brainstorming, oil pressure has dropped

[neo71665]

Fresh rebuilt 3.4, new bearings, oil pump, rings, and everything. Was running fine and all of sudden the oil pressure dropped to nothing. No oil getting to top of engine. Engine not making any knocking sounds or acting like there is a problem. Less than 300 miles on the engine since rebuild. Only code being thrown is for the O2 sensor cause I haven't had a chance to put the heated sensor in yet since I put the long tubes on it.

Only 2 things I can think of is a spun cam bearing or a brand new mellings oil pump went bad. Anybody got any other ideas that I can try before I have to pull this thing back out and tear down again?


Frankly with having to order parts, wait, getting wrong parts, the headache of not having my main truck since last September I'm about sick and tired of this. I'm to the point I have a running 350 and all the parts short of a 4x4 700r4 to swap this out. If its gonna require me to tear this headache back down and start over I might just say screw it.

[pocket-rocket]

I would start by draining the oil and cutting the filter open to hopefully rule out bearings. Hopefully it's something simple like the pickup tube fell out.

[neo71665]

Pickup tube is welded on, I always do that.


Oil was drained and everything looks great. The oil still looked golden in it.

[pocket-rocket]

That sucks... Do you have enough room to get in there to put a primer tool in the dist. hole? I know you could feel resistance by hand when the pump started pulling oil on the last engine I had on the stand.

[neo71665]

Yeah I primed it, it ran fine for 2 weeks has almost 300 miles on it already with me taking it easy for break in. It just started dropping on the way home from work the other day. I was only 5 miles from home so I limped it in. Dropped down to around 10lbs that day, cranked it up the next day and its steady at 15-20lbs. Still runs fine with no knocks or anything. I'm working on getting a manual pressure gauge to hook up to see what it is exactly but I know its not the sender/sensor cause there is no oil coming up from the push rods at all.

[Superdave]

I'd drop the pan and start checking bearings...


I've been there a few times. it sucks.

[neo71665]

Yeah prolly gonna do that this weekend. Put a 350 in the blazer and try to get this 3.4 running for my truck.

[pocket-rocket]

I guess I should have clarified my last post. I was under the impression that you had no pressure at all and was suggesting the prime tool to see if the pump was sucking anything from the pan by way of feeling resistance to turning. But then you mentioned you had some pressure which throws my idea out the window, and now I would agree with Dave. Pulling a pan in a 4x4 sucks. Heck, it sucks in a 2wd too...

[Weatheralls Auto]

Sounds like bad pump.
Could be relief valve jammed up?

[neo71665]

Pulling the pan in a s-series sucks period, only way to do it is to yank the motor. 4x4 or 2wd is the same. Its just a bit easier in a 2wd cause you don't have near as much stuff in the way.

[60dgrzbelow0]

http://60degreev6.com/forum/f97/3-1l-losing-oil-pressure-radomly-t44910

...after you drain the oil...get a pair of tin snips and autopsy that oil filter if its still around ...wash it carefully with some fresh Kersosene and look for shiny slivers or plates that do not react to a strong neodymium magnet... if it does NOT react... you may have spun a bearing and the Babbitt on the bearings somewhere is shedding and peeling off. If the bearing shifted over the block oiling hole...its compromised further oil passing that part of the oil galleries and in fact will be more suspectible to spinning around completely once the oil pressure manages to get between it and the race/journal in the block. If you stopped this in time... it will keep your repair expenses to a minumum concerning a re-machined crank and con-rods...otherwise... some parts may say "Adios, Muchachos..."

By the way... I designed this tool to make certain that the Pre-Oiling of the engine actually pressurizes in the same manner that a regular Oil Pump Drive works... in order to guarantee the Oil Pump is properly primed and all the air spaces will be vacated...

http://s557.photobucket.com/albums/ss19/60dgrzbelow0/ANEWV6OILPUMPRIMINGTOOL/

[neo71665]

I have a big pipe cutter I use to cut open my filters.

The engine coming out this weekend and getting tore down. Pulled the dizzy just a min ago and put my primer in it and still the same. I'm saying its either a spun cam bearing or the oil pump went bad. I'm hoping its the cam bearing cause then I'm calling my machine shop and putting the blame on them.

[60dgrzbelow0]

If you are going to install another brand new pump if the one in there now is Tits Up... you might consider an Old Racer's Trick that can help it perform better under stressful operations... You will need to keep your wits about you, because this procedure demands attention to detail and a very thorough tidying up afterwards.

First... get the torque and re-assembly specs on your new OP and then disassemble the pump...making certain you make some indelible marks on the gears so you can re-install them in the exact same way they came out. Next... Using a 1/16" drill...find the very center of the valley (equi-distant from top to bottom and right at the bottom of the valley between any two Idler sprocket Teeth) on the Idler gear and drill an arrow-straight hole through to the inside of the sprocket shaft hole... and stop the drill before it can score the interior of the opposite side of the post hollow so as not to damage the bore. Remember... Drill ONLY ONE HOLE! Then...carefully dress up and radius the Idler Gear's new shaft oiling hole with a Jeweler's Diamond File and of course, clean out any residual metal flakes, spalls or filings before you re-install the gears and pack the pump with some Medical Petroleum Jelly and then torque the pump face plate bolts down carefully. The Petroleum Jelly will almost gaurantee that the OP will NOT go dry and cavitate during the pre-oiling episode. Please ...DON'T hold the Oil Pump in a Vise...and NEVER work on the pump while it is mounted on the engine!!! The OP casting is very sensitive to being warped or cracked and the gears can bind if too much force is exterted to hold the thing down... Follow the Melling Video on how to install the Oil Pump Pickup Tube and you should have a very reliable Oil Pump ready to go back into your New Power Plant:

http://www.melling.com/Info/TechTipVideos.aspx