JStragWS6

Just put in a new GM oil pump. Started it and had about 50 psi. After I let it idle for a few minutes the pressure started to drop then went to 0. Shut it off and started it again and the same thing. Now it fluctuates between 10 and 40 then drops to 0. It's not the sending unit because it starts to get a lifter tap and rocker chatter. Any ideas of what the problem might be?

Che70velle

iTrader: (6)

The o-ring for the pickup tube seems to be a problem spot for many.

LethalZ28

Oil restriction tube and can retainer plate. My buddy told me to replace mine when I put my motor together because they loose pressure there

Bramlok

iTrader: (7)

I would bet money it's a pinched/kinked o ring for the pick up tube. Happens all the time.

JStragWS6

**** man, I dont want to pull it apart again. That would cause it to go from high to no pressure? Any chance of a clogged filter?

Does the o-ring go above the "lip" on the pick up tube?

SWEET98SS

iTrader: (8)

It goes here, not above the lip. I put lucas oil on mine so it slid right into the pump.

Could be a stuck pressure relief also. I would remove the pump and check it. Mine stuck open, thus my rebuilt engine now.

JStragWS6

Thanks for the pic. Yea that's how I put mine on. Just as a side note, the previous owner said it needed an oil pump because it dropped pressure. So while I was taking off the under drive, I noticed there was a point indent from a pulley puller on the crank bolt. When i got to the pump it looked fairly new, no sludge build up or anything. Could we have both messed up the o-ring or it's something else? And there's no way this would be a clogged filter? Im just confused of how it starts with pressure, then drops, then comes back some, then drops.

SWEET98SS

iTrader: (8)

Is this a new pump? Melling, ls6? Maybe you both messed up the oring. I would take it apart again and do it slowly when you take off the pickup tube, see if it is pinched under there.

There are 2 things that make the oil pressure, oil flow and the bearing clearances, if you have large bearing clearances, you wont have alot of oil pressure. it really sounds like a pump o ring problem. I would put a new pump in it, thats what I did, 1000 miles later, lots of metal in the filter, I cut it apart.


It could be the oil pressure relief stuck open, but when my car did this, it had 0 oil pressure on start up. I took my pump apart and carefully inspected it. I noticed the passage way open for pressure relief. I eventually figured out how it worked and pushed on the relief, it was stuck in the open position.

On a side note, your motor will only live a short while on low oil pressure. My car did not run long, I had to rebuild it after my mishap.

JStragWS6

Yea I know, I'm not running the motor now. I was really worried about bearing clearances but if it was a clearance issue, it would be a constant low pressure right? Yours was a brand new pump? Yea it's a brand new GM high volume.

oxblood!z28

It sounds like an O-ring problem from what I was told when I installed mine. I would check it.

SWEET98SS

iTrader: (8)

I had 20,000 miles on the setup, pressure relief stuck. I pulled the pump, put a texas speed ported pump in. Ran fine for 1000 miles then oil pressure kept dropping to 25 at high rpm.

I would put a new pump and o ring just to be safe.

JStragWS6

Alright. Me and the car arent off to a good start lol. That's the only thing you can think of that would cause a fluctuating pressure?

SWEET98SS

iTrader: (8)

yup, there really isnt much too it. A pump , a gauge and bearing clearances. I doubt a clogged oil filter. You could try thicker oil and a new filter. I would lean towards bearings if this gets better.

JStragWS6

Alright. Thanks for the help man.

StripedSS

iTrader: (3)

Im having a similar problem... but mine doesnt read oil pressure at all... i started it up after a cam swap but it stays at zero. Oil filter filled up, took it off then started it again n it shot out oil so i assumed it was my sensor i replaced, took it off n started it again but no oil up top, took a valve cover off n clean as a whistle so no oil is going upstairs.

JStragWS6

Alright, don't mean to drag this out but I also have a brand new melling pump sitting in the garage. Should I change the pump as well because of a freak bad pump or its probably just the o-ring. I'm almost at the pump and want to make sure this thing isn't coming apart again.

scatillac

iTrader: (12)

@ StripedSS

Is the diverter plug (plastic barbell) in the rear of the block?

It installs in the oil gallery behind the rear cover (with it's o-ring to the rear), sending oil into the filter and then to the gallery that feeds the rest of the motor.

JStragWS6

Well got it all apart today. Slowly pulled the pick-up tube away from the pump and the o-ring was on the pump, not fully seated and somewhat pinched. I took it out, covered it in oil(which I didnt do the first time and probably why this happened) and straightened out the o-ring and it sat pretty flat. This time I pushed the tube up and tightened the bolt as opposed to tightening the bolt and letting it pull itself up. Hopefully ill be good to go this time.

SWEET98SS

iTrader: (8)

Keep us posted

91sonomast

Yes, interested in the results. Are you on dakota-durango.com as well?