i came across a 4 door sidekick that im pretty sure has the 16v engine in it. (bad engine) i have the 8v engine at home and dont wanna spend the money on a 16v. so could i just drop in the 8v with no problem...does it have the same wiring harness? same bolt locations? thanks in advance guys

it has a diffrent harness and ecm,but should bolt up and in no problem, there was a 8 valve harness for sale real cheap in the for sale section, that would be real easy to put in and the ecm should be cheaper also, plus I would buy some of the 16 valve stuff off ya to help out just p.m. me.

Yes, there is a very good chance it has a 16V engine in it.  Since 91 4 doors are the only 4 doors that didn't get the 16V engine.
As mentioned, you will need a complete engine wiring harness and ECM.  Basically, you need every wire connected to the ECM.  You could run the 8V harness in piggyback with the 16V harness (keep the 16V harness for running everything non engine related).

piggy back? what does that mean and how do i do it?

piggy back? what does that mean and how do i do it?

Basically, you would remove all the wires out of the 16V harness that connect to the 16V ECM and you would use only the wires in the 8V harness that connect to the 8V ECM.  Therefore the 8V harness is "piggybacked" onto the remaining 16V harness.
You will have to search for answers on how specifically to do everything, as I don't know enough about it to explain all the details.

ok..but how do i plug the 8v harness into the 16 valve ecm? or should i just use my 8v harness ecm on mine now and just hook that up to the 8v engine? Are the wires on the harness coming from the ecm only go to the engine or other places also?

you can not use the 16 vlave ecm on your 8 valve harness or engine, put the 8 valve engine in, put your cut down wiring harness on the engine withan 8 valve ecm and relays, attach the wire to the points that it tells you to, like battery, ignition, fuel pump, the yellow wire on the back of the speedo (vss) those are just a few that I can think of maybe one or two more but thats it, cut the wires you need off of the 16 valve harness and hook them up to the 8 valve harness like the fuel pump and the vss,the others you could just hook them up in tandem. not that hard there are plenty of online manuals.

ok..but how do i plug the 8v harness into the 16 valve ecm? or should i just use my 8v harness ecm on mine now and just hook that up to the 8v engine? Are the wires on the harness coming from the ecm only go to the engine or other places also?

You will use the ECM and wiring that goes with the engine you are installing......so if you are putting in an 8V engine, in place of the 16V engine.....
You are going to use the 8V ECM and use all the wiring the plugs into the 8V ECM.  
You will remove the 16V ECM and all the wiring that plugs into the 16V ECM.
You can leave the 16V wiring in place that runs stuff like your headlights, turn signals, wipers, and other non-engine related stuff.

The majority of the wires coming/going to the 8V ECM will go to/from the engine and related sensors and some will be power and ground wires.  Find some good wiring diagrams and that will help you out considerably.

Find out if the lower end is what is bad. If it is then use the lower end from the 8v. I believe  by reading that they are the same short blocks.

The 16 valve bottom end is real close but the pistons have to have four valve reliefs each for the 16 valve head the 16 valve crank shaft is also double conterweighted.