So you swapped out an LLT Direct inject engine for an LFX engine it sounds like.
Also sounds like you used the wire harness and PCM from the original engine.
in 2012 the LFX is a different engine. Your biggest issue is that they changed PCM's between 2011 and 2012. The tune for the LFX is different that the one in the LLT and you can not burn the tune from the 2012 PCM into the 2011 PCM as they are not compatible.

The easiest solution is to use the sensors, wire harness and the PCM off the donor vehicle. You will have to change the VIN in the PCM to match your car but not a big deal.
The LLT also had a typical exhaust manifold, the LFX has an integrated exhaust manifold into the head thus the squarish port it has coming out of the heads which then has a down tube and not a manifold connected to it.

There are other ways to do this but the least hassle is to just use the original wire harness, sensors and PCM, assuming it was out of a CTS it should be totally compatible with the 2011 as a unit.
You could be chasing demons in your tune otherwise for the time you have your car.

 

So you swapped out an LLT Direct inject engine for an LFX engine it sounds like.
Also sounds like you used the wire harness and PCM from the original engine.
in 2012 the LFX is a different engine. Your biggest issue is that they changed PCM's between 2011 and 2012. The tune for the LFX is different that the one in the LLT and you can not burn the tune from the 2012 PCM into the 2011 PCM as they are not compatible.

The easiest solution is to use the sensors, wire harness and the PCM off the donor vehicle. You will have to change the VIN in the PCM to match your car but not a big deal.
The LLT also had a typical exhaust manifold, the LFX has an integrated exhaust manifold into the head thus the squarish port it has coming out of the heads which then has a down tube and not a manifold connected to it.

There are other ways to do this but the least hassle is to just use the original wire harness, sensors and PCM, assuming it was out of a CTS it should be totally compatible with the 2011 as a unit.
You could be chasing demons in your tune otherwise for the time you have your car.

Brother I feel your pain . Man I went through the same exact thing with my 2011 CTS . Bought another 3.6 from an auto shop that had a CTS coupe that had been rear ended pretty bad , but the engine was perfect and only had 43,000 miles on it . I’ve swapped a few engines in my life, but never on a Cadillac…lol. So, the technician promised me everything would bolt right up and hook up the way the original motor did and after pulling it and looking at it, it looked identical. let me just make this story as short as possible. Got the motorhome. Dropped it in . It Bolted up perfect. The transmission bolted up perfect. Started putting the wiring harness on. Everything was snapping together perfect until you get to the last few plugs and start realizing you got leftovers so I look up the wiring harness diagram on both models and spent hours trying to figure out what was missing and what was going on . So I called the mechanic and he says it’s like doing an LS swap that I’ve gotta find a new intake , a plastic one off of a Camaro or something because that was gonna be the problem . So Iget one from a Pick and Pull and put it on . That was only one plug out of about four or five that still needed to be plugged in somewhere then realizing it was a direct injection motor, which has two fuel pumps, one in the fuel tank and one on the back of the motor which needed to be plugged into and had no plug because my original car was not direct injection . So I go to buy a new wiring harness for the car and find out they don’t make them anymore , they’ve been discontinued by GM for that year model motor. I start searching the Internet and find one in Mission Texas for 750 bucks at a shop that says they were fixing to ship it back to GM. It was in the box with stamps ready to go. I told him I wanted it and got it shipped to me ,installed the new wiring harness and everything was plugging up perfect . The car was turning on but the engine would never fire , so I called the mechanic and he said it’s gotta be the ECM and I told him it was ridiculous that he told me this wasn’t gonna be a problem when I bought the motor and now I have to buy a new ECM after paying 750 for a new wiring harness also he said he would give me the ECM out of the car the motor came out of , but he normally charged 400 for them, so I picked it up ,installed it and it still was not turning over . I finally was able to get a hold of a certified Cadillac technician at Sewell Cadillac of Dallas and he informs me that the ECM , BCM , PCM and Key would all have to be flashed together with special software in order for the car to start and function properly .The whole time I’m doing this I’m paying for a rental car and it took almost 4 months before I finally gave up and sold the car for $1,000. A complete loss . That car was immaculate…except for the motor problem , lol. Never again !! The best part of the story is I went out and bought a 2013 CTS coupe that I’m in love with. Absolutely beautiful car , the only thing that would make it better is if it was a V model, lol.

 

Thanks for the info, i been searching the web and it seems you are correct, only problem is i chopped the donor harness near the back because it was connected underneath, gonna be fun fitting all those back together lol. Also i was reading that i will have to swap out the transmission as well because of a compatability issue with the different years. Do you know about this?
And lastly, exactly how does one change the vin to match the pcm?
Side note, I do appreciate the single exhaust manifold ports on the lfx head. Makes me want to explore turbo install later on with the additional room and simplicity of the manifold.

 

Should still be doable as is. My understanding is that your original wiring harness is in use. If that is correct, you only need to make sure your wiring harness is plugged into every sensor it needs for your on board computer. Next you need to make sure that all sensors in use are compatible with your engine management system, in other words, continue along the path you did with the throttlebody. Extra sensors not used with your original management system are not a problem, leave them in place where you can and ignore, like the MAP sensor.

After the above is taken care of, you need to find someone who can tune the car, or buy the HPTuner equipment ~$500 and do it yourself. Since the injectors are upgrades (LLT & LFX has different injectors) from the old motor, you don't know exactly how much fuel they flow, couple that with the fact your original computer does not know either and is pulsing them as if they are the original. If they flow more than the original, your baseline pulsewidth will deliver too much fuel causing misfires.

There are also efficiency improvements that a tune can account for as well. The LFX has some differences, but not so much that it needs its original computer to run properly, you simply need the fuel delivery mismatch areas addressed and HPTuner's scanner program can identify that easily since the motor runs and data can be logged of the fuel trims to identify where fuel is too much and too little.

The above is what I'd do, make sure all necessary sensors are in place and the correct ones and then tune it, or in your case if you don't have the equipment, or know-how pay someone onsite to do it. I would not put the 2012 harness in that car because I know all of the pin assignments are not exactly the same from a swap thread I read up on some years back.

 

The original (LLT) wire harness was like 95% plug and play with the LFX engine that i swapped in.
The differences are as follows:
1) no map sensor connector
2) one sensor wire thats attached underneath dipstick area, was further down on the lfx engine
3) the throttle body connector was different
4) the air tube/purge valve was connected differently but plus the same
5) the fuel rail assembly is different, but connector is same

Everything else lined up perfectly in the same position, with the same connections, so much so that i could snap them in with my eyes closed. That being said, i think my only option is to actually switch out the harness

 

Everything else lined up perfectly in the same position, with the same connections, so much so that i could snap them in with my eyes closed. That being said, i think my only option is to actually switch out the harness

If you're saying the sensor plug ease of connectivity is a good indicator that the PCM end connections/pin assignments (between two entirely different PCMs) will follow the same trend then go for it. Make sure you consider the transmission portion of the harness also, those two computers are different as well.

Just because the harness plugs match in location on the sensor end, doesn't mean they match on the computer end.

You have 3 codes now, and if the car was drivable, there's no guarantee you wouldn't end up with a few more that need to meet more parameters before they set. Further more, changing the perfectly good native wiring harness to a damaged donor, that you intend to repair could result in the exact same codes plus some extras.

Think long and hard. I'm raising concerns for your benefit from my experience with what I've encountered over many projects of this nature and what I've read about the system you're working on.

 

After hours of searching and watching videos and reading articles from guys who have done the engine swap, it is now conclusive that to swap out the LLT engine to LFX engine, you MUST change the ECU, HARNESS and TRANSMISSION, this is with 100% certainty, the reason is the LLT is Bosche and the LFX is Delphi which is 2 entirely different systems and because of the bosche encryption it is just not compatible. I would have loved it to be as simple as swapping the engine out and then programming it to correspond accordingly.
I suppose it is possible only to get a map out of the wires leading to the ecu, cut them at the connect port and create a new ecu connection to match the new ecu. That way you won't have to remove and replace the harness but the time and energy may ultimately not be worth it. Fortunately i have a full donor car so i can change the ecu and transmission and not have to flash anything. Its just a dreadful amount of work. I truly believe pulling the original LLT and doing an overhaul would have been far less of a headache and work. I literally stop many times looking at the engine sitting in the corner wondering if i should just stop and fix it instead

 

I truly believe pulling the original LLT and doing an overhaul would have been far less of a headache and work. I literally stop many times looking at the engine sitting in the corner wondering if i should just stop and fix it instead

Just take the LLT heads and get them thoroughly broken down, cleaned and prepped and put them on the LFX short block and take the benefit of the extra tenths of compression increase and call it a day.

 

Lol, if i still had the LFX out and sitting i probably would take your advice. But its already sitting in the bay. And ive just finished pulling out the tranny from the donor car as we speak. Im too far gone in the project now, tomorrow ill just sit by my pool side play some music and work on repairing the harness. Got a nice wire repair kit off amazon that should make the job easier. I suspect i should have the harness, transmission and ecu installed by Thursday and at least drivable by the weekend. Im kinda excited to reap the benefits of the swap now that im this far gone. Will definitely be tuning for maximum output as soon as im done and adding twin turbo chargers in a few months. The single port exhaust out the block makes it perfect to put two there and still leave room for furniture.

 

Will definitely be tuning for maximum output as soon as im done and adding twin turbo chargers in a few months. The single port exhaust out the block makes it perfect to put two there and still leave room for furniture

Keeping the increased torque loads associated with turbos in mind, did you know you're switching from a 6L50 transmission down to a 6L45 transmission in the 2012 model?

 

Hey guys, so im here again to give an update. I got the LFX to successfully work in the LLT. Long story short, the LFX will work if you simply use the LLT fuel rails, injectors and fuel pump mounted at the backside of the engine and just swap them over on to the LFX engine. Thats all that is needed. While doing the swap over the fuel rails will be a little tight to come out, but with patience and wiggling they will come out. The fuel rail clearance will be cause you to have to shave a bit of the (lfx) plastic manifold at the back where one of the aluminum fuel lines comes up a bit high and also either the fuel rail sensor will have to be shaved rounded or shave a bit off the inside area of the intake on cylinder #1. I did both and it gave me the clearance it needed. I will write up the full detail on another post. But for anyone looking to do the llt to lfx swap, dont bother with wire harness change, dont bother with ecu change, or transmission change, just swap the fuel rail and fuel pump and injectors coming off your llt motor onto the lfx engine before you put the engine in, its far easier to do with the engine out the car.

 

This is a topic that many have wondered about, however info was limited, which caused my trial and error into successfully making it work.
Quick intro on the engines before i detail how to swap them successfully. While this works for the cadillac cts, it will also work for camaros and commodore alike that uses the same engines
Intro-
The LLT and the LFX engine are used in the 2008-2011 and 2012 to 2014 respectively.
The obvious difference between the two are the intake manifold and the exhaust manifold/ports. The LLT carries an Aluminum intake manifold and 2 three port exhaust manifold bolted on each side. While the LFX carries a plastic intake manifold with 2 single port exhausts. Other notable differences are the map sensor on the lfx manifold, the ecus. The LLT is built on Bosch system (hard to tune) while the LFX is built on Delphi. The fuel system is also notably different with the LFX being a high pressure fuel system.
Trial and Error-
I had swapped over an lfx engine from a donor car into my LLT, it fired up successfully but then threw multiple codes and misfired like crazy. After reviewing some forums i decided to swap over the wire harness and the ecu and the transmission, all from the same donor vehicle as well. This did not fix the issue and in fact, the car would simply not start ( dash gauges would just go up then back down.) After more research, i decided to get the donor ecu vats deleted and get the bcm from the donor car installed to match the ecu and also change the transmission. My chain of thought at this time was that if i swapped everything then the system would recognize itself as the lfx donor car. Well this also did not work and made matters worse as it triggered the cars anti theft system. Even brought the car to the dealership to see if they could somehow integrate it on a software level but they were unsuccessful.
Successful Route -
After all that work and failed attempt,and almost feel defeated, i decided to explore the possibility of swapping the fuel system. I swapped back the transmission, ecu, wire harness, bcm back to the original LLT and swapped over the LLTs fuel system to the LFX and sure enough it worked like a charm. Use LLT throttle body on the LFX intake manifold as well
Details -
The fuel system between the LLT and LFX are different, the LFX carries a high pressure fuel system and as such feeds too much fuel for the LLTs tune. Switching over the LLTs fuel rails, fuel injectors, and fuel pump unto the LFX engine will allow the engine to run without tune as if it was the original LLT engine. The fuel rails will be a bit stubborn to remove but with patience and wiggling and angling they will come out. The passenger side fuel rail came out with removing the water/coolant hose out the way at the back and angling the front part of the rail upwards while moving the rail backwards. I also found success with removing the passenger side rail first. For the install, i placed the injectors in with their wiring first, then lubricaded the rubber seals and then once the rails were successfully possitioned over them, i slowly bolted the rail down evenly and allowed the force of the bolting process to do the work of fitting the rail on the injectors. The fuel rail sensor, which is on the passenger side rail at the front had to be unscrewed during this process. It does not refit without shaving it rounded. You can alternatively chose to shave the edge of the cylinder port 1 to get the clearance you need. I did both with an angle grinder and diamond blade and got good clearance. You can also use an angle grinder. Make sure all holes are taped to protect from the metal shavings. The back part of the plastic manifold has a bolt hole for the fuel line shield to attach to on the driver side, i had to shave that off completely as the fuel line would cause it to not sit properly. I also had to shave a bit from the underside of the plastic manifold where the fuel rail sensor would touch. A good trick is to use thick grease wherever you think touching is happening and place the plastic manifold down and when you remove it, there will be grease residue where you need to shave. If you dont have grease, use peanut butter. Once the fuel rail is installed, its just a matter of reinstalling the lfx intake gasket and bolting down the intake manifold accordingly. Dont worrk about the MAP sensor on top of the manifold, just leave it as is, the LLT MAP is integrated in the throttle body sensor. Once done your car will fire up and should throw no codes at all as mine did not.
Notes-
The fuel rail system will certainly be much easier swapped if it is done while the engine is out of the car. The engine is made to be removed with the cradle but as i had no hoist, i unbolted it from the transmission and lifted it out the front with an engine lift. To do this you will remove the front wheels and axles (plenty of youtube videos on this), unbolt engine mounts from underside. Remove starter and remove the 6 flyweel bolts from transmission. Dont worry about draining engine or transmission oil, you dont need to. Only coolant will be spilled during this engine swap.
When removing the engine from transmission, there will be a bolt difficult to remove from the top left on the bell housing as the water hoses at the back are in the way and need to be removed. The bell housing has many bolts and this one does not need to be reinstalled if you want to save yourself headaches in the future IF you need to some how remove your engine or tranny. There is also a sensor at the driver side of the engine near the dip stick that you will need to extend wires for. I believe its the oil temp sensor, i just cut it off my donor wire harness with lots of wire to spare and connected it. The wire color codes are the same so dont worry. I unbolted my a/c compressor and moved it over to the side where my air filter box sat so i didnt have to open my a/c lines (i removed air filter box). I also removed my radar and fan for clearance but realized i really didn't need to. Of course your rad hoses need to be disconnected and your strut tower brace at the top needs to be removed for the engine removal. There are a few videos on YouTube that will help with the engine removal process.

 

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Its being set as as an independent thread because it is not a map issue, it is its own writeup now on how to successfully do the swap