So I just got my 86 fiero, and there are several upgrades I want to do to it, but getting performance out of the iron duke seams difficult. The consensus seam to mostly be that the tiny throttle body is one of the biggest restrictions, followed closely by the head. My plan is to swap the stock throttle body with a 4.3 tbi setup from an 88 1500 pickup. It seams to be essentially two 2.5 throttle bodies in one, using two throttle flaps and two injectors. The mounting is similar (I will have to fill one hole and drill a new one on the intake), the electrical connector is the same. I more or less plan to do this and am taking into account things like injector size (same injector as the 2.5, just two of them), throttle linkage, fuel flow rate, etc.

My biggest question is this: Can the stock fiero ECM handle the amp draw from two injectors? Does anyone know? Has anyone done this? I think the stock ECM can properly adjust the fuel rate using the 02 sensor. Just trying to cover all of my bases. I will also be posting photos as I work on the project.

Thanks in advance.

the stock ecu would handle the current draw but you would need to reprogram it as far as how many injectors and there lbs per hour ratting as the ecu uses math formulas to compute how long to turn the injectors on so if the ecu has the wrong info on the injectors as far as the amount of fuel being delivered due to adding another injector or increasing the size of the injectors will result in over fueling

Doubling the throttle body and injector size will likely cause issues with cold start, transient fueling, and WOT as these functions are not adjusted by the O2 sensor. Even closed loop will likely have issues because you are planning a 100% increase in air and fuel and the ECM has maximum and minimum fuel trim limits that are much less than that.

If you can tune the ecm you can adjust the cold start, transient, VE table fueling and the fuel trim limits and probably get it to work. But I highly doubt you can just bolt it on and have a drivable car. If you are looking for a bolt on an go solution, you probably don't want to go over a 20% larger TB and Injector.

The head swap is one of the more effective ways to improve the power potential of a duke, but like everything else it will work best with supporting mods.

For that throttle body to work properly an ECM reprogramming will be mandatory. The O2 sensor readings are only set to govern the fueling for a given injector size and only under cruise conditions. Here is what must be done to start things out. The base pulse constant setting must reference your injector size/flow rate. With larger injectors this setting goes down. Then the fueling table must be scaled to correspond to the new injector size and so on and so forth. Its doable but you will need an eraser,a prom editing program (Tunercat) and a prom programmer, to make the changes. If you do not wish to buy all this equipment, there are people on this forum that can do the programming work

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Thanks for the information. I will be getting the stuff together. I have NO experience reprogramming an ECM, so I am going to have to look into options to have to done or do a lot of learning. Any recommendations on who on the forum can do it?

2 4.3 injectors would be too much fuel. The are like 45lb/hr flow. The stock injector is something around 60 or 65 as I recall.
You could get close with 2 - 2.8 TBI injectors which are 33 lb/hr flow

But again, as others said, without the ability to tune the computer it would never run right.