So my build is slightly different. The ls4 is going on a Nissan 240sx but I have run into electrical issues. When I hook the battery up and put the power wire to the fuse box it's starts cranking. I have no fuel running to the engine yet and I am also not getting spark. I have the Tcm and ecm hooked up and I'm not getting power to the dash. It's seems like the fiero guys are experts on the ls4 swap and I was looking for assistance to get my car running. Any info would really help and if you need pics or anything please let me know and I will show you everything I can. Thanks fellas
It's the stock harness from a 2007 Monte Carlo ss donor car. What exactly is vats? I'm usually he the stock key and immobilizer I don't have the fuel hooked up I was going to just hot wire it to a switch for safety purposes
The fact of the matter is that you cannot throw a stock LS4 harness on a swap application and expect it to work. Even if you reuse the LS4 power center/fuse box , at the minimum there are 7 or 8 new connections to make. The LS4 PCM in a different application also isn't seeing the inputs of the body control module, antilock brake module, auto transmission and the VAT signal. This is why it is customary to rewire and reprogram the PCM for the new application. I would remove the harness and send it to a professional that can streamline the harness and make it work.
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Its been 2 years since I did my 07 LS4 swap and my service manuals are buried in storage... so some of these comments won't be a precise as I would like.
Your car is an 07 and the BCM is more highly integrated into the engine controls than the 06 and earlier LS4's. Without it, the ECM will not see the brake switch (brake pedal pressed) to trigger the starter crank function. The brake switch is wired to the BCM and then communicates with the ECM/TCM via the GMLAN wires.
The ECM triggers the starter relay control (C1 Pin 26), but the input from the stock LS4 ignition switch goes to the BCM first and then communicates the start command to the ECM via the GMLAN wires.
Also, the ECM sends the power up signal to the powertrain relay panel (C1 pin 40) that energizes all power feeds to the coils, injectors, etc... However, the signal from the ignition switch still goes through the BCM and GMLAN to get to the ECM.
VATS/PASSKEY resistor values from the key are also sent to the BCM and it sends a pass/fail signal to the ECM. You can turn off this check within the ECM
Most (but not all) of the Fiero LS4 swaps have had the harnesses reworked to eliminate the LS4 fuse panel and BCM. They used the stock Fiero fuse panel for all power feeds to Coils, Injectors, ECM, O2 sensor, etc... They also used the stock Fiero engine harness wiring for the starter function and other basic engine functions. Once this is done, then you just have to keep the ECM happy and turn off the DTCs that will be set.
At least in the 07 Impala SS calibration, removing the BCM did not set a single DTC for me. As long as there is power to all needed components, the ECM will allow the engine to start without use of the ECM starter relay control (like when using car chassis starter wire), but it will set a DTC that can be turned off. You will also get DTCs for the fuel tank sensor and brake booster sensor if those are not wired up, but those can be turned off.
You will need to do some reworking to your stock harness to get it to run... its not as simple as just setting it in place and turning the key.
You might find these documents handy as it shows the pinouts for the ECM, what they do, and what I did about them. The 203 and 500 connector references are Fiero chassis wiring connections. The other The thing to keep in mind on the section TCM is that my swap was with a Manual transmission, but I kept the TCM and tricked it into being happy.
Originally posted by fieroguru:
Speaking of documenting... I am nearly done with all the ECM/203/500 termination documentation (might have a few typo's still) and I hope the E67 LS4 guys will find this helpful.
EDIT: Drawings updated for some revisions on 10/18... If you saved the earlier versions, delete them and save the current ones.
The fact that you have said this makes some people believe that you don't know what you are doing.
For it to be safe, your set up would need to shut down the fuel pump in the event that the engine stops...and it needs to do this without human intervention. Is this how you plan on setting it up, or are you just putting in an on/off switch?
neils88- why are you going to post an ignorant statement. I am here looking for information about a swap. You saying to someone they don't know what they are doing is an insult considering the fact people have done it before, just on a different platform. If you can't provide useful knowledge I can use, then why post on my thread.
Fieroguru- thanks for the diagrams. I am using all the stock components from the donar car (pcm, bcm, tcm, ignition, abs module, brake switch, etc.) all the parts were saved. My issue now is the car will not crank with everything hooked up. The ign has power and the dash turns on, my dlc scanner is picking up faults and the car info screen is working. I don't know where to start at this point. The diagrams should help. Thank you again for those and I will continue poking around.