I’m guessing the 3.4 will drop right in, considering it’s the 3.1’s big brother
That said . . . what about the pcm?
I’m anticipating some possible problems, because the pcm won’t know you’ve now got a 3.4 under the hood
pcms usually have different programs and/or calibrations, to reflect different engines
Might have to use the pcm that goes along with the 3.4 . . . whatever donor vehicle that happens to be from
I was thinking that, and I’ve gotten everything from I should use the donor PCM to don’t do it. The best advice I found was a few guys who were doing swaps on them, who advised heavily against it, having dropped a 3.4 in place of a 3.1. What they were saying was the 3.1 PCM worked fine on the 3.4, and they decided to go use the 3.4 PCM to get that extra power. What they found was the PCM from the donor didn’t play nice with the body computer, and vehicle wouldn’t start, until the recoded the donor PCM to match the VIN of the receiving vehicle. That said, the argument was either way will work, and it’s a if you can live with the 3.1 PCM, it’s easier, if not, then you’re facing reprogramming the parameters of the 3.4 PCM. If I was more involved in this, and had some money to invest in programming hardware/software, I might mess with it. But, I’ll keep updating what I find, as very few actually post the results of the details that tend to be problematic.
Reprogramming the pcm . . . either the 3.1 pcm or the 3.4 pcm . . . shouldn’t cost more than an hour labor at your local Chevy dealer, I would think
That is assuming it’s even possible . . . I mention that, because I believe the 3.4 was never an option for your 1999 Malibu
No, the 3.4 was never offered as an option, which is what made me wonder. Then I found the 3.4 is a bored/stroked so-to-speak 3.1L. That made me think it’ll work. The junkyard dogs all said it was a bolt-in replacement, but I still wasn’t convinced enough to spend $250 for the 3.4, so I consulted Google, (because if it’s on the net, it’s GOT to be TRUE! J/K) and referenced a bunch of different people saying it’s possible, but haven’t done it themselves, and had own ideas of problems.
Then, I guess some bored mechanics had one from an 02-03 grandam laying around, and for some reason decided to put it in a malibu. So to shorten the thread, they looked it over, decided it looked like it should work, & put it in, thing fired ul and ran fine. So, then said bored mechanics started changing things out, like PCM’s and a couple transmissions, and started documenting what was going on in that thread. They finally decided that leaving it as a bolt in motor, not changing the PCM was the easiest. I guess when they changed the PCM to the 3.4 PCM the VIN wasn’t syncing with the other computer, and threw a code, kept fuel pump off. I found that on one of the grandam forums from '05 era. This made me think it’ll work, so I’m going to pick it u tomorrow.
Like I said, I have absolutely no idea if this will work, it seems to point to that it’ll work, with basically a bolt-it-in, plug-n-pray theology. But, if it doesn’t, at least I have an engine that’s assembled, which seems to be a better position than one in pieces/buckets with questionable bearing races. I’ll keep working on it, and see what I come up with, and post details as I come across the problems, if any.
Btw, does ANYBODY know how to R&R an engine/transmission and NOT end up with extra bolts/nuts/parts? The answer always seems to be that’s impossible, LOL
So let’s get this straight . . .
You’ll drop in the 3.4, and use your existing pcm, with no modifications?
I believe the engine will start up
I have a feeling you’ll report back to us in awhile, to inform us that the operation was a success 
But, that’s the rumor mill, that a 3.4 will work as a drop-in replacement, no mods. I’m hoping the tranny will mate nicely, and from what I’ve read, the sensors are all interchangeable on the engine… so…like I said, here’s hoping it works…my guess is someone knows what I’m about to run into, and probably the nuances and issues surrounding it… but we’re looking to learn mostly, so I guess we’re about to start another great phase of that… lol
Wow . . . broken clean in two
not an everyday occurrence
Yeah, almost perfectly in 2…it was, as far as the lobes go, but… Guess the cam sensor throwing a code for over 2 years actually meant to check it, and wasn’t a faulty sensor, lol. I kinda doubt the outcome would have changed much, given the rest of the evidence against it.
Well, we just got the boneyard motor. 3.4 with ram air intake. Everything included, power steering pump, alternator, serpentine belt, every single wiring harness was cut off, all hoses, fuel lines, etc were just cut off it to get it out. I see a front engine cover leak and oil pan gasket leak on it, that’s not a big deal, I don’t think… Maybe an oil pan sensor leak as well, but again, not big deal, I don’t think. Fix it while it’s out, I guess. Working on checking plugs and wires, exhaust manifold is in same position as old one, all motor mounts and transmission mounts appear in exactly the same place.
Donor was a 99 grand am, unknown mileage, vehicle was in pristine condition until it was wrecked, interior spotless, paint was in real good condition, all lamp assemblies were good condition. Oil in engine is pretty clean. Anything else we should be doing while it’s still hanging in the air?
Well, the oil pan had zero sludge, some stains, but degreaser took it off on the first pass. Plugs and wires are getting replaced, my 6 year old put the oil pan on himself, my crew dismantled what we needed to under supervision. We used the hoist and old oil pan to remount transmission, extact fit, everything bolted right in place. So, I guess next is replacing what should be done while it’s out, and seeing about bolting it in Wednesday.
The 3.4 indeed bolted into place of the 3.1L, exact fit. Now, I have the front and side mounts in, and realized I forgot the rear mount. Any tricks to getting that put in without dropping the engine… again?
Side note: RTV doesn’t work for the oil pan gasket, or I did it wrong. Started leaking, so just did it the right way.
Is this an RTV product designed for use w/ engine gaskets? I’ve never had much luck using the kind of general purpose silicone rubber rtv sealant you find at hardware stores. Not for engine use anyway.
I haven’t either. But, in a futile attempt to get it done faster, I tried oil resistant black RTV. Didn’t work. All I did was secure the practice of dropping the oil pan and tranny… twice… 
Oh well, live and learn … lol … if you hadn’t tried it, you wouldn’t know it doesn’t work. So that’s something anyway.
Absolutely, and that’s what this project started as, and still is. On a
humorous note, you should have heard my wife calling around for the gasket
prices. It seemed they were surprised a woman called in, and even more
surprised when they found out she not only was requesting the price, but
started schooling them on where it went on the engine. She went and got it
while kids and I tore the tranny and pan back off. She came home, and they
were asking her if she was doing it herself or what. She never did tell me
their reaction, but I believe it must have been priceless…
Using RTV sealants requires special attention to cleanliness and and the parts must be installed in a timely manner, this can be difficult for the inexperienced.
None of the modern engines that I work on have gaskets for the timing chain cover or oil pan, RTV is used from the factory.
