88 Chevy Oil pressure sender

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Hey guys first time poster here. I’ve got an 88 1500 with the 5.7 tbi. I’ve got an issue with low oil pressure that I am stumped on and really need some help.
When truck starts the gauge displays about 10psi and slowly goes down as it warms up. First thing I did was change the oil pressure sender near oil filter (PS269), no change. Then I checked pressure with external gauge and found that I was getting about 30 psi at idle after warmed up. Figured maybe I got a bad part so swapped out the sender again with no change. Tested gauge by disconnecting sensor wire and gauge pegged out at 60. Grounded it and gauge read 0.
So actual oil pressure is good, sender is good, gauge is good.. but still getting way too low of reading on the truck gauge vs external gauge. So what do you guys think I should check next? Leaning towards gauge on instrument cluster but don’t know a better way to check it. Any help is appreciated
 

454cid

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Those air core motors can go bad. Mine will suddenly jump, but I haven't messed with it, so mine could be the sender. My gas gauge however flutters, which I believe to be the air core motor. There is a guy (last I knew) on ebay that sells them.
 

Nad_Yvalhosert

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So the gauge, wiring, and sensor are good. What about a plugged, sludge filled passage in the engine where the sensor threads in?
It is a 33 year old engine...
 
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Thank you for the replies. @nad, I checked the pressure with the external gauge from the same port the sensor threads in.
 
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@454, by “air core motor” are you referring to the gauge on instrument panel? Replacing that is my next step. I did see one on eBay for $25 for just the oil pressure. Not quite sure how to change just that one out but I can figure it out
 

454cid

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@454, by “air core motor” are you referring to the gauge on instrument panel? Replacing that is my next step. I did see one on eBay for $25 for just the oil pressure. Not quite sure how to change just that one out but I can figure it out

Yes, the gauge. Check Youtube for a video on how to do it. I've watched it done before, and I don't think I saw anything that was too difficult.
 

DerekTheGreat

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If yours has the factree moonie cluster, the oil gauge pod pops right out. Just drop the replacement in, so long as we're talking about a complete unit and not just the motor. Try your local treasure yard and see what you come up with.
 
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If yours has the factree moonie cluster, the oil gauge pod pops right out. Just drop the replacement in, so long as we're talking about a complete unit and not just the motor. Try your local treasure yard and see what you come up with.


Yes it sure does. Alright thanks guys, I will do that and see what I can find out!
 
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The new gauge works! Thank you guys for your assistance on this.

Now, for some odd reason the parking brake is flashing at me. It flashes 8 times followed by a longer flash. Just a coincidence or is there something I could have forgotten to connect?
 

DerekTheGreat

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One of GM's more brilliant ideas (sarcasm) was to use the brake light for more than one purpose. The service manual states the light will illuminate brightly for brake faults (when grounded by the combination valve) or brightly for the parking brake itself and then medium or lower brightness for RWABS faults. I've never seen it flash though- it must be indicating a specific fault within the RWABS system. What all did you touch? Sometimes you can get away with just disconnecting the battery for a few minutes and then reconnecting it- might clear the fault.
 
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