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Why did GM do this?

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Old 03-10-2015, 10:13 AM
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Car: 92 Firebird--02 Grand Prix GTP 2Dr
Engine: Poncho 400--3.8 Supercharged
Transmission: T56 6 Speed--4T65EHD
Axle/Gears: Open 10 bolt 3.42--Internal 2.93
Why did GM do this?
Looking at my factory manual I noticed that all 8 TPI injectors are fired from a single ECM ground. On the MPI 3.1, the fuel injectors are fired from 2 separate ECM grounds. Why would GM do that to the higher performing model and give the base engine the better route as far as injecting the fuel?

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Old 03-10-2015, 03:23 PM
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Re: Why did GM do this?
Since all 8 fire at the same time, I don't understand the concern?
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Old 03-10-2015, 03:50 PM
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Re: Why did GM do this?
It may sound crazy, but the wiring and injector grounds for the two are identical. Even though the 3.1 MPFI drawing shows what appears to be two injector drivers, there is only one in the ECM.

The drawing for the TPI setup is more accurate.

Note that the '90 - '92 TPI engines and 3.1l MPFI engines used the same ECM. But with different code bases in each.

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Old 03-10-2015, 05:44 PM
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Car: 92 Firebird--02 Grand Prix GTP 2Dr
Engine: Poncho 400--3.8 Supercharged
Transmission: T56 6 Speed--4T65EHD
Axle/Gears: Open 10 bolt 3.42--Internal 2.93
Re: Why did GM do this?
Ah, well that was simple! Just something that had had stuck out to me when I was looking through diagrams. Makes more sense that way.
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