• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

At the time of rebuild, I replaced all sensors with Mopar sensors, new OEM O2 sensors, Dynomax cat back, Magnaflow cat, cowl intake, Mopar waterpump, stainless exhaust manifold from A1, Clearwater 630-clone cylinder head (new casting), etc. Basically, everything was replaced and I went overboard a bit...

Thoughts?
Just out of curiosity, what is the exhaust diameter?
 
2.25" exhaust diameter.

Here's thing - it runs really well. Well, I guess smooth would be the more accurate word. I starts immediately, revs up w/o backfiring, drives fine, doesn't buck/surge, no stinking exhaust, etc. I've taken it hunting/climbing mtns several times. It runs well, just no power.

I'll do a compression test to see if that tells us anything. I installed a new, aftermarket, distributor back when I built it. But, I can't remember the name @ this second. I'll have to look through receipts.
 
After the basics you may want to check the cat. Aftermarket ones are not all that great and can clog or just completely melt. Just something else to consider.
 
I read precisely what he wrote.





And he has had shit for sensors/tuning/injectors........etc from the start.
Are you dense? He very clearly said it has been under powered since the rebuild. You very clearly said if it was mechanical it would have shown up "long before".

So he's had the problem for 14K miles, make up your mind.
 
I rebuilt the engine in my '99 at 114k miles because the previous owner let it overheat, cracked the head and trashed the bearings in the lower end. I did a stock rebuild with proper machining and quality parts.

At the time of rebuild, I replaced all sensors with Mopar sensors, new OEM O2 sensors, Dynomax cat back, Magnaflow cat, cowl intake, Mopar waterpump, stainless exhaust manifold from A1, Clearwater 630-clone cylinder head (new casting), etc. Basically, everything was replaced and I went overboard a bit...

Aside from the stock items, I am running a ZJ HD fan clutch (272310), 4.56 gears and 31" ATs and a lowish/light lift. I'm not heavy with tons of armor or anything. But, I live in CO at 6k feet.

Here is my problem... This thing just feels slow. I thought with a "new" engine (has 14k on it now), 4.56 and 31s that this thing should feel fast (for a XJ). I know the fan is WAY noisy - could the additional drag from the HD clutch cause significant power loss? I'm getting about 11.5mpg around town (with a correct speedo).

Thoughts?

You might want to reread what the op stated.

Yes, so does a mis ground cam.

Im not suggesting it is likely, I am only stating it is a possibility and should be checked.

Are you dense? He very clearly said it has been under powered since the rebuild. You very clearly said if it was mechanical it would have shown up "long before".

So he's had the problem for 14K miles, make up your mind.

I know what I said.

A mechanical issue would have shown itself somewhere in the 14K and would have made the Jeep undriveable.
 
I know what I said.

A mechanical issue would have shown itself somewhere in the 14K and would have made the Jeep undriveable.
Actually, a misground cam or cam timing, will never "show" itself. It never gets worse, never makes noise, never quits running. It can simply be low on power from the day it is built til hundreds of thousands of miles later when it gets rebuilt again.

I'm only suggesting it is a possibility and shouldn't be overlooked. I feel you have misled the OP by suggesting it can't be mechanical.
 
I agree with johnx 100%. That's why you should always degree a cam when installing it. Just because it's new or a regrind does not mean it was done correctly or that the timing set was made correctly. If you've built numerous engines this becomes very apparent as each cam can show slightly different timing, even among the same grinds.
 
I agree with johnx 100%. That's why you should always degree a cam when installing it. Just because it's new or a regrind does not mean it was done correctly or that the timing set was made correctly. If you've built numerous engines this becomes very apparent as each cam can show slightly different timing, even among the same grinds.

Which adjustable timing set do you have? because I have yet to see one.

When was the last time you dialed in your cam? How often do you dial it in?


I'm +4 at the crank, Mopar Performance (Cloyes) double roller. Most guys bitch and complain about $60 for a stock set...........


You?
 
I've only built high performance SBC,BBC, and drag race 440's so all had adjustable sets put in them and all get checked and adjusted. Bushings can be used or you can buy adjustable gear sets. When I build stuff I don't go cheap as that's what you get when you do, cheap. Not all cams work well advanced/retarded some work best straight up. Some need to be adjusted a bit to get them to the correct specs.
 
I am constantly amazed by how much of an idiot jeep driver is.

And yes I'd be looking for a compression test as well, followed by fuel pressure test under load.

I've retimed the cam on 4643 several times now and it makes a *drastic* performance difference, but its not less or more power, just moves the curve up and down the tach. I doubt the issue would be there. With the distributor off a tooth it is a clear problem, as it either won't want to idle or won't want to rev up.

Did you re-use your fuel injectors or replace them? I don't remember reading that.
 
Last edited:
I've only built high performance SBC,BBC, and drag race 440's so all had adjustable sets put in them and all get checked and adjusted. Bushings can be used or you can buy adjustable gear sets. When I build stuff I don't go cheap as that's what you get when you do, cheap. Not all cams work well advanced/retarded some work best straight up. Some need to be adjusted a bit to get them to the correct specs.

With the cam, timing set and lifters that the op used I seriously doubt that its the issue if it was installed straight up and properly broken in.
 
I am constantly amazed by how much of an idiot jeep driver is.

And yes I'd be looking for a compression test as well, followed by fuel pressure test under load.

I've retimed the cam on 4643 several times now and it makes a *drastic* performance difference, but it not less or more, just moves the curve up and down the tach. I doubt the issue would be there. With the distributor off a tooth it is a clear problem, as it either won't want to idle or won't want to rev up.

Did you re-use your fuel injectors or replace them? I don't remember reading that.

I'm more amazed by the arrogance than the stupidity to be honest.
 
I am constantly amazed by how much of an idiot jeep driver is.

And yes I'd be looking for a compression test as well, followed by fuel pressure test under load.

I've retimed the cam on 4643 several times now and it makes a *drastic* performance difference, but its not less or more power, just moves the curve up and down the tach. I doubt the issue would be there. With the distributor off a tooth it is a clear problem, as it either won't want to idle or won't want to rev up.

Did you re-use your fuel injectors or replace them? I don't remember reading that.

Show me an adjustable timing set for the 4.0

Post it.
 
https://www.amazon.com/JP-Performance-component-4-0-Cylinder-Cheroke/dp/B00TO63LE8

714NVLHz32L._SL1500_.jpg


That's the one I currently run. -8 to +8 in 2* increments.


https://www.amazon.com/Cloyes-9-3127-Original-True-Roller/dp/B000NGN6NE

71rlUvBn5yL._SL1500_.jpg


Cloyes -4 and +4. I've run this one in the past.

Here's the post where I changed from one to the other.

http://www.naxja.org/forum/showpost.php?p=246332309&postcount=1766


I know for a fact there are others out there, but these are the two that I have run in the last year alone.
 
I'm not sure how you can claim it doesn't exist, and talk about using one, in the same post.


Your claim to idiocracy is more general though.
 
Back
Top