SwapStang

The OP was saying the exact opposite of this. Run a dodge motor with an LS computer.

8+ years later it makes LESS sense. The OP talked about using an LS computer to run a dodge engine. Which I've seen proposed before for all kinds of other engines. The reason for the LS computer is they're cheap, plentiful and extremely easy to manipulate with a wide array of programming platforms. The Dodges still aren't on par with the LS PCMs even though there's a little more now than there was when this thread was started. California's laws run far deeper than just the OBD2 system. They are the toughest state in the country for emissions compliance. Tricking a dodge computer to not reporting a check engine light running an LS engine I would say is damn near impossible. I vote for a piggyback with a terminator IF this has to be done. With the time and money spent you'd still be better with an LS platform to begin with though. This thread never continued for a reason.....

BiskitzAnus

So, I gotta know how this is done!!! I've got the POS 2.7 CHRYSLER/DODGE MOTOR, was in my 2007 dodge Magnum. Tired of throwing my time and money away after 3 total rebuilds top to bottom and now finally turning to a 2005 Chevy 5.3 with shaved and ported intake, running on a 4L60e freshly rebuilt transmission. My issue is the wiring, I don't understand how anybody is piggybacking one computer to another? I want the dodge lights and cluster and fuel pump, but need to still have the computer for the 5.3 programmed with vats delete, but how do I piggyback them so that I can still use all the original car accessories????

SwapStang

If I recall correctly the OP wasn't even referring to this exact scenario so there seems to be some confusion here but the piggybacking you happen to be looking for has been done for a long time, especially if you factor in the pre-stand alone units. I guess the name in it itself is a tad misleading because piggybacking is exactly what it sounds like but you really want to run the computers in parallel for your application. You'd have one controlling motor functions and one controlling body functions basically. I had to do this in my mustang to get the gauges to work. I've seen other people do this to get away from a "key on" situation where it would time out if it didn't see engine RPM. You want to feed the Dodge computer some of the signals it needs to run whatever you're looking for. What I mean is if you want RPM you will have to find a tach signal and feed it into the stock computer. Same would go for oil pressure, coolant temp, etc etc. Not a difficult task but it can be time consuming. However as discussed if you live in a state where OBD2 compliant emissions systems are necessary you may not be able to get away with this. Do some research I'd bet money someone has swapped a Magnum out there somewhere. Good luck.

LS1 TJ

Just a thought. Lots of Jeep JK LS swaps going these days. You can buy a complete harness that integrates the LS to the Jeep. Runs all the stock Jeep stuff. I would research the Jeep swap guys, contact them and ask them if your Magnum close enough to a Jeep harness it may work. Both are made by Dodge.

BiskitzAnus

So,I am actually an ex TJ but current YJ, and DJ5 owner and have done the swap of the 5.7 into an 87 YJ and it's been close to 4 years since that Frankenstein project started and still doesn't start on its own, with painless wiring harness and I'm now ready to throw a 6.0 in it and junk the 5.7 for the headache it's become due to the injectors getting key signal and fuel, etc... But not a bad is as far as checking with painless, just kinda on a really tiny, let me be honest, zero cash flow budget and trying to work with what I have on hand or that I can make a quick call to someone who might have what I need that I can trade for or pay later. Off subject... Any thoughts on why the injectors won't signal after fully wired and turn the key on the YJ???

BiskitzAnus

So, how do I make the two brains come together I guess is what I'm asking. If I run dodge body and ignition but run gm motor how do I wire them so that they don't fight each other. What do you mean as far as parallel, just tap into the power on the doge and run to the hot for the GM? And what do I do about the dodge controlling 6 cylinders when the 5.3 is 8 ??? This is a new one for me, I've checked atleast a half dozen shops and even with our local LSpros shop and nobody seems to of even considered doing what I'm doing. They all think it's awesome a girl is even attempting to do what most men won't even dream about accomplishing. I just need some solid advice so I can feel more confident that I didn't make a huge mistake by doing this swap.

LS1 TJ

On my LS swapped Wrangler the LS ECM runs just the engine. The stock Jeep ECM runs the rest of the Jeep. My stock speedo works because it gets its signal off the transfer case. When I did my swap about 12 years ago there wasn't an interface for the LS to Jeep tach signal so I'm running an aftermarket tach. Today there is. Oil and temp gauges are just a matter of switching the senders on to the LS engine. Took the bulb out of the check engine light in the gauge cluster.

BiskitzAnus

Okay, I'm starting to understand a little better the whole piggyback power jumping/coupling the two brains, my problem or misunderstanding is with how I should feed one to the other. Am I supposed to completely cut the connected plugs for specific accessories that will be for running on the dodge ecm, or do I just splice into the GM harness and kinda join the two but basically the GM is just mating up to the existing dodge harness, where necessary, and everything is technically running from dodge ecm. Or do I get power for each individually from the battery or fuse block. Also, in the standalone harness, it shows everyone doing 12v constant and 12v switched on all the damn pink wires, how in the hell do I know which are switched and which aren't based on a diagram??? I'm no dummy and I'm pretty intelligent, most days, haha, but I'm kinda overthinking this whole project I think, but I just st don't want to have to do this again, repeating the same mistakes is killing my mechanical mojo and I'm ready to throw some wrenches at this damn car.

SwapStang

It sounds like you got the motor into your jeep and have some basic knowledge of the mechanical workings so I wouldn't call your mechanical mojo into question, maybe just your electrical mojo! haha On my first swap I actually put the entire car together with the turbo kit and everything before tackling the electrical portion of the swap because it seeming so overwhelming. After doing it it really wasn't that bad.... and now I've done several and helped a few friends along the way. I think I can depin a stock harness in my sleep at this point. For me the best way I've come to think of these swaps is the engine is basically stand alone. What I mean is it could basically run on it's own with 12v. That was the beauty of the way GM made their harnesses in my opinion. Remove the things you don't need, disable the VATS in the computer, give it fuel and these things will run sitting on a stand or on the ground. Apply that to the swap and that's basically all you are doing. Tying in the wiring combined with the fuel system is what completes the swap and makes them work together in my opinion.
So the wiring.... you're asking about the 12v constant and 12v switched. Read through Lt1swap.com about making your own wiring harness and he explains a lot about how it works. He even has a video where he thins out a stock harness step by step. Even if you don't make your own its really helpful to just understand how everything works and that may sway you to make your own or buy one. Now most of the basic ones you buy will come with a 4 place fuse block and 1 relay. The relay is how it handles the 12v run and start to power the things that don't need constant power but need to be on with the key and stay on during the starting process. What you would need to do is provide 12v constant to the fuse block, which should just run right to the battery, then provide a 12v switched or triggered hot with key on and in the starting position of the key. It is very important that it remains 12v while the key is in the starting position because if it cuts out during it'll just crank and never fire because all the things that need to be on at that moment will have turned off. At the very most basic that will be PCM, injectors and coils. Obviously necessary things to start an engine. The PCM also has a 12v output to control a fuel pump relay so more than likely that will also have to be wired in unless controlling your fuel system is done another way. This is to get a running engine in the vehicle. After that its just integration to get things like the gauges working etc etc. Sounds like a lot, but once you understand what the engine needs to run it really isn't. I always find the hardest wire to find is that 12v hot in run and start trigger wire. This can be cheated as well by wiring the starter to a button which I have also done but I won't confuse you with that. As for your jeep if you already have a 5.7 I can't imagine switching engines will help your electrical issues, just find what you need and get that thing running it really shouldn't take much if it's already installed.
Sorry so long winded but I hope that helps. Nothing worse than struggling with electrical questions or issues. Good luck.

LS1 TJ

Just FYI on the start and run power. I found a fuse in the stock TJ fuse block and piggy backed off that for the 12 volts in start and run. Been fine for over 12 years.
2X on the 5.7 or 6.0 same ECM (depending on the year of the engine and trans).