RPM's I am at about 40 lbs and anything above that it's just shy of 60 lbs of pressure.

Maybe just try a bit heavier oil and see if that might help in the long run. Otherwise, I would say you're going to be pulling the pan off for a new pump.

 

[mowlasley]

Today I finally had time to pull the pan. The first thing I noticed was a bolt in the bottom of the pan. It had fallen out of the . . . oilpump. The oilpump was held up by just the one bolt and was all askew, so I don't think that the output of the pump was centered on the passage in the block.

Got the new pump installed. Installing the sifter on the pump was a PITA! Had to sand down the pickup tube.

Long story short, it worked, and my pressure is back up!!

Thanks to everyone for their suggestions. I guess I will have to swap in the SBC in a few years (knock on wood).

 

[Brett]

The first thing I noticed was a bolt in the bottom of the pan. It had fallen out of the . . . oilpump.

 

[Tacoma]

hoooooolllly cow.

 

[Ken]

Where did ya get the parts and how much did they run ya. Whats the difference in the pressure.

 

[mowlasley]

Where did ya get the parts and how much did they run ya. Whats the difference in the pressure.

I just got the Vatozone(TM) special high volume oil pump ($130), and the one-piece oilpan gasket ($25). The OEM-style oil pump was $75.

Pressure at idle is now just over 30 psi, and with a bit of throttle is a touch over 60 psi.

 

[Ken]

Started mine up after following this and it idles at a constant 60 pressure. (90 xj with 175k miles) I did have some moments of low pressure though for a while. I think I had some clogs happening or low oil. Good to see that you found the problem.

 

[Brett]

Started mine up after following this and it idles at a constant 60 pressure. (90 xj with 175k miles) I did have some moments of low pressure though for a while. I think I had some clogs happening or low oil. Good to see that you found the problem.

I'm hoping that the motor was cold if that's how much pressure it had at idle.

 

[Ken]

Well the temp was sitting at about 210-215. You thinking thats too much?

 

[Brett]

Well the temp was sitting at about 210-215. You thinking thats too much?

Seems high to me. My motor runs at about 180 degrees (210 always seemed too hot to me) when it's warmed up. 60 pounds is just high for a hot motor I would think. There might be others on here that would have a better opinion though.