1976 530i ECU internal circuit boards view

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keehn
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1976 530i ECU internal circuit boards view

Post by keehn »

Everyone,

I wanted to fork off this post from my "Eleanor" rebuild project so it would be easier for search queries to find (should anyone find the internals of an ECU interesting).

I've been reading Robert Bondi's excellent write-up on adding Lambda control to our L-Jetronic vehicles http://firstfives.org/faq/ljet/lambda530i.html and was curious if my ECU as-is had the pinouts to include an oxygen sensor to the wiring harness.

If you look at http://firstfives.org/faq/ljet/ecu_pinout.html, you'll see that pins 23 and 24 are meant for O2 connection. My ECU does have these pins intact as shown below:

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Here's my ECU, follow the pinout in the link above to see the corresponding pinouts. You'll note that 23 and 24 are present on my ECU.

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Disassembly is very easy. On the back are two flathead screws. Remove them.

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And slide the aluminum housing backwards. The circuit boards will be exposed then.

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One side of the ECU.

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The other side of the ECU.

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And an image of both circuit boards removed from the holding bracket. Note there are ZERO microchips! Yes, all of the air/fuel mixture "calculations" are done with clever usage of capacitors, resistors, diodes, and other circuitry that we nowadays relegate to microchips.

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A closer look at one side...

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And the other side.

I am amazed that the "complex" air/fuel ratios are controlled by these two circuit boards. But remember, this sort of technology also got a man to the moon...so while this is simplistic in comparison to modern DME's, it shows that clever usage of various electrical components can do these complex jobs.

(And yes, I am aware that microchips are effectively super-small versions of what we see here, but to see that in 1976, Bosch chose not to design a silicon microprocessor in lieu of this design, is kind of like seeing how the "sausage" was made.)

Mike
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keehn
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Re: 1976 530i ECU internal circuit boards view

Post by keehn »

Actually, after re-reviewing the pinouts, I realized that it said FEMALE end pinouts are listed.

...It appears that I do NOT have the ECU that can handle an O2 sensor...

I'll have to search for another ECU which has the appropriate pinouts that will allow me to add Lambda control.

Mike
tlake
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Re: 1976 530i ECU internal circuit boards view

Post by tlake »

Great pictures :!: Of course L-jet came out in 1973, so had been going a few years before they reached BMWs. The 1975 US 530i was the first use of L-jet on a BMW. Previously it was D-jet, but only on Euros. 8)
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keehn
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Re: 1976 530i ECU internal circuit boards view

Post by keehn »

So, I went ahead and found a used ECU (Bosch 0-280-001-122) on eBay. Purchased it today.

I'll take that one apart as well and take pictures. I'm curious to see what is different between these two ECU's. If you see on my current board, there is nearly 1/4 of one board that has no components soldered. I wonder if those components were present, what this ECU would be capable of?

Mike
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Robert Bondi
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Re: 1976 530i ECU internal circuit boards view

Post by Robert Bondi »

Hey Mike,
Great pics. Good to see the FAQs are still getting used so many years later. Scott Stewart pioneered the conversion; I added the visuals after doing the project myself. Yeah, the E12 ECU is a basically a simple analog computer in a very large box by today's standards.
Robert
77 530i
77 Euro 528
tlake
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Re: 1976 530i ECU internal circuit boards view

Post by tlake »

Robert Bondi wrote: Sat Feb 22, 2020 7:22 pm Hey Mike,
Great pics. Good to see the FAQs are still getting used so many years later. Scott Stewart pioneered the conversion; I added the visuals after doing the project myself. Yeah, the E12 ECU is a basically a simple analog computer in a very large box by today's standards.
Thank you Robert and Scott for the write up.

I wonder if a Euro 1980 528i ECU has the pinouts for the oxygen sensor :?:
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keehn
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Re: 1976 530i ECU internal circuit boards view

Post by keehn »

I got the updated ECU and tore it apart to see the differences between it and my 76' version. Turns out there are substantial changes.

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Starting out with the bottom of one circuit board.

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And the bottom on the second ECU board. It should be noted that all but three pins are soldered to the board.

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In my 76' ECU, I remarked at the lack of microchips, but on this board, there are three chips present. I haven't pulled up any schematics on any, but the fact that microchips are present shows how different just a few years can bring.

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On this board, there are three daughterboards present. I didn't explore any further, as there is a conforming coating present, and I intend to use this board when I add lambda control (i.e. O2 sensor installation).

I wanted to share these pics to answer questions that nobody bothered to ask... :lol: . But seriously, it is fascinating to look behind the curtain and see how our E12's work.

Mike
tlake
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Re: 1976 530i ECU internal circuit boards view

Post by tlake »

Great pictures Mike :!: Thank you. :)
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