Jeep 4.0L question

[jeepster]

Rear mains leak on 4.0L's running synthetics or not. I've probably literally made mortgage payments off the commissions I've made selling 4.0 rear main seals.

This is a true statement!

But, mine did not leak until 185k on one and 206k on the other using dino oil. And almost all of our XJ group who switched at high miles, leaked within a short time. Way too many for it to be coincidence.

What' a MJ?

A Jeep MJ is mommy's Jeep

Kidding aside, its the Comanche, the Cherokee based pickup


Yeah my tj leaks and has leaked for a while, I've ran synthetic whenever I could afford it for the last 5 years, and regularly for the last 2. Bought this thing used in 07 with 14,000 miles and plan on having it alot longer.

Guess I've been working on diesels too much... If they run like crap, change the oil, do the valves, drop in new injectors, give it new filters and call it done

So if you say put on a new cat and 02 sensors, couldn't I bash the kitty and install dummies? It's not like I'd ever have to get it emmision checked, I live on North Whidbey and plan on going to Alaska, so, I'd never smog it.... Not exactly legal but.... It don't bother me. Probably would be  cheaper... And would never have to worry about it again.....thoughts?

[Alchase]

Rear mains leak on 4.0L's running synthetics or not. I've probably literally made mortgage payments off the commissions I've made selling 4.0 rear main seals.

This is a true statement!

But, mine did not leak until 185k on one and 206k on the other using dino oil. And almost all of our XJ group who switched at high miles, leaked within a short time. Way too many for it to be coincidence.

What' a MJ?

A Jeep MJ is mommy's Jeep

Kidding aside, its the Comanche, the Cherokee based pickup

the Wish-I-was-a scramber pickup

[jackelope]

Oh My they get no respect! LOL
The MJ is the Comanche pickup, an XJ with a bed, LOL

Gotcha. We never saw too many of them at the dealership. I can remember 1 guy who spent a God awful amount of money on one, but that's the only one I can reliably remember.

[HUNTINCOUPLE]

Our 97' TJ had a rough idle so I pulled all the injectors and took them into DR. Injector. He pulled them all apart and ckenned them. He said they didn't look bad at all. This was at about 50,000. He said the stock injectors are very well built. I did do the O2,sensor and others. Still idels more rough than I like but always starts and runs. As for fuel miledge 12 on a good day.

[Thehowler]

Dealers just love to report back that you need a injector cleaning anytime your in for a running issue. jeep or Ford dealers didn't matter.
Before I did all my own wrenching, I had a jeep wrangler in for a running issue at 99,000 miles. One thing they called back that needed to be done urgently, was my very dirty fuel injectors needed cleaning, and also a new Map sensor. I had them only do the map sensor and it ran light a top. I never once cleaned those fuel injectors and ran that motor for 275,000 miles before rebuild. Always Chevron gas.

[jackelope]

I repeat, injectors in a 4.0 hardly ever go bad. I can say the same thing for Ford injectors since you brought it up. We don't replace too many gas engine injectors in Ford vehicles. It's never a bad thing to maintain your vehicle and clean your injectors once in a while, but it's not too often that they go bad. Back in the day, we used to fix lots of GM misfires doing a Motorvac injector cleaning. Ive seen that the effectiveness of an on-car injector cleaning varies greatly from machine to machine. A Motorvac machine works well and some of the other machines suck. If someone is telling you your injectors are very dirty, ask them how they know that. That should give you an idea of whether they know what they're talking about or not. Chevron fuel is great and has techron in it, an injector cleaner, that will work over time. I can't speak for all dealers but I've seen just as much "snake oil" sold at independent shops or jiffy lubes as I have the dealers. Try going to jiffy lube for an oil change some time. The BS meter will be pegged on high.

[rudysts]

I had a 2001 Cherokee that had an idle issue it had nothing to do with the injectors. it was much worse it turned out to be a cracked head this is actually a common problem for 99-01 years. I hope you don't have that problem good luck to you. you can easily google this problem.

[Thehowler]

Jackelop,

Have you heard of a injector- fuel system cleaner called BG44K, PN 208? I've talked with a few folks recently that swear by dumping a can of this in a full tank of gas.

[jackelope]

No I haven't but that's not saying much. I believe that those type cleaners are best used every so often as a preventative maintenance type thing. I've always heard that Techron is/was the best.

[Wacenturion]

I've got a 2003 Sahara Wrangler as a tow behind for my motorhome.  All stock with the 4.0, manual tranny and I get 16.5 plus or minus.  Has 65k original miles.

[dewandgin]

Jackelop,

Have you heard of a injector- fuel system cleaner called BG44K, PN 208? I've talked with a few folks recently that swear by dumping a can of this in a full tank of gas.

Used BG44K all the time when we used BG. I have friends that use it to smog vehicles in California. Vehicle will not pass running to dirty. Put a can of 44k in the tank fill it up and go drive it for 30 miles and smog it. It will pass almost everytime.

We have 2 CDJR dealerships and I have rarely/never seen a 4.0L with a automatic 4X4 get more than 15mpg on a really really good day. Check for exhaust leaks at the exhaust manifold cracking and make sure you use champion plugs (in my experience the run better and smoother) and as others have said tires aired up, tuned up and smooth starts and stop.

My 4.0L Cherokee has never got more than 14mpg.

[Alchase]

Forgot about the rear exhaust manifold bolts. The are notorious for breaking.

I had a 2001 Cherokee that had an idle issue it had nothing to do with the injectors. it was much worse it turned out to be a cracked head this is actually a common problem for 99-01 years. I hope you don't have that problem good luck to you. you can easily google this problem.

A cracked head on a low miles 4.0?
That one is new to me. Even the ones that had the cooling system issues and overheated rarely ended with a cracked head.
 The MAP or MAT sensors, EGR, TPS can cause a loss of power or MPG as well.

[jackelope]

I've seen the cracked heads  thing.
The exhaust manifolds break all the time. Down near the collector.

[Thehowler]

The cracking of the cylinder head on the late 99, all through 2000, and the first part of 2001 was a major problem for many jeep owners. Head casting #0331. If your looking for a used jeep to fix up in those years, look at the cylinder head on the driver side top. If you see those numbers, slowly back up and walk away.

[coachcw]

your fuel trims could be off do to a weak oxygen sensor slow to respond . opening up the exhaust could aversely effect your millage by causing a loss of bottom end torque. I'd make sure that your thermostat is a 192 and works , and possibly throw a fresh upstream oxygen sensor in it . as far as injectors spary pattern will effect idle more than cruise and probably isn't effecting millage in less its running rough.