4.0 Rebuild, what to do?
11-26-2018, 11:12 AM
#31
Old fart with a wrench
From my FSM for both my 00 WJ and my 00 XJ. The coil rail has 3 coils, the PCM has 3 ignition drivers. How else are you going to fire 6 plugs? The auto industry has used waste spark for many years.
11-26-2018, 11:48 PM
#32
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Year: 1994
Model: Cherokee
Engine: 4.0 L6
Just for your edification, the coil rail ignition on the newer 4.0 is a "waste spark" system in which 2 plugs fire every revolution, one on compression and one on exhaust. This was done to reduce emissions by burning any fuel-air charge that made it out of the cylinder without being burnt. This is one reason the cats are small on these engines and the exhaust manifolds are cast iron because of the heat. You should stick to a distributor for simplicity and not having to deal with finding a PCM that's compatible. Actually, the intake ports and passages are smaller in the 0331 head, but are straighter going into the valves. This redesign was the reason weak spots were cast into them. The later intake manifold flows better than the early one however. A bored throttle body and 4-hole injectors will round out the set-up nicely.
Good to know, thats probably a mod I'll do at some point.
11-27-2018, 04:06 AM
#33
Old fart with a wrench
Not an easy thing to do. The PCM is different because it grounds those coils, then opens the circuits to fire the coils thru drivers inside it. The cam sensor is just a position sensor to tell the PCM which cylinders are at TDC. The actual spark advance is computed from sensing the windows in the flex plate, the manifold pressure, TPS and rpm data. The PCM even knows what gear the transmission is in thru the output speed sensor and wheel speed.
11-27-2018, 06:23 AM
#34
CF Veteran
I am aware the coil rail is wasted spark. What I'm not aware of was how wasteful the 4.0 was that it would need a secondary spark on the exhaust stroke to burn off the extra fuel...
11-27-2018, 12:46 PM
#35
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Year: 1995
Model: Cherokee(XJ)
Engine: I6 4.0L
You would think that the 4.0 would benefit from the fancy spark plugs if fuel wasn't being fully burned during the normal combustion process. The fact that it doesn't seems to imply that there's not much, if any leftover fuel for a properly operating engine.
11-27-2018, 04:08 PM
#36
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Year: 1995
Model: Cherokee (XJ)
Engine: 4.0L
No matter how efficient there will always be unburned hydrocarbons being exhausted, with the way emissions were/are going it's not surprising that Chryco was looking for ways to make the 20+ year old engine design to pass newer emissions standards. I'm sure a wasted spark setup not only allowed them to use less coils (and save money) but also cut down on emissions at the same time.
11-27-2018, 07:18 PM
#37
Old fart with a wrench
If you'll recall, they stopped production of the 4.0 largely because it wouldn't meet future emission standards required by the Feds. It seems a smaller displacement high reving engine burns cleaner than a long stroke engine designed for low end torque. Now explain to me how a Progressive Firing Hemi V8 wheeling dead cylinders at low rpm fits this scenario!
11-27-2018, 10:03 PM
#38
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Year: 1995
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I wonder if the fact they sell a bunch of tiny cars in addition to the big engine cars and the aluminum heads as opposed to selling only suv vehicles is part of the reason - isn't it the fuel standards across the board that they measure by?
Perhaps it's the fact that they realized that making an engine that routinely lasts 300k+ miles (and very often goes 400k and 500k) was a factor...
My family has had many toyotas - often regarded as top quality vehicles - yet not a single one breached 300k.. and all were meticulously maintained. On the other hand, the two Jeep I6's that were purchased new went to 400k and 302k (and could have gone more).
It's sad because a brand new Jeep Wrangler 4-door with the fancy VVT and stop/start 3.6 v6 engine still doesn't get any appreciable mpg over the 20 year old XJ model. So really, what exactly is the reason they couldn't have enhanced the I6 and kept it around as an option?
Perhaps it's the fact that they realized that making an engine that routinely lasts 300k+ miles (and very often goes 400k and 500k) was a factor...
My family has had many toyotas - often regarded as top quality vehicles - yet not a single one breached 300k.. and all were meticulously maintained. On the other hand, the two Jeep I6's that were purchased new went to 400k and 302k (and could have gone more).
It's sad because a brand new Jeep Wrangler 4-door with the fancy VVT and stop/start 3.6 v6 engine still doesn't get any appreciable mpg over the 20 year old XJ model. So really, what exactly is the reason they couldn't have enhanced the I6 and kept it around as an option?
11-29-2018, 10:48 PM
#40
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Year: 1994
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Not an easy thing to do. The PCM is different because it grounds those coils, then opens the circuits to fire the coils thru drivers inside it. The cam sensor is just a position sensor to tell the PCM which cylinders are at TDC. The actual spark advance is computed from sensing the windows in the flex plate, the manifold pressure, TPS and rpm data. The PCM even knows what gear the transmission is in thru the output speed sensor and wheel speed.
11-29-2018, 11:09 PM
#41
Senior Member
Reliable, long lasting engines are not profitable for starters . Unfortunately pushrod engines are a thing of the past . The strict EPA regulations have greatly reduced the ability for engines even remotely similar to be produced . As years go by tolerances get smaller and smaller , materials become lighter and lighter and things become less and less rebuildable. Unfortunately all of these “advancements” come at a cost of reliability and affordability.
12-01-2018, 12:09 PM
#42
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Year: 1994
Model: Cherokee
Engine: 4.0 L6
Reliable, long lasting engines are not profitable for starters . Unfortunately pushrod engines are a thing of the past . The strict EPA regulations have greatly reduced the ability for engines even remotely similar to be produced . As years go by tolerances get smaller and smaller , materials become lighter and lighter and things become less and less rebuildable. Unfortunately all of these “advancements” come at a cost of reliability and affordability.
12-02-2018, 06:39 PM
#44
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Year: 1992
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Engine: Rebuilt 4.0 H.O.
Sah dudes, its that time, the good ol' 4.0 don't have much left on her, she's tapping and knocking and won't last much longer.
If you can, please take a few minutes to read and just leave at least a small sentence or phrase that will give me something to work with as I do more research.
I have a vague idea of what I need to do and how I want to do it, but I'm not exactly sure what all of my options are, so I'm needing some help to learn all of them so I can figure out where to go and what my budget is going to look like. I also plan on eventually putting a low psi turbo on it, but that can be done after I get this thing rebuilt, so I want to upgrade whatever I need to while the engine is out and whatever can be done afterwards will be dealt with then. I also want to switch to a stronger, standard transmission, like the AX15 or something else like a NV3500.
Currently the Jeep is just my daily driver, but I plan on doing a small lift and 31s to be more capable as a trail runner in the future. I don't want to struggle too much while towing, though I don't plan to do heavy loads, a small trailer if anything. I don't plan on racing, but I definitely want a bit more giddy-up and not have to be as nervous to get up into the 3 and 4k rpms if I need/want to.
What are some good quality brands to look for, some to avoid (like Jasper), and what are things to watch for good or bad when looking for a machine shop?
I may have to stick with my own block, but if I can get my hands on another engine to work on separately, what should I look for?
I plan on having the block bored or honed, whichever it is, 30-40mm is the numbers I've heard, as well as new pistons. And what about an acid and/or hot bath?
The crankshaft, do I reuse it or invest in a new one? What do I look for to find out if its still good or not? Do I get a stroker shaft instead, or will that be too much for the rest of the engine or drivetrain when the turbo is added?
The camshaft, I want to upgrade it as well, what am I looking for considering what I plan on doing with the jeep? Or do I spend the extra money to get a significantly better one?
Should I get a new head, or would I be better keeping the original head and having it machined and upgrading the valves, springs, rocker arms, the like? Or is there really a need/difference between the two?
I've heard that '99 and up have better intake manifold flow, is this true or significant and do they take up more bay space than say a '94?
What about injectors? What would be a good way to go with those? Obviously new, but should I upgrade and what should I look for?
The old exhaust manifold definitely has to go, so what is a good brand to go for and is there really that much of difference between a stock manifold and a header to justify the cost?
What about the ECM? Should I get a new one or stick with the old? One that can be tuned? Do I need to worry about it when switching the tranny?
With all the change going on with the engine, I doubt the AW4 is going to last long or be enough even if I spent the fortune to have it properly rebuilt.
So with switching to a standard, what is there that I need to consider?
I've thought of switching to the AX15, its widely available and definitely stronger than the AW4, but is it strong enough? Can I upgrade it or would I be better off looking for something along the lines of a NV3500? I don't know much about it so I'm limited with that at this point. What are some other good options that will still be good for highway speeds?
And the transfer case, NP231, it will obviously need rebuilt, or is there a stronger case that I should be looking for instead?
I know its allot to go over and I'm sure there are plenty of things that I havent thought of yet so if you guys could help me out and lend your opinions to a young, avid jeeper looking to make his first vehicle and pride and joy last, I would greatly appreciate it.
Blessings, friends
If you can, please take a few minutes to read and just leave at least a small sentence or phrase that will give me something to work with as I do more research.
I have a vague idea of what I need to do and how I want to do it, but I'm not exactly sure what all of my options are, so I'm needing some help to learn all of them so I can figure out where to go and what my budget is going to look like. I also plan on eventually putting a low psi turbo on it, but that can be done after I get this thing rebuilt, so I want to upgrade whatever I need to while the engine is out and whatever can be done afterwards will be dealt with then. I also want to switch to a stronger, standard transmission, like the AX15 or something else like a NV3500.
Currently the Jeep is just my daily driver, but I plan on doing a small lift and 31s to be more capable as a trail runner in the future. I don't want to struggle too much while towing, though I don't plan to do heavy loads, a small trailer if anything. I don't plan on racing, but I definitely want a bit more giddy-up and not have to be as nervous to get up into the 3 and 4k rpms if I need/want to.
What are some good quality brands to look for, some to avoid (like Jasper), and what are things to watch for good or bad when looking for a machine shop?
I may have to stick with my own block, but if I can get my hands on another engine to work on separately, what should I look for?
I plan on having the block bored or honed, whichever it is, 30-40mm is the numbers I've heard, as well as new pistons. And what about an acid and/or hot bath?
The crankshaft, do I reuse it or invest in a new one? What do I look for to find out if its still good or not? Do I get a stroker shaft instead, or will that be too much for the rest of the engine or drivetrain when the turbo is added?
The camshaft, I want to upgrade it as well, what am I looking for considering what I plan on doing with the jeep? Or do I spend the extra money to get a significantly better one?
Should I get a new head, or would I be better keeping the original head and having it machined and upgrading the valves, springs, rocker arms, the like? Or is there really a need/difference between the two?
I've heard that '99 and up have better intake manifold flow, is this true or significant and do they take up more bay space than say a '94?
What about injectors? What would be a good way to go with those? Obviously new, but should I upgrade and what should I look for?
The old exhaust manifold definitely has to go, so what is a good brand to go for and is there really that much of difference between a stock manifold and a header to justify the cost?
What about the ECM? Should I get a new one or stick with the old? One that can be tuned? Do I need to worry about it when switching the tranny?
With all the change going on with the engine, I doubt the AW4 is going to last long or be enough even if I spent the fortune to have it properly rebuilt.
So with switching to a standard, what is there that I need to consider?
I've thought of switching to the AX15, its widely available and definitely stronger than the AW4, but is it strong enough? Can I upgrade it or would I be better off looking for something along the lines of a NV3500? I don't know much about it so I'm limited with that at this point. What are some other good options that will still be good for highway speeds?
And the transfer case, NP231, it will obviously need rebuilt, or is there a stronger case that I should be looking for instead?
I know its allot to go over and I'm sure there are plenty of things that I havent thought of yet so if you guys could help me out and lend your opinions to a young, avid jeeper looking to make his first vehicle and pride and joy last, I would greatly appreciate it.
Blessings, friends
Also, the AW4 transmission is an EXCELLENT transmission, but hey, maybe you don't care about the headaches in switching it for the manual, AND the constant shifting in city driving. My AW4 has 320K miles, it was running fine, but new LIME GREEN engine, seemed to include rebuilt Trans. SO it's in the shop having just a minor tune up with new minor parts.
As for the T-Case, find a T-Case from a family cruiser Cherokee. Mine was literally from an older guy that only used it during the occasional snow storm when the roads hadn't been plowed yet, so basically the gears were newish. The realities are that most people that bought Cherokees weren't off road warriors.
If I haven't already caused your eyes to roll, I am presently looking at several turbo kits available on EBAY, to hell with 505Performance, $4000+ !! Um no. Um F--- NO! Now don't laugh, I haven't done a lot of due diligence, but I'm seeing turbo kits for $300 on EBAY. I havent called the various suppliers, but the Ebay fitament says it will fit my 1992, and they claim "possible 300hp increase" I know that some are really rolling eyes now, we shall see.
Maybe you're an heir to the Chrysler fortune, or you invented some cool smart phone app, and you can spend $10K. Why do it though, if you can barely tell the diff?
Can I also suggest going with a color other than black or dark blue for the engine? If you ever have an oil leak, you're going to want to see where it's coming from. I chose VHT Grabber Green. It was a wild hair, but it's great looking.
Oh, I failed to mention, I'm a very rich guy that has had this 1992 Cherokee since 1994. I used to sleep in it during college, and building my little empire. It carried the various injection molds for my first patented product, and all the prototypes and when I made money, it was kept in one of my garages under a tarp. Then It was the first car for two step daughters and kinda got beat. It may sound further stupid, but I love my Cherk. It never stranded any of us, and now I wanted a little project.
Last edited by ProGunOne; 12-02-2018 at 06:50 PM. Reason: More info
12-02-2018, 08:01 PM
#45
Senior Member