L83 engine swap summary, finally getting to the finish line

[2015TahoePPV]

I've been using ChatGPT 4.0 as a research tool as I did my swap, the nice thing is that it "remembers" things, so I was able to get it to make a summary, which I tweaked quite a bit.​

2015 Chevy Tahoe Engine Swap – What Went Wrong & What I Learned​

So, you’re thinking about swapping an engine in your 2015+ Tahoe? Let me tell you what can go sideways—so you can avoid a week of frustration, fuel trim nightmares, and talking to your truck like it owes you money.

The Backstory​

I've had my truck since the Covid "there are no used cars available" madness. I bought it with 126K on it from Chicago motors. Fourth truck from them, good folks. At the time of failure, the engine had 14,000 hours on it, mostly idling to keep the dog cool, and idling at crime scenes. The initial failure? AFM failure, P0306 (misfire on cylinder 6), thanks to a collapsed lifter on the intake valve. That lifter had one job. It failed.


Wanting a fresh start, I chose a remanufactured engine from Accurate Engines. Unfortunately, I found out after the fact that they have some reputation issues online. To be fair, my experience with them has been fine, they built the engine without the AFM components and handled my ECM programming for ~$4300. They built/ shipped the engine in 2 days, I borescoped all of the cylinders, all of the torques were good and marked, I don't have anything to nitpick on their work. Obviously, I’ll update as I get more miles on the new motor.

The Swap & The Fuel Rail Disaster​

The long block came bare, so I swapped all of the externals over from the original engine. Everything was going fine—until we removed the passenger-side fuel rail. It was so stuck that when we finally pried it off, we:

1. Destroyed the rail.
2. Probably crushed the injector wiring harness between the pry bar and the rail. The insulation is that soy bases rodent attracting stuff from the factory, so its weak after 10 years of baking in there on a good day. Remove the wiring before prying, duh.
3. Created new problems before the engine even fired up. Once I swapped the harnesses, I verified all of the pin outs and resistance for all 8 injectors. I had installed 8 "new OEM" injectors I got from Ebay for $125....red flag

After replacing the harness, the misfire codes were gone—but that just unlocked the next level of headaches. Oh yeah I also had left the #8 coil on finger tight, oops.

Counterfeit Injectors & The Knock Sensor Grounding Issue​

With the misfires gone, I still had some major issues. The truck ran ok, but didn't idle as smooth as I would have liked:

• Codes: P0430 (Catalyst Efficiency Below Threshold - Bank 2) & P2099 (Fuel Trim System Too Rich - Bank 2).
• Long Fuel trims were still way off (-14% on pass bank, -3% on the other).

Turns out, I had counterfeit injectors that were completely messing up fueling. After swapping to verified GM injectors, the trims evened out, but then…


Enter the knock sensor errors:

• Codes: P0324 (Knock Control System Error) and P0325 (Knock Sensor 1 Circuit Malfunction)

The Knock Sensor Grounding Issue – Lessons Learned​

Alldata says if you're getting these codes without other ones, its almost certainly a physical connection fault with the circuit. The problem? Knock sensors use the engine block as their ground source. Since I installed a reman engine, the block was coated in aluminum paint, which meant the sensors couldn’t properly ground. I also had a weird wire routing issue around the starter for the pass. side sensor.

Fix:
✔ Removed the knock sensors, starter, front driveshaft, etc. Scraped the paint off the mounting points, and torqued them to spec.
✔ Once properly grounded, the codes disappeared.


Bonus Tip: These engines have ground issues on a good day. If you’re swapping an engine, take extra time to scrape and clean EVERY ground connection before bolting things down. It can save you from chasing electrical gremlins later.

Catalyst Code P0430 – The Final Boss​

Once the fuel rich issues were fixed, the truck finally admitted the passenger-side catalytic converter was cooked. The signs were all there:

• The original fault or the following long-term fuel trim issues likely ruined the converter over time.
• Self-test failures eliminated the O2 sensor as the cause, pointing directly at the cat.

Temporary Fix: The Anti-Fouler Trick​

Rather than dropping $$$ on a new converter immediately, I installed a spark plug anti-fouler on the B2S2 O2 sensor. It’s not a forever fix, but it bypassed the P0430 code while I decide my next move.

Lessons Learned (So You Don’t Suffer Like I Did)​

✔ If your Tahoe has 14K idle hours, it’s probably on borrowed time.
✔ Be careful removing your fuel rails—remove the wiring before prying, verity the wiring is ok before reusing
✔ Avoid eBay injectors like the plague. Fake ones will wreck fuel trims and cats.
✔ Knock sensor issues can be caused by bad grounding—scrape the paint off your new block!
✔ If you’ve had a long-term misfire, your catalytic converter may be in trouble.
✔ Anti-foulers work as a temporary fix for P0430, but you still need a plan.
✔ Before bolting things down, scrape and clean every ground connection. These engines are sensitive to bad grounds.

Final Thoughts​

What started as a simple engine swap turned into a mystery thriller featuring lifter failures, fuel trim conspiracies, and a catalytic converter betrayal. Hopefully, my misery helps someone else avoid these pitfalls and keep their Tahoe on the road.

The L8T swap with a lower mile donor engine is probably a viable option over a reman, cost and peformance wise.

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