Original 914 ECU schematic?

[Beetle_X]

I found the hand drawn ECU schematic/diagram but it does not seem complete. Is anyone aware of a link to the factory one? Is it in the factory manual?

Thanks for your expertise!

[GregAmy]

Inside the ECU? That's not going to be part of any regular diagnostic manual; ECUs are "if it doesn't work then replace it".

Sounds like someone just getting in there and drawing it up. Find out who did that and contact them.

[Beetle_X]

I want to see if I can make a Powerbox for the D-jetronic system. Great point on the factory manual. I thought I read where it was in one though.

Power Box - Giving drivers real power and real gains

https://tdi-tuning.com/tuning-box

Here's a link for the hand drawn schematic.

https://members.rennlist.com/pbanders/ecu.htm#ECU%20Schematics

[Dave at Pelican Parts]

The factory manual does not have electrical schematics of any of the components, just functional schematics and system layout. There are no official publicly-available detailed schematics that I know of.

The drawing in the link was done by Frank Kerfoot, who I think worked at Bell Labs at the time. He was trying to figure out how to fix some specific part of his ECU, so he took one apart and diagrammed it. He sent a copy to someone who was a mutual friend, and I convinced the friend to get the drawings scanned.

I don't think you'll find any significant power gains in just re-tuning the stock ECU, which appears to be the aim of the "powerbox" you mention. The main reasons it works on the TDI are that diesels make more power by injecting more fuel (up to a point), and that software can raise the boost level stuffing more air in. Neither of which is true for a N/A gasoline motor like the 914's.

The D-jet ECU is also a messy analog system, which uses some very odd stuff to open and close the injectors. For instance, the primary load metering is done by the MPS. The amount of time the injectors are open is determined by how long it takes for the inductive coupling between two coils of wire to build up and break down. Good luck fiddling with that...

--DD

[Beetle_X]

I have almost 2 complete D-jet systems , a bunch of electrical meters , a romulator, a decent hobbyist understanding of analog/digital electronics and the desire not to spend 3 grand on a fuel injection system.

It just looks like to me that the sensors are biasing the transistors. I guess I will have to thank you and owe you credit if I can figure something practical out. I'm crazy Dave. It can take you a long way.

[Dave at Pelican Parts]

Excellent! Believing you can do it is the first step to doing it! (Continuing to try after you fail is also very useful along the way.) See if you can email Brad Anders, keeper of that website. He has analyzed the schematics and also messed with the actual hardware, and probably has the best understanding of anyone at the current time.

If you're not into spending $3K on a system, have you considered MicroSquirt? That's very DIY friendly, is all digital, and has robust support. You can use some of the original 914 hardware (e.g., manifolds and such) but must adapt other stuff (e.g., pressure sensor, throttle sensor, etc.) from other applications. But those are solved problems; others have gone there and can provide examples.

--DD

[John Rogers]

As Dave noted, fiddling with the "D-Jet brain will result in little if any power gains if that is all that is done. I raced with vintage racer in the L.A. area, the company named NARW in Reseda and the owner (I think) had bored the throttle body to allow more air and coupled with a modified brain and injectors and cam shaft and head work, ETC, ETC had a 2L four making a bout 140HP at the rear wheels. I think the trans mission gear set was also changed to M-S-X for better track work.

Soooooo as you can see to squeeze some additional HP out of an engine made to power stationary power plants it takes a lot of work.

[GregAmy]

Have to agree with the above from Dave. You want a better engine management system, so don't bother trying to adapt all that 1970s stuff. Go with Mega- or Micro-squirt.

[Jeff Hail]

Originally Posted by John Rogers

As Dave noted, fiddling with the "D-Jet brain will result in little if any power gains if that is all that is done. I raced with vintage racer in the L.A. area, the company named NARW in Reseda and the owner (I think) had bored the throttle body to allow more air and coupled with a modified brain and injectors and cam shaft and head work, ETC, ETC had a 2L four making a bout 140HP at the rear wheels. I think the trans mission gear set was also changed to M-S-X for better track work.

Soooooo as you can see to squeeze some additional HP out of an engine made to power stationary power plants it takes a lot of work.

Jeez John, NARW in Reseda on Canby Ave? Klaus Holthaus? I'm feeling old, haven't heard that name in a long long time. That was like twenty years ago.