Engine Swap Search = More Questions

My search for information about an engine swap has generated more questions than answers for this non-mechanically inclined 4-wheeler. I have a 1990 XJ and want to replace the original engine with a later model HO engine.

My searches have come up with everything from only replacing the head to knock sensor and cooling problems. I want to keep the swap as simple as possible. Is it possible to take the entire engine, fuel system, cooling system, air conditioner, PS pump, sensors and computer from a later model XJ and put it all in the 1990 XJ? Will this complete swap pose any additional problems or make the swap easier? Will the addition of after-market headers be a problem? Would any year engine be easier than another? Is there anything else I should consider? Is such a swap documented and, if so, where can I look for help?

This forum has been a great deal of help to me with my other XJ modifications. I hope you all can come through for me again. Thanks.

You can, but it's not, strictly speaking, totally necessary.

The main difference between the RENIX (1987-1990) and HO (1991-1995 OBD-I and 1996-2001 OBD-II) engines, mechanically, lies in the cylinder head and manifolds - the block really didn't change much.

The HO heads make more power by increasing the volumetric efficiency of the engine slightly - mainly by making the "corners" of the intake and exhaust runners a little smoother than they were before. By making a less drastic turn, the air can actually fill the cylinder a little faster.

The HO head will bolt right to the RENIX block, and the RENIX block is usually stronger.

You will need to carry over the HO head and manifolds, since the manifolds mount differently, and adapt the HO TPS to the RENIX wiring, or adapt the RENIX throttle body to the HO manifold (and both can be done.) It will also be necessary to block off the EGR port on the exhaust manifold. NOTE - if you have a "visual" smog check, YOU WILL FAIL IF YOU DELETE THE EGR VALVE! You Have Been Warned...

The RENIX system will have no trouble adapting to the head swap - as far as it can tell, nothing's changed. The fuel injectors are the same, and most of the sensors are the same (and if you use RENIX sensors when you hook everything up, you'll be just ducky anyhow.)

Of course, all this is moot if you have a "late" 1990 - the quickest way to tell is to check for an EGR valve bolted to the intake manifold, back by the master cylinder. 1990 was the transition year - from about September onward, you'd have an HO engine anyhow (OBD-I with the desirable #7120 cylinder head casting.) You can also check down the driver's side of the head for the casting number - if it's 2686 you have a RENIX engine, if it's 7120 you have the HO.

5-90

The main difference between the RENIX (1987-1990) and HO (1991-1995 OBD-I and 1996-2001 OBD-II) engines, mechanically, lies in the cylinder head and manifolds - the block really didn't change much.

Thanks for your help. I just looked and I have the RENIX engine. From what you have said, I may want to change my modification to just swapping to a newer head. Fortunately I do not have any kind of smok check. Is one year of head better than another? Also from what you told me, I guess I should look with a head complete with throttle body and manifolds. Do you think I would have a problem changing the exhaust manifold to after market headers?

Anything else I should change or problems I might encounter?

5-90 said:

It will also be necessary to block off the EGR port on the exhaust manifold. NOTE - if you have a "visual" smog check, YOU WILL FAIL IF YOU DELETE THE EGR VALVE! You Have Been Warned...

Click to expand...

You might want to speak w/ my smog guy

Edit: As far as heads go, the earlier are better than certain post 97 ones which had a cracking problems, but should have probably made themselves noticeable by now. If you searhc around here (I don't remember how to ID them) there are lots of posts on this and which casting # are "better".