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  1. Default oil press problem

    I've had my 421 rebuilt twice in 2 years. Both times by shops that have been in business for many years. The first time when I got the motor back it leaked oil so bad it was all over the outside of the back bumper, there was a bad rap when the motor was cold and it pinged terribly. I got the engine back in the Fall and didn't get it in until Spring. When I complained I was told it had a 90 day warrenty and it was up. I drove it for the Summer and pulled it out in the Fall.
    When I got it back from the second shop it sounded just like a diesel until it warmed up completely. I was told the forged pistons had to be loose for expansion. My GTO has forged pistons and it doesn't sound like this. The first time I took it any distance the oil pressure dropped until it was 15 psig on the hiway and the gauge didn't read anything at idle and the oil light came on. My engine it turns out was the last engine built before this place went out of business. Boy I wish I knew before I had the engine done.
    I pulled the engine and replaced the oil pump with a Sealed Power SLP-224-43364S. Removed several bearing caps and found no damage, checked oil plug in rear of block behind core plug (ok) and reinstalled engine. Today drove it about 35 miles. At hiway speed (2500 rpm) oil pressure cycled between 50 psig and 30 psig at a steady speed. Lower pressure under acceleration. At 500 rpm idle guage just barely read ( maybe 5 -8 psig) . Light was not on. There is no noise at all from the engine. I use a good brand of oil (30 weight this time) with break in additive. I don't understand why oil pressure goes up and down with no load or rpm change. Can anyone help?

  2. #2


    what kind of oil pressure gauge? mechanical or electrical, where is sender located? if mechanical, use metal tubing, no plastic and be sure line has no air bubble in it. What brand oil filter are you using? did you check oil pump bypass spring and check ball before installed? use a new pickup screen? oil pump shaft is driven by distributor which is driven by camshaft. did you replace the shaft? shaft is suported by block internally, is yours? how tight is distributor shaft? too much end play or worn distributor gear affects oil shaft. do you have a tach, is it steady, if no tach, no way to confirm engine load is steady. did you preclean oil pump gears under cover plate before install? prelube gears before as well? pressure at idle of 5-8 is not a problem. Remember Pontiac are high volume oiling systems, not high pressure like Chevy. High pressure does not involve Pontiac performance. usually happy with 10 psi per 1000 rpm. so 30 is good, don't like the cycling though. remove straight weight oil and use multi grade, 10w-30. 30 is fine for break in, but not normal operation. You have since changed oil since break in? if you removed caps, did you check plastiguage them to check clearances and torque them back.

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