secondary injector module/ecu
 

Continuation of the discussion from the for sale thread:

What does the secondary injector module actually do?

As determined by Marc's testing, all ECU's are interchangeable with the correct PROM. Which would lead me to believe that either the circuitry exists in both ECM's, or it's done entirely through the PROM.

One would think, that with the proper programming, a simple wiring change should be able to eliminate the secondary injector module from the car.

On another note, I have one of the DIYautotune megaquirt LT5 ECUs. When ordered, I had to specify 1990, or 1991+. They cited an internal wiring change between the two. Does anyone know if this is due to the secondary injector module? Why does the stock ECU handle both with a programming change, but the megasquirt requires internal differences to the circuitry?

Re: secondary injector module/ecu
 

The LT5 ECM and engine controls are a derivative of the L98 logic. The ECM ONLY controls the secondary injectors by energizing the secondary relays sending power to the secondary injectors. It essentially provides the ground
(-) for energizing the secondary modules. The pulsewidth for the secondary injectors is controlled or “shared” w the primary injector signal from the ECM. Once engaged, the ECM basically cuts the pulsewidth by 50% so two injectors now share the fueling needs of the motor.

So NO, a simple change would not do the same thing. The secondary module substitutes for injector drivers.

Re: secondary injector module/ecu
 

So if the ECUs are the same except for the PROM, and the 93-95 cars don’t have a secondary injector modules, it stands to reason that with a reflash and wiring change, the 90-92 cars wouldn’t need them either. Unless the 93-95 cars are doing something else.

Re: secondary injector module/ecu
 

Where do u get the idea that 93-95 LT5s don’t use secondary injector relays?

Re: secondary injector module/ecu
 

Yep the secondary injector relays are located on the passenger rear in the later model years. To be honest I forget that as well Dom.

Re: secondary injector module/ecu
 

The secondary injector modules are present in all ZR-1 s from MY 90-95. They simply moved in the later years to the rear passenger side. This makes sense why the ECM are all backwards compatible because they still have these secondary injector modules. I think they are the same the entire model run with the exception of the first 200 MY 90s for some reason.

Re: secondary injector module/ecu
 

In the very first post that I quoted in the thread that was edited 10 minutes ago. I guess that clears that up. I assume the injector impedance changed between 92 and 93?

So on to the second part of my post. What is the internal difference in the DIYautotune ECU? They listed the year cutoff at 1991 and up.

Re: secondary injector module/ecu
 

You’ll need to ask MegaSquirt. I was not aware that MS used 16 injector drivers or do they just replicate the LT5 ECM? I have no idea why a 92 would be different than a 91.

Are you saying the injector impedence changed in 93 or that is what must have happened IF the modules had been eliminated?

Re: secondary injector module/ecu
 

My best guess for 1990 to 91-95 variation has to do with the power key and how it works..

Re: secondary injector module/ecu
 

:happy1: