Oil pressure gauge
 

1996 blazer. With engine off key switch on the oil gauge works normal but with engine idling the gauge is pegged past 80 like in pic. Is this the gauge or the oil sending unit? Is there a way to test it. Thankshttps://cimg6.ibsrv.net/gimg/blazerf...fd1effa711.jpg
https://cimg9.ibsrv.net/gimg/blazerf...a0471db381.jpg

I'm sure there is a way to test it but it looks like the sender is likely bad. Did this happen all-at-once or gradually get worse?