no oil pressure

I hate to say it, but I don't think this shop has obligated themselves to perform the work in a specific short time frame, but is just contracted to perform specific work. Does not sound like you have anything in writing to go on. So, 3 weeks is not going to give you much to go on legally, especially since you have no financial losses that are occuring due to their delays. About all a lawyer can do at this point is to write a serious letter, and hope it lights a fire under those guys. but, it could backfire in that they throw it together crappily again and just shove it out the door. If you contact a lawyer, see what he/she says is best before you get too fired up on a plan of action; they deal with the miserable side of human relations all the time.

Sorry all this is happening....make sure you publish the name of this shop far and wide once you get this back and it runs. And don't tell them that you are going to do anything like that of like getting a lawyer....verbal threats at this point are probably just going to backfire with these clowns.