I have a 88 xj with 4.0 and I want to know if Performance Parts such as throttle body and spacers, cold air intakes are the same as on a 91 xj

 

No, not all of it will work

 

Depends on if the 91 is Renix or H.O.

 

From 87-90 the XJ uses the Renix engine control system and it changed to the Chrysler system in 91. The intake manifold is different and the throttle body is also. A cold air intake system should be the same for both setups. A throttle body spacer is a waste of money since the XJ uses a multi port injection with the fuel injectors on a rail spraying directly into the intake manifold. The "throttle body" as it is called on a XJ is simply the air intake. A spacer does nothing to enhance the air/fuel mixture. A bored throttle body on the other hand allows more air into the intake so the engine can breathe better.

 

All 91 and up are H.O

 

Renix has 3 bolt throttle body and H.O. has 4 bolts. Easy way to determine.