# No oil pressure at idle on refreshed 428



## GoatGuy (Apr 17, 2014)

Hi everyone... I hate it that my first post is about a problem... but here goes:
I have a 66 GTO with a 428 in it from a 69. I recently "refreshed" the engine with new main and rod bearings, and swapped the original heads for some 6x-4 to get a more livable compression ratio. Had found the car after it sat for more than 25 years, and I guess the rings had taken a set because it smoked badly, but ran great. The main and rod journals measured like new clearances, as did the cylinder bores, so I just put new stock size bearings and rings on her. I also installed a new Melling MF54DS oil pump. 
After the rebuild, oil pressure was fantastic.. 35 psi at idle when warm and 60+ at 2500 rpm. After about 200 miles on the new engine, I noticed that oil pressure was reading zero at idle. it still goes up to 40 at 3000 rpm, but drops rapidly back to almost zero when idling at 800 rpm. I verified the pressure with another gauge, same results. The engine sounds like a very quite sewing machine, no abnormal noises or clattering at all, so I guess it do still have a little oil pressure at idle, but it doesn't look like it on the gauge. I changed the oil filter (AC Delco PF-61) with no effect. 
Have I spun a bearing? Its very quite, I have a hard time believing it is a bearing issue. Has anyone had trouble with sticking relief valves on oil pumps? The way the pressure builds with RPM makes me wonder about the relief. Is it possible to jack the engine up enough to pull the pan with it in the car?
Thanks for any help you can provide!


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## geeteeohguy (Feb 2, 2008)

Relief valve on the pump can get stuck/jammed with debris. It's a good call, and a possibility. Did you measure the clearances with the new bearings? (I've seen mis-boxed bearings!!) What about the cam bearings? Worn cam bearings can cost OP, and tend not to make noise, etc. If your engine is quiet, you didn't spin a rod or main bearing.


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## GoatGuy (Apr 17, 2014)

Thanks. It's good to know I'm thinking correctly. I didn't change the cam bearings, didn't even remove it, it looked so good. The oil pressure was so good the first couple hundred miles I doubt a cam bearing issue. I did not measure the new bearings! But the caps all went on so perfect I hope the bearings were correct. Can I get to the oil pump without pulling the engine?


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## Indecision (Oct 24, 2010)

Just for clarification... you said you verified the oil pressure with another gauge. Did you use a different sensor as well? It could be as simple as that.


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## GoatGuy (Apr 17, 2014)

I just removed the tubing from the back of the installed gage and threaded onto a spare. Are you saying I should have replaced the tubing? If the tubing was parially plugged it would hold pressure at the gage and not bleed it off?


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## PontiacJim (Dec 29, 2012)

Have a very similar story after a fresh rebuild, but never figured out what it was...yet. Have the engine out, but just have not had time to rip into it. Building another engine.

My oil pressure would climb very slowly to 60 plus pounds, drop to about 40 when hot and idled at around 15. Then it began to get worse over time until it went to 0 at idle. Did the gauge check, used the oil pressure hole near the distributor to check (you may want to hook your line and gauge here to check as I did). Swapped out the oil filter housing, swapped different makes of filters, checked the rocker arms to make sure all was well here. Ran the car hard for about 25,000 miles until it went bad. Never heard any clatter or unusually sounds.

Can you pull the pump with the engine in the car? Yes, very difficult. I did this when the oil pump went on the original Pontiac 1968 350CI I had in the car. You have to lift the engine fairly high to get the pan to drop enough to squeeze your hand into the engine. You will not get the pan off to take it out, so it has to remain in place. Wiggle room to get to the oil pump bolts and loosen then up. Then the oil pump shaft to the distributor will drop out as I recall. I believe I used some heavy grease to keep it up from falling out before installing the new oil pump. Cleaning the old gasket off the pan was no fun, but it had to be done on mine. Make sure you don't break the dist. cap as it will be close to the firewall. Don't put a fan blade through the radiator or tear up your fan shroud if using one. Block the engine well so it doesn't fall on your hand when its in the pan. Have a buddy near by in case you do. Not something I recommend and only if you are really skilled, desperate like I was, and a little crazy. Hahaha.

Did get the engine all together, no leaks, had my oil pressure back, and drove the car for some time before installing the above rebuilt 400CI - that had bad oil pressure. Did not want to repeat the oil pump swap out ever again. It ran great, no strange sounds, so just ran it locally until it finally quit, which was the 25,000 miles and about 7 years of driving. I just added STP to thicken the oil to get better oil pressure until something like honey would have made no difference anymore. Knew I would have to pull it when the day came, but I had another engine/plan in mind for my next build.

I have heard things like the thrust bearing could have taken damage and got wiped out and this can kill oil pressure. It may be the pump went bad or is defective. It could have gotten debris in the relief ball in the oil pump. I was told the oil pick-up might have fallen off the oil pump housing. I was told an oil gallery plug could have come loose or when the new ones were put in the front, they were sunk too deep and this could have cut off some oil. Wrong lifters, sometimes you get Chevy lifters supplied in a rebuild when Pontiac are indeed different with regards to the oiling band around the lifter body - did you check these when it was apart? So many theories and things to check, but most require disassembly. Look for the simple first.


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## GoatGuy (Apr 17, 2014)

*Low Oil Pressure Fixed!*

Miracles do happen! I was on my way up the road to my buddies garage (with a lift) to start trying to lift the engine and drop the pan. The engine was cold and had about 30 psi pressure at 2000 rpm as I was shifting through gears. The engine only has a couple hundred miles on it, but I kinda went wild and decided to push it... I shift from 2nd to 3rd at about 4500 rpm and when the rpm's dropped back to 1500, oil pressure was at 50 psi! Pulled over and the idle oil pressure was 35. After it fully warmed up, oil pressure stayed steady between 20 and 25 psi. (It has 10w-40 in it.) I guess my high rpm sprint must have flushed some debris out of the oil pump relief valve. I drove it home, changed the oil, and went for a long drive. At 3000 rpm the oil pressure is 65 psi, and it is now about 20 at 800 rpm. I guess problem is solved! Thanks everyone for the help and support!


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## Indecision (Oct 24, 2010)

Awesome it worked out... as for my comment, I'm used to electric gauges so my mind automatically goes there. I was thinking "if the sensor is bad, just swapping the gauge won't fix the problem."


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## PontiacJim (Dec 29, 2012)

Excellent. Must have had something sticking or a bit of trash somewhere. I have read of a small piece of cured silicone that cause problems with the relief valve on the oil pump. Lot better than pulling an engine.


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## geeteeohguy (Feb 2, 2008)

Goat Guy, I think your diagnosis is spot-on. You effectively blew a chunk of trash out of the oil pump relief valve, and now it's able to do its job. Excellent news!!


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