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**Joseph Upson** · 01-14-2010, 01:16 AM

Originally posted by mongo View Post

I have a Fiero that is quickly dying. I got an offer today of a 3500 with Tranny all still mounted to a big aluminum cradle from the donor car. It even has the the driveshafts and spindles and brake calipers still attached. I was told it had less than 30K on it and it looked so clean I have no reason to doubt it. The guy wants $700 for it. The only down side is that there is NO wiring harness whatsoever.

Any opinions on how difficult it would be to create a usable harness, find a compatible computer, and so on to make this swap work?

You need to provide all of the specs for your car. Year, 4 cyl? 6 cyl? automatic? manual?

The engine itself will bolt right up and right in with very minor alterations plus fabrication of a dogbone mount. If you have a V6 you can easily adapt the stock wiring harness to the engine. WOT-TECH has everything you need mechanical wise to help change out the few incompatibles like the electric throttlebody.

Goto this thread (http://www.fiero.nl/forum/Forum2/HTML/079574.html)
for the how to on the ECM upgrade that will be needed to run the engine as the donor car equipment it came from is way ahead of what's reasonable for trying to swap into the Fiero.

If you have an 88 you'll have to do an additional clearance at the engine mount pad on the cradle for the oil pan.

**mongo** · 01-14-2010, 11:24 AM

Thanks! I'll check out that link!

To answer your other questions: I have an 86 Fiero GT with a TH125 automatic. I have a spare cradle also out of an 85 or 86 to aid in the swap.

**Joseph Upson** · 01-14-2010, 12:23 PM

Originally posted by mongo View Post

Thanks! I'll check out that link!

To answer your other questions: I have an 86 Fiero GT with a TH125 automatic. I have a spare cradle also out of an 85 or 86 to aid in the swap.

You will need an older automatic if you're looking at swapping in a four speed transmission. The one attached to the 3500 is too advanced for OBD I computers. You need something from the late 80s to early 90s to work with a 730 ecm.

**mongo** · 01-14-2010, 01:34 PM

There is a LOT of information to digest in the link you posted. There were 22 pages of posts!

I guess I should be a little more plain about what I intend to end up with rather than telling stories about what I have... so here goes:

I would like to end up with a modern RELIABLE engine AND transmission in my Fiero that is more fuel efficient than what I have. I will NOT be re-using my current engine or transmission. Consider them both junk.

My options:

A 3400 engine and trans with wiring harness out of a 04 Grand Am.
This engine is still in the car, has low miles, and will be pulled for me. I can get all the accessory pieces (harness, PCM, axes) when it is pulled. No price is set yet.

A 3500 engine and trans with NO wiring harness out of who knows what.
Engine is out of the car (still on the cradle) and is complete from brake disk to brake disk with the exception of the wiring harness and PCM. It has less than 30K on it. Price is $700.

A 3800 series engine and trans out of a Grand AM.
I found a supercharged version with less than 40K still mated to the transmission missing the wiring harness and PCM for $700 pulled from a car a tree fell on.

Since I would like to use a modern transmission with OD, the PCM and wiring harness are of GREAT concern to me at this time. I don't want to trade one evil for another (saving time on an engine build just to waste even more doing electrical work). The 3400 is probably easiest but if building a wiring harness isn't a big deal for the 3500 I would go that way. I should be able to easily locate a harness and PCM for the 3800 so I am leaning a little in that direction due to the HP gain I would get. That would offset the extra work getting the harness and PCM replaced. Also the 3800 is a common swap and a lot of parts are available.... But that 3500 looks mighty nice as well....

**bszopi** · 01-14-2010, 02:20 PM

Using a "modern" transmission is going to be an electrical nightmare, due to how the engine, transmission and PCM are all intertwined with the BCM. And I just don't think you want to try to make a GA BCM work in a Fiero. Your best bet for a semi-modern tranny with OD would be either the 4T60 or 4T60E. Both were available on OBD-1 vehicles, and can easily be controlled with either a 7727/7730 or 9396 (?) ECM. The 9396 ECM would be needed if you want to use a 4T60E, as it has extra memory built in for the tranny. And this way, you would be able to use the 3500, as it will bolt up to either tranny.

**flimbob** · 01-14-2010, 11:45 PM

You could use an ecm from a 99 and up chevy venture. It supported the 3400 and 4t65e tranny. That is what I intend to do. ECM code changes to support the 3500 lx9 engine can be done.

**mongo** · 01-15-2010, 04:36 PM

I am getting a little confused here or maybe I am just naive. I thought if you had and engine, transmission, wiring harness, and PCM out of say... a 04 Grand Am... you had EVERYTHING you needed (except fuel pressure) to make that thing run. It shouldn't matter if you were putting in a Fiero or in a shopping cart. I do understand that mounting it in a shopping cart would be more of a challenge than a Fiero but what am I missing about engine swaps in the modern era?

**bszopi** · 01-15-2010, 05:13 PM

Many of the newer vehicles (00+ ?) tie the PCM and BCM (body control module) together, so that the PCM can talk to the BCM. The BCM is what powers things like the gauges and diagnostics screens (you know what I'm talking about if you've seen a newer GM vehicle). Sometimes, even the radio is in the mix, as I remember hearing people talk about not being able to swap to an aftermarket radio without extra pieces and parts so that the BCM wouldn't freak out. The computer systems in vehicles nowadays are becoming more and more integrated so features, such as OnStar, can work properly. How do you think OnStar (or the GM Vehicle websites) can tell you when your engine needs maintenance done to it?

**mongo** · 01-15-2010, 05:52 PM

Ahhh! That explains the earlier BCM comment. Is there a date when the BCM became commonplace?

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