Gen 5 LT Swap Questions Answered (and Myths Busted)

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 47 (as of January 2019) vehicles we already have on the road.  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 so we know it works.

One Example is the 34 Ford on our home page.  It was swapped with a L83/6L80E over two years ago and has logged nearly 20,000 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 2.5 years now 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)

LT1, L86 and L83 Harness modification is available.  Gen 5 LT Standalone conversion pricing is $536.00 for L83/L86 and includes a Delphi fuse/relay block with dust covers and fuse diagrams, OBD Port, and Pedal Connector.  Camaro LT1 $24.00 extra due to extended Pedal and OBD Harness sections.

 Current turn around time just 2 weeks.  Feel free to call with questions on your swap at:

​(321) 604-1963

Gen 5 LT1 Startup Video (at 15 seconds)

  • Every Gen5 LT harness fuse block contains relays for controlling the Starter Solenoid, Fuel Pump, Fan, Sensors and the power circuit of the ECM/TCM just like GM intended.  All circuits are correctly fuse protected also. 
  • 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.
  • 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. The ECM can be set to cycle a standard fuel pump at key on just like an LS.
  • 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 Fuel Pump Module or a PWM Pump if I want to use it anyway? -  Keep in mind that the Fuel Pump Module was only an 12V energy conservation device in the donor and is not required in the typical standalone setup.
  • 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.
  • 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.  We can however provide tach and speed output pigtails if requested.
  • 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.  We can also add length to the MAP and EVAP connectors if changing your intake to a different style.
  • 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?  We've used 8L90E, 6L80E, 6L90E, 4L60, 4L65, 4L70E, 4L80E, T56 and TR6060.  The 4L family of transmissions work well using a TCI or US Shift Controller.  We can prewire the harness with pigtails for those standalone controllers on request.