Heart Transplant for 91' XJ

[tarantula8]

Hello y'all, I just paid my first-time membership dues for NAXJA and now finally I am able to be a part of these killer forums. An absolutely amzazing amount of information wealth located on these forums!!!! Much thanks to all who have been blessed with more knowledge than me from the JEEP GODS!
Already be the proud owner of a 97'TJ and realizing that a man can never have enough jeeps I just bought an high milage 91' XJ Sport 50th aniversary addition with the 4.0 L HO I-6 in it. My father previously owned this XJ and I have been there while he put all 256,000 miles on. I have decided it should stay in the family and therefore needs a facelift. Since I absolutely swear by the 4.0 I-6 that Jeep has put in there vehicles since past decades I bought an used, low-milage (15,000), 4.0 I-6 engine with the intake manifold, injectors, fuel rail, etc attached from a guy in Milwalkee. The guy I bought the "donor" engine from did not know the VIN of the vehicle it came from and only said that when he purchased it he was told it would fit his 1996 Grand Cherokee. After checking the serial number and other numbers cast into the block I do know the engine was built in 1996 but unsure if it is out of a Grand Cherokee or a Sport? Is there anyway to tell by the numbers on the 96' engine if it is HO? What makes the engine HO, the fuel intake system or the ECU? If the 96' engine isn't HO will it still work with my 91' ECU and harness? Since the TJ or YJ was not produced in 1996 I know it is not from either of them. The last thing I want to do is run a whole new wiring harness and a new ECU.

Also, I want to buy Borla headers and Borla cat-back exhaust but unsure which ones to purchase? When looking at the borla header and exhaust they show different part numbers for both the 91' and 96' Cherokee? I know the exhaust I will need to purchase will be for the 91' as to fit the under-body contour but unsure exactly which headers, the 91' or the 96'. Are the bolt configurations for the exhaust/intake manifold into the head of the engine different from the 91' to 96'? Should I use the old 91' intake manifold and put it on the newer 96' engine? Or should I keep the intake manifold that is already on the 96' engine and just swap on the fuel rail from the 91'?

I will pray to the JEEP GODS to summon all who know answers to my questions to post them.

Thanx,
Dustin

[5-90]

Ok, here goes...

1) Any 4.0 made after the 1990 model year is, by definition, HO. The difference will be either OBD-I control (1991-1995) or OBD-II control (1996-2005.) For your purposes, they are essentially the same, and you'll just have to make sure you have the right sensors for your control electronics.

2) There were very few fundamental changes to the outside of the 4.0 - in 1991, the intake runners in the head were raised to increase airflow, but the later parts will swap. There was also added a main stud brace in 1996 (which you should have) which increases the rigidity of the engine assembly. This is desirable for stroker assemblies. (Kinda like finding a four-bolt main Chevvy or Ford for a HP buildup.)

3) I do not believe that the motor mount pads ever changed on the 4.0, so vehile and model year are mechanically a non-issue. Like I said earlier, just transplant all your 1991 sensors onto the 1996 block.

4) Why are you changing the engine? Frankly, 256K is little more than break-in mileage for most of us (I've got an 88 with 245K and an 87 with 275K - and the 87 is only down because the oil pump blew up. My 88 runs like a beast.)

5) The main mechanical difference between RENIX (1987-90) and HO (1991-2005) is in the cylinder head - the intake runners, as I mentioned. Also, the RENIX engine used a knock sensor as a timing input, which was deleted on the HO (along with the EGR valve.) Apart from that, the difference is mainly electronic, since the RENIX ECU was not OBD-compliant (termed "pre-OBD." I go roundy-rounds whenever I get my trucks smogged because I don't have "Check Engine" lights.) It's fairly common to put HO engines into RENIX XJ's and MJ's - some people change the electronics, some don't. The heads will swap easily.

The 96 intake isn't bad, and should be no trouble for you to keep. As I recall, the throttle body hasn't changed much from 1991 to now - but I'd have to check.

Anything else we can help with?

5-90

[tarantula8]

Thanks for the previous reply,

Also, I want to buy Borla headers and Borla cat-back exhaust but unsure which ones to purchase? When looking at the borla header and exhaust they show different part numbers for both the 91' and 96' Cherokee? I know the exhaust I will need to purchase will be for the 91' as to fit the under-body contour but unsure exactly which headers, the 91' or the 96'. Are the bolt configurations for the exhaust/intake manifold into the head of the engine different from the 91' to 96'? >>>>>>>>So are you saying that since little has changed with the I-6 engine, either the 96' or 91' headers would work??? Is there any "performance" issues that would differ if used either the 96' or 91' headers.

Dustin

[tarantula8]

Can anyone answer my header question? I called Borla and they couldn't help. I took the xj in to the shop yesterday to start the engine swap but still have not ordered the headers cuz I don't know which ones to order? The engine I bought to swap into the 91 body is a 96' but I am unsure if it from a Grand or a Sport? Borla shows different part number for both. Will the 96' intake manifold interfere with the 91' headers and vice versa? If not, that means I can purchase either the 91' or 96' headers, right?

Help!!!!