2007 1500 Classic with 4.3L v6,

[tmpass]

Hey all, new here and I have had plenty of GMT400's, a gmt900 sierra and also currently own a GMT455 (c3500HD) but this is my first V6 powered vehicle.

The previous owner ran the engine without oil pressure, so it is now completely locked and I'm searching for a replacement. This is a mid 2006 build truck with the LU3.

I've read that I can use any 99-06 4.3 as a replacement, but I want to confirm what I should use or any caveats

ALL the external accessories will be transferred from the old motor to the new, so basically I could go with a short-block if needed. TIA

 

[Tonimus]

I would suggest staying with the 2003-2006. Those are the years the LU3 was produced and used the same electronics, and should be a direct replacement. Earlier 4.3s may work, but they have a different cam and fuel injection system, possibly other nonsense. You never know what you may run into with that swap. There should be plenty of '03-'06 4.3s out there.

 

[ORVietVet]

Welcome to the forum from Oregon.

Good luck with the 4.3 search and build. There is an Under Construction section here to document the work and results.

 

[stutaeng]

Does your truck have drive by wire (DBW) or cable? EGR? IDK if the last 4.3s in the GMT800s got DBW, but if you do, then stick with another engine that has that. The earlier 4.3s had the poppet style spider injectors, so stick with the version that had the MPFI. Swapping a shortblock would be another option; I don't think they actually changed anything on the engine (99-07 classic) except for external stuff.

Or you can just "LS swap it"

 

[tmpass]

thanks, like i said EVERYTHING external will swap over. I got my eye on a 99 longblock for cheap.

 

[tmpass]

I live in NEW England, the Silverado is from VA.. no rust so I grabbed it. It will replace the '01 3500HD which I saved from the junkyard... it's way too much truck for what I need. I was toying with dropping the 8.1 into the Silverado

 

[stutaeng]

That's clean! I like it! The last of the Mohicans...

Do a 8.1 swap like Lawerence Tolman's "Ugly Truck."

The good thing is pretty much any engine can be swapped into your truck, since they came with them from the factory in this generation. 4.8, 5.3, 5.7, 6.0, 6.2LS. The 8.1 is kinda a hybrid because it's a BBC, but used ignition almost identical to the LS-based engines. In fact, the factory LS wiring harness can be used on the 8.1, I think you just swap 2 injectors IIRC.

 

[Tonimus]

The cam is definitely different in the '99 4.3. If you do decide to go that route, please document it for others.

 

[tmpass]

yeah i watched a guy do a 5.3 swap... best is to get complete DBW harness/pedal he did a 5.3 and all the V6 exhaust, fuel lines and 4L60 bolted right up. he wasn't going for performance, just wanted to the cheapest LS swap he could do, which is where my head is at.

For now i just need to get it under its own power the quickest way.

 

[stutaeng]

yeah i watched a guy do a 5.3 swap... best is to get complete DBW harness/pedal he did a 5.3 and all the V6 exhaust, fuel lines and 4L60 bolted right up. he wasn't going for performance, just wanted to the cheapest LS swap he could do, which is where my head is at.

For now i just need to get it under its own power the quickest way.

Yeah, the exhausts bolt right up right after the manifolds. Even the V6 oxygen sensors will work on the V8. I left the exhaust on my 99 just like it was with the V6. Just get the V8 exhaust manifolds if the engine doesn't come with them.

Get the matching frame mounts if your truck is a torsion bar vs coil spring suspension.

 

[Cadillacmak]

I was toying with dropping the 8.1 into the Silverado

I vote yes for the 8.1 swap! But you got to show us pictures.

 

[tmpass]

The cam is definitely different in the '99 4.3. If you do decide to go that route, please document it for others.

I will probably look for something more compatible

 

[tmpass]

@Tonimus how is the cam different?

 

[Tonimus]

@Tonimus how is the cam different?

They changed the cam profile. Supposedly to make it "quieter". When GM is vague about stuff like that, it makes me very wary of other possible changes. I'm not saying not to do it, just to make sure the parts you do swap on are exact. I would expect that the heads or valve springs would be a little different with a different cam profile. Check the head hole patterns against each other. If you keep the '99 heads, make sure the intake patterns are all the same. I would also check to make sure all the accessory holes you need from one block are present on the other.

 

[tmpass]

For simplicity I went with a 4.3 out of an '05.. just want to get it done for now.. being from New England its been so nice to work on a rust free truck

PITA to split a tranny from a locked up motor. Especially in my cramped space.

I'm currently at a standstill as I didn't have a beefy enough box wrench to get at the torque converter/flex plate bolts, need to order a "zero offset" 15mm

ETA: I still have the 8.1 truck if i decide to go that route later, lol.

 

[stutaeng]

Nice.

Have you tried heating the bolt heads?

I have used a 15 mm shallow socket on a long ratchet on the torque converter bolts. The flexplate will rotate until the ratchet head hits the block, then i use that as a leverage action-reaction.

 

[tmpass]

this engine wont rotate, so i only have a 1/2" gap between the block and flexplate to get at the bolts..

 

[stutaeng]

this engine wont rotate, so i only have a 1/2" gap between the block and flexplate to get at the bolts..

Ah, ok. That makes sense.

 

[tmpass]

Engine is in and running good, no CEL on dash, runs nice and smooth.

One minor slip up on the motor mounts, I didnt swap the adapter plates on the block which pushed the tail-shaft to the right... must have been a 4x4 truck that the "new" motor came out of.

I also missed one ground at the back of the of the engine box which caused the truck to run only with the lights on. And it would not shut off until the lights were turned off, lol. my left headlight was also at half power.

All good now and thanks for steering me straight on which engine to buy.. it was plug and play.

One of my front airbag sensors apparently needs to be replaced.

 

[stutaeng]

AWESOME! A running truck is always better than a non-runner, no matter what.