4.2l to 6.0l Envoy

GMC steezy

6.0l In 2004 gmc envoy swap in progress need pointers on difference between 4.2l pinout and 2006 gmc envoy Denali pin out


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Master Blaster
Sorry I don't know the answer to your question but that looks like a cool project. Are you beefing up the rest, like the diff, tranny and front brakes to SS specs?

@MRRSM does have the links to pinouts of some of them. Might have to reference the 5.3L flavour to get the right ones.


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Amen, @Mooseman ...

From AllData DIY:

This Link may prove VERY useful for some of the Pinout Diagramming for the Envoy Denali:

Then for comparison to the 4.2L SUVS, visit this thread for the GM Trailblazer – Envoy – Rainier PCM Pinout Diagrams (Post #4)


And finally... If wire looming a unique, modified Engine Harness looks overwhelming… Consider doing research along the lines of an After-Market Power Train Control System as described below. These are New and Pricey Ideas for solutions when LS Engine Swapping:

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GMC steezy

Thread Starter
Sorry I don't know the answer to your question but that looks like a cool project. Are you beefing up the rest, like the diff, tranny and front brakes to SS specs?

@MRRSM does have the links to pinouts of some of them. Might have to reference the 5.3L flavour to get the right ones.
Yes complete swap from a 2006 gmc envoy Denali for harness and lq4 6.0l


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Keep in mind that you've got a Gen III engine in the LQ4, and a Gen 4 harness with the LH6. They also use different ECMs -- the LQ4's P59 is a 'pure' Gen3 controller, and will control the transmission as well. (you'll see why I call it 'pure', below).

The LH6 has an E40 PCM, and by the time it was released, transmission control was moved out to a separate TCM (it'll be attached to the RH side of the case, and those transmissions have updated wiring harnesses.

Other things about the LH6:
- While it was considered a Gen IV engine, it still uses a 24x reluctor through 2006 ('07 and later made the switch to the 58x). It has AFM (so I would get this tuned out, even though the LQ4 *should* run with it intact in the ECM (it might throw codes, though, so tuning it out would be smart). Because of the 24x / 58x reluctor swap, I think the ECM for the LH6 is better described as a 'hybrid' style ECM (signifying a technology mix, not dual-propulsion)

- Being a Gen4 ECM, the E40 has a lot more tuning parameters than the P59. The P59 is a good controller -- but the E40 is one of GMs best. That said, there are some distinct differences between the two (the E40 using 'virtual' volumetric efficiency tables being a big one). So the P59 will be a bit easier to tune than the E40.

Getting to pinouts, they're not the same. You can find the layouts in the GM service manuals, and I'm sure someone has them online. Myself, I'd see if I could get a matching P59 for that 6.0, or give some thought to an aftermarket ECM, like MRRSM suggested. With that, you'd have a good shot at putting a base tune in yourself, and get the thing running halfway properly to start with. Downside is acquisition cost, vs. using the factory ECMs.

- If you have the intake / fuel rail from the LH6, I'd swap it onto the LQ4, as the stock LQ4 is a 'return' fuel system, while the LH6 was returnless. This is assuming your original '04 is returnless, as well. If it's a return system, then I'd go with the LQ4 intake, to start with.

- Injector leads will be different between the two. LQ4 used the original Delphi 'Multec' connectors, while the LH6 used the more modern 'EV6' or 'USCAR' style. Adapters are available.

Other fueling differences (one being very important):
- The LQ4's injectors are rated at 24lb /hr -- they're barely big enough for the engine in stock format, so if you're also adding a cam, planning on E85, etc. -- you're going to want bigger ones.
- The LH6 uses 30lb injectors -- a little better, but that's not the main problem...

The fuel mapping in the E40 is going to be set for the LH6 injectors and cylinder size. What this means for you is that if you just throw the LH6 fueling on top of the LQ4 and start it up... you're most likely going to be running lean, because the combustion chamber sizes are smaller, per cylinder. That increases chances of detonation. So don't be stomping on the pedal before you get the fuel / air maps done, if you start out with the stock ones.

So, whichever injectors you go with, make sure you've got the fuel mapping for them, and have that info ready for your tuner to update the fuel tables in the ECM.

As a quick reference, the LH6 has 65cc combustion chambers, and uses flat top pistons. The LQ4 has 72cc chambers, and has dished pistons. So it's a lower compression engine (9.4:1) vs. the LH6 (9.9:1). The LQ4 pistons are probably the weakest point of its bottom end. So you don't want to be introducing detonation. Remember that the knock sensors are in different places between the engines / ECM versions -- so you may want to update to a Gen4 relocation kit for the sensors, if you keep the E40 ECM.

Since the factory HP ratings are similar between the two engines, I imagine you have your reasons why you chose the LQ4 over just getting / keeping the LH6 that would have the matched harness. And that's fine. You just have to plan for the differences (which is why you're here). :tiphat:

If you had the LH6, you'd have stronger rods / pistons, as they got the better Gen4 internals. Cranks are the same (cast iron), but they're strong. 1000hp can be had with a LQ4 crank (although if I got to that point, I'd spring for a forged stroker).

This isn't 'everything', and I'm sure I've left some important things out (like, injector height, for one).
'Do your research' is the operative word here. The second piece of advice would be to hire a tuner and discuss fuel / air maps, timing, etc., preferably before putting everything together and firing it up. We have a member here (Limequat) who does mail order tunes for the stock 4.2 / 5.3 / 6.0L engines that the TBs and Envoys had -- he knows enough to probably 'get you to bright' on the tuning, and could set it up while you're installing the parts. But, since this is a more 'custom' job, it's probably going to run you a few more bucks. Worth it, IMO. Send him a PM thru this site, or contact him at lime-swap.com, and get his input.

Good luck, and let us know how it works out!
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Registered Member
How's it coming with the swap? I've been watching hoping for updates 😆. I'm currently doing a swap myself and was going to make first post with lots of questions..

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