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Now I’m familiar with engine swaps and where they can be useful, but the idea behind the engine management system throws me off.If for example , I have a stock engine in my 2008 Chevy impala , then I decide to install let’s say a k24a4 into my impala , will I need to get a whole new ecu with the engine management software already installed on it? or can I just install the engine management software on my oem ecu? , and if so where would I even get the engine management software for the engine? and how would I install it on the device?. I have a lot of questions , please try your best I’m just really looking to understand this concept.

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    How about get the matching ecu with the engine you buy.
    – Solar Mike
    Mar 19, 2019 at 6:19
  • That is a simple answer thanks , but is it possible to upload the engine management program on my old ecu ? Mar 19, 2019 at 6:29

4 Answers 4

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There are 3 options:

1) use the ecu matching the engine

2) purchase a third party tuning ecu and get it programmed to suit

3) have a tuning company re-program the existing ecu from the old engine - this may or may not be possible - they will tell you

For all 3 you will probably need the dealer level computer software to code the ecu to the engine and security ie keys etc

1 is likely to be the cheapest but I have no figures for the others - check out the performance tuning companies...

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GM engine management software (from your old Impala ECM) is not going to be able to run a Honda engine. If you managed to flash the Honda software onto your GM ECM, you'd likely brick the device.

A Honda ECM - which you'll need to run the new engine - is not going to talk to your BCM. Even if you could get the thing plugged up correctly, which is going to require a ton of electrical work, compensation for missing or extra components, etc., you wouldn't be able to start the car unless the ECM and BCM can talk to each other and are speaking the same language. That is most definitely NOT the case here.

Installing an engine from a different manufacturer is non-trivial. I would not recommend that you attempt this unless you can find a kit for installing this engine in your car that includes all of the necessary electronics, wiring harness, etc., or if you are an electrical and automotive engineer that's done this before, or if you're happy with the car sitting for a year while you figure all of this out.

You need to think about things like O2 sensors vs wideband sensors, ignition coil differences, variable valve timing - Honda and GM's systems are very different.

This is a huge project.

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    Yours is the correct answer. Mike assumed it was another GM engine...
    – Moab
    Mar 19, 2019 at 21:13
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With modern "engine" swaps, it is very easy to miss the point.

What you traditionally think of as an "engine" is really not much more than an air compressor.

The beating heart of the engine is actually the "bundle of" the fuel induction system and the so-called emission control systems, which are really part of the fual system these days. The ECU and everything it connects to -- from the MAF sensor clear down to the trailing oxygen sensor, from the evap canister to the smog pump. ALL that stuff. Stuff that most people think is trivial, annoying, or "best torn off". That attitude needs to go back to the 1970s because it's all integrated now. It will run worse with anything missing.

That system has some tolerance for variation in the "air pump" part. E.g. a common Miata hack for fuel economy was to fit the 2-valve head from the Ford Aspire. The ECU just went "huh, OK" and adjusted accordingly. It worked.

However, all that stuff has to match and work.

Or your car will run like crud if it runs at all.

You can't create a Frankenstein with some ECU/smog stuff from the donor engine and some from the original car. That package is just not gonna work. Nobody is that good at customizing! (it might be possible on simple systems like EVAP Purge, or maybe, EGR).

That means you need to be "all in" with one or the other. And usually, you have a fitment problem, e.g. where you can't physically adapt the vehicle's EGR to the donor car's engine. Or the injectors won't fit. Or the smog pumps work a completely different way. It ends up being an integration nightmare.

And believe you me, there'll be plenty of integration challenges already!

Take everything from the donor car

So the best option is usually to take ALL the systems from the donor car - again from evap to smog pump, MAF to trailing O2 sensor - and move them as a single unit. Together. When I installed my conversion, I didn't drain the motor oil, and I didn't disconnect the ECU. There was no need to do so, it was part of the engine package I swapped. And this is actually easier because you're not having to mess with any of those systems.

Believe you me, there'll be plenty of integration challenges. I think there were over 20 interconnects between my new engine package and the body. And I followed my own rule of "take over everything".

Including the EVAP canister. Really. (if you don't know why I said "Really", you may need more skill.)

When I say complete, I really mean complete.

Transmission too. Modern transmissions are so electronically integrated with their ECU that it would be a Manhattan Project to adapt dissimilar transmissions. It is much, much, much easier to have someone machine custom driveshafts.

In my conversion, I didn't separate the engine from transmission, and didn't drain fluid from the transmission. No need.

Getting it to pass smog

Yeah. You can do that. Really.

Generally you need to follow the top 5 rules of swaps:

  • Donor engine must be same year or newer model year
  • Donor engine must be same or lighter class (car vs light truck vs heavy truck)
  • ALL emission controls must work and match the donor engine (isn't that what I just got done saying?) You change the emissions sticker on your hood to match the donor engine.
  • Diesels ONLY if your same model and year was offered in a diesel.
  • Electric conversions remove the fuel tank and never need smog again.
  • Swapping an engine from your same model and year doesn't even count as a swap. So '93 Camaro 4-cylinder to LT1, just do it.

If you are in smog country (CA and the 11 other states that follow CA's scheme), you will need to see a special smog referee for them to inspect that the conversion was done correctly. This is a one time thing.

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So I do swaps all the time and by that I mean for example swapping a Mercedes amg engine into a non Mercedes car. You can do one of two things here. 1. Use a stand alone aftermarket ecu or 2. Reprogram the ecu immobilizer. The first you can do yourself the second cheaper option you will likely need to send it off. Now as for someone on here saying in either case it won’t work with the rest of the car unless you buy a kit or something they couldn’t be more wrong. All you need is the wiring diagram from both the donor car the the engine came from and the recipient car. You will need to connect the proper wires to the proper sensors or secondary modules which is simple to do. In those instances where you are connecting to a module you need to use the proper interface I.e. is it canbus or is it just an analog signal wire that measures resistance vs getting a digital signal. If it is canbus you can get a canbus mstandalone box or use an arduino that allows you to set each input connection to whatever type the input is and translate it to the output type. The reason this can all be done is because after 1996 all cars in the US use OBD2 and there are only two canbus standards.
Now is all of this easy? No but it’s not difficult either. Rather it just takes time, patience, and varying levels of work and frustration to get it to work. But it’s all worth it in the end if you are building your dream build for a car. If you can’t do it then that’s why there are guys like me that you can pay to do it for you. You will find plenty of tuners and builders out there that do everything from the mechanical to the electrical and will even build custom harnesses and make custom wiring diagrams for your car. Is it cheap? No but neither is it cheap if you DIY it either because all that time you spend doing it can be equated to money. Hope this helps as it’s coming from someone who actually does this and has done it with so called impossible engines to boot.

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