1999transamls1

iTrader: (5)

im going to put a manual gauge put on to verify what the stock gauge is reading before i do anything esle. alot cheaper then building a new motor and it still do this because the gauge/sending unit is messed up.

1999transamls1

iTrader: (5)

Well, minor update, now the stock oil pressure gauge reads 20 psi with the key not even in the car, so it's some sort of electrical gremlin

speedyss

Hey guys, I was thinking someone would have said something about the pressure release in the pump by now. I had this problem for some time now, i had a 402 stroker that i had put a melling pump on and it was shimmed for higher pressure. The way i see it, if the pump builds up and the blow by spring releases it, could that be what we are seeing? The pressure drop from the pump releasing extra pressure, b/c thats what happens when you turn more rpms, the pump builds more pressure and blows the excess off.

OldCobraGuy

iTrader: (2)

But it will hold the pressure at whatever pressure the spring is rated.

01ssreda4

iTrader: (96)

^^^That.

gun5l1ng3r

Did you ever find a solution? I've had a similar problem too.

My motor is a factory ls1 replacement built back in about 2001 and installed in 2009(bought from dealer). It has about 40k miles on it.

My problem is that the oil pressure will drop 3-5lbs with moderate throttle input (20%) and NO or very little RPM change. This doesn't always happen but seems worse when the oil is hot.

It has a new OPS unit from Gm that was put in with the new motor.

Has anyone else had this problem?

some of you mentioned crank endplay or walking cam bearings... can someone provide a little more info on those?

My other thought was excessive blowby from improper break-in(I was kinda easy on it for the first 150-200miles)

Kinda long post, but any help is appreciated

01ssreda4

iTrader: (96)

Check crank endplay, remove drive belt, dial indicator on the front of the crank pulley and prybar behind the pulley pushing against the front cover. Gently pry forward and you should hear/feel a small clicking at .004/.005 with a healthy thrust bearing. Anymore then 8 and you are beyond spec.

1999transamls1

iTrader: (5)

My car is still doing the same thing, will check crank end play when I get a dial indicator, but I have put 3k miles and 20-30 track passes on it with our it getting worse. I noticed that my gauge after dropping at high Rpms freezes at 45 or so and won't budge unless I slow down a ton, or accelerate a lot.

1999transamls1

iTrader: (5)

Bump for people that posted in here, did you fix your problem? I have recently noticed that there is a ton of oil residue above the oil filter, and there is a good amount of oil on the bottom of the oil pan as well

SWEET98SS

iTrader: (8)

Yup, had to rebuild the engine to fix my problem. bearings were going, took out cam and a couple lifters

treybadd

Im going to revive this thread. A little history first. I just installed my 403. I had mains align honed, cylinders honed for 4.005" nominal piston size, studs on mains and cam bearings installed at machine shop. I built engine and checked all clearances with dial bore gage. Mains were .0019"-.002", rods were .0022", crank thrust .005". Scat crank, Scat I beams, wiseco -8cc dish. LS3 milled and ported heads. I am using a melling high pressure pump. I left the DOD relief valve in the oil pan (2006 GTO) because I was told its not an issue. I now wonder if it is. I never used an aeroforce to monitor oil pressure until now. Cruising at 2000 rpm I have about 40-45 psi and if I give it a little throttle it drops about 5 psi and then climbs with rpm. Mobil 1 0w-40 oil. Is this just due to the sender location or do I have a problem? I can hear a slight whine at startup like the relief in the pan or pump is acting stupid.

treybadd

So I removed the afm/DOD relief valve in the oil pan and it fixed this problem.

82cetuner

iTrader: (9)

that red ss guy is way to stuck on the thrust bearing thing, just cause you had that issue does not mean every oil drop issue is related to that, you should notice quit a lot of things if your thrust is that far out. and being under load and high rpm does not cause the crank to push forward if the thrust is out it will move any way it wants. HOWEVER a manual car should see a lot of problems when the clutch is engaged, quit a lot of noise because the pressure plate will be pushing the crank as far forward as allowed by the bearings. BTW I had the exact same cam and lifter issue and OP. I suffer from the same drop in oil pressure under load and high rpms 3 years later after the cam failure. I had tons of metal in my engine and I never rebuilt it because oil pressure was holding. However metal going threw the Oil pump will damage it and cause it to not build pressure like it use to. adding oil helped is problem so that was clearly the issue. cam and lifer damage will not lower oil pressure unless the bearings themselves have a issue

MMorgan9812

iTrader: (6)

My car does the exact same thing fine when normal driving but when WOT oil pressure drops to 0 and it sounds like a singer sowing machine. I am taking the motor out now for Crate Engine in my sig but my thoughts are bad Lifters, Cam, and now everything else thats messed up. Funny thing is when Lifters start to rattle after WOT, I can turn the car off let it sit a few mins then turn it back on and oil pressure is fine. It only does the awful rattling after going WOT. I bet money Lifters and Cam are toast like OP

01ssreda4

iTrader: (96)

Sorry you don't approve of educated responses. The truth is lots of readers here may not think of the thrust causing an oil pressure drop, when it does. We are actually trying to solve peoples problems here and not all answers are going to be correct but its trial and error after investigation that gets to the root of issues like these. If you don't agree with that, why don't you go back to reading the cam of the month threads OK fella??

82cetuner

iTrader: (9)

educated maybe but your looking for zebras when you should get the horses out of the way. drop in oil pressure like this his common, having it caused by the thrust bearing is not. the guy measured his and it was fine, mines fine I always check things every so often. I had metal go threw my motor and anytime metal goes threw a engine it will definetly mess with the oil pump for sure. first things first check the oil. I tend to have to run mine a qt higher just to keep the oil light from coming on with this high volume pump on a stock pan. then after that you can dig deeper, yes measuring thrust is a quick and easy way to rule that out but its rarly ever going to be a problem. especially if its a 6 speed. everytime you disengage and engage the clutch on a vehicle with a lot of thrust you will most definetly notice it

82cetuner

iTrader: (9)

my point is everything that was said, all you kept sayin was check thrust its your thrust, you didn't give any other advice other than that

Lonne259

I have this exact same problem, Did you ever figure out what was going on with your motor?

G Atsma

The guy you're quoting hasn't been here for over a year, and this thread is over 9 years old....