stevied916

iTrader: (30)

I just purchased a 98 z28 with 99k. I noticed the oil pressure was a little low. It's not too bad but at idle its around 30 and it holds 40-45 at 3k. The oil level is fine and I dont think its a rod bearing because there is zero knocking. How can I tell if it's the oil pump? Also, the idle is around 1200 rpm...what other possibilities can there be besides a vaccum leak for this?

Z28LS1camaroguy

iTrader: (3)

Thats about normal, mine does it. Changed the pump and oil pressure sending unit, no problems so far but it could be valve seals wearing out.

tylerdj

iTrader: (31)

Have you changed the oil since you bought it? I would do an oil change and make sure it has some good synthetic oil in it since you don't know how long it's been since it's been changed or what's in it.

edcmat-l1

iTrader: (10)

WTF do valve seals have to do with oil pressure?

ComNGetSum

iTrader: (11)

Thats sounds about right. When I start my car the pressure is usually at 45psi and drops to about 35psi at idle (1000rpms). A key factor in this also is the weight of the oil used and how hot it is outside. On a really hot day in rush hour traffic my psi dropped to about 20psi. I'm running 10/30 fully synthetic oil, a little thicker than normal because high heat will thin it out.

edcmat-l1

iTrader: (10)

10/30 is no thicker than 5/30. The first number, followed by a 'w' is the 'winter' weight. These oils are 'multi weight', or muti viscosity, so they act like a 5 weight oil under like 34 degrees, and then when they heat up and the polymers expand, they act like a 30 weight.
The last number in the series is all you need be concerned about in any weather over about 34 degrees.

5_02ls1

iTrader: (20)

that's about what mine holds....im installin an ls6 pump so im hopin it raises the pressure a little

ComNGetSum

iTrader: (11)

Thanks for the correction. I think I got things a little confused.

stevied916

iTrader: (30)

o, it looked clean. I just put in seafoam and bought a k&n filter and mobil 1 to put in tomorrow. What about the high idle?

edcmat-l1

iTrader: (10)

Try just backing the set screw out some.....
Is the motor all stock? As in stock cam?

stevied916

iTrader: (30)

I think it is the stock cam, it isnt lopey or anything. I bought it with cat back exhaust and a lid. thats all the mods I can tell have been on the car

3fingas

iTrader: (16)

port that oil pump and get a shim for the relief spring. You should see +8-10 psi easy

edcmat-l1

iTrader: (10)

The pressure relief spring will do ABSOLUTELY NOTHING for the oil pressure at idle. The pressure relief doesnt come into play until the engine is at high rpm, and the oil pump is pumping its *** off, and then the pressure relief opens, against the spring pressure, to release oil, and therefore maintaining a certain pressure by bleeding off some of that pressure.

stevied916

iTrader: (30)

So I changed the oil with mobil 1 and k&n filter and the pressure is better but the idle is still high. I adjusted the set screw all the way out and it's still at 1100-1200 rpm. Should I start looking for vaccum leaks? Where do these cars usually leak at?

Hell'sChariot

iTrader: (24)

It needs to be tuned. Mine did the same thing after my cam swap.

stevied916

iTrader: (30)

It's the stock cam though

GT Griller

iTrader: (8)

Ive noticed...atleast in my experience that 98's usually hold lower oil pressure...so urs sounds about right....

Mine holds 40 at a hot idle and just under 80 at WOT....but if i run it around town with the AC on it only holds about 30psi at hot idle. not to jack the thread but is mine the only one that does that?

stevied916

iTrader: (30)

mines only about 45 at wot when the oil is warm

TopFlite

The 1998 computers tend to be low about 200-250 rpms at idle and when redlining the tach. Your idle is really around 750rpms.