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2004 Jeep 2.4, Chrysler I-4

Hello, Guru’s…

I have here a 2004 Jeep Wrangler, 2.4 Chrysler engine, In-line 4. Not mine, trying to assist a neighbor.

They (with almost no mechanical knowledge) determined there was a “stuck valve”. I didn’t agree, but that’s not the point. A “mechanic” friend pointed them in that direction. I’m providing free support when asked, and only when asked. They ordered a new head from RockAuto. head arrived, proceeded to rip it apart. Now they’re getting ready to put it all back together, and I was advising them on cleaning the tops of the cylinder wall, pistons and to prepare the block for the new head.

As we turned it over - no head - it binds just as it’s coming to TDC. You can pull through it without too much trouble, but it’s far from as smooth as it should be - there’s a definite stop you can feel. There’s nothing left on the crank but the transmission (still binds with the clutch in) and the oil pump.

Have inspected the oil pan - no damage. Drained the oil and filter, still binding. The only component we haven’t removed is the starter. It wasn’t vibrating excessively, so unless the flywheel is bent, the starter shouldn’t be in the way, and there’s no metal - to - metal sound that we can hear.

So unless there’s something wrong with the crank, I’m kind of at a loss as to what it could be.

Our next step is to drop the pan and inspect the bottom of the cylinder walls. I don’t see how the bottom of cyl 2/3 could be causing it, but I’ve seen stranger things.

Any thoughts?

Thanks a bunch…

The engine shouldn’t bind at any point with the head removed.

As a matter of fact, it should rotate freely with little effort.

I’d pull the pan and see if there’s a problem with lower end before I’d install a new head.


That’s where we’re at. I’m finally fully involved now, but I can’t see anything obvious. Drop the pan it is. I was hoping there was some magical “I’ve seen that before” answer, but I’m with ya…

I did tell them we need to figure this out before we do anything else. And, I agree, there should be no bind whatsoever.

Cylinders develop a ridge at the top of the cylinders that needs to be reamed off to remove the pistons or the rings will hang up. I know you don’t plan to remove the pistons, but that ridge might need to be removed.

I absolutely agree with Tester that you should solve whatever’s causing the hangup at TDC before installing the new head.

How many miles has this beast got on it?

We went through the top, and cleaned that little ridge. In fact, the bores looked (and felt) really good. The “ridge” that was there was only what felt like burnt oil. Not terribly unusual.

I did get more information, and although I’m not positive exactly what’s wrong, there are a couple new bits of info:

I asked them to run a full compression check a couple weeks back, and handed them the tool. They did, told me #1 was at ~90, the rest at ~120. 120 us a tad low, but 90 is way low. Something’s up with #1. Just found out they ONLY tested 1 and 4, so they have no idea what 2 & 3 were.

Upon further inspection, it’s clearly visible that #1 and #2 sit lower in the cylinders that #3 and #4. So either the crank is twisted, or there are a couple bent con-rods.

The solution, at this point, is to return the reman head, and get a complete reman engine.

Now they’re debating going to a 6. These guys are amazing… Not sure exactly where to file this one. Thanks for reading, and the opinions. I’m still trying to figure out how he did it. It was running fine for the last year. However, he’s a young guy (17), and not really familiar with engines - but he’s learning now, and fast. Some sort of catastrophic damage occurred, but I have no idea what caused it, and he claims there was nothing unusual in the way it was running before this damage. I believe him - he’s a good kid.

Oh, TSMB: it’s just in the region of 100K. Not too terribly high.

You can’t do that.

The EPA gets pretty upset when you install an engine that isn’t matched to the computer.


OK, so it’s better to junk the entire thing?

OR, are you talking specifically about replacing the 4 with a 6?

There are plenty of places that will replace the existing engine and upgrade it to just about whatever you like. From a 4 to a HO V-8. I’m sure part of the replacement process is the computer, but don’t say it can’t be done - it’s done all the time.

You’re not taking the transmission into consideration

Will it even bolt up to the straight 6. . . ?

And if so, can it handle the extra horsepower and torque

The exhaust certainly won’t work without major changes, or a complete swap

The 4 liter straight 6 is almost certainly longer than the 4 cylinder, so the driveshaft might be a different length

You need the motor mounts, wiring and pcm from the donor 6 cylinder

Just tell the kid to stop daydreaming . . . get a working 4 cylinder engine for that Jeep and keep driving it. A used engine from a rearended Jeep would be ideal, if they can prove it runs well. A compression test on the donor engine would also be in order

What he’s proposing is opening a can of worms, which will probably lead to the Jeep NEVER running again.

If he wants a 6 cylinder Jeep Wranger, tell him to get his own Jeep running again, with a used engine, then sell it and buy a Jeep Wranger that came with a 6 cylinder from the factory. It’s a lot easier


Some twenty states perform no emissions inspections at all, and some others do it only for certain areas within the state. If you live in one of the twenty, there’s absolutely nothing to be concerned about in going to a different engine, and those that simply download the OBDII system checking for any codes never know the difference anyway as long as there’re no codes stored. Frankly, even if there are still states using combustion analyzers (“tailpipe sniffers”), it won’t matter as long as the emissions levels are below the requirements.

The problem you’d have upgrading to a different motor is mechanical. The powertrains need to be changed over too. Mechanically, you cannot generally plug a V6 into a tranny and drivetrain designed for a 4-banger. Trannys will be different, differentials will probably have different ratios, driveshafts will be different lengths, exhaust systems will be different, etc. The ECU needs to come with the V6 too, but I’d think that’s obvious. If you’re willing to spend the money, it’s certainly possible.

This year jeep didn’t come with a V6, Jeeps did com with a Buick V6 but that was many years ago.

The other option for that year Wrangler was the tried and true 4 liter straight 6

Over and above that factor, there is the reality that the engine will never run properly, and if the trans is an automatic, it will likely never shift correctly when the engine is hooked up to the wrong computer.

Actually, in California, it would be legal for the kid to show up to the smog station with a 2004 Jeep 4 liter straight 6 under the hood . . . as long as he has all the emissions equipment that engine is supposed to have, and it’s actually hooked up and functional.

You don’t even need to get the referee involved, in that specific situation. The smog technician is supposed to treat it as a 2004 Jeep Wrangler that left the factory with a 4 liter straight 6, because that was one of the engine configurations for that model year. But if the engine is supposed to have egr, and the kid just has a block off plate, he will fail the visual inspection, all the same

However, if the kid wants to install an engine which was never offered for that model year Wrangler, then you need to contact the referee, who will thoroughly inspect the vehicle and affix a referee label. That is a one-time thing. After that, you can get it smogged regularly, and the smog technician will refer to the bar referee label

“Binds” is a relative term that difficult to determine on this end. On a 4 cylinder when #1 & #4 are reaching TDC #2 & #3 are reaching BDC and the pistons changine direction, then vice versa in 180*. Is the binding the same when 1&4 are approacing BDC? If so move all the pistons to mid stroke and pour ~1/4" of ATF onto each and then oscillate the crank without pushing the ATF out of the bores and it will soon seep past the ring gaps to lubricate the skirts. Once the ATF has seeped down rotate the crank through several full turns and then check for any change in the binding.

Of course the symptoms that caused someone to guess that a valve was stuck might have some bearing on the binding.

I’ve never personally checked, but I was told by a fella at a car show that had built a V8 Vega (it was gorgeous) that the vehicle must meet the emissions requirements of the year that the engine was manufactured. However, if the vehicle was offered with a V6 as an option when new, I doubt they’d even bother to check the YOM of the engine unless there was a test failure.

There used to be a rumor that Chevy had originally planned to offer a smallblock V8 option in the Vega, but its other problems and subsequent plummeting sales figures caused Chevy to abandon the idea. The engine compartment was definitely capable of comfortably holding a smallblock V8. At least one aftermarket company even offered a kit that included everything necessary to do the engine swap, including a tougher rearend, subframes, a new powertrain, etc. I miss the old days. :cry:

A local hot rodder made a lot of money buying discarded Vegas and installing V-8s in all levels of performance upgrades. He would cut down truck axles and weld a collar onto the firewall to handle the really stong engines. For a while his daily driver was a Vega wagon cut down El Camino style with a 305 automatic that drove like a factory model when the streets were dry.

The 1971 Vega was an H body GM car that morphed into the Buick Skyhawk and Olds Starfire and Chevy Monza in 1975. All offered 4’s and V6’s while the Monza came with a 305 and a 350 V8’s. They barely fit and were a serious bear to change spark plugs requiring the engine be unbolted from the mount on one side and jacked up to reach the plugs. The Vega was not designed to hold a V8 - officially - but I’m sure the designers overlaid the V8 engine drawings, just in case.

Nothing I’ve read so far would make me think the owner could swap in a different engine and get it to run well. Either find the source of the binding (it’s not a ridge at the top of the cylinder, that’s only an issue when installing new rings), or put in a used matching engine.

With the head off and the problem still a mystery it will likely require pulling the engine and if the Jeep is worth saving a used engine with a fresh timing belt, clutch, plugs, etc., seems preferable to patching up or rebuilding the old engine. But I hope we find out what was causing the binding.

I waited until all the thrashing was over with.

OK, I know what’s wrong now, but it took some digging to force him to admit what happened. He had previously told me he was off-road, 4-wheeling, and went through some water. I immediately suspected water intrusion, but he assured me it was OK, water did not get into the engine, or even make much of a splash. Fool that I was, I took him at his word. That was exactly the problem.

I had no idea about of the details of any of this. I wasn’t involved at all until they had the engine mostly torn apart (well, the top part - they didn’t rip into anything serious), cleaned up and put back together. It ran, but rough, and with a heck of a “rattle”.

Found out that the intake was replaced with one of those hi-flow K&N style air filters. That’s fine, if you keep it out of water. He didn’t, obviously. They finally told me the intake filter and tube was full of mud, “but we cleaned it all up - it should be good”. Of course, that wasn’t the real problem. Mud is carried by water, which kept on truckin’ (probably with more mud), right into cylinders 1 & 2.

Now, for some answers to the above: I’m in Texas, which overall isn’t a smog state, although certain areas are testing, we’re not in one of those. If we want to stuff a V8 in it, we can. No one will be overly upset about it, and it’ll not get tested. In fact, we found a couple “kits” complete with engines, computers, wiring harnesses, mounts, everything you need to swap to whatever engine you desire.

I guess you guys think I’m nuts or something, too, and you’ve all forgotten I’ve been here for a while, and doing this for longer. The computer for that little 2.4 won’t properly run a 6 or an 8, so that would have to be swapped, along with motor mounts, fuel service lines, exhaust system, to mention just a couple. Every accessory on the engine will have to relocate forward to accommodate the shift in mounting position. Changes to almost every hose and wire in the Jeep engine compartment would be required. I’ve talked them out of being silly about it, and now they’re just looking to get it running again. Then, after a while, save some money, sell it, and get another with the engine they want.

Story closed. Hope you enjoyed it. They’re looking at somewhere around $1800 to get the existing rebuilt. I suggested used from an '04 Sebring or something (it was used in a few vehicles), but they don’t want to mess with a used motor.