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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 22989
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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1994 Infiniti Q-45T. 180K miles.. Changed oil & filter and one mon

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1994 Infiniti Q-45T. 180K miles.. Changed oil & filter and one monthlater the oil pressure light came on and teh engine started ideling rought. Chabged the oil pressure sensor sw. No change. Told that the Knox sensors need changing. I wonder IF-? Any thing simiple-? Use M-#1 and F &N filters.
Rich M

Hello and welcome to JustAnswer!


This engine has variable valve timing so low oil pressure can cause engine performance issues.


The first thing that should be done is use a mechanical gauge to measure the actual oil pressure to see if there is an engine mechanical issue or if it's electrical. You'll want to remove the oil sender and thread a mechanical gauge into the port and check pressure.


With the engine at operating temperature oil pressure should be at least 15 PSI at idle, and at least 67 PSI at 3,000 RPM.


If oil pressure is low then you might try replacing the filter again. It's not unheard of for a bad filter to cause a pressure drop.


If that doesn't help then the problem is either a restricted pump pickup, bad pump, or a bearing wear issue. If you aren't hearing any knocking noises then it's not as likely to be a bearing issue.

Customer: replied 4 years ago.

Thank you for your reply! Like your "picture" ! Ex-USAF long ago.

Noticed you did not specifically comment on/about the Knox sensor issues that a local car repair place advised me needed replacing. Beyond the OIL issue I am of course concerned about the serious $ required to replace the sensors---and maybe for no reason. If I read and understand your response correctly (?) the effects of low oil pressure will or may cause/create a condition that will activate the Knox sensors....there by effecting the electronics-timing system. Is that correct-??

Rich M.

Are you setting a knock sensor fault code?

Customer: replied 4 years ago.

I think so...based on what the repair shop owner told me that changed the oil pressure sensor. The car was --as noted--running rough especially if in gear with the brakes on. I never heard of them until he mention it. I then educated myself by reading--Looking at the very think detail owners manual.

Rich M.

If the running rough started at the same time as the oil pressure issue then I would most suspect an oil pressure issue. Without proper oil pressure then you won't have proper cam timing. Even if you have knock sensor fault codes setting I would still investigate the oil pressure problem first because lack of oil pressure will cause it to run poorly. On occasion I've seen knock sensor codes set because of the way an engine was running, rather than the sensor causing the issue.
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