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99 Malibu Engine Replaced By 99 Grand Am 3.4 Boneyard Motor9

Okay, so in another thread, I started to repair a 3.1 malibu engine, to find a broken camshaft. Now I’m installing this 3.4L boneyard motor and running into problems. First one is, my wife and daughter are working on it more than me.

Now, the actual first is playing with sensors. The wiring harness to the car (no, didn’t get the donor PCM, for various reasons), has 3 connections I can’t find anywhere stemming from around the power steering pump/alternator area. The other major issue I’m having is there’s a pipe running around the front of the motor, with 2 connections like the MAP sensor has, but is apparently part of the emissions. I no empty plugs to put in it, and there’s an opening at the top. There’s 3 pipes going to each bank, so it’s a per-cylinder thing, I guess, all metal. What are they? And can I just remove the thing? Also, what advice for these sensor connections with no sensor home? My idea is to fill it up, turn it on, and see what codes fly… probably not the best idea, though. I’ve searched high and low to figure this out. I know that it didn’t factory spec out to 3.rL and there’s a make/model issue. Just figuring out how to make it run. Thanks!

I know it’s not what you want to hear… but this will likely be a lost cause. The Malibu came with a 3.1L V6 (I used to have one) or a 4 cylinder engine. The engine you’re trying to install may be “close”, but it wasn’t physically designed for the Malibu you have. Let alone trying to get the computers (sensors, etc.) to talk to each other. You’re just going to spin your wheels on this, sadly.

I’d recommend trying to find a 3.1L engine. Sorry. Good luck to you.

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I totally agree. Without the complete suite of computers and wiring and sensors, there is no way this will ever work.

The 3.1 and the 3.4 are very similar but as you’ve found, not identical. Treat the 3.4 as a long block. Maybe even to the point of swapping the 3.1’s intake system onto the 3.4. You’d be worlds ahead to find and swap the sensors that are ON the 3.1 TO the 3.4 as well as ditch those pipes since they are not on the 3.1. You may also want to get an adjustable fuel pressure regulator to boost the fuel pressure just a small amount to compensate for the bigger engine, I think that’s your best chance of getting this thing running.

You really need a wiring diagram, too.

Good Luck!

The fuel pressure spec for both the GM 3.1L and 3.4 L engines is 35 PSI.

But it doesn’t matter. The 3.4L engine isn’t going to work in the vehicle.


sigh I wasn’t asking if it would work, was asking if there are common threads with swapping these out. I know there will be differences, and trying to work around them rather then say “it won’t work” and move on.

MustangMan, thanks for the input, neighbor and I were contemplating that, but not sure how important it was to the system. What we figure is if we can get the PCM to see everything it wants to see, we should be able to get it running. There’s a pdf I found about doing it, but it doesn’t address these particular pipes. The intake matches up perfectly, it’s sensors on the “front” of the motor around the pulleys, that we’re fighting with and those pipes.

I’ll take some pictures tonight and post them to better illustrate what I’m looking at. It may be a “that’s not important, don’t worry” or may have to mod it a little.

I’ve replaced many GM engines.

And I can tell you is that even when replacing an engine with the same displacement it might not work.

Every time I’ve ordered a used replacement GM engine, the first thing I’m asked is what the VIN is. And the VIN determines whether or not the engine works.


It’s a VIN “E” 3.4 into a VIN “M” which was apparently the same across the
entire GM line at the time. That’s also the discussions I’m finding. It’s
an L82 to LA1 swap.

Here’s where I’m coming from. These engine all work the same, intake,
compression, power, exhaust. Air+fuel+heat makes it go. I get that. I
get the computers and sensors control fuel and heat, and timing to some
degree. I also get that no matter what the engine, if the computer gets
the input signals with in the designated range, it’ll produce a certain
output. If the signals are compatible, then it works. By my estimation, it
should, by others, it does. Outside those ranges, the MIL lights. It seems
straight forward, to me. Now I’m just to get the sensors matched up to the
harness so the PCM plays nicely.

I’ll get it to work, some how. I just need to know what I’m looking at, and
if I need to discard it or modify it.

To ALL degrees the timing is controlled by the PCM. Which may be an issue to be sorted. The sensors on the front of the engine that you don’t have on the 3.4, Are they screwed INto the water jacket or maybe into a boss that points at the crankshaft? If its a point at the crankshaft, that is the crank position sensor. No CPS, no fire! The PCM won’t know what to do. Is the CPS in another location, say mid-block?.Brings up another question… are the triggers the same number of teeth? GM V8’s have this problem, they went from 24 teeth to 58 around 2006. If they are not the same, you will need to have the PCM reprogrammed, Possible, maybe? Not sure.

I did find this nugget on a Fiero site, may be helpful:

3100 and 3400 LA1 V6’s use two separate crank sensors; the 7x (mounted in the block) drives the coil pack, base fuel and spark functions while the 24x (mounted behind the balancer) was thought to only be used for misfire detection. The newer generation 60 deg V6 engines use a single sensor which connects directly to the ECM, which in-turn, drives the ignition coils directly (which makes the newer gen engines directly incompatible with earlier generation OBD2 PCMs and OBD1 ECMs)

There may be a hint here… L82’s use 2 crank sensors. It SAYS the LA1 does, too, but maybe they dropped the front cover sensor? That complicates the PCM as well.

No, the missing sensors are all the top, around the alternator/power
steering pump, with maybe an inch or 2 before the connection. At first, I
was looking for sensors with longer wires, maybe deep in the engine, but
they’re all connected. I thought I missed something on the fuel rail wiring
harness, which one of the 2 prong connections is on. So I took off the
pkenum, examined fuel rail, nothing there.

The 3.4 power steering pump didn’t fit because of metal tubing routing, so
I used the one off the 3.1. The 3.4 pump had a sensor connection to it that
a connector fit perfectly into, but the 3.1 (original ps pump) doesn’t.
This somewhat baffled me. When taking it apart, we took extensive pictures
of it, trying to leave enough breadcrumbs to follow it back, but not having
any luck… Well, not true, had a lot of luck, minus the mentioned issues.

I don’t know if hooking it up, putting power and trying it might produce a
code to direct me where to go. Desktops/laptops go through a POST test,
not sure if the PCM’s do or not. Thinking if they do, and it doesn’t detect
something or detects an open circuit, looking for a closed circuit, it
might be enough to guide one to the error? I dunno, the goal is to get it
to start and run… that’s what my kids really want. They’re excited to work
on it, and they want to see it fire up🙃

Update here:

After moving. The wiring harness around, we found homes for all sensors. We bolted everything in place, forgetting the bracket to mount the shifter cable, of course, and tried starting. After manually shifting to Park, starter tried engaging, and my jumper cables started smoking. So, diagnostic on that was wrong wire connected wrong place. Got another starter. It engaged, no turn of engine. Replaced battery. That wouldn’t even hold a surface charge. It fired up. A lot of smoke, presumably from old gas. Really rough idle. Wouldn’t run under 3k rpm without stalling. Throwing 2 evap codes. Okay, but it runs.

Evap codes are from d/c’d sensor. That much is figured out. Rough idle is possible TPS, we think, but from. The bell housing, there’s a rubbing/grinding noise. So, engine hasn’t run but a minute, at max. So what we’re going to do is take a look at transmission/torque converter and see if I made the rookie mistake of installing it incorrectly and check the converter pump for damage, and flex plate for damage/warp/bends. Starter is disengaging fine. I have a spare flex plate for it…just wondering now if there’s anything else I should be looking for…

Btw, kids went insanely joyous that this thing came to life, even with the problem. They’re so happy to see this start up, something they helped work on… kinda made me feel happy, right when I was ready to turn this entire thing into paperclips, they said, “it’s okay, we just have to fix that now. We’re almost there and done.” Made this car last just a little longer while we continue to sink more money into it for the sake of learning, lol


Make sure all the air entering the engine is following allowed paths, paths that meter the flow rate. Otherwise you’ll get lean mixtures & misfires, stalls, at lower rpms. Torn air inlet boots, the brake booster path to the intake manifold and the pcv system are common ways air can sneak into the engine unmetered.

Well, starts, moves, Kids and my wife are ecstatic. A little loud, disconnected the exhaust after cat converter turned a nice bright glowing red. Runs a little rough, have some crushed wires on exhaust manifold sensor that are throwing 3 transmission codes I think… at least, that’s what research has came up as possible cause. Other than that, new cat, new muffler (why not?), and $1,000-$1,200 after beginning this journey… a lot learnes, and if I had known this before, probably would have thrown it out for paperclips.

But, I can sell it after replacing it, learn from it, and get enough hopefully to recoupe my money spent, and try it again. Broken cars aren’t in short supply, it seems.

Good for you. You got some free education on auto repair and a daily driver almost ready to go, what’s not to like? It’s actually pretty amazing what all the cool stuff you can buy for just a few hundred dollars in the form of an old car needing improvements to make it road worthy again. BTW, don’t presume there’s any problem w/the engine (e.g. the rough running) until you’ve fixed the exhaust system. Modern engines just don’t run well with any exhaust leaks at all. Fixing the exhaust may well solve that rough running problem too.