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2002 gmc envoy_slt
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Hello all,

This is my first post on this site although I have been reading here for years. Usually I am able to find answers to my questions in threads created by others, but I can’t seem to find threads about an issue like I am having.

A couple of weeks ago I noticed that my wife’s 2002 GMC Envoy SLT (4x4) was making some awful noises. After reading some threads and giving the fan a wiggle (moved ¾ to 1” up and down and side to side) I learned that the water pump needed to be replaced. The car has about 150,000 miles on it, so I figured I would go ahead and replace the fan clutch too. After using several different tools, busting my knuckles, and a lot of cussing I got the fan assembly out, replaced the water pump, and popped a new fan clutch on. While testing for leaks prior to putting the fan assembly back on I noticed that the tensioner pulley started making some racket too. I ran to the parts store, bought a new tensioner pulley and serpentine belt, and popped them on. I put everything back together, started it up, and it sounded better than it ever has. Drove around a little bit, and still everything seemed good.

A couple hours later while on my way into town I noticed the “Check Gauges” light had come on and the message center was telling me “Low Oil Pressure….Stop Engine”. The oil pressure gauge was dropping from the 40-range to 0. I stopped the car, shut it off, and started it back up. After a few minutes the same thing happened (check gauges, low oil pressure, stop engine). I got back home and began playing around with it to see if there was anything obvious causing it. I was about a quart low on oil, so I topped it off but the problem continued. I did notice that when idling in park there are no problems. If I rev the engine a few times there is a loud, rhythmic, ticking noise that sounds like someone tapping two screwdrivers together. The ticking will go on for 10-15 seconds and then stop. If I rev again, same thing. After I rev the engine a few times, I start getting the low oil pressure, check gauges, stop engine thing. I replaced the oil pressure sensor about 50k miles ago, but it just seems odd that that would go out hours after all the other work I did. Plus, oil pressure sensor wouldn’t explain the ticking I’m hearing that seems to coincide with the oil pressure messages.

I assume the new water pump is doing its job because the motor is not running hot, but the ticking noise I’ve been hearing seems to be coming from that area. After letting the car sit for a few hours last night I started it and just let it idle for about an hour… no oil pressure drop, no ticking. As soon as I began giving it the gas, the ticking and oil pressure drop returned. This site has saved me a lot of money at mechanic shops, so I’m hoping someone here has some idea what might be going on.
 

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2004 gmc envoy_sle_xl
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1,239 Posts
Does the oil pressure only drop when idling or at higher revs as well? If it is only happening at idle, what is the idle RPMs? If the RPMs are below 600 and you had the battery disconnected when doing the other work, you should clean the throttle body.

Also, I would suggest posting at G M T N a t i o n . c o m / f o r u m s (no spaces), most of the experts from here went there a couple of years ago.
 

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2002 gmc envoy_slt
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Discussion Starter #3
I did not disconnect the battery when doing the other work. The oil pressure only drops after the engine revs. I let the car sit idling for about an hour yesterday and there were no drops in pressure. If I rev the engine to about 3,000 RPM a few times the pressure drops, then goes back up, then drops, etc. The engine is idling at around 5-600 RPM.
 

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The same exact thing is happening to my 02 trailblazer.. I can't seem to figure out what it is because I've put three qrts of oil in.. but it still is doing the same thing..
 

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Hello all,

This is my first post on this site although I have been reading here for years. Usually I am able to find answers to my questions in threads created by others, but I can’t seem to find threads about an issue like I am having.

A couple of weeks ago I noticed that my wife’s 2002 GMC Envoy SLT (4x4) was making some awful noises. After reading some threads and giving the fan a wiggle (moved ¾ to 1” up and down and side to side) I learned that the water pump needed to be replaced. The car has about 150,000 miles on it, so I figured I would go ahead and replace the fan clutch too. After using several different tools, busting my knuckles, and a lot of cussing I got the fan assembly out, replaced the water pump, and popped a new fan clutch on. While testing for leaks prior to putting the fan assembly back on I noticed that the tensioner pulley started making some racket too. I ran to the parts store, bought a new tensioner pulley and serpentine belt, and popped them on. I put everything back together, started it up, and it sounded better than it ever has. Drove around a little bit, and still everything seemed good.

A couple hours later while on my way into town I noticed the “Check Gauges” light had come on and the message center was telling me “Low Oil Pressure….Stop Engine”. The oil pressure gauge was dropping from the 40-range to 0. I stopped the car, shut it off, and started it back up. After a few minutes the same thing happened (check gauges, low oil pressure, stop engine). I got back home and began playing around with it to see if there was anything obvious causing it. I was about a quart low on oil, so I topped it off but the problem continued. I did notice that when idling in park there are no problems. If I rev the engine a few times there is a loud, rhythmic, ticking noise that sounds like someone tapping two screwdrivers together. The ticking will go on for 10-15 seconds and then stop. If I rev again, same thing. After I rev the engine a few times, I start getting the low oil pressure, check gauges, stop engine thing. I replaced the oil pressure sensor about 50k miles ago, but it just seems odd that that would go out hours after all the other work I did. Plus, oil pressure sensor wouldn’t explain the ticking I’m hearing that seems to coincide with the oil pressure messages.

I assume the new water pump is doing its job because the motor is not running hot, but the ticking noise I’ve been hearing seems to be coming from that area. After letting the car sit for a few hours last night I started it and just let it idle for about an hour… no oil pressure drop, no ticking. As soon as I began giving it the gas, the ticking and oil pressure drop returned. This site has saved me a lot of money at mechanic shops, so I’m hoping someone here has some idea what might be going on.
I would do an oil change add one quart of Marvels Mystery oil and then add your preferred oil to level. Install new oil sensor. Note on AFM Trailblazer engines there is a small screen near the oil sensor that gets dirty due to sludge. Must be cleaned/replaced. Another area that is prone to low oil pressure is the oil pick-up tube O-ring know to fail.
 
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