ECM and wiring harness questions

**edfiero1** · 02-10-2015

As part of my Engine swap on my 1984 Pontiac Fiero, I am switching the ECU to a slightly newer 1227747 model so I can have better support when trying to tune it. I've also got a new wiring harness to go with it. Just started looking things over this weekend and a few things have me puzzeled.

1. The new harness has only 1 single wire with no connector on it for the VSS. Am I correct in my thinking that this harness does NOT get it's signal from the sensor in the transmission, but instead it comes out of the speed-o ??? If so, can I connect this wire to the one which fed the stock Fiero computer? In other words, is signal feeding the stock computer in the right format, voltage, etc, to be read by the 1227747 or does it need to be converted in some way?

2. On my new harness it has a connector which will accept 4 small pins from the ICM at the Distributor. The Fiero ICM uses large lugs, not small pins. Can anyone recommend a connector/adapter to go from the big lugs to the small pins? I'm sure I could solder and heat shrink somehting up myself, but I would prefer a cleaner look, and plug and play will save me some time.

Thanks.

**fastacton** · 02-11-2015

On the VSS, it probably depends on how it's been wired into the harness. I assume that you're using a factory speed sensor? I'm not familiar with the specifics of a Fiero, but normally a 7747 ECM requires the use of a DRAC or VSSB between the VSS and the ECM and will have to have the wiring for that. If it's just a single wire going straight to the ECM and not through a VSSB/DRAC, then it probably won't work that way with the factory VSS. That setup would have one wire to the VSS and the other VSS wire would just go to ground (there isn't a speedo output or a way to adjust for tires/gears this way).

I'm not sure what connector the Fiero uses for the ICM, but it sounds like it's probably a weather pack connector while the harness has a metripack connector. There might be an adapter available for this, but I'm not aware of one. If it was the other way around, you could use an IAC adapter, but that won't help you here.

Again, I'm not very familiar with the Fiero, so everything I've said should be taken with a grain of salt. What engine are you swapping in?

**edfiero1** · 02-11-2015

I can't find any good pictures of the Fiero ICM connector.
It is shown in this picture, but its hard to see. http://cliff.hostkansas.com/images/2011b/IMG_0491.JPG
My car is in storage for the winter so its hard to get a pick now. But I think this is similar to what you are calling a 'weatherpack'

My engine swap is a Pontiac Super Duty 4 engine. This is based on the Iron Duke that's in the car now, so on the one hand its very similar as the block is same dimensions, but on the other hand, many things are different. Different crank (2.7 displacement), aggressive, roller bearing cam shaft. different head, agressively ported, 2 BBL throtttle body, Hooker Tri-Y exhaust.