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99 Suburban Oil Pressure Sensor

This is a discussion on 99 Suburban Oil Pressure Sensor within the Technical / Maintenance forums, part of the General Discussion category; Just bought a 99 Suburban 1500 5.7 2wd to flip and the oil pressure gauge was jumping all over the ...

  1. #1
    Registered User Mr_Shamrock's Avatar
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    99 Suburban Oil Pressure Sensor


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    Just bought a 99 Suburban 1500 5.7 2wd to flip and the oil pressure gauge was jumping all over the place. I went to the auto parts store and bought a new sensor. I didn't have the old one out yet and I had the choice of a single wire or 3 wire. I didn't know, but figured it would be the 3 wire so I bought that one. I removed the old sensor and it was a single wire BUT the harness going to it has 3 wires coming out of it. So now I don't know if I have the right one and the PO put the wrong one or what. I "ass"umed that since there are 3 wires coming out of the harness it would need the 3 wire sensor so I installed it. The gauge was still dancing around. I then went and got a used cluster from the local u-pick and now it doesn't jump around, but when cold goes to 45 and within minutes drops to 0 and the check gauges light comes on. It doesn't drop smoothly though - it will drop in increments of 5 or so in a single tick. If I give it a little throttle once it reaches 0 it will go up to around 5 (again not smoothly but in a single tick) and the check gauges light will go out. Let off the throttle it goes back down to zero and the light comes back on. The motor never misses a lick and never makes the slightest tick or knock and has good power when driving. I am going to put a manual gauge on it tomorrow, but was wondering if anyone knew for sure how to determine if the truck needs the single or 3 wire sensor. I would put the single wire back in, but it broke when I removed it. It looks like it has been in there a very long time.
    2004 Suburban 2500 Quadrasteer 4WD 6.0L
    1985 Silverado C-10 RCSB 2WD 5.7L
    1992 GMC Sierra 1500 2WD 5.7L
    1999 Chevrolet Tahoe Limited

  2. #2
    Registered User Mr_Shamrock's Avatar
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    Re: 99 Suburban Oil Pressure Sensor

    I got a chance to work on this some more today. I put a mechanical gauge (the one that replaces the oil filter) and the cold oil pressure went up to 60. I am not sure if that is due to no restriction of the filter or what, but the mechanical gauge and the dash gauge matched. As the truck started getting warmer the pressure dropped on both gauges, but now the mechanical gauge was bouncing very rapidly between 15 & 30 PSI while the dash gauge was steady. Once it reached operating temp the dash gauge was at zero again and the check gauges light was on however the mech. gauge stayed bouncing between 15 & 30. While under there I noticed the truck had the typical leak where the oil pan and timing cover meet so I dropped the oil pan. There was some large chunks of sludge in the bottom of the pan so I am going to degrease everything and go ahead and replace the oil pump while I am there. I am also going to remove the valve covers to make sure the oil return passages are clear. If this doesn't fix it then I guess it is just a tired motor - I can't tell by the way it drives though it has plenty of power and sounds like a new one running.
    2004 Suburban 2500 Quadrasteer 4WD 6.0L
    1985 Silverado C-10 RCSB 2WD 5.7L
    1992 GMC Sierra 1500 2WD 5.7L
    1999 Chevrolet Tahoe Limited

  3. #3
    Registered User Mr_Shamrock's Avatar
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    Re: 99 Suburban Oil Pressure Sensor

    Finally had time to work on the Burb today. I got the valve covers gaskets changed and the oil returns were clear. The heads actually look very clean inside. I also dropped the pan and put the new oil pump in, replaced the pan gasket, and the oil cooler adapter o-ring and gasket. The pan had a little residue on the bottom so it got a good cleaning too. I fired the truck up after priming the pump and the oil pressure went to right at 50 according to the dash gauge. I let it idle for about 20 minutes and it reached operating temp. The pressure went down to just under 30 at idle and jumps up to between 40 and 45 when given a little gas. I think I had a bad relief valve in the old oil pump - when I tapped out the retaining pin the spring barely sprung out. The ones I have messed with in the past have basically jumped out and they take a little bit of creativity to get them to go back in. It also felt really soft so I am thinking it was staying open partially at least and the pressure was bleeding off. Anyway it seems to be fixed.

    I want to thank you guys for all your help - I couldn't have done it without you LOL!!!!!!!
    2004 Suburban 2500 Quadrasteer 4WD 6.0L
    1985 Silverado C-10 RCSB 2WD 5.7L
    1992 GMC Sierra 1500 2WD 5.7L
    1999 Chevrolet Tahoe Limited

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