Jeep 4.0 experts, I have questions!

"Tristan" (casselts) 09/30/2018 at 17:40 • Filed to: None

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Ka-Chow!

My ‘97 XJ has a 4.0 transplanted from a ‘95 XJ. The engine’s been with me since high school and the XJ’s been with me for roughly 8 years. There was nothing wrong with the ‘97 engine, I just wanted to keep as much of my original Jeep as I could. It has barely-in-spec oil pressure, but it’s in spec, it has 150-155 PSI of compression in each hole, it has no relevant MIL codes (it has an EVAP code that refuses to go away), the ignition system is tuned up and in good nick, the exhaust is free flowing (Borla header, Magnaflow cat, Dynomax cat back exhaust), the air filter is clean...

but it is absolutely, positively GUTLESS. It has been for years. When it had 3.55 gears and an automatic, 4-low was the only way to get through anything, and the only real difference I noticed going to 4.56 gears was more RPM and I could use OD with the air conditioning on going up hills. The AX-15 swap certainly helped, but it’s still a gutless wonder. It’s not crazy heavy, having barely more than a winch and a spare tire to weigh it down over stock, the gearing is appropriate for the size of tires- what gives? I remember in high school thinking it really ripped and could walk all over my friends lowly 3.1 liter Monte Carlos and Grand Prixs.

It seems to run fine, if a bit rattly. Could I have flattened cam lobes without lots of missing/rough running? Could the timing chain be stretched enough to affect power? I’ve lived with it this way for years because I gave up trying to get it back to how it used to be- but now my interest in fixing it is ramping back up again. Anyone have a clue?

Dr. Zoidberg - RIP Oppo > Tristan 09/30/2018 at 18:07

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[isn’t an expert]

[so here comes a stupid question]

Did you do a compression test yet? My pickup in college was functional but weak, so I had it checked out by my shade tree guy. Compression was 120-149 on all cylinders. Eeee. Drove it for another three years. Meh.

Tristan > Dr. Zoidberg - RIP Oppo 09/30/2018 at 18:22

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150-155 in each cylinder. Spec is 120-150 with a max variance between cylinders of 30.

Dr. Zoidberg - RIP Oppo > Tristan 09/30/2018 at 18:25

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Hmmmmm that’s too bad. I could take it off your hands for a few years and do a thorough inspection? Free of charge, of course.

Tristan > Dr. Zoidberg - RIP Oppo 09/30/2018 at 18:27

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Tempting... You have that bigly driveway and all.

Dr. Zoidberg - RIP Oppo > Tristan 09/30/2018 at 18:38

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It’s not bigly so much at it is largely vacant. It’s a proportion thing.

unclevanos (Ovaltine Jenkins) > Tristan 09/30/2018 at 18:40

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Your clutch may be slipping. I did a tune-up on my gutless YJ 2.5 and now it can do highway speeds all day and pulls pretty good. Maybe a tune up but I have no idea whats causing your 4.0 to be sluggish.

Tristan > unclevanos (Ovaltine Jenkins) 09/30/2018 at 18:45

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Nope, the clutch still grabs fine, and it had the same amount of power with the automatic. I’ve done a couple of tune-ups over the years... it made zero difference!

LastFirstMI is my name > Tristan 09/30/2018 at 19:17

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I think I see your problem.....

Seriously though, it may not be one thing, but lots of little things on a high mileage engine; a little loss of valve train “oomph”, dirty injectors, crud on the valves and cylinder heads....

I do hope you find an easy fix! Keep on Jeepin on. 

Tristan > LastFirstMI is my name 09/30/2018 at 19:22

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I’m thinking it must be valvetrain related. The rattles lead me that direction. In 16 years I’ve never so much as removed the valve cover from this engine. It’s been through 2 Jeeps, 3 exhaust manifolds and 3 intake manifolds, and a water pump, but it’s never been opened up.

Highlander-Datsuns are Forever > Tristan 09/30/2018 at 19:36

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Has it sucked a foreign object into the intake and blocked the air filter? Don’t laugh this happens more often than you would think. IIRC the Cherokee that I had was a 1996 model and it had plenty of power. Offroading was a breeze and it went up long grades on the interstate just fine at 75 mph. 

Highlander-Datsuns are Forever > Tristan 09/30/2018 at 19:39

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Have you ever redone the timing set? It could be way off and seem to still run fine. It will decrease power by 20-30% if it’s off a tooth or two... Personal experience here... I drove a car like that for a year until we figured out what was going on.

Tristan > Highlander-Datsuns are Forever 09/30/2018 at 19:39

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Mine will go down the road at 80+, but I just feel like I’m always flogging it to get there. I doubt the intake tract could be restricted, but I’ll give it a look!

Tristan > Highlander-Datsuns are Forever 09/30/2018 at 19:42

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I never have, no. It’s sort of what I’m suspecting. It runs smoothly, though. It just feels like it’s towing a heavy trailer all the time. The engine has somewhere between 180-200k miles, so it could very well have a stretched chain.

Spamfeller Loves Nazi Clicks > Tristan 09/30/2018 at 20:05

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Okay, so, you know I know my shit. Because I wrenched on don’t ask how many of these.

Y ou have a big red flag. Compression is too high, oil pressure is too low. There’s a mechanical issue here. Over 150 is not a number I want to see on a ‘95 block - especially not coupled to marginal oil pressure. Doubly so with mechanical noise.

The motor’s mileage is too high for the compression to be that high. Period. Coupled with noise? This is a sign of a serious mechanical problem. The head has to come off, period, and pray it’s just the head . NO SEAFOAM IS NOT AN ACCEPTABLE ALTERNATIVE. Head has to come off and be checked over in depth and properly cleaned up.

You also NEED TO FIX YOUR EVAP PROBLEM . OBD-1.5 and OBD-II 4.0's are extremely aggressive about recirc, and with a non-functional evap, they will coke the ever-loving shit out of the engine if they don’t burn it first . Especially if you hack up the exhaust and fuck up the O2 readings . Crappy Borla headers? Yeah. (They’re crap. Use Banks 51327 ‘Revolver ’ tube manifold. )

THESE ARE NOT SMART COMPUTERS. THESE ARE VERY DUMB COMPUTERS. Under MANY scenarios, the PCM will force you into half-limp. Even when Chrysler insists it isn’t supposed to. And no, just fixing the EVAP alone is not enough - not when you have tick. And there is a non-zero chance the EVAP is a false positive as a result of bad exhaust setup . (Again, these computers are FUCKING DUMB and I HATE THEM.)

Hopefully properly cleaning the top end solves the oil pressure problem, but there is a non-zero chance it won’t. In which case you need to drop the pan, which is not a huge deal. When you do, replace the pump with Mopar P4529241 - 4.0 HV PUMP (includes all required parts except oil pan gasket .)

Tristan > Spamfeller Loves Nazi Clicks 10/01/2018 at 01:40

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Why would the compression be reading higher than it should? Combustion chambers coked up? If oil passages were blocked, wouldn’t I see high oil pressure?

Where can I start with the EVAP problem? I’ll read the code again tomorrow since it’s been a while and I forget what it was. I thought there might be an issue with the charcoal canister - the gas tank WILL NOT fill past 7/8 and I’ve heard that this could be a cause.

The Borla has only been on there for a couple of years and I’ve been 100% underwhelmed by it. About 3.5 years back I traced a major driveability problem down to a melted O2 harness. I repaired it with new wires spliced into the factory harness with telecommunications-type sealed connectors, as I’ve heard solder is a no-no on O2 harnesses. The EVAP code has been there through a few exhaust setups. Prior to the Borla was an APW header that cracked badly after a few years.

I have no fear of tearing into the engine, and I’ve sensed it coming for a while now. I just need the time!!!

Spamfeller Loves Nazi Clicks > Tristan 10/01/2018 at 02:15

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Because of coking in the top end. And no, you’d get low oil pressure because of poor feeding. Not high. This is a volume system, not a pressure system.

Starting with EVAP, I’d have to know code and symptoms. It sounds like the common charcoal can breakage though. It’s also not unlikely you have busted lines in there. That’s all way the hell back near the rear axle, which is why it’s common breakage.

Solder is fine on the O2 harness itself; gods know I did enough repairs with the officially blessed Dumber-Chrysler kit. It’s a pigtail you solder in. There’s just rules about how to solder it in and it needs wrapped properly. That’s all. The problem is aftermarket setups locate the O2 physically badly. Leading to poor or inaccurate readings. Which sends the fuel maps into a tailspin fast. Also it’s possible your fix may have screwed up the heater. It’s a common thing and the heater is why the kit is solder-in.

That’s what the official kit looks like. Well, pretty much. The O2 kit specifies a black connector depending on location.

Not surprised some no-name headers crapped out. The whole reason I recommend the Banks is because they retain a proper manifold mounting despite being short tubes. Means they are far less likely to crack at the mounts. Also a better quality part in general.

But at this point, the real question is: what do you want to build here? You’re already pulling the head on a high mileage motor with suspect internals. Could be sticky lifter, could be bent rod. Basically what I’m saying is: this is going to be your most convenient opportunity to do a full rebuild and to modify it correctly.

If that’s the goal, then step one is to take a big step back and decide exactly  what you want the Jeep to do. Because that’s going to dictate everything including all the axle parts you’ll be ripping out and the transfer case you may be chucking in the bin. Doing it right means nothing is ‘sacred.’ Doesn’t mean everything goes in the trash, but no component can be left alone from tires to springs and shocks to piston and injector choice.  

Tristan > Spamfeller Loves Nazi Clicks 10/01/2018 at 02:46

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If there were a fault in the O2 harness, wouldn’t it remain in open loop? I can monitor it with my scangauge and see it enter closed loop mode when it should and stay there until it shouldn’t.

I’m going to the junkyard tomorrow and I’m going to keep my eye out for a non-cracked manifold. The Borla needs to die.

My goal is to make the thing fun to drive again. The driver seat is terrible and it’s got no power. I’m probably going to swap some ZJ front seats in. If the engine needs a rebuild, I’m okay with that. The transmission was rebuilt in 2014, the rear axle was rebuilt and regeared in 2013, the transfer case was rebuilt in 2010, the front axle was rebuilt in 2013 and again earlier this year, the tires were purchased just 2 years ago, it’s got new bushings throughout the front end, 2 year old Bilsteins, BDS front springs, a fresh track bar, blah, blah, blah... I’ve got no shortage of time and money into this pig. It also rarely gets driven... I had a goal to get it out and enjoy it more in 2016. That summer it had 209k miles on it and I wanted to get to 215k miles by the end of the year. Well, here we are in October 2018 and it’s at 214,800 miles.

Spamfeller Loves Nazi Clicks > Tristan 10/01/2018 at 03:21

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“If there were a fault in the O2 harness, wouldn’t it remain in open loop? I can monitor it with my scangauge and see it enter closed loop mode when it should and stay there until it shouldn’t.”

Nope. This year can have intermittent heater faults and stay in closed loop. Also, it will enter closed loop even if the O2 is poorly positioned. Unless there’s a true circuit fault or completely bogus reading, it will stay in closed loop. These things could pass OBD-II smog tests pouring soot out the tailpipe.

“I’m going to the junkyard tomorrow and I’m going to keep my eye out for a non-cracked manifold. The Borla needs to die.”

The stock manifold is not one I recommend, only because it is prone to cracking. It can be reworked to add power, but it’s more expensive than bolting up a Banks. The other option is a custom fabricated manifold-and-tube setup, but that’s even more money. However, a properly tuned one for the specific engine build can add absurd amounts of torque.

“My goal is to make the thing fun to drive again. The driver seat is terrible and it’s got no power. I’m probably going to swap some ZJ front seats in. If the engine needs a rebuild, I’m okay with that. The transmission was rebuilt in 2014, the rear axle was rebuilt and regeared in 2013, the transfer case was rebuilt in 2010, the front axle was rebuilt in 2013 and again earlier this year”

But, fun to drive how? Off-road? On-road? Mixed? These all have completely different builds from engine internals to gearing. (And lesson one here is: DO NOT LISTEN TO THE JEEP-BROS.) I mean, you could just rebuild the motor, but to what end? If it’s got the same engineered-in problems, it’s just wasted money. This is years of basically ‘throw random parts at it’ in hopes that it fixes things, instead of stepping back to analyze the whole to understand why you aren’t happy with it.

Nominally, this is a build I’m interested enough in to take on. But the logistics here do not necessarily work. You’re in Oregon - I’m in Ohio. I’m also short on a bay until December . Plus, in all honesty, I am terrifyingly expensive. (Seriously. The paperwork legally says you agree to whatever it costs without a firm quote . ) But you would get a result t hat makes ICON look like the pile of shit it is, and then some. However, I totally understand the answer of “yeah, no, I don’t need a hand-built to my spec interior with exotic wood inlays and machined titanium .”

I mean honestly, just thinking and looking at it... I think the whole thing has to be redone and redone right. You’re not happy with the interior, you clearly weren’t happy with the engine before, you weren’t happy with the drivability - that’s why you made all these changes. (Yep, there’s some psychology involved in it.) You’re happy with the skeleton, but that’s about it.

If you wanna get on the phone and talk at some point, we can probably work that out. Talk is cheap and I ain’t Galen. Sure there’s a ton of stuff I can do that you simply can’t. There’s nothing wrong with that. (Not like you’re talking a 10k RPM 4.0 that can leave mile long elevenses.)