Low TJ oil pressure = new oil pump?
 

The oil pressure gauge on my TJ is high, 40+, while the engine runs at
road speeds, but at idle the needle sometimes drops to zero, and then
climbs up to about 10 pounds. Sometimes while at idle it swings back
and forth between 0 and 10.

I disconnected the electric oil pressure sending unit and attached a
mechanical gauge... same behavior... the pressure falls and rises at
idle like before.

The Jeep is a 1997 TJ 4 cylinder, with 71,000 miles.

Apparently I need a new oil pump. But I wonder if the oil pump might be
good and something else is causing the deviance.

Is the pump driven by the distributer shaft?... could the pump be good
and something else is causing the oil pressure to sometimes drop and
rise like that?

The Jeep runs well and behaves normally at idle or road speeds.

I change oil and filter every 3,000 miles.

TIA for your advice.

Ralph


God exists, or God does not exist, or I am God and I am dreaming all
this.

Low TJ oil pressure = new oil pump?
 

I would check the connections starting at the sending unit.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

Ralph DL wrote:
>
> The oil pressure gauge on my TJ is high, 40+, while the engine runs at
> road speeds, but at idle the needle sometimes drops to zero, and then
> climbs up to about 10 pounds. Sometimes while at idle it swings back
> and forth between 0 and 10.
>
> I disconnected the electric oil pressure sending unit and attached a
> mechanical gauge... same behavior... the pressure falls and rises at
> idle like before.
>
> The Jeep is a 1997 TJ 4 cylinder, with 71,000 miles.
>
> Apparently I need a new oil pump. But I wonder if the oil pump might be
> good and something else is causing the deviance.
>
> Is the pump driven by the distributer shaft?... could the pump be good
> and something else is causing the oil pressure to sometimes drop and
> rise like that?
>
> The Jeep runs well and behaves normally at idle or road speeds.
>
> I change oil and filter every 3,000 miles.
>
> TIA for your advice.
>
> Ralph
>
>
> God exists, or God does not exist, or I am God and I am dreaming all
> this.

Low TJ oil pressure = new oil pump?
 

Ralph DL wrote:
> The oil pressure gauge on my TJ is high, 40+, while the engine runs at
> road speeds, but at idle the needle sometimes drops to zero, and then
> climbs up to about 10 pounds. Sometimes while at idle it swings back
> and forth between 0 and 10.
>
> I disconnected the electric oil pressure sending unit and attached a
> mechanical gauge... same behavior... the pressure falls and rises at
> idle like before.

Sounds pretty cut and dried, if it's not the Oil pump then you've got
something very strange going on like a cam bearing with a crack that's
letting oil pulse out or something like that...

On the other hand if it is the pump and you aren't hearing lifter noise
yet then it's probably not too late for your bearings... lifters deflate
and start clattering below about 9 or 10 PSI.

--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Low TJ oil pressure = new oil pump?
 

Bill Hughes

Please re-read my post... the oil pressure varies even when I replace
the electrical measurement of oil pressure with a mechanical oil
pressure gauge.

The mechanical oil pressure gauge is attached to a tube which screws
into the block... oil actually goes from the engine up the tube and
applies direct pressre to a diaphragm/spring coil loaded needle... this
is the most accurate albeit old-fashion way of measurine engine oil
pressure.

That's why I asked if it could be more than an oil pump problem.

Ralph

God exists, or God does not exist, or I am God and I am dreaming all
this.

Low TJ oil pressure = new oil pump?
 

If these oil pressure readings are real, then your symptoms point to worn
out bearings. The pump itself is not likely to wear out, because it is the
best lubricated part in the engine. Other possibilities are a blockage on
the pump intake, perhaps from sludge, or idle speed too low. Clean the idle
air control valve to address that problem. It is odd to see a vehicle of
this mileage with this low oil pressure, even at idle, especially if it has
been maintained well.

We had a woman in the commune who drove probably sixty miles, to find
someone who could tell her what the little blue dash light on her Karmann
Ghia was all about. :o(

Earle

"Ralph DL" > wrote in message
...
> Bill Hughes
>
> Please re-read my post... the oil pressure varies even when I replace
> the electrical measurement of oil pressure with a mechanical oil
> pressure gauge.
>
> The mechanical oil pressure gauge is attached to a tube which screws
> into the block... oil actually goes from the engine up the tube and
> applies direct pressre to a diaphragm/spring coil loaded needle... this
> is the most accurate albeit old-fashion way of measurine engine oil
> pressure.
>
> That's why I asked if it could be more than an oil pump problem.
>
> Ralph
>
> God exists, or God does not exist, or I am God and I am dreaming all
> this.
>

Low TJ oil pressure = new oil pump?
 

Possible broken oil pump bypass valve spring:
http://www.billhughes.com/temp/oilPump.jpg
God Bless America, Bill O|||||||O


Ralph DL wrote:
>
> Bill Hughes
>
> Please re-read my post... the oil pressure varies even when I replace
> the electrical measurement of oil pressure with a mechanical oil
> pressure gauge.
>
> The mechanical oil pressure gauge is attached to a tube which screws
> into the block... oil actually goes from the engine up the tube and
> applies direct pressre to a diaphragm/spring coil loaded needle... this
> is the most accurate albeit old-fashion way of measurine engine oil
> pressure.
>
> That's why I asked if it could be more than an oil pump problem.
>
> Ralph

Low TJ oil pressure = new oil pump?
 

http://amccf.com/tech/I6-oil_pump_assembly.jpg
>
> Possible broken oil pump bypass valve spring:
> http://www.billhughes.com/temp/oilPump.jpg
> God Bless America, Bill O|||||||O
>
>
> Ralph DL wrote:
> >
> > Bill Hughes
> >
> > Please re-read my post... the oil pressure varies even when I replace
> > the electrical measurement of oil pressure with a mechanical oil
> > pressure gauge.
> >
> > The mechanical oil pressure gauge is attached to a tube which screws
> > into the block... oil actually goes from the engine up the tube and
> > applies direct pressre to a diaphragm/spring coil loaded needle... this
> > is the most accurate albeit old-fashion way of measurine engine oil
> > pressure.
> >
> > That's why I asked if it could be more than an oil pump problem.
> >
> > Ralph

Low TJ oil pressure = new oil pump?
 

Paraphasing FSM:

Low oil level
Faulty sender
Worn bearings
Clogged filter
Thin/contaminated oil (water/coolent)
Oil pump relief valve stuck
Suction tube loose or damaged
Oil pump cover warped/damaged


"L.W.(Bill) Hughes III" > wrote in
:

> http://amccf.com/tech/I6-oil_pump_assembly.jpg

Low TJ oil pressure = new oil pump?
 

Earl Horton;

Which bearimgs might be worn out?... in the pump?... camshaft?... ?

Ralph

God exists, or God does not exist, or I am God and I am dreaming all
this.

Low TJ oil pressure = new oil pump?
 

Bill Hughes

Thanks for the schematic... that helps my understanding of the TJ's pump
operation... seems typical for engines.

Over the past 56 years I've had many cars... starting with a 40 Hudson,
33,34,36,37,38,41,67,73 Fords, 47,49,53 Lincolns, 41 Plymouth,
49,49,51,47,65,80,86,97,51 Jeeps, 65,67 Scouts, 65,73 Chevies, 88 Dodge,
and none ever had oil pump failures. I just don't get it.

If the camshaft turns a "jackshaft" which drives the pump, can worn
bearings be the culprit? The pressure does not always drop when the
engine is at idle... I'd guess only about a third of the times when the
engine speed drops to idle... most of the time it drops to about 20-25.

It NEVER drops at road speeds... city or highway.

Ralph



God exists, or God does not exist, or I am God and I am dreaming all
this.