V6 to V8 swap?

[Black04LS]

First, let me give some back ground info. I have a 2004 LS V6 that was bought used in June 2006 with 29,000 miles. It's currently at 170,000 miles. The engine was replaced with one from a wrecked car in the spring of 2007 at 63,000 miles due to a screw up at an oil change joint, and it's still running fine, well, sort of... Despite that I just did plugs and new coil packs recently, it still has a bad miss-fire on really cold mornings and it's in general getting terrible gas mileage, but at least the constant miss-fire it had is gone.

The transmission started going screwy at about 125k and continues to do so at 170k. Holds out shifts and then jerks violently when it does shift, sometimes it refuses to shift and you have to put it in D4 and put the pedal to the floor to get it to straighten up. Sometimes the car starts miss-firing in a manner that almost sounds like it's doing it on purpose, looses all power and won't go faster then 20 mph. A little wrench light flashes on the gauges when it does this. Have to shut the car off and start it back up, then it runs normal again.

As for the body of the car, the suspension is still tight and rides great. The steering has play in it though, however I can't find anything loose or worn in the suspension, so I assume it's a problem with the steering rack itself. It also has a bit of body damage where someone backed into the drivers side door.

So to the point... I found a guy that is selling a totaled out 2003 LS V8 for very cheap. The engine and trans are in great condition and relatively low mileage.. Has good doors, some interior pieces I need that are worn in my car, etc. So I'm thinking about picking it up and swapping the engine, trans and everything over to my '04 to freshen it back up. Need this car to run at least another 100k miles.

I am very mechanically inclined and have no doubt about my aptitude when it comes to physically being able to swap the drive train, as I have done engine swaps in several older cars and trucks, however I'm just wondering what I'm getting myself into as far as interchangeability goes? Will it be pretty much plug and play with the harnesses and PCM, or what? What about the exhaust? Keep in mind I'd have the complete donor car available to take what ever I need.

Any input is greatly appreciated.

 

[Quik LS]

it's possible but will include much more than just the drivetrain, exhaust, ..etc. Not sure about driveshafts, but suspension is different for rates (anti-sway bar, shocks, springs, ...)

THere are many threads on this - if you can spend some time reading through those...

but in short - much of the electronics are different/matched - even the gauge cluster. If you have a complete donor car - then you stumble through the swaps - which would include wiring harnesses, pcm, ...etc.

 

[Outkast]

be better off swapping your good parts to the wrecked car..

 

[Black04LS]

That's not feasible for a number reasons, including the fact that the wrecked car is totaled with a salvage title, it's hit in the front and rear. My car has never had any structural damage, clean title and currently registered and driven daily.

 

[SoonerLS]

Swapping in the V8 is a no-go on the practicality front; it can be done, but it's not going to be cost-effective.

Now, one possible solution to your problem is repairing the dreaded V6 PCV elbow. That can cause misfires, and misfires could be the root of all of your problems, including the transmission problems--if there's a misfire, the engine power goes down, the transmission sees that as a signal to shift, then the power comes back while the transmission's in mid-shift, and things get ugly.

When you can't get over 20mph, you're almost certainly in ETC Failsafe mode--the PCM determines that there's a failure in the electronic throttle control (ETC) system, so it drops it to a minimal throttle position to keep you from being stuck with a run-away. In the V8s, this is normally caused by a failure in the COP on cylinder #4--the RF interference throws a false ETC failure code. In the V6, cylinder #3 may be close enough to the PCM to do the same thing, but replacing the COPS should have taken care of that. (V8s will tell you when the car is in ETC Failsafe, but V6es don't have th eMessage Center to display the message.)

If the transmission is really broken, you could take the V8's trans--it's the same 5R55S that's in your V6.

 

[Right on the Mark]

The v8 and v6 trans have a way different bellhousing bolt pattern and will not interchange.