injector issues with 3400 on 3.1 ecm in fiero

[Froggx]

To my understanding the 3.1 used 17# injectors at 45 psi while the 3400 uses something around 23# at 55psi. I am working on a swap with a 2000 3400 into a fiero, using the ecm from an 89 3.1L gp. Does anybody know what it takes to overcome the issues that will be caused by using the stock 3400 injectors. I plan on burning my own chip for the ecm, so I will be able to adjust settings in it. Would it be easier for me to convert the 3400 to the fiero fuel rail and injectors or something to that effect?

[sharkey]

the 3400 injectors are sequential, and the engine will run rich with them. the best thing to do at this point is swap your fiero injectors (or just 3.1l injectors), they will fit right into the fuel rails for the 3400, and use the 3.1l harness as well.

for the fuel pressure issue, get an adjustable fuel pressure regulator for the 3400 rails and a fuel pressure gauge, and turn it down to 45psi.

[Froggx]

would it be possible for me to use a fiero fuel rail and not have to get an afpr? I have 2 extra fuel rails for fieros lying around doing nothing. Also, wouldn't I need to go to larger injectors since the 3400 would have greater airflow requirements than the 3.1 ecm expects, and would therefore cause it to run lean?

[SappySE107]

Since you will be able to tune your car, use the 3400 injectors. Change the BPW vs EGR constants to get the fueling decent as a start, and tweak the VE tables from there. I dunno about using the fieo fuel rail but im gonna guess that is a no.

The 3.1 injectors will work but will not be good for performance once you start tuning the car. Tuning it with the 3.1 injectors will make it difficult to put the 3400 in later so just start with the 3400 injectors and go from there with the computer.

[Froggx]

Alright, and in terms of using the 3400 injectors, is the injector harness of the 3400 injectors directly interchangible with the ecm, will I have to use the harness for the 3.1 injectors, or do some kind of wiring hybrid. To my understanding, the ecm I'm using was batch fire instead of sfi.

[GPXSS]

The engine and injectors don't care if they are used for MPFI or SFI. If you are gonna use a 3.1 ECM for this, you will most likely need a 3.1 harness and adapt it for the engine (lots of people have already done this). You won't need the cam sensor (large 3 or 4 pin connector going behind the front timing cover) or the 24x crank sensor since you're using the 3.1 ECM.

[Froggx]

Change the BPW vs EGR constants to get the fueling decent as a start, and tweak the VE tables from there.

When changing the bpw vs egr constants, is it as simple as setting up a proportion between the ratio of fuel injector sizes to get the new value. For example, assuming 3.1 injectors are 17# and 3400 injectors are 23# would I just do 17/23 = old value/new value where old value is what is already in binary and new value is what I'm solving for, or is the formula more complicated than that?

[SappySE107]

Its complicated but I havent figured it out since I did it for my 3.1 years ago. I would honestly just scale it like you want to do and see if that works. Turn the EGR off though to start with so you only have 1 value to deal with. I think the value you want is 150-160 for 0% EGR. It may be lower though but that should get you in the ball park. Once you get it to start up and idle, just watch the idle BLM and if its extremely off, change the constant a bit. Then change the idle fueling to get that set and go from there. The real issue is to have the constant be close so that the fuel tables are never at 100% VE combined...as that will stop your tuning and cause you to redo the constant.

[v6h.o.]

yes you will need the 3.1L injector Harness. it is wired properly for MPFI(the 3.1L ECM setup you are using) compared to the way the injectors are wired separate for the stock SFI on the 3400.