I have and 85 EFI pickup 4 cylinder. The problem is purchase an oil pump for 85 vehicle when I remove the old oil pump it did not match the one I purchase. The oil pump match one for an 83 engine. I would like to know what year engine is in my vehicle there is a number on the block 111873 does this means any thing?.

 

Where did you buy the oil pump from?

 

I purchase the oil pump from O Riley Auto Parts.

 

Well my guess is that your engine is an '85, especially since it's an efi I'd be surprised if it was a somehow modified '83 block...
So I don't really know the answer to your question, but I'm just saying: don't rule out that they may have given you the wrong part. Are you saying though...that your old oil pump matches an '83 model, not the new oil pump? I was kind of thinking the new one matched an '83 but I may be reading your post wrong. It's possible you've got an '83 block with an '85ish head. There is a way to tell...there's some symbol to look for on the drivers side bottom center-ish area of the block. Can't quite remember, but I know somebody here knows.