View Full Version : LS1 PCM in a LT1 Car... changing firing order

Mean Green Z28
February 27th, 2016, 02:55 AM
Hi guys, hoping to pick your brains a bit...

Helping a friend out with a Impala SS that has the LS1 harness conversion on the LT1 engine. It's quite a mess of a story, but in short, one shop did the engine and ECM conversion (hundreds of miles away) and another did the tuning (closer to home) and the car is having issues when rolling into the throttle at highway speeds. One cylinder bank goes crazy rich! We've swapped coil packs and the problem stayed on the same side. I traced the injector and IC wires from the PCM and they have the 3-2 and 7-4 wires swapped on both to bring the firing/injector order from the LS1 to the LT1 order.

Here's where we're left scratching our heads... We've tried it both ways on changing the Injector Bank Assignments in the tune. Using the Stock LS1 order and then the SBC order, and the issues is still prevalent. I'm wondering if we should use a Van tune that came with the firing order we need already programmed by GM instead of changing it in the program ourselves as we're not sure if there's anything else that needs to be done. Is there any other setting to be made to change IC firing order? Seems like that's hard coded and only the injectors can be assigned (or maybe that follows the injectors?).

I was reading ... http://www.lsenginediy.com/gm-gen-iii-ls-pcmecm-change-firing-order/ ... and it says the tune should follow the wiring so we assume the wires need to be swapped as well as the assignment table. Is that correct? Or do you not have to change the assignments since the wiring is already changed?

If this proves to be set up correct, we'll have to start tearing into the engine itself.

Thanks for your input!