jermzz

iTrader: (18)

So I bought a motor off a member of the forum. It's an ls6 block 420ci. I pulled the pickup tube and windage tray off my 2000 z28 LS1.

After I installed the motor, everything seemed fine. I had a warm 38 - 40 idle and it climbed with rpm. Granted i didnt floor it cause it wasnt tuned, but it was ok. Then Yesterday it went in to get tuned. The tuner said everything looked good for oil pressure when he was tuning it. I took it out for a joy ride right after it got tuned and when it warmed up it was idleing at 20 PSI. I know thats not normal for a ported ls6 pump. Anyway thats not the worse part. At WOT, the pressure goes up to about 50 then decreases rappidly to 30lbs or less. Then when I let off, it goes back up to 40 or so, then drops back to 20 at idle. What could have happened in this time to make this happen??

I'm going to get an external guage so I can check to see if it's acurate, but if not, what else can it be? I dont think the pump would just go bad all of a sudden would it? I'm puzzled.

jermzz

iTrader: (18)

Here's an update. I just took it out to verify a couple things. When I cruse it sits at 40-45 psi fine like it should, but as the rpm go up, the pressure does not as it shoud. It just IT seems like 1st gear is the only gear that the pressure actually drops. The other gears it just stays at about 40 - 43 psi to redline then drops back to 20 - 23 at idle.

IT kinda seems like the pump cant keep up with the motor at the higher RPM, but that doesn't explain the low pressure at idle..

any imput would be appreciated!!

thanks!

ArKay99

iTrader: (1)

Sounds like cavitation or air in your oil. Pull the dipstick and see if you can see bubbles after running it. You may have a pinched or messed up o-ring.

Studytime

iTrader: (15)

When your oil is low, pressure will dip when you get on the throttle.

Ben T.

jermzz

iTrader: (18)

I changed the cam also, is it possible that after 30 dyno runs or so from tuning just made the oil lose viscosity therefore making the pressure drop?

slow trap

iTrader: (22)

i doubt the oil will lose it's viscosity from only 30 dyno pulls,i would check the o-ring.what weight oil are you using btw ?

jermzz

iTrader: (18)

Amsoil 20 50 Series 2000 race oil. The pressure is fine when the car is cold, it's just when it warms up. If it was the O ring wouldnt it consistantly have low pressure?

jermzz

iTrader: (18)

TTT, anyone? There was some oil bubbles on the dipstick when the car was cold. I started it for about 2 minutes then checked the oil. Once the car was warm and i drove it around a little, there was only a few bubbles on the dipstick right where the line of oil was.

gun5l1ng3r

You did check the level right? I had the same problem when my car was low on oil.

jermzz

iTrader: (18)

Yes, oil level is full on the dipstick.

jermzz

iTrader: (18)

TTT

HELP!!

I'm thinking cause I have good pressure when the motor is cold that maybe the valve in the pump is stuck open?? Then when the oil warms up and thins, the valve is letting too much oil out causing the low pressure?

bah...

slow trap

iTrader: (22)

that could be it,i took it you had 40 psi when you first started it but since then it is less,even idling,my bad.did you check the cam bearings for wear ?

jermzz

iTrader: (18)

Well, the motor only has 3k miles on it, I dont se why the cam bearings would have ware.

marv

iTrader: (40)

I'd almost bet it's the o-ring...probably pinched. I worried about mine when I did my H/C swap, but luckily everything turned out fine.

I've heard many stories though of people with good pressure at cold start up, but as the temps rise, pressure falls. That's apparently a common sign of a bad o-ring.

Just make sure you lube that thing up good with oil before it's pressed in there. My pickup tube (with new o-ring) wouldn't go up in the pump at first. I drenched it in oil, made sure it was lined up right and it popped right in there.

Good luck man!

turbotacoma

iTrader: (1)

Get a good mechanical oil pressure gauge on that thing first. You could have a bad sender. And this will help give you a better idea if the oil pump is going bad on you or a faulty sender or oil pump o'ring.

jermzz

iTrader: (18)

How could you tell the difference between the O ring being pinched and the pump going bad by hooking up a mechanical guage?

Is it better to get one that attatches to the sender behind the block, or the tap by the oil filter?

As for the common oil pump O ring simptoms, I have always read a pinched O ring will show low oil pressure on cold startup and warm idle?