91 should have a knock sensor. Other than a CEL light you won't notice any symptoms unless you have a ping problem. Its a safety device. To test the sensor bring the rpm up to about 2k and rap the block with a hammer. The rpm should drop. You can also measure this with a timing light. The timing should retard.

 

My cel is burned out. So the rpms should drop if the sensor is working?

 

1:yes you have a knock sensor,
2: NO you cant replace it,
3: It will run fine without it and not set off any codes.

 

Ok thanks everyone. I'm in the process of cleaning my EGR valve and man oh man is that thing STUCK.

 

Why would you not be able to replace it?

 

From my knowledge they're extremely hard to find for my truck because they don't make them anymore. I'm not gonna worry about it but I am currently soaking the egr.

 

what ol'navy said they are not made.
auto parts stores dont have them,
dearlers dont have them,
i've looked all over online and came up empty handed.

unless you buy one used somewhere,

 

Wow that's bogus. Its a simple little piece and they are all pretty much the same design. I wonder why they are so hard to get.