Guide for LQ4 Swap into 1999 K2500

stutaeng · Aug 5, 2022

Drive by cable is (DBC) going to easier for you. Even if you engine has drive by wire (DBW), you can just swap the throttle body from a DBC, and bring in the wiring harness from a DBC. BTW: I made a mistake on my first post, I meant DBC. I corrected it.

DBW you have to remove the pedal and get that TAC module and new pedal in there. Lot's of folks say DBW is more "responsive." I honestly can't tell, and I have trucks that have both. IIRC DBW was used as early as the Corvette LS1. Not sure if that was not as "responsive" as the guys from the GMT800 claim.???

I think it really depends on what engine/ECU you buy, then decide if you want to keep DBW, or convert to DBC. If you get an engine that is DBC, then it makes sense to keep it...

xXxPARAGONxXx · Aug 5, 2022

stutaeng said:
Drive by cable is (DBC) going to easier for you. Even if you engine has drive by wire (DBW), you can just swap the throttle body from a DBC, and bring in the wiring harness from a DBC. BTW: I made a mistake on my first post, I meant DBC. I corrected it.

DBW you have to remove the pedal and get that TAC module and new pedal in there. Lot's of folks say DBW is more "responsive." I honestly can't tell, and I have trucks that have both. IIRC DBW was used as early as the Corvette LS1. Not sure if that was not as "responsive" as the guys from the GMT800 claim.???

I think it really depends on what engine/ECU you buy, then decide if you want to keep DBW, or convert to DBC. If you get an engine that is DBC, then it makes sense to keep it...

Were the 6.0L LQ4s all DBW from the beginning (starting 1999 or 2001...whenever they were first offered)?

stutaeng · Aug 5, 2022

No, they were DBC. I think somewhere in 04 is when they started changing to DBW, and the Express Vans took longer to change to DBW.

I think a 99-02 ECU/wiring harness is going to be the best option for you. Those were all DBC. You can use a later engine, but the electronics of the earlier are closer to the GMT 400.

0xDEADBEEF · Aug 5, 2022

xXxPARAGONxXx said:
Understood. Seeing that wiring modification is inevitable, I think I can accept that. I'll look for the best means to do so to keep it looking OEM.

Another question I have is —

Currently vehicle is drive-by-cable. Is modifying it for drive-by-wire necessary? I have seen some websites that offer a conversion pedal. Still trying to determine which would is the best quality.

I reused the original cable on my swap. Easy peasy.

xXxPARAGONxXx · Aug 5, 2022

stutaeng said:
No, they were DBC. I think somewhere in 04 is when they started changing to DBW, and the Express Van took longer to change to DBW.

I think a 99-02 ECU/wiring harness is going to be the best option for you. Those were all DBC. You can use a later engine, but the electronics of the earlier are closer to the GMT 400.

That year LQ4 still has the heavier iron cylinder heads though, right?

I read that with DBW, you can eliminate the cruise control module/cable since it is no longer necessary with DBW. Is that correct?

Hope you all don't mind. Going to have lots of questions before I make a decision especially on what year engine/harness to buy.

stutaeng · Aug 5, 2022

xXxPARAGONxXx said:
That year LQ4 still has the heavier iron cylinder heads though, right?

I read that with DBW, you can eliminate the cruise control module/cable since it is no longer necessary with DBW. Is that correct?

Iron heads LQ4 I think were only 99-00. They had the longer crankshaft that only works with a stock 4L80e. Not an ideal swap for the 1500 guys that want to keep their 4L60e. I read an article one builder said he actually prefers the older iron heads. Something about them taking more boost in a turbo application? LOL.

What I was getting at was that I would use 99-02 electronics/harness/ECU, and any Gen III 99-07 LQ4.

Yeah, that TAC module replaces the cruise control box. The mounting is the same bolts.

BeXtreme · Aug 5, 2022

Dropped88 said:
And the PCM doesn't have to have the "0411" service number it just needs to be a 99-02 red/blue connectors PCM.

This is not necessarily true. If you are doing DBW, then this is true. If you are doing DBC, you need to have a P01 ECU that has the TAC drivers in it to run the IAC circuit. Using an ECU without those drivers will not be able to run the IAC circuit and the engine won't idle at all. Here's a list of hardware and service number PCM's that tells you whether they have the drivers or not. https://www.mrk-motorsports.com/gm-iac-pcms/

Dropped88 · Aug 5, 2022

BeXtreme said:
This is not necessarily true. If you are doing DBW, then this is true. If you are doing DBC, you need to have a P01 ECU that has the TAC drivers in it to run the IAC circuit. Using an ECU without those drivers will not be able to run the IAC circuit and the engine won't idle at all. Here's a list of hardware and service number PCM's that tells you whether they have the drivers or not. https://www.mrk-motorsports.com/gm-iac-pcms/

That's an issue with the 03 + pcms and they have the blue/green connectors and the OS is different in how they operate some functions.

And the TAC is different from the IAC chip on the pcm the Throttle Actuator Controller is the black box on the firewall that the 03+ use for drive by wire except for the express van,S10, corvette and that where you get into those later computers having the chip or not

L31MaxExpress · Aug 6, 2022

Faced with the same decision I built a 383. I did not want to deal with the problems that come along with a ~200k mile used and neglected LS. You can probably do a swap for $2,500-3,000 but at the end of the day its still a 200K mile junkyard engine. I have a LQ9 to build next.

Schurkey · Aug 6, 2022

Perhaps a moderator will move this thread to the LSX + Carb Swaps sub-forum.

Guide for LQ4 Swap into 1999 K2500

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