Jeep LS Swap Part 1: Introduction
Shaver Lake, CA featuring Ulysses S Grant “Grant” the pug

Which brings me to the vehicle’s problems. While the AMC-derived “High Output” (by early 90s standards) 4.0L inline 6 and associated Aisin-Warner AW4 are a notoriously bulletproof combination, this Jeep has traveled enough miles to circumnavigate the Earth 10 times. Many of those 240,000 miles have been questionably maintained before I got it, and life hasn’t been easy for it since. Since this is California, and Chrysler’s electrical engineers wired it, every other year’s required smog check is a game of Russian Roulette hoping our trusty steed doesn’t throw a code while being inspected. While the AMC engineers who designed the original I6 architecture went with maximum Soviet overkill on the mechanicals of the engine, Chrysler’s electrical engineers went with “we’re sending this shit to the moon” levels of wire weight savings. 18AWG is ubiquitous. 120A alternator? 12AWG got this. Starter? Schmaaaaaybe 4AWG. Strain relief is hilariously non-existent, nothing is supported and thermodynamics apparently doesn’t apply since regular plastic loom protects wiring mere inches from the non-heatshielded tubular exhaust manifold.

This harness connector isn’t important or anything: it only houses the key-on wiring to the ECM’s relays which you can hear clicking away with every movement. Really awesome experiencing this herky-jerk engine on-engine off-engine on-engine off action on the freeway and even more fun to diagnose. How you see it is exactly how Chrysler designed it: vertical orientation for maximum water intrusion and zero support.

My ever-present companion. I’ve named him Clarence.

One of the biggest problems with the HO 4.0 I6 is heat. This damned thing runs hot, all the time. Even with a larger radiator, nearly locked fan clutch, external coolers for power steering and transmission fluid and hood vents to help evacuate heat, the all-iron construction, hilariously poor BSFC (11-13mpg for a 4000lb, 190hp vehicle), small nose blocked by a winch, 100lb wheel/tire combination, armor and brick-like aerodynamics conspire to make for a vehicle that requires constant coolant temp surveillance. The reverse-flow cylinder head takes all of this heat and cooks the many sensors on the intake manifold to a nice crispy consistency. The wiring to engine management sensors was designed as what I can only believe was a practical joke: poor insulation, encapsulated trays running the entire length of the head near the exhaust manifold, and pitiful wire gauge. Currently, my Jeep’s main sensor harness above the intake/exhaust manifolds is one-piece: all of the plastic insulation has melted together. This makes any repairs to this wiring a complete end to end replacement.

A common sight for me, that hashmark represents 225*F coolant temps. This is just driving around on a 90* day with the AC on. Rockcrawling at 110*F with the AC set to stun? Let’s say this: luckily Chrysler added an audible alarm to alert the dipshit behind the wheel to look at the gauges when the temp creeps toward engine replacement time.


  1. Holy shit! Every time I come to this site “to just see what’s happening” I run into a project I’ve been thinking of doing myself for a while. Somewhere in this computer I have a massive bookmark folder (I do need to thin them out) titled “swap “LS” engine into different 4X4s”
    I think I was researching ZJ and WJ Grand Cherokees (I want the front and rear coil suspension) And quite a number of Land Rovers.
    Looking forward to this build.

    1. WJ is the current sweet spot in new vs capability vs cost. Gas tank hangs waaaay low, but can be tucked, and the suspension is JK version 0.75 and isn’t terribly hard to swap JK axles into. ZJs are piles, but if you’re not keeping any of the drivetrain and electronics, not terrible. Both come with shitty stock axles (generally LP D30 and D44A, A for aluminum pumpkin), so don’t plan on keeping them for long if rock crawling.

  2. The problem I run into with the different generations of Grand Cherokee (or jeeps in general) You get a relatively reliable “engine” (318, 360, 4.0, 4.2) As long as you pay very close attention to heat management. And wiring harnesses that could best be described as Soviet Chinese tractor.
    Or hand grenades with the pins pulled most of the way out (4.7, 3.7) but kinda stout transmissions. But in all generations the axles are pretty weak. The 30s not that bad if you truss and sleeve and chromoly the entire thing. An explorer 8.8 swap is an easy and cheap upgrade for the rear.
    I was planning on the WJ with the 4.0. Hanging the spare tire on a bumper or roof. Cutting out the spare tire well and tucking the gas tank. Then doing the stroker. But as you said you are already $5Gs in the hole for that. And you still have to deal with (more) heat and the wiring harnesses. That’s why I’m kinda looking forward o this project. I know it won’t be a definitive swap and all. But here in Arizona they (phoenix) basically follow California’s emissions laws. I’ve asked the smog referee about doing this is the engine has to match the vehicle class (no CTSV supercharged engines) and it had to retain all the emissions equipment. But he had no list or detailed answer to what “emissions equipment” includes.

    1. All of it needs to be there. Basically, if it sets off a MIL, it’s required. AZ is a little less stringent on engine changes, but…

      D30s are stronger than you think, just don’t be stupid with it. Locked on 33s with stock shafts (welded 760x caps) for years now, no issues. If you’re jammed in a spot, back out or winch. If you have to give it more than 1/4 throttle before wheelspin, you’re probably gonna break something. The truss went on when I got a set of 3 tube bypasses for it, but turned out an XJ doesn’t have the axle width to clear them without touching a tire or the frame or both. The Fox Factory 2.0s baaaaarely fit.

  3. You left out the LQ9, visually indiscernible from the LQ4, and should have landed in the correct weight/emissions class. Thus an LQ4 branded as an LQ9 should fly. If I were to guess though, this 5.3 will run cooler than the 4.0 and your cooling issues should be behind you. I wouldn’t crack the motor open myself, keep the magic smoke inside. They run forever. I’d also toss that 4L60 time bomb in favor of a 4L80. Either way I think you’re going to like this rig once it’s swapped.

    1. Yeah, completely forgot about the LQ9, but it’s pretty hard to find as well, people will fight you in the junkyard if you do find one, and I bought a donor that didn’t have it, so shoot me. Updated the article. 🙂

      Yeah, cooling should be better with the 5.3 since it’s an engine designed in the last 20 years, has aluminum heads, and doesn’t burn huge amounts of gasoline to make small amounts of power.

      Motor should’ve been cracked open. There were timebombs in there. Stay tuned for part 2. 🙂

      4L60 to 4L80 swap may be something for the future, but it’s physically much larger and the mounts I’m using were designed with the 60. Clearance for the driveshaft, links and all-important cats will be bad enough as it is. There’s also the need to re-parameter the PCM for 4L80 operation, which I’m told is something the ref might check. That being said, the original 4L60E has a shorter 1st for better crawling, and motivated that pig of a suburban around for well over 100k miles (including RV towing) and still shifted firm when I drove it home. It’ll get refreshed while it’s out, but I think it’ll be just fine for mild towing (tent trailer at most) and barely warmed over 5.3.

      1. I’m curious what a smog ref would look for on a reflashed PCM? Does he know it’s modified and fails you on that? Transmissions aren’t emissions items and that segment can be swapped without touching anything emissions related or VIN related. Speaking of VIN, how does that work in a swap in CA? I don’t think you can punch a Jeep VIN into a GM PCM (never tried). I’m curious what mounts and parts you’ll be going with here, but I’m guessing that all comes out in part 2.

        1. Transmissions aren’t, but the sensors involved will throw check engine lights, therefore under their purview. Either way, the 4L60E is plenty for a 4000lb Jeep that will rarely see 5000rpm, and the gearing better suited as well.

          VIN is easy: they add a new barcode/label over the existing emissions label so when the tech scans it, it comes up as 2003 Chevy Suburban.

  4. Steve any thoughts on how the BSFC/MPG may change based on the swap you’re doing? Seems like the EPA ratings put the Suburban as worse fuel economy than the Cherokee but I realize there’s a decent weight savings in the Cherokee.

    1. The stock 3200lb Cherokee 4×4 on 28″ tires (13/18) was marginally better than the 5500lb Suburban 4×4 on 30.6″ tires (13/17), sure. The Tahoe was 14/18 so better/same than the Cherokee and still almost 2000lbs heavier than the stock Cherokee. Currently, my XJ gets 12-14mpg mixed driving, and a ridiculous 9-11mpg when wheeling. A large part of this is due to heatsoak: the Cherokee’s ECU massively retards timing to protect the motor, which then increases heatsoak, and it also bumps engine idle speed to make the mechanical fan run faster, which forces me to use the brakes more to compensate and makes even more heat. It’s a shit show to say the least.

      My assumption is the Cherokee will get similar mileage to the stock Tahoe despite the short gearing, large MTs and extra weight from armor. Being able to run a large electric fan (no slim fan that will fit will provide nearly enough airflow for the 4.0) and larger radiator will help a TON to keep fuel economy reasonable. Factory ECUs do stupid things to protect the motor from heat, and a negatively sliding timing curve is one of them.

  5. Great job writing this. I dig your style and look forward to the rest of the project. I just crammed a supercharged LS3 into my XJ and it will be 49 state legal, couldnt waste my time with CA approved headers… It can be done but might not be worth it for most.

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