Pulled together pinout data from the manuals and checked on the bench to confirm. Then added the resistors and diode... Looks like it works! Much thanks to Dieselbenz for his experimentally determined resistor values.

I disconnected the control wire from the EGR vacuum transducer and changeover valve, then warmed the car up to 80C and put the pedal down. The turbo spun up as expected.

Brought it back to the shop and revved the motor in park, pressure built in the manifold and pressure control flap still moved back and forth to contain overboost. Is that it? If it works hot, it works?

I always get excited about doing a full reverse engineering project, but there's also joy to be had in a fix that you can buy with the nickel you found under the seat cushions.

See photo of the underside of the board - diode (Used 1N4002), 470 Ω resistor, 1kΩ resistor. Pins are numbered 10, 18, 12 from left to right.

It's fortunate that this sensor is just a variable resistor as there is quite the assortment here. The fuel rack sensor appears to be some sort of resolver with a 10kHz drive signal, and that would have been a lot harder to fudge.

Nice work most people would mount external but you stepped it up a few notches. Also like your descriptions you used for the pin outs..... keep us tuned in on your next project.

Wow, nice work!! So this enables full vacuum operated boost with the EGR disabled?

Want to do mine? ;)

Thanks, I feel like it actually might be easier to do it internally since the EDS is so easy to open up, and you have the PCB to mount to. Certainly a lot easier than the actuator swap, anyways!

The other pins are hooked up internally... any idea what they might do from the pinout that you once had? Programming/diagnostics maybe?

I still might do the telemetry setup just for fun, see what kind of boost pressure map they ran from factory. If I can figure out how to read the fuel rack, it would be neat to see as it should show how much fuel the ALDA is allowing. Definitely something to play with in the summer.

Edit: JHZR2 this is actually a pretty basic level soldering project - pretty hard to mess up if you've done any soldering before. I'd encourage you to give it a try or see if you have a friend who does electronics. You can always practice on some junk PCBs from the dump or something...

Yes boost is under vacuum operated control as it is from the factory, as is overboost protection using the pressure control flap - but the EGR is gone!

The other pins that I recall are for oil pressure, engine temp and a bunch I never did figure out. The diagnostic pins come from a different module.

Was the wiring diagram shown on the first page, with black and red lines, used here? It looks like this was perhaps only the one half of that diagram?

For easier viewing I took a screenshot so it could be hosted.

https://i.imgur.com/7abioIEl.jpeg

https://i.imgur.com/uMvqpycl.jpeg

That diagram is two copies of the same, the black is the "proper" circuit diagram and the red is how you would fold it into a stub to pot in epoxy and attach to the wiring harness. So you only need 3 parts, being a small diode, a 470Ω resistor, and a 1kΩ resistor. Any diode from the 1N4000 series will do the job (actually just about any standard diode will do the job).

I connected the 1k resistor to a 5v source instead, for safety and convenience. As we discussed that voltage isn't critical.

Finished product potted in epoxy as noted above.

Nice! Is this a better bet for resilience and ease of install?

The components need protection hence the potting sealed from the environment. They are inside a fuel line to protect against vibration.

That makes sense, can you share some photos of your final installation and how you connected it into the harness?

I’ve had some small electronics like this for my AT in my 96 Dodge Ram CTD. Potted in epoxy in an ice cube form.

My on pcb soldering skills, plus concerns about shock/vibration give me some level of concern for doing it on there.

Yup it's pretty much personal preference, I chose inside the EDS because it's already protected in there, no need for epoxy, and also to avoid extra splices and having to identify various coloured wires inside of harnesses, which I find more of a hassle than soldering.

Vibration is not a concern as long as you don't leave components swinging from long leads but if you're concerned about damaging your PCB definitely do it as an external "dongle".

I would probably use the EGR vacuum transducer wire and tap into the MAF cable in that area above the airbox. You can identify the EGR wires easily by unplugging the vacuum transducer and turning on the key, one wire will be the +12v with the key on, the other will be the wire marked "EGR Pin 1" on the diagram.

If you have a spare euro plug of the right gender you can even just plug that in instead of the EGR transducer to get 2 of your connections in a tidy way. Don't gut the transducer though, as that's now a spare for the wastegate transducer.

Then you just need to find which wire in the MAF cable is attached to pin 10 and crimp on a wire tap, possibly orange as noted, but there can be variability between models. This one will vary in voltage as you move the flapper. Usually you can test these by sticking a sewing needle through the insulation to measure.

I only have a om648 now and it's inside the SAM unit so can't photo it.

I think factory boost was 10.5 psi, I really liked running 12.5 psi when I had mine. Boost should start spooling at 1600-1800 rpm. See if you can use the boost analog signal from the bosch sensor close to the battery.

I found the calibration chart for that sensor and it looks like it will run in the 0-3.3v range where I can feed it directly to an ESP32 input. I suspect from the documentation I've read that 10.5 is max boost, but it tries to run intentionally lower levels at partial loads.

It's too bad that it's so hard to measure fuel flow with a mechanical injection pump, because it would be interesting to try to tune the boost pressure for cruise efficiency. Though I wonder if fuel rack position could be effectively used as a stand-in for fuel flow.

Sometime when the weather is nice I'll have to get the scope out and run the EDS with the lid off, try to find a pulse width or filtered voltage on the PCB that corresponds to rack position.