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MG MGB GT V8 Factory Originals Technical - PCM Location

I am in the process of tearing apart a 93 Camaro V6 automatic for a conversion into my wife's 75 RB Roadster. With the intention of retaining the EFI, where in the world has anyone else found to put the powertrain control module (PCM)? This is no small item, and I would like to find a good place for it that doesn't look like an after thought.

Would appreciate any ideas.

Wayne
Wayne Pearson

Wayne,
I install these 1993-1995 'L32' 3.4L F-Body V6 PCM's in two locations depending on where people want it. Either where the charcoal canisters used to fit or fabricate a shelf and install it above the passengers feet.

If you are installing the automatic behind the motor, email me. There are a number of issues you are about to come across in both fit and computer issues that will seriously effect the end results. I have done quite a number of the L32 V6 conversions and have parts available for these on our website too.

-BMC.
BMC Brian McCullough

not familiar with the GM control box, but you can also consider the removable panel behind the front wheel in the fender (wing) recess. use a hole saw to cut hole in the innner fender and place the box in that secure area. the bolt on panel cover and protects it from elements. this is accessed from near the cannister area also. if oval hole is needed, use a 1 1/4" hole saw (2 holes)and connect them for the proper size. worked for my Ford ECM. good luck
kelly stevenson

Wayne, I'm not familiar with the later PCM, but if it's similar to the ECM or 'computer' used on an 87 Camaro then I might be able to help. I wanted the ECM to remain in the passenger compartment to keep it away from undue heat or moisture, mounted it to the firewall directly behind the engine and just above the trans tunnel. Made up a sheet metal box/bracket for it and covered the outside with carpet. "Invisible" in the interior and easy to access if necessary.
Bill Young

This PCM is about 12 X 10 X 3 to 4 inches thick (if memory serves) and has three 32-pin connectors for the harness. On the Camaro, it's located right behind the RH side shock tower in the engine compartment, so I can't go too far without serious modification of the original harness - but I can do that, if necessary.

I have the complete donor car and am just now stripping it out. I will have the rear axle narrowed (10-bolt) and axles made and all the normal stuff.

I'm nowhere near trying to fit the PCM, or the engine for that matter, but this just struck me as a potential "annoyance".

Wayne
Wayne Pearson

I used the original engine wiring harness from the Camaro and modified it to fit, having to shorten some wires and lengthen others. The PCM sounds almost the same size as my ECM although might be a bit thicker. In the 87 it was located behind the passenger side kick panel up high. Wasn't too much difference in length to move it to the rear of the firewall. One thing that almost stopped my project, there was a color code change across a connector which wasn't shown in the Haynes schematic. I had to get the original GM wiring book to figure it out.
Bill Young

That's a big honkin piece of hardware alright. 96 wires you say? Have you looked into a MegaSquirt? Might turn out to be easier and maybe even cheaper in the long run, and it is a lot easier to mount (7 x 4 x 1-1/2) and about a third of the wires. Just a thought. The underside of the passenger side shelf is going to be about the easiest and best location you are going to find I suspect. Hope you don't have to splice too many wires.
Jim Blackwood

Well, it's a little smaller than I guessed - about 10 X 7 1/2 X 3. Still pretty big.

I haven't ruled out the MegaSquirt - but there is one question that comes to mind...is it compatible with this automatic trans? Up and down shifting appear to be electronically controlled, and, of course the speed sensor is wired in.

Wayne
Wayne Pearson

I know there are some guys using it to control the transmission but I am not familiar with the details. On the plus side (for you that is) the majority of the lead guys on this project are bow-tie enthusiasts so trannys such as the 4L80E would be the first to be controlled by the MS. Any of the other GM's with computer control would use the same signals so you should be in luck. But like I said, I know they've been doing it but am not sure exactly how. Best way to find out is to go to
http://www.msefi.com/
and just post a question on the general MS board. Chances are you'll learn more about the topic than you ever wanted to know!

Jim
Jim Blackwood

Wayne,
The 1993 has a 4L60, not the 4L60-E of the later 94 and 95 3.4L motor. I know these later ones have additional issues to deal with... As to what i have been told, the 4L60 is basically a 700R4 renamed. I dont recall what is or is not controlled, but if there are ANY issues with that, you may want to consider replacing it with a slightly eariler auto and a 3.4L manual PCM which will elliminate issues that you may come into. Sorry i dont know more about that one year automatic. It is unique to the 1993 only.

In our earlier cars, we installed the PCM with the stock plastic bracket with the plugs facing the firewall. Fit nicely, but i have been elliminating all the wiring in the engine bay for more up to date conversions. The nice thing about that PCM is it is weather proof, but i will stillkeep them away from the heat as much as possible so the wiring and plugs don't become brittle with time.

As far as going aftermarket ECU, I think its a waste of time if you do not plan to add a huge amount of engine changes. I have worked with aftermarket ECU (Haltech) and found that the numbers produced were not worth the time on a stock or slightly modified 3.4L. These will produce power all over the board without much change and run very nicely when everything is set up correct.

-BMC.
BMC Brian McCullough

Thanks for everyone's input. I'm just in the thinking and musing portion of the swap as I strip out the Camaro. However, one way or another, this engine and trans is going in the '75. The good thing is that I drove the car up and down the street a few weeks ago, and I know the car history. It belonged to my son-in-law from new, my daughter was driving and the car was rear-ended on a rainy day by a 18-year old son of a county policeman. Totaled by the insurance company, I bought the car back for $500. Crinkled the quarter panels and rear frame.

Wayne
Wayne Pearson

I *do* know a little about the 700r4, as I developed an engine-to-transmission adapter to put that transmission in International Harvester light line vehicles and I still sell that adapter. The 700r4 has a solenoid operated lock-up clutch in the torque converter but no other electrical controls. Look on the body of the transmission for a plug with two wires for the solenoid. If that is all it has then it probably is the 4L60 which is a renamed 700r4. Wiring for that may not even go to the ECM. On the 700r4 power for the solenoid was routed through the brake light switch then through a vacuum switch and then to the solenoid. Sometimes there is an oil pressure switch in the circuit which is mounted on the transmission to help control cycling of the clutch and there may also be a temp sensor inside the tranny. The control circuit is a simple series circuit so if you are willing to take on the job of reworking a factory wiring harness it is a piece of cake to do the lock-up clutch circuit. Alternatively instead of the vacuum switch you can wire it through the column mounted overdrive switch but keep the brake light switch in the circuit. This will make it a manual control but eliminate cycling entirely, and it would be operated exactly like the stock overdrive transmission. The brake needs to stay in the circuit for when you stop the car but I understand that the clutch gets no oil pressure in 1st and 2nd gear so it would disengage anyway. So far as I am aware nobody has tried wiring it this way yet. You will need to get a double switch with N.O contacts for the brake lights and N.C. contacts for the clutch, or else wire a 5 contact relay into the circuits and take power for the clutch solenoid from the brake light source.

Then all your other wires of course. It's hard to convey the difference between converting a stock wiring harness for use in the B and using the MS harness. I've done both, using Ford components. Can't see GM being that much different. You can buy a wiring harness already pre-assembled for $50 and when you are finished the wire bundle is 5/8" in diameter. You won't even start to get close to that with the stock harness, probably closer to 1-1/4" I'd guess, maybe larger. The wires have pre-crimped gold contacts which you just insert into the back of the connector and they snap in, and the wires are plenty long enough to go where they need to, and are stamped every few inches with an identification so there's little likelihood of making a wrong connection. Overlaying the MGB wiring system with the EFI is a simple matter, and the stock sensors can be used and in the software the default sensors are GM so there are no conversion issues. If you choose to install a wide-band O2 sensor (a good idea) this makes the MS capable of tuning itself. I've not tried that yet but from all reports it works quite well. Tuning can be done in real time and is essentially a two button affair while driving, richer or leaner. You can expect to spend $500 if you buy a pre-assembled MS controller, the wiring harness, and a few other odds and ends, the WB-O2 will set you back another $150 to $200.

Anyway, cudos to you Brian, for what you have accomplished with the stock system, but having done both I would not even consider using the stock system under any circumstances if I had to move it to another vehicle. Too much work, and too ugly when finished. Just my opinion.

Jim
Jim Blackwood

This thread was discussed between 28/03/2006 and 31/03/2006

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