AMC 304 sudden loss of oil pressure - Pirate4x4.Com : 4x4 and Off-Road Forum
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Old 02-02-2011, 02:50 PM   #1 (permalink)
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AMC 304 sudden loss of oil pressure

I have a "79 AMC 304, pretty much stock which I freshened up about 3 years ago. One of the items I replaced was the oil pump components. I did not replace the timing chain housing which by most accounts is sometimes the problem with oil pressure loss (from what I have read within this forum). However, my particlar problem is the oil pressure is perfect for about 99.9% of the time and then sudden loss which recovers almost immediately. The other day, I was out trail riding (nothing crazy) and my oil pressure dropped to zero and the lifters started clattering (sure sign of oil pressure loss). I shut off the engine and checked under the hood for any obvious damages or leaks. I couldn't find anything abnormal and decided to start the engine just long enough to move the rig off of the trail. Upon doing so, the oil pressure came right back again and was fine for the rest of the way out of the trail.

Operating pressure is between 40 and 60 psi depending on RPM and about 20 psi at idle.

Does anyone have any ideas to the cause of this phenomenom?
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Old 02-02-2011, 03:00 PM   #2 (permalink)
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Sticky oil pressure relief plunger. Take 7/8 bolt off the side and remove the plunger and clean it then re-install and try again.
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Old 02-02-2011, 04:38 PM   #3 (permalink)
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Either that or possibly low oil/bad flow causing the pump to pick up air
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Old 02-03-2011, 06:31 AM   #4 (permalink)
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Thank you both MC and Provience for your quick replies.

I will check the plunger as you suggested. During the failure the oil level was checked and was good. When this problem occurred, I was on a flat portion of the trail (dry riverbed / wash).
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Old 05-04-2012, 08:18 PM   #5 (permalink)
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I'm having psi problems now with my 304. What did you find out your problem was?
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