4g54 Oil pump / preasure issue

[phat-customs]

I have an 85 pajero with the Asron 2.6 4g54 motor which is giving very high oil pressure. It has the factory gauge in the dash, and its off the scale, where normally it runs arond the 2 or the 4 mark.
I have put a mechanical gauge in the block and measured the exact amount of oil pressure and its in the vacinty of 90 PSI when cold/highway revs. This traslates to about 550KPA when the book states that it should have 350 to 450 KPA MAX pressure.

My mechanic beieves there is something blocking an oil gallery which in turn is not letting something get lubricated but has also heard that there was a service artical released from mitsubishi some years ago about the oil pump or oil pump gasket causing problems too???

When I purchased the machine, the timing chains had just been done, is there a chance that the oil pump was removed to do this and something put back wrong, or is it more likley that a gallery blockage is the culprate??

What is the best way to attack said problem and has anyone else had experience with similar issues???

Thanks Heaps
Rob.

PS. Im really keen to get it back on the road for a wheel so PLS PLS PLS help!!!

[-Scott-]

It's a few years since I did it, but yes, the oil pump was probably "removed" while replacing the timing chains. The 4G54 has two timing chains - one does camshaft, the other does balance shafts. The driver's side balance shaft runs in the opposite direction to the crankshaft, which is achieved using a reversing gear. The reversing gear is also the oil pump, and I can remember needing several attempts to have it all go back together with all the bits lined up properly, so I guess it's possible that something isn't in properly.

Also, I can't remember on the Astron, but the earlier Saturn has a pressure relief "plunger" to prevent excess oil pressure (from a conventional oil pump, driven from the end of the distributor shaft.) On my Saturn, this plunger wouldn't operate when cold (despite several attempts to improve it), so I normally had 90 psi cold, dropping back to around 60psi once the plunger opened.

[steverisingsun]

The oil pump has a relief valve, it controls maximum oil pressure.
Steve

[phat-customs]

The oil pump has a relief valve, it controls maximum oil pressure

Been there had that out, the plunger was a little scored which could have been making it stick, but I gave it a hit with some wet and dry which should have freed it up.

Put the engine alllll back together again with new timing cover gasket and sump gasket and oild anf filter an such, still high oil pres.

The silly thing is, I drove it for 2 and a half hours up the highway to my parents place, and then I went for a 20 min put around in their dryed up creek bed, and i just noticed that the gauge was off the scale. Havnt been game to drive it since then. When i puled the sump off the fitst time to check the reliefe valve, there was a lot of "shit" all over the oil pump pickup, looked like little strings of silistic, thinking that something like that may have been picked up and pumped through the system whilst we were wheeling up and down te river banks.

???

Sound plausible? Feasible? Believable???

[epitrochoid]

What viscosity oil are you running? maybe try a 10w-30 or 5w-30 and see how it goes.

Was a new oil pump put in when the timing chains were done? i believe the magna pumps were larger internally and provided more oil pressure.

Is the pressure relief spring the correct one?
Usually when the relief valve works, the oil pressure gauge will move up to the top then drop down a bit as the plunger opens and drains the excess oil back to the sump.
If the spring has been changed or shimmed it may not open until a higher pressure.

REgards

Epitrochoid

[phat-customs]

I am running shell 20W50, but I only changed this after i had experienced the problem, the car had high oil pressure before I changed the oil so I don not believe this to be the problem, changing to a thinnner oil may result in lower pressure, but It may not be the cause of the problem.

I do not believe that the oil pump was changed, and I see no reason why the pressure relief spring would be different to factory, the fact that the oil pressure was FINE for 250Kays of highway driving indicates to me that there shouldnt be a problem there, only after the car was put on a steep up warard and subsuquent downward incline did the oil pressure go off the dial, which is why I believe there to be a blockage.

However, I have been told by a Mitsu Mechanic that there was a recall on the oil pumps or something along those lines, something to do with a gasket problem or something trivial like that, that gave trouble.

Thanks for the input folks, the more heads working on this the better :-D
Keep the ideas f-l-o-w-i-n-g