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Old 10-31-2012, 11:33 PM   #1
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Question 98 Cavalier low oil pressure and compression

Hi all, I'm having a little problem with my 98 cavalier.Sorry if it seems a little long I just wanna give all the info I have. Any help would be appreciated as winter is right around the corner and I dont think she will make it through it. I've been having low oil pressure, and just found out I have low compression in all cylinders. Someone told me it sounds like my main bearings are bad. I just want more opinions before i have to pull out the motor and replace parts.

I've been having low oil pressure to the point where the oil light comes on as high as 1700rpm after highway driving and about 1300-1400rpm when just driving around town. I've replaced the oil pump, screen, and sender unit. I have an aftermarket gauge installed also. When the car is cold i get between 40-50 and after if reaches about 110 degrees it starts dropping. I'm running 20W-50 and still have the low oil pressure

At the same time I'm having low compression in all cylinders. The range when hot is between 80-110. I'm pretty sure its supposed to be up around 180. We have replaced the rod bearings (after I replaced the head due to leaking head gasket) just in case.

My car is throwing the P0401 code for insufficient EGR flow. I have tested it with a 9 volt battery and when i engage it the cars idle doesn't change at all. Could this be tied into the low compression?
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Old 11-01-2012, 03:02 AM   #2
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Johnny,
seam like u did a lot to it. New head, Oil pump/screen and sender, right? Why did u replaced the head, why not just the head gasket? i wonder if the head u replaced actually is a bad one instead, wonder how "new" it is? I am not familiar v cavaliers but i know they all have 4cyl in them, some do Eco-techs some regular once, regardless the reason i asked about the head, is because u mentioned that low press is on all cylinders. I wonder if ur head have evenly wore out components, specifically suspicious about springs. a compression reading isnt always low because of the rings, if valves do not seal well, u will have a low compression as well. That said, what i would do is a wet comp test, but first do dry one (regular one). Then add little oil into a head and see if it raises comp. if it dont, its not the rings which i am guessing not cause i newer seen rings go bad on all cyl at once in a same range. and if its not that then it have to be upper part of engine - its head, since head gasket itself usually lowers compression on one or two cyl, at which it leaks. let me know how it works.
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Old 11-02-2012, 12:15 AM   #3
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Yeah all those have been replaced over the coarse of the last year. We replaced the head because the coolant leak was only when the car was hot and we couldnt see a crack in the gasket so we suspected a cracked head. We bought it brand new tested last January. I don't have to ever add oil nor do I lose oil so I dont really suspect the rings to be bad either. My main focus is the low oil pressure though because of winter coming up. Someone told me these problems could all be caused by bad main bearings. I will do the compression tests tomorrow though after I get out of work and let you know.
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Old 11-02-2012, 12:41 AM   #4
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In regards of oil pressure: wonder if engine was gummed up at some point and have clogged up oil passages since?
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Old 11-02-2012, 12:59 AM   #5
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Is this the standard 2.2 engine or the DOHC Quad 4 (Cavalier Z24)?

If the low oil pressure is caused by bad main / rod bearings then you can try to fix it by replacing them, but the only way to really do that right is to take the crank in and have the journals polished and mic'd for the proper size bearings to make sure you don't get ones that are too large and have the same issue again.
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