​We get a bunch of calls and emails every week about what is needed to make these swaps run and what works and does not work.  Since there is already a ton of false info out on the internet about these swaps, I'll try to clear up the Myths and Factoids out there. 


My answers are based on the over 1500 LTx Swapped vehicles we've supported since 2016.  Below is original content.  Nothing is a repeated myth from the internet or a magazine article.  We've applied and tested each answer given below and in our FAQ videos so we know it works.


One Example is the 34 Ford on our home page.  It was swapped with a L83/6L80E nearly 3 years ago and has logged nearly 30,000 miles on it since the swap was completed.  Not only is it our customer's daily driver, it's been driven from Florida to California and Tennessee so the swap is proven.  It went through the mountains, through 120 degree heat in the desert and has been in freezing temps without a hiccup.  Note:  This vehicle uses a Walbro 255 LPH fuel pump with a C6 Corvette Fuel Filter Regulator Combo just like an LS Swap.  Don't be fooled into thinking the L83 needs 75 PSI.  This one was dyno tuned by Jeremy Formato at Fasterproms and is running perfectly with just 58 PSI for 3 years (over 29,000 miles driven) without a hint of fuel starvation at this pressure.


This list is not all encompassing but as the questions come up I'll post them and the answers based on what we know works.     - Ken

Gen 5 LT1 with T56 Manual (Modified from a C7 Corvette Donor)

PLEASE READ THESE BULLET POINTS CAREFULLY AND EMAIL US FOR PRIOR AUTHORIZATION BEFORE SHIPPING ANY GEN 5 HARNESS AS WE DO NOT SUPPORT ALL OF THE POSSIBLE GEN 5 CONFIGURATIONS:

  • Every Gen5 LT harness fuse block contains relays for controlling the Fuel Pump, Sensors and the power circuit of the ECM/TCM just like GM intended.  All engine/trans side circuits are correctly fuse protected.
  • All wire is TXL high temp automotive wire and we use the same PET fabric tape GM used for a factory look. 
  • The OBD port and Accelerator pedal connectors will be an appropriate length depending on the donor harness provided.
  • Every wire and connector is tagged with laminated plastic labels that will not fall off or smear.
  • Installation instructions are clear and concise along with detailed graphics.

Gen 5 LT1 Startup Video (at 15 seconds)

Gen 5 LT Swap Questions Answered (and Myths Busted)

Plain English Disclaimer:  Over the years we've presented a ton of information here on this website, in videos, verbally over the phone, in printed instructions and supplements.  We've done our best to test and verify each suggestion made and at the time any information is conveyed it is believed to be accurate.  However GM makes calibration changes to each of their Electronic Modules internal software and hardware systems on an irregular basis.  We will do our best to update and modify the information we convey here on this website in a timely manner once a new challenge is discovered.  In the end, it's up to you the customer to check back here for updates to suggestions and installation techniques and make the appropriate modifications to your installation approach  if needed.

 

  • ​Your Lead time says 2 weeks, are you running on time? - That is our current lead time and we take great pride in meeting our agreed completion dates.  If we are running longer the website will be adjusted to reflect accordingly.  Please watch the video What Happens and What to Expect on the contact page for all of the details on timing.
  • Does the ECM need to be Tuned/Programmed for Standalone use? - Yes the ECM will need to be reprogrammed in order for your engine to run.  We have been aligned with Speartech since January 2019 and they know exactly what to do so your stock engine will run perfectly with a standalone harness.  For ECM and TCM programming questions please contact them directly at Speartech.com
  • Can components be mixed and matched like we used to do with the old Gen 3 LS?​ - It's not recommended.  Think of a Gen 5 LTx swap like a human organ donor scenario and you will save yourself a lot of headaches.  Everything must match exactly.  Your Engine, Harness, Sensors, Throttle Body and ECM were a matched set from the factory and the transmission was a part of that set also.  Changes to the High Pressure Fuel Pressure Sensor in 2017 have made upward and downward compatibility of the systems not possible without changes made to the harness, sensors and ECM.  It's not as simple as just one wire of difference so we only get involved in mix/match scenarios on a very limited case by case basis.  Please call for more details.
  • Can 2017, 2018 and 2019 LTx harnesses and ECMs be setup for Standalone? - Absolutely.  A matched set from a single donor can be modified to run perfectly.  You do not need to replace the ECM and Fuel Pressure Sensor with an older 2014-2016 style.  We have numerous 2017-2019 Setups on the road running perfectly saving those customers hundreds of dollars by ignoring this latest YouTube myth.  Take a look at our YouTube Channel for videos of 2017's (with their original harness, ECM and Fuel Pressure Sensor) running perfectly.
  • Is a PWM Fuel Pump Module Required? - It is not required.  Yes, I've read the Hot Rod Magazine Article.  Believe what you want.  See the note about the 34 Ford directly above.  It's your choice, we can set the ECM to control a relay that runs a standard Walbro type Fuel Pump and a regulator just like an LS Swap.  The relay will be integral to our fuseblock.  We've used 255 LPH on the L83 5.3, 300 LPH on the L86 and LT1 6.2 Liter Engines.  For all setups we recommend that a manually adjustable Fuel Pressure Regulator (0-100 PSI) is used and the pressure is set at around 63-75 PSI.  Never has an engine starved for fuel with this setup.  Some companies will try to sell (scare) you into believing a PWM pump is required.  If I were selling the more expensive ($600) PWM pump, I'd do the same.  Ask your PWM pump seller if the Engine's ECM is controlling the PWM.  If it's not that means their PWM pump is in fact delivering a static pressure in the fuel feed line and it's not really an ECM Controlled PWM pump.  The only advantage to an aftermarket "PWM" pump is that you don't need a return line to your fuel tank.  If you want to save $400 on your fuel system figure out how to install a return line and run a standard pump/regulator setup.  In the end, feel free to use whatever pump you like and set the pressure at whatever you want to believe.  As long as the engine gets between 60 and 75 PSI everything will be fine.
  • Does a standard fuel pump cycle for 3 seconds when the key is turned on?  Yes and no. The ECM can be set to cycle a standard fuel pump at key on just like an LS.  It will however only command the pump on when everything is perfect (Cranking RPM, timing, VATS, etc) and the ECM sees the engine is trying to start.
  • Are there any drawbacks to using a standard fuel pump?  Only if you use a low quality (cheap) pump or pressure regulator that allows pressure to bleed off when the engine is off.  Use a quality pump from MSD or Walbro and a quality pressure regulator and there will be no drivability, starting or pedal response issues.
  • Can you set up for the Factory Fuel Pump Module (PWM Pump) if I want to use it anyway? -  We no longer support the use of the factory PWM pumps.  There's absolutely no need to do so.  See above.
  • Can the PWM Fans from the donor be reused?  - Yes.  We can tag the wire in the harness that controls the PWM Fan(s).  This is the easiest way to have a fan work perfectly (from an electrical perspective) in your swap.
  • Can a standard electric cooling fan be used? - Yes.  It is strongly recommended that you use a Derale Thermoswitch DER-16731 with an ICT Billet M28 to 1/8NPT adapter installed in the engine block to control your Fan(s).  Unlike the previous LS ECM's the Gen 5 ECM's only have an output for one fan but the factory output is a pulsed (PWM) signal.  A truck ECM may not be able to control a on/off relay depending on the original calibration in your donor vehicle.  This means it may not click on a relay on it's own regardless of how it's set up in the tune by the programmer when the standalone tune is done.  In these cases you will need a thermo-switch (mentioned above) or aftermarket fan controller if you plan to use a non PWM Fan or if you want two fans independently controlled.  
  • Will the Alternator work normally?​ - The Alternator is controlled by the ECM and will start charging at a minimum voltage of around 11 Volts and stop at around 13.8 Volts.  Since the ECM relied on a voltage sensor and the BCM in the donor to keep voltage at a more steady state smoothing these transitions in the ECM program is not possible yet.  If a steady state voltage is critical due to big stereo system, off road lighting or winch loads consider having your alternator converted at a local shop to be self exciting.
  • Can the Variable Displacement AC Compressor be reused? - Yes.  The donor compressor can be set to run full displacement and is perfectly compatible with aftermarket AC systems and Factory AC setups in older vehicles as long as the refrigerant is compatible with both the compressor and system.  See the Videos on the FAQ tab for details on how to make the compressor work in your swap.
  • What should I do for gauges?  - The easiest solution is to use CAN Gauges that plug into the OBD port provided.  They are truly Plug and Play.  
  • What about Power Steering? - A few options exist in the aftermarket from companies such as ICT Billet, Kwik Bracket, Holley and Dirty Dingo.   Each has a unique approach so take a look at their offerings and make your decision based on your unique situation.
  • Can you lengthen the harness? - We do not offer lengthening of the entire harness.  If you need the ECM mounted in the Dash you will need a new harness from Speartech.  We will add length to the Alternator and AC Circuits if those are relocated due to bracket and mount location changes.  
  • Where will the ECM mount if I have you rework the factory harness?  -  If your Donor (L83 or L86) was a Truck or SUV it will mount on the driver side fender liner roughly 24" from #1 Ignition coil.  If the Donor was a Camaro (LT1) the ECM will mount on the right front corner of the vehicle behind the Passenger Headlamp.  If the Donor was a C7 Corvette (LT1) It can mount on the passenger side firewall or fender liner.
  • What Transmissions can you set the harness up for?  Your original factory configuration is the easiest and lowest cost option.  However we can help you change to a 10L90E, 8L90E, 6L80E, TR6060, 4L60E or 4L80E.  Note that any transmission changes must be properly planned for and are quoted on a case by case basis.
  • Will you build a Plug and Play harness for OBS, GMT400, GMT800, or GMT900 Chevy - GMC Trucks to swap in a Gen5? -  Due to the complexity of modern vehicles and their control systems we specifically avoid any "Plug and Play" swaps. 
  • Do you support the L8T, L82, L84 or L87? - At this time we are only supporting 2014-2019 L83, L86 and LT1.  When we are ready to support the newer engines we will advertise them.
  • Can you build a harness to swap a L83 or L86 where an LV3 was? -  Due to the Federal Emission Certifications we specifically avoid any "Plug and Play" swaps such as going from a V6 to V8 in a vehicle newer than 1996.


WE ARE LIMITING THE NUMBER OF GEN 5 HARNESSES IN OUR WORKFLOW.  PLEASE EMAIL US FOR AURTHORIZATION PRIOR TO SHIPPING ANY GEN 5 HARNESS FOR MODIFICATION. (Duramax is unaffected and can follow normal shipping instructions on the Contact Page)


We're leaving the Gen5 web pages with FAQ's and videos live for existing/previous customers to reference with questions.


LT1, L86, L83 and LV3 existing Donor Harness modification is available.  Gen 5 LT  Standalone Harness conversion pricing is $XXX (L83, L86, LV3) or $XXX (LT1 Camaro or Corvette) and includes a Delphi fuse/relay block with dust cover and fuse legend. The correct Pedal Connector and an OBD Port are always included.  Your Donor Harness is Cleaned and Degreased and GM spec Tape is added where/as needed.  We offer a Fan Relay Block (+$45) for powering 1 or 2 Fans.  You will need to purchase a thermoswitch and adapter separately.

 Typical turn around time is currently 2 weeks. 

We've compiled questions received since we started building Gen 5 harnesses in 2016 and have set up the Q&A section below and over 40 videos on the Gen 5 FAQ tab above for answers to hundreds of the questions you may have.

After building over two thousand Gen 5 harnesses since June of 2016 we've learned the hard way what a few of the failure modes on the other end can be.  If you want this to be a good experience for you and/or your crew please understand the following details:

  • Due to limited parts availability, any Gen 5 LT harness with crash damage, missing sections or pieces must get authorization from us prior to shipping.
  • If you do not own a scan tool with live data capability you will need to purchase one and learn to use it prior to starting your engine for the first time.  Any and all tech support starts with us asking for codes and live data values.
  • We no longer support engines with a cam change.  Mail order tuning is a recipe for failure and the best LS tuner can really botch a Gen5 tune.  Finding a local tuner who is competent with Gen 5 is hit or miss at best.  As a result, we work only with Speartech for tunes on engines with a stock cam profile.
  • Mix and Match "Frankenmotor" setups are not supported.  If your takeout is not complete and stock L83/86 or LT1 configuration from a single vehicle we are unable to support your project.  See the videos for the possible mix-match failures.  We do not support mix-and-match compatibility in any way.
  • We do not support any Silverado or Sierra donor configuration after 2018.  Exceptions are the LT1 from a Camaro through 2023 and Fullsize SUVs such as Suburban, Tahoe and Escalade through 2020 have the E92 ECM and we can support them also.  It is up to you to confirm your donor has an E92 or E92A ECM before sending a harness.
  • Note the 8 and 10 speed transmissions must be an exact match to the year of your harness, ECM and TCM.  There are differences in the valve body and harness after 2018 and the wrong combo will fry your transmission in short order.  It is up to you to confirm your components match yourself by watching the videos on the FAQ tab.