I was thinking of setting up a dual fuel system gas/propane for an off road project with a GM ECM. My plan so far is to use a bin switcher to toggle between the gas and propane tunes as they require different timing to be optimal.

My question is can the ecm run all of its normal functions with the injectors unplugged or with resistors in their place? Is it bad to fire them dry? Is there an easy way to do an ignition only tune with a gm ecm?

 

Sure, I did for a year before I finished the fuel delivery on an EFI set up. ECM ran the SA while the carb supplied the fuel. Did a write up on it which can be found on the DIY_PROM board here on TGO.

In the Tuning Guide Book sticky, chapter 5, under the '8063/'7747/'8746 ECM section, SA Logic link.

You don't want to dry fire the injectors. Can use a relay to cut the power to them. May even be able to use an ECM output to switch the relay. No need for resistors in place of the injectors or such. The ECM won't care if there are there or not.

RBob.

 

Thanks. Thats good news. Any reason this couldn't be done with a 749?

I couldnt think of any way that the ecm would know if the injectors were actually there. I was just afraid of burning up the inj driver some how. I was thinking at worst it would just require forcing open loop to keep the ecm from realizing that its fueling changes were not taking effect. On second thought I have bottomed the INT and BLM without a CEL before so I guess its not picky.

Now to make it unnecessarily complicated. Do you think the inj/relay power cut trick could be done with a series II3800 buick motor E-trans and pcm? Were the electrons to smart by the late 90s to get away with it?

Wow the possibilities are endless.

 

The '7749 will work. Not sure about the late '90s PCM. The problem there is that the code gets complicated. It is ODBII stuff. You end up spending more time figuring out the code and how to change it then on the actual project.

RBob.

 

Those mid/late 90s FI systems are pretty intimidating to me. Seems like there were a lot of rolling changes through the 90s. I guess I could go ask around in the Supercharged Grand Prix community.

I really like the NA3800 for its power, weight, size, fuel economy, and price. It would go great in my little toyota 4x4. Guess I will just have to get one and run it with the 749 and non E-transmission. Would be nice to keep all of my tuning stuff similar between my vehicles instead of trying to learn OBD2.