Question about GMC Yukon

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Hi, My problem with GMC Yukon 2002 is that it always shows "low oil pressure" msg when the car is running, when i press the gas then it goes away, i believe the problem is the RPM is very low, and not responding to raise up when i start the AC in the car for example, and it is affecting the AC performance. can anybody guide me through this issue?

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  • talal hamra Mar 13, 2011

    thanks for answering so fast, but i believe the oil pressure is really dropping, its not a fake because the AC is affected, it will not run properly until i press the gas pad. plus i always maintain the car as per schedule, and there is no oil loss or burn.
    I d like to highlight that i changed the gear clutch and converter, after that i had this problem.
    i appreciate it if you have something to add for my problem.

  • talal hamra Mar 16, 2011

    I resolved my problem by cleaning the throttle and idle air control valve.
    the Yukon is performing much better now.
    anyway thanks for your help an i appreciate it if you can tell me some details about cleaning the AC air ducts so that i can fix the IN/Out air control and clean the fan for a stronger air push.



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. I wish I knew the total mileage your Yukon has traveled since 2002 . Also , heavy loads and off road driving habits can affect the overall life of an engine . Regardless , I will assume the problem is not a worn out motor. Also , I will assume that you change your oil and filter regularly as outlined in your owner's manual. And finally , I will assume the engine appears to be running smoothly , in other words: running on all the cylinders without missing, backfiring, and so on.

Now , if my assumptions written above are all correct , replace the oil pressure sending unit . In my years of experience working on G. M. motors, it has probably gone bad. Also , it is very inexpensive to purchase and easily replaced with a deep well twelve point socket in about five minutes . If that solves your problem, great . If it does not change anything , the Nextstep would require a Automotive technician with a accurate oil pressure gauge to measure your engines oil pressure at idle , and then the rate of the oil pressure increase while accelerating from idle to about 2000 RPM, to help determine whether not you have worn out bearings in the engine or possibly a worn out oil pump. Think positive , replace the sending unit first . Good luck .

Posted on Mar 13, 2011

  • Cool Blue Services
    Cool Blue Services Mar 13, 2011

    . Allow me to clarify something for you . A common misconception regarding oil pressure in an engine is that the oil pump provides the pressure . This is not so . The oil pump provides a continuous flow [or volume] of oil through specific oil galleys , bearings , and finally the lifters and push rods . However oil pressure itself is actually the measured pounds per square inch of the resistance in the flow created by the crankshaft and camshaft bearings . This is why a brand new motor will it easily provide 40 to 60 PS I while it is idling . The bearing clearances are very minimal thus providing a resistance to the flow of the oil which allows for a greater pressure . However as the engine heats up Clarence's become greater and the heated oil is thinner as well, which causes the reading to be lower when hot , versus cold. Now , back to your problem . If this problem only occurs when you turn the air conditioner on , then you need to check the AC idle solenoid, and or the AC idle control . Because the AC compressor loads the engine when it is running the idle must be compensated to offset the load on the engine . Basically , it takes the idle up just enough to compensate for the compressor load . If this is not functioning correctly , the RPM of the motor is probably dropping below the RPM threshold required for the oil pump to sufficiently supply the minimum volume flow of oil for the engine . However , if this issue occurs without the AC on , in other words , all the time , my first suggestions would be the proper procedure to follow . One is cheap , as the sender could be malfunctioning . Once you eliminate the sender by replacing it , and if the problem still exists , I would suspect worn engine bearings , crankshaft , rod , etc. . Or , a faulty oil pump .

  • Cool Blue Services
    Cool Blue Services Mar 14, 2011

    . I read your comment to my first post . Also , I read your original post again. If the engine idle RPM is not correctly compensated (raised up a little higher) when the AC is turned on , the compressor load on the engine could cause the RPM to drop below the oil pump threshold , with respect to providing the minimal flow of oil required to maintain a proper oil pressure at idle.

    The computer automatically adjusts the idle to compensate for the additional load of the AC compressor . The controlling mechanism is the idle air control or IAC.

    I must ask you a question . Is your service engine soon light or check engine light on after the engine has been running for a little while ? If so , scan the computer with a scan tool to obtain the diagnostic codes . Repair as necessary to obtain a pass . If these lights are not on , the first thing to check would be the vacuum circuit . Check all vacuum lines and connectors on the intake manifold . Also , check all vacuum lines related to the computer controlled sensors and controlling devices , especially the map sensor and IAC control valve . Proper manifold vacuum is very important . The computer monitors it and uses it to control several functions relating to the engine Idle as well as acceleration and driveability.



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