Sinking Creek 4WD Association

Thought I'd start a new thread with hopes of more responses. Needing some details in how to go about throwing a 91 YJ 4.0 into a 98 TJ. I appreciate the help fellas.

you might run into some inspection/emissions problems with this if the inspector knows what hes looking at.

not too concerned with that little tid bit. certainly more worried about the nuts and bolts and getting it in there w/ all of the sensors and what not

thats what im saying, not only are you not allowed to put an older engine in a vehicle, im sure that the emissions systems changed in those 7 years. Along with several other systems. Youre going to have mismatched vacuum hoses along with a hell of alot of other stuff. if you want to do this right, its going to take a shit ton of work and money. And frankly, youll be putting all that effort and capital into an endeavor with negative return.

You've said I would have to change over a few things. I'm thinking I can take some goodies off of the 98 4.0 and make it work. You say other systems but lack a description. Please be so kind and elaborate.

i would be but I dont know many details about the 4.0, i was just giving general insight from an overall view of the concept of taking a non-compatible engine and putting it in a newer vehicle.

tsouth07 wrote:You've said I would have to change over a few things. I'm thinking I can take some goodies off of the 98 4.0 and make it work. You say other systems but lack a description. Please be so kind and elaborate.

Not to be a dick, but based on this and other questions you have been asking, you seem to be in way over your head. Many people have suggested you not try to do this and you blow them off and keep asking the same question twenty ways basically wanting someone to give you a step by step on how to do what they are telling you not to do. If you don't want to take the advice and think you can do it, then go for it and by all means best of luck to you, but don't expect someone to hold your hand the whole way.

Not tryin to be a dick either. Simply trying to know why this and that wont work and is not compatable. It's easy to say I'd have to change over a few systems. As far as asking more questions go I am digging for a reason.

Do some research on what emissions system they used on the two vintages, look at some schematics (wiring, vacuum system, fuel system, mounting, serpentine belts, etc.) of the two vintages, and check out the ecu differences and youll see what we are talking about. Im sure that many many things are different and in order to get an electronically controlled vehicle to operate properly your ecu will need to be able to read and understand the feedback its getting on all the different systems that are plugged in. For, example your accessory drive system might be arranged differently, your ac might be different, there are sooo many factors and variables that could play out and cause you problems between the parts on the 98 and the new engine on the 91. I have no experience or technical knowledge about the 4.0 beyond generic engine operation and this is all speculation and I am not sure what precisely to look for but these are the types of things to look for and the type of information and research you need to do for this to even begin to pan out. Im sorry I cant give you specifics, but they only engines I know details like that is on the 351 and 302. For example, my vintage 351 has the EEC IV emissions control system on it, and that and earlier EEC systems (I and II) are not supported by the updated technology of EEC IV (EEC III is, mostly), and if I were to try to put an 84 351 in my bronco which I would never do due the difficulty and terrible specs), it would be a bear.

The 91 is OBDI and the 98 is OBDII. They are controlled completely differently so you will have to rewire the whole engine bay. Not worth the time. Just find a Tj 4.0 to put in it.

Jwlman wrote:The 91 is OBDI and the 98 is OBDII. They are controlled completely differently so you will have to rewire the whole engine bay. Not worth the time. Just find a Tj 4.0 to put in it.

Bingo, exactly what I was talking about, or just rebuild the old engine. its really not that hard to replace piston rings.

All of that would be assuming he keeps his 98 ECU. If he swaps in the 91 ECU as well most all of those issues would be null. The yj fuel rail will have a return on it whereas the TJ I believe is regulated at the pump and returns there, so that will have to be addressed. With the two years you will have OBD I vs. OBD II to deal with so some serious rewiring will be in order.

I would still put my vote in for a newer engine but if you're set on this one it can be done, its just not going to be easy.

edit: james beat me to it

willhf1011 wrote:All of that would be assuming he keeps his 98 ECU. If he swaps in the 91 ECU as well most all of those issues would be null. The yj fuel rail will have a return on it whereas the TJ I believe is regulated at the pump and returns there, so that will have to be addressed. With the two years you will have OBD I vs. OBD II to deal with so some serious rewiring will be in order.

I would still put my vote in for a newer engine but if you're set on this one it can be done, its just not going to be easy.

edit: james beat me to it

He would also lose operation of his instrument cluster. The 98 cluster is completely computer controlled.

The 91 intake manifold is different. The throttle body and sensors for the earlier intake do not fit the later one. The later intake does not fit the earlier head either. So, head swap. Head gasket kit: $107. Head bolt set: $40. Probably add at least $50 to that for misc. parts you'll need to get it done. That plus what you have in the engine already puts you at $397. Well, now if you have bad valves, you're stuck using the head with them in it! Did you see the vehicle the engine you have was pulled from? Can you guarantee the mileage? If not, I think I'd pull the oil pan and check the bearings. Did it come from an automatic vehicle? If so, the bearings may all be good but the thrust bearing where an automatic puts forward pressure on a crank shaft. I pulled down a running 350 one time to find that the crank was about ready to start hitting the internal webbing in the block because of this very problem.

You also have an older motor. What shape is the timing set in? How about piston cluck? Did the guy lie to you when he said it only has xx,xxx miles on it? Holy crap, I've spent $500 putting the wrong engine in my jeep and now it won't move it's self and is making a horrible banging noise where the bearings are all shot!

However, you could take the $500 to Agee's or Bills, get a used engine with known mileage, put a thermostat and oilchange in it and have a 6mo warranty, and an engine you can just plug in and go in about a day's time.