1990 and 1991 4.0l engine differances

The reason for this question is that I have a 1990 xj lerado and I'm looking at aftermarket headers and everyone I see for sale is for 91 and higher such as the banks. What is the differace

first problem is you didn't list enough info for specific help.

but here is a link for a 90 laredo 4.0L automatic 4door 4wd header.
http://www.borla.com/applications/lookup.aspx/1991/Jeep/Cherokee/LaredoHeader/17020/

now that took me bout 3 seconds to find. so give it another try on google.

its not that I haven't seen ones out there for mine but I also see other companies out there listing ones for 91 and on and then ones for 90 and before as well as other parts. I'm new to jeeps and so I guess what my real questions are what are the differeances in the motors is there some sort of referance to swapping to a newer engine then what I have? Pros and cons sort of thing I'm trying to learn here thats all. If you can suggest info I can read then any help is appriciated. Sorry to sound like a dumbass I got the xj for 300 when I had no wheels and like so I want to learn

can anyone help me with more info on this

The engine went from basic 4.0L to High-Output 4.0L and the electrical/computer/etc systems were upgraded in 91. So, the sensors, vacuum lines and whatall in the intake are different. The intake and exhaust bolts up differently to the block also. So, there's kinda a big difference when purchasing parts.

The reason for the differece is 87-90 had an EGR (Exhaust Gas Recirculation) valve and the 91-up don't. There is a tube from the exhaust manifold to the intake manifold.


Mike R

Essentially correct.

In 1991, the EGR system was deleted in the ChryCo conversion. The cylinder head (#7120 instead of #2686) was modified as well - the intake ports were raised to give the airflow a straighter shot into the cylinder, but the exhaust ports were, as I recall, unmodified.

The engines are otherwise the same internally (I think the block casting number is the same, but I'd have to check to be sure,) with the boss that was for the knock sensor going unmachined.

The intake underwent major changes - to accommodate the raised intake ports in the head, to preserve injector location relative to the intake valve, and going to a four-bolt mount throttle body, rather than the RENIX three.

The main exhaust difference is the deletion of the EGR valve for 1991 - which isn't that big a problem, and isn't really, internally speaking, that big a change (the cam remained the same, and they probably used reversion to make up for the loss of the EGR system.)

Does this answer your question?

5-90

JCW said:

The reason for this question is that I have a 1990 xj lerado and I'm looking at aftermarket headers and everyone I see for sale is for 91 and higher such as the banks. What is the differace

Click to expand...

5-90 said:

Essentially correct.

In 1991, the EGR system was deleted in the ChryCo conversion. The cylinder head (#7120 instead of #2686) was modified as well - the intake ports were raised to give the airflow a straighter shot into the cylinder, but the exhaust ports were, as I recall, unmodified.

The engines are otherwise the same internally (I think the block casting number is the same, but I'd have to check to be sure,) with the boss that was for the knock sensor going unmachined.

The intake underwent major changes - to accommodate the raised intake ports in the head, to preserve injector location relative to the intake valve, and going to a four-bolt mount throttle body, rather than the RENIX three.

The main exhaust difference is the deletion of the EGR valve for 1991 - which isn't that big a problem, and isn't really, internally speaking, that big a change (the cam remained the same, and they probably used reversion to make up for the loss of the EGR system.)

Does this answer your question?

5-90

Click to expand...

Mike R

thank you for all your help this does clear up things now is one version better then the other or is ther a combination that is better than one the reason I'm asking is because I bought this jeep for three hundred dollers and it has almost 300,000 on it so I'm looking at building a motor for it and then swaping it in when its ready. are there any books or tech articels or anything that I could read or print to help with this matter to give be the best bang for my buck and I'm not affraid of swapping more then engines the onlything I need to do is make sure it stays auto so the wife can drive it if neccery

There's no issues with the block that I can think of - and the RENIX head is adequate. If you can source the OBD-I head (1991-1995, casting number 7120) it is preferred over the RENIX (2686) head because it "breathes" better - especially in the intake. However, switching to the 7120 head requires either modifying the RENIX manifold, or adapting the OBD-I manifold to accept the RENIX throttle body, OR adapting the OBD-I throttle body to take the RENIX TPS (and I'm fairly sure it's all been covered here before - so try searching here, or maybe at the strokers group - groups.yahoo.com/group/strokers.)

Perusing the strokers group should prove enlightening to you, and I've also got a book I've written on (re)building the AMC inline six - which focusses on the 242/4.0. See my website for details.

There are, I believe, headers out there for the RENIX engine (with the EGR port) if you look - although I think Borla makes one. So, perhaps, does PaceSetter - you'll just have to check, or have a decent parts guy check for you.

5-90