I've read some threads on this and never saw definitive pictures of it being done. Many said it wouldn't reach, but I decided to try it out myself and made it work. Here are the step my step pictures:

I decided to use an existing hole in the firewall and enlarge it to run the ECM harness through. The hole is just below the non-ac heater box that I have. I'm not sure if it was originally used for my a/c heater box or if it was for some other option that my vehicle didn't have


from the dash side:


I used a 1 3/4" hole saw. I had trouble keeping it lined up because I had the auger inside the existing hole. I went slowly and it didn't take long to break though.


engine side (after cleaning up the cut with a drum sander):


I found that it was easier to feed the harness through if i separated the top plastic piece from each of the four connectors.


here it is passed through on the dash side:


I couldn't find a large enough grommet in any stores, so I ended up using the stock LT1 grommet that was used for the C210,C220, and c230 connectors. I cut it open so I had a shot in hell of getting the larger ECM connectors through it:


It's good this grommet can stretch because it took some work to roll it over each connector:


Here it is all put together with the ECM attached:


And the whole reason for this work... a nice clean engine bay where the wires will be tucked under the heater box:


What's left to do is to mount the ECM in place behind the dash. I'm expecting to fabricate a mount for it that attaches to the black plate behind the fan motor. I won't do that until I get the dash back into the car though. I had my dash out for other reasons, and I would expect that this work can be done with all the dash and HVAC stuff installed. I'd suggest that someone try using a 1 1/2" hole saw because the grommet is a little loose in the 1 3/4" hole. I'm going to put one or two layers of tape around the inside diameter of the hole to get a tighter fit on the grommet.

So I'm just here to share with everyone that it CAN be done and looks very clean! I see no reason why this wouldn't work for an LS1 swap also.

 

looks good, what did you use for a harness for the lt1? did you make yours work or order one from somewhere?
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do you think this would work on a car with a/c heater box?

 

I'm just starting to go through all the wiring diagrams to mate my 3rd gen dash wiring with the LT1 engine harness.

The hole that I enlarged might be used to mount the A/C box. I swapped to non-ac several years ago and don't remember if it was or not. Even if it is though, you can probably make the hole just slightly further towards the drivers side of the car and clear everything. Don't go too far to the drivers side though, or you'll hit the HVAC diverter box on the inside of the car.

 

man that looks sweet

 

Well I finally got further along in my project and mounted the ECM/PCM/Computer behind the dash. Here's how it looks now:



I was able to reuse the original LT1 plastic mount. The only other supplies I needed was some perforated square steel tubing, some nuts and bolts, and a drill. The plastic holder was mounted to the metal plate that covers the blower motor impeller.



As you can see above, I positioned the tubing so that the hook looking piece on the plate went through the center hole. That hook is actually a block-off for a vacuum line coming from the heater controls of an A/C car. I've seen some 3rd gens that have a different part in place of this plate, so my exact method may not work for every 3rd gen.

After drilling through and bolting the tubing to the plate, this is what I had:



And with the plastic mount in place:



reinstalling the plate into the car was a pain with the plastic mount in place. In retrospect, it may have been easier to mount the plate into the car and then mount the plastic piece with the ECM already inside it.





I did a test fit of the plastic under dash panel and it appears to fit with no interference. The computer can bounce around a little due to only being mounted on the top. I installed a strip of foam with an adhesive backing between the plastic mount and the firewall, and also have foam between the under dash cover and computer. I believe this will keep it fairly stable and quiet.

I hope some people find this useful during their swap. It helps keep the engine compartment very clean.

 

Very nice job!

-jason

 

i like it. i plan on moving mine inside sometime. i have it sitting in the corner near the master cylinder right now. i know it's supposed to be weather resistant, but i don't want to chance it...especially since i have a power bulge hood.

 

Hey i just got my lt1 motor yesterday. been trying to figure out where all the wires and everything go on my car before i start ripping things apart and this is exactly what i wanted to do. But i was wondering if i need to run my C230, C220 and C210 plugs into my car? and what are they for because i know they ran them inside the passenger compartment on the 4th gens?

 

tight. A+ on the workmanship.

 

Those connectors do need to be routed inside the car. I had them run where the original 3rd gen wires did into the passenger fender and through behind the kick panel. They have plenty of length. I won't get into what they're for as it did vary some from year to year. Most were for guages though. Go to shbox.com and look at the pinouts. He has them for every connector on an LT1 harness for several years.

 

Sweet job, keep up the good work!

 

how does this look with the headers installed

 

X2...I have issues with header heat giving my wires a run for their money in that spot. Havent melted any wires yet, and I was more careful when I did it for my second swap car. I also wrapped a couple of them with a heat sleeve. The LT1s might have better header placement, since there are more header choices.

J.

 

I'll take some pictures near the passenger side header and post them next week. So far so good though. The wires pretty much sit right against the firewall and are high enough to avoid melting. There is plenty of slack to create more clearance if needed.

I recently installed the under dash panel on the passenger side and it had no interference with the LT1 PCM. There is even a vent built into that panel that lines right up with the PCM since that's roughly where the stock computer was located :-).

 

well, i started on mine last night. i still have all of the a/c stuff though, so i drilled a hole right beside the hole you used. right now, i'm rewiring connectors, since i originally cut and spliced them. my plan is to relocate as many wires as possible from the engine bay to hide them better.
the header was one of the problems i was thinking about, but right now, it looks like it will run against the firewall and under the evap box. i'll get pics up when i'm done.

 

well, i was able to route the harness inside the firewall and mount the ECM under the dash on the pass. side. i took the evap out to do it, then put it back in. fits nicely and isn't close to the headers at all. i also extended the wires for the a/c sensors so i can hook them up later. the C210, C220 and C230, as well as the C100 are inside the firewall as well. i'm going to locate the wires under the dash on the driver's side and run them inside the car to the pass. side to hook them up inside...making the engine bay a lot cleaner.

 

You don't have a vacuum motor in this location? I'll try this tomorrow or Monday since I'm about to wire in the LT1 harness.

 

I, too, was thinking this wouldn't work with an AC car.

I'm just planning on putting it on the passenger fender wall. I'll have to reroute the AC lines, but I was going to have to do that, anyway.

 

You're going to mount it around where the 4th gens have it? I have seen them mounted all around the engine bay, lol.

 

I've only gotten fleeting glances at 4th gen engine bays (my LS1/T56 were a remote purchase). If I understand correctly, it's in the rear passenger corner. I've checked into putting it there, doesn't look promising. I was thinking more along this line http://i307.photobucket.com/albums/n...engslpcold.jpg .

 

I spent a bit of time today looking this over. The hole with the arrow pointing to it in the first picture is an AC housing mount hole. There is room to the right of those two holes (left in the first picture). But, the AC housing inside the car leaves no place for the PCM to go except up where the ECM was. And, I just don't see how the harness would reach that far.

I'll have to look some more. The kick panel wasn't on as I was checking this out, perhaps if it was trimmed it would mount between the AC housing and wall.

 

from what I recall when installing mine, there was still some slack in the wires. It would be very close, but I did get the feeling that you could stretch just far enough to mount the pcm in the stock location. I can't guarantee it, but it was close.

 

Might be some differences between LT1 and LS1 as well. For instance, the LS1 connectors are a lot longer. They would have to be poked through the hole lengthwise.

 

mine doesnt reach to the exact factory location. yes, i do have the evap and blower motor in place. i made a new hole beside the one with an arrow. i also made a bracket to bolt the ECM up near the factory location. the panels then hide the rest.
i also re-routed all the connections at the bulkhead connector to run under the dash and connect inside with the other wires from the factory C210, 220, 230, 100. i hardly have any wires showing in the engine bay now, except for what's on the engine.

i also relocated the battery to the rear and have a distribution block and junction block in front of the blower motor near the strut tower.

 

With my LT1, i had to push the connectors though lengthwise. in fact, you can see in one of my pictures how I half-disassembled the connecter and slid the hard plastic part back on the wires so i could push the connector itself through first and the plastic cap afterwards.

I also have my battery in the trunk and the power distribution block retained from the 4th gen donor car. I ran the battery straight to the starter and then another cord from the starter to the distribution block. I believe the distribution block is powering the headlights and the underhood fuse box (cooling fan and injectors). I placed my distribution block in front of the passenger side strut tower on the battery tray/ air cleaner location.

 

Do you have a picture of the bracket? I installed a 4th gen dash and am trying to fit the LT1 PCM under the dash. I plan on extending the wires and routing them along the fender.

 

no, i don't have a pic of it. i used some metal strips that have holes in them (i forgot what they are called) and bent them the way i needed them. then, i frammed them around the ECM, tacked them together, and bolted them to 2 locations under the dash. basically, i put the ECM where it would fit, then made a mount for it in that location.


for the battery relocation, i used 1/0 (single ought) gauge wire running into a distribution block. the block has 3, 4 gauge outputs...one for starter, one for alt. and one for the junction block. the junction block has all of the constant power feeds for the car.

 

Were the metal strips w/ holes similar to angle iron? I was thinking of that.

 

yes, but without the angle

they are called mending braces, or mending plates...just came to me.