LS-swapping my ’87 Jeep Grand Wagoneer did not go as planned

The decision to tear out a perfectly good engine from a classic vehicle and replace it with something more modern is not one to be taken lightly. As with skydiving, abandoning a reasonable status quo for the rush of the unknown is not without its costs, and you’ll encounter a bleating chorus of naysayers all too happy to remind you of this prior to your plummet through the atmosphere—or the equally-steep plunge in your bank account balance.

When it comes to my 1987 Jeep Grand Wagoneer, however, the terms “perfectly good” must be followed by at least three asterisks when describing its factory drivetrain. As I described in a previous piece pondering the “to swap or not to swap” question with the fervor of a four-wheel-drive Hamlet, the stock 360-cubic-inch AMC lump in my Jeep was best described as an anachronism from the days where 140 horsepower was reasonable and 6 mpg a nuisance rather than a second monthly mortgage payment.

So it was time to yank it. I girded my loins and dove into the surprisingly deep well of folk wisdom cultivated online by the hundreds of other full-size Jeep owners who had trod the same path in a bid to better their daily drivers, trail rigs, and tow vehicles. When I emerged on the other side, several months later, I was sitting on a pile of parts, had made a significant dent in my own net worth, and was staring down the consequences of a few decisions that, in retrospect, made me feel more than a little foolish.

The answer is always LS

1987 Jeep Grand Wagoneer engine
Benjamin Hunting

“What is the best engine to put in your Wagoneer?” is the famous question posed by a thousand Internet posts. The answer typically comes back as some variant of “whatever you have lying around, because that’s what Jeep usually did.” It’s no lie that Kaiser, then AMC, and then finally Chrysler each went with motors sourced from outside its own corporate borders when building the Wagoneer, and that swap-friendly options from a dozen more candidates litter the landscape.

I had my heart set on GM’s LS V-8. This paragon of push-rod packaging is neatly self-contained, readily available from the millions of trucks and SUVs that Detroit churned out from late ’90s until today, and supported by one of the strongest aftermarkets in automotive history. And yet, I still managed to mess up what should have been the most straight-forward aspect of my swap: locating the right engine at the right price.

At first, the struggle was real. I pored over online classifieds seeking a complete donor truck that would provide me with the wiring harness and accessories that had the potential to nickel-and-dime me to death should I instead opt for a bare block. The bargain pickups I ventured out to see were typically high-mileage basket cases on their last legs. On occasion, this descriptor also applied to their owners, as in one memorable encounter where the seller had to ask his best buddy to breathe into his ignition interlock device so I could hear the tired lump rattle and tick its way to life. This was just before he told me it would cost me an extra $600 for a specially-permitted mechanic to remove the court-appointed vehicular ankle bracelet.

Finally it happened. I chanced upon a Facebook ad for a low-mileage 5.3-liter LMG out of a rolled over 2008 Chevrolet Tahoe. I inquired as to whether I could get the transmission, too (a 4L60E four-speed automatic) and was answered in the affirmative. What’s more, I could have whatever I wanted out of the wreck, and subsequently pulled and delivered to my shop, for the reasonable sum of $3000 Canadian dollars (about $2300 USD). Money was exchanged, promises were made, and in short order I had a once-beating heart ready to be surgically implanted in my still-running, no-real-issues Jeep.

Getting ahead of myself

1987 Jeep Grand Wagoneer view of back and passenger side
Benjamin Hunting

Immediately, my choice in engine posed somewhat of a problem. Initially, I had been targeting the older LM7 version of the 5.3-liter, liking its balance of respectable horsepower and relatively frugal fuel consumption versus the similarly-priced 6.0-liter V-8s. Despite this, I jumped on the LMG due to its price and meager 40,000 miles of life experience.

What I didn’t realize was that by 2008 General Motors had introduced its “Active Fuel Management” technology, which allowed the LMG to run between four or eight cylinders depending on load. The system worked just fine, until it didn’t, and the standard practice for most truck owners from that period was to either disable it via an OBD-II plug-in or ECU flash—or remove it physically from the engine prior to failure.

Since I was determined to do things “right,” and since the motor was still sitting on a stand and easily accessible, I chose the latter route and picked up a kit from Texas Speed & Performance. This instantly added $1000 to the cost of my motor, because not only did I have to replace the lifters that would no longer need to pull double duty, but I’d also have to swap out the cam that was still expecting the occasional four-cylinder shuffle.

As any hot rodder knows, sticking with a stock cam when the lure of extra, trouble-free horsepower was just a re-grind away is completely impossible, and so I ordered not just an AFM delete kit for the motor but a stage two cam setup aimed at boosting low-end grunt. The end result would be just under 400 horsepower and just over 400 pound-feet of torque, which was probably more than I needed but certainly a nice insurance policy to have when towing my Datsun through the mountains of New Hampshire on the way to the race track.

It starts to add up

1987 Jeep Grand Wagoneer engine block
Benjamin Hunting

With the engine issue solved—or so I thought—it was time to turn to the supporting players. Adapting the stock New Process 229 transfer case to the GM engine and transmission was possible, but expensive, and required a bespoke adaptor. Besides, my NP229 was the only part of my Grand Wagoneer’s mechanicals that didn’t actually work, due to a fried vacuum connection, so I decided to replace it with a cheap, $300 NP241c from a ’90s-era Chevrolet pickup—still a manual unit, so I could easily connect it to the Jeep’s existing linkage.

Next up were engine mounts ($165), built by Flop Shop and sold through BJ’s Off-Road, a Grand Wagoneer specialist I would turn to again and again while plotting the course of my swap. BJ’s also sold me the radiator I would need to replace the suddenly-leaking stock unit (all-aluminum, with a transmission cooler, $590), the injection-friendly fuel pump for the stock tank ($360), and the new gearing for the front and rear axles (3.73 to replace the 2.73 in the factory Dana 44s so I could take advantage of the LS power band and additional forward gear versus the departing 727 tranny), which cost me $630. Finally, when I realized that the stock, “maybe we’ll stop maybe we won’t” brake setup on the Jeep wasn’t going to cut the towing mustard, I broke down and ordered stainless steel brake lines ($195), and a hydroboost brake system with a new master cylinder to leverage the power steering system’s helping hand ($625).

With those major items out of the way, I turned my attention to dealing with the smaller but still crucial aspects of preparing for the swap. After a considerable amount of research, I realized that long tube headers simply wouldn’t fit my application without considerable alteration and that shorties were the sticker package of LS power adders. With that in mind, I stuck with the stock manifolds that came with the 5.3-liter. I also sent the engine wiring harness and ECU out to Washington’s Easy EFI Solutions to have it thinned and reprogrammed to function in the prehistoric, sensor-free AMC environment ($450). Finally, I managed to locate a gas pedal to graft under the Jeep’s dash, as the drive-by-wire setup found on the LMG wouldn’t play nice with a mechanical throttle linkage ($45).

Disaster strikes

As the boxes of parts kept arriving, I dropped the Jeep off at WeTune/AGM Performance in Lachine, Quebec. The racing shop run by Andrew Grubb had been solving problems on my 280Z track car for many years, and was open to the idea of an over-winter project. Andrew himself had owned a Wagoneer in a past life, and was confident in the simplicity of the swap process given just how primitive the stock Jeep drivetrain was, and how easy the LS was to Lego into an engine bay.

With my vehicle propped up on the lift that would serve as its perch for the remainder of the snowy months, Grubb and his team decided to go through the LMG engine prior to ripping out the 360. It was a wise decision, because it was here that the my apparent haste in snapping a good deal on a motor and transmission combo was revealed to be too good to be true. Although the inside of each cylinder bore was clean, and the engine itself was in good overall shape, one of the connecting rods was bent like a ’70s glam singer reaching for that elusive high note.

1987 Jeep Grand Wagoneer bent connecting rod
Benjamin Hunting

Disaster. Given that LS engines don’t feature balance pads, and that rods are installed as a balanced set rather than individually balanced themselves, I was looking at substantial machine work to ensure the condition of the crank, the harmony of the new rods, and the honing of the cylinders to go with the new rings and bearings we might as well do at the same time. Andrew pointed out to me on the piston where it had rubbed against the crank in the video the seller had sent me of the engine turning over (but not catching) with a battery connected directly to the starter.

1987 Jeep Grand Wagoneer crankshaft
Benjamin Hunting

After initially ducking me, and then eventually being shamed online by the local LS community into returning my calls, the embarrassed seller revealed that the engine must have hydrolocked from oil leaking into the piston after the roll-over and subsequent start attempt by the auction house he had purchased it from. Although we remain at an impasse as to how I will be made whole on what was presented as a fully functional engine, a used set of rods and pistons have been located, and after about $750 I should have a fairly fresh, 5.3-liter V-8 ready to go into my Jeep.

1987 Jeep Grand Wagoneer 5.3 liter
Benjamin Hunting

The fun is just beginning

1987 Jeep Grand Wagoneer connecting rods and pistons
Benjamin Hunting

There are always bumps on the road to any automotive project, especially when cross-pollinating a vehicle’s drivetrain with the fruits of another manufacturer. Although I had prepared myself for contingencies during the swap, I had thought they would occur much later in the process when fine-tuning the installed engine—not right at the beginning, due in part to my own poor judgment when purchasing a drivetrain. The thought that I could have selected a cheaper, higher-mileage motor and done the same refresh has entered my mind more than once, joined by the offers of guaranteed LS engines from friends after they learned of my predicament.

Still, I’m staying the course, and truth be told, I’m still quite excited about the entire thing. Dropping it off at AGM in November had me pause, realizing that this was the last time I would ever drive my Jeep under AMC power. That melancholy was quickly replaced by the anticipation of how completely transformed the truck’s on-road character will be this coming spring.

Trouble-free starts, the ability to pass both gas stations and slower traffic, and of course the fact that I won’t be fumigating my neighbors while the truck idles in my driveway are simply a few of the many benefits I’m looking forward to—after I spend the price of a brand-new compact SUV on marrying ’60s design with modern(ish) technology, of course.

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