Question about 1990 GMC Sierra

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1990 GMC P/U sudden drop in oil pressure

I have a 1990 gmc p/u 5.7 liter two wheel drive the engine has been rebuilt and the rebuilt has about 95,000 on it.When it was rebuilt i had a high volume oil pump installed it usally runs about 45 pounds of pressure suddennly in has droped to 30 pounds when running down the road,however when i stop at a light it drops to about 5 pounds or less causing the check gauge indicator light to come on,any suggestions on where to start looking.

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  • Anonymous Dec 27, 2008

    Same issue in a 97 sierra 5.7, if i find a fix i'll post back.

  • antony mosby Dec 31, 2008

    i have a 1990 gmc p/u. how do you install a cd player? mosbyantony@gmail.com

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  • Expert
  • 40 Answers

Did you do the rebuild on the engine?
Answer No: Check if the oil pump is the high volume oil pump you purchased? Also you can look at the site ThirdGen.Org they have great answers to

Posted on Jul 02, 2017

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  • GMC Master
  • 3,278 Answers

I would check the the oil pressure sensor is not foul up this can happen sometimes, as there is vain in the sensor. this reads the pressure. and tell the ecu. and your display.

Posted on Jul 02, 2017

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Posted on Jan 02, 2017

  • 38 Answers

SOURCE: sudden change in oil pressure gauge

It is normal on a Chevy for the oil pressure guage to fluctuate based on the rpm's of the engine. The faster the engine is turning, the higher the pressure. If it is fluctuating without a change of engine speed, then you may have a REAL Big problem such as low or no oil in engine or the oil pump itself is going bad. Could also be a blocked oil filter. You surely change your oil regularly....right?

Posted on Feb 02, 2009

dennymulford
  • 1055 Answers

SOURCE: fuel delivery

yes i had the same problem like too never found it but it was the fuel pressure regulator
and on that engine its located below the upper intake you have too pull it off too get too it!!!
it takes about two hours too do the job!!!

Posted on Apr 23, 2009

garputo22
  • 127 Answers

SOURCE: My oil pressure gage just drops to 0!!!

You need to replace the oil pressure sending unit, this is what tells your gauge what the pressure is. For future information if your oil pressure drops again and its a real failed oil pump within a few minutes you will internally damage the engine. I would get a new Oil Pressure Sending Unit. Let me know if you have any questions.... Thanks!

Posted on Jun 05, 2009

  • 59 Answers

SOURCE: low oil pressure 93 GMC P/U w/350 motor w/205,000 miles gauge

While engine is running, open the cover where you add oil to engine and see if you see a good flow of oil, if good flow, could be as easy as replacing oil sending sensor. got to realize that if poor maintenance history your engine may not be building enough pressure at iddle to move your hydraulic operated valves, only when you rev it up it will pump enough to run smooth. if running engine too long, you may cause more damage to other engine components such as crankshaft and cam shaft bearings. if you can spare a few bucks, have a good mechanic check your oil pressure with a mechanical gauge. another cheap option is to replace oil pump. last resort if you love your truck as much as we do,replace engine or rebuild it. At 205,000 this is a normal symptom, other than timing chain problems, most engines don't make it that far. hope this helps!

Posted on Mar 01, 2010

fixitriteman
  • 431 Answers

SOURCE: LOW OIL PRESSURE ON 2007 GMC SIERRA 1500. CHANGED

have it tested using a manual gage if still low then main baring ore most likely bad that would mean a over hall if is really low and bearings bad should be making rattle noise when started up first few seconds

Posted on Mar 11, 2010

Testimonial: "thanks alot.truck is not making a rattling noise.we did check it with a manual gauge.it read about 10 at idol. press. gets better as you incr speed"

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