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Old 11-10-2018, 07:51 PM   #41
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Default Re: '94 SL2 manual trans, electrical help needed

The third item I see in that Mouser link is TI #TPS793475DBVR; that is a SOT-23 SMD part, not DIP, and has to use at lest 4 pins, 5 preferred. What am I missing?

As I look for another PCM, will any other year have a chance of working without re-flash? On mine are two numbers, "21022767" and "21022422" (service #?); which is the unique number I should be looking for?

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Old 11-10-2018, 08:24 PM   #42
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Default Re: '94 SL2 manual trans, electrical help needed

How many pins on the device on the board?

The only thing that works is the correct year as you have major wiring issues with a 95 PCM as well as functionality. You have to have the CA emissions 94 PCM.

Less than $20 and it might actually work. Probably have to swap in the OEM box for the biannual smog check though. https://www.ebay.com/itm/ENGINE-CONT...S!-1:rk:3:pf:0

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Old 11-10-2018, 11:46 PM   #43
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Default Re: '94 SL2 manual trans, electrical help needed

3-pin TO-220 package

Ha, now I see the trick with ebay: you have to search for ECM, not PCM

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Old 11-11-2018, 09:20 AM   #44
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Default Re: '94 SL2 manual trans, electrical help needed

I used 94 Saturn PCM to find that one. Using ECM instead of PCM does pull up more results for the 94. Looks like lots of choices to pick from.

I suspect the electronic EGR will function with a FED emissions PCM as there is a signal converter under the battery tray on your car.

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Old 11-13-2018, 11:00 PM   #45
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Default Re: '94 SL2 manual trans, electrical help needed

Well, time to end this one. I ordered a "rebuilt" PCM. I will keep trying to drive it until the replacement is available by simply turning the ignition on and letting it cook for a minute or so until I try cranking.

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Old 11-13-2018, 11:21 PM   #46
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Default Re: '94 SL2 manual trans, electrical help needed

That will work and provide a clean fix. I was thinking about the difficulty of getting an outboard 5v supply integrated into the PCM signal system without getting into EFI issues as a fix.

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Old 11-14-2018, 12:20 AM   #47
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Default Re: '94 SL2 manual trans, electrical help needed

I couldn't even find where to disable the existing 5V supply, and didn't think it would work well to scab-on an external one and have them fighting each other.

Maybe repeating myself, but I removed the unknown 3-pin device, it wasn't the source of 5V. I also replaced the suspect 47uF cap on the 5V, the only "big" one on the PCB. That made no difference. I have put both the stock devices back in. It seems to be a 4 (or maybe 6) layer board, and the 5V line quickly disappears under the connector, so tracing the 5V circuit back is near-impossible. It also looks like the active devices are proprietary, so even if I had schematics and could trouble-shoot it, chances are I wouldn't be able to get suitable replacements. I even tried applying heat, cool, and shock/vibration to the board; was not able to discover what component is changing to allow the 5V to come alive after those first seconds (well, maybe up to 60 sec!) after first power-up.

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Old 11-14-2018, 12:41 AM   #48
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Default Re: '94 SL2 manual trans, electrical help needed

IN theory you disconnect the 5v output lines and connect the replacement sorce between those lines and the PCM ground. The internal 5V reference is coming up fast enough to not be generating any fail codes so if the patched in supply does not fail the sensors on the new 5v reference all should be good.

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Old 11-14-2018, 01:18 AM   #49
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Default Re: '94 SL2 manual trans, electrical help needed

No, I think the internal 5V is not coming up proper, it is the same supply as what goes out external. Note that the cooling fan and FP relay are going nuts as the 5V comes up. I think no codes (or erratic codes) are being set because the CPU function that could recognize and record those problems isn't alive when the 5V is flaky.

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Old 11-14-2018, 10:24 AM   #50
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Default Re: '94 SL2 manual trans, electrical help needed

The ECTS/fan is on that 5v supply and most of that 5v load can be externally powered. You would have to live with the FP part of the issue and it might disappear on its own.

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Old 11-26-2018, 12:42 AM   #51
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Default Re: '94 SL2 manual trans, electrical help needed

Okay, hopefully this will be the end now. I put in a "refurbished" PCM and all is fine now, but I haven't driven it much yet. I bench-tested the replacement before putting it in. The 5V comes up quick-and-clean, as expected; but the 12V drive for the FP relay behaves in the same odd way as the old one, so I think that is normal.

A side note: I had put the old PCM back in, to make sure the engine could still run fine before installing the "new" PCM. I did the necessary 1 minute wait for the 5V to come up and the PCM boot properly, then went to start it and... no fire! After a second of panic, I remembered that I had disconnected the MAP, TPS, and EGR several days ago when I was still trouble-shooting with the PCM in the car. It started fine once those were re-connected.

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Old 11-26-2018, 09:58 AM   #52
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Default Re: '94 SL2 manual trans, electrical help needed

It will require several starts from ambient temperature for the new PCM to relearn the car, do not expect final results of this swap until then.

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Old 11-26-2018, 01:38 PM   #53
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Default Re: '94 SL2 manual trans, electrical help needed

Yeah, on the first start the idle wan't quite normal. After the second start it seems pretty normal already. Our weather is tame, so I suppose not much re-learn is needed.

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Old 11-26-2018, 02:24 PM   #54
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Default Re: '94 SL2 manual trans, electrical help needed

Regardless of weather the ignition timing is a time consuming process. The rest of it except the auto trans adaptives is done in 1 or 2 cold starts.

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