Rich9928p

Mark sent the spark module from the Holbert 928 to me, Electronik Repair, Inc., for inspection.

Facts:

Holbert 928 spark module.
- Case Markings: EZ 121 K, B 227 400 017, Muster Nr. 28,
- EPROM Markings: P8 114 FA ZH 8 M4 24.03.86 [Date March 24, 1986]

Initial observation:
- The housing appears to be a production item
- The part number sticker is a “one-off” (composed on a typewriter with no ribbon)
- Only 25 connector pins, vs Porsche EZK 35 connector pins
- The microcontroller is an Intel 8031 (same vintage as used in Porsche EZK)
- There are two “jumper wires” on the bottom of the PCB, indicating some deviation from the standard design

Supporting Facts:
It is interesting that the EZF module used in the previous generation of Porsches (EURO 1984 – 1986 and US 1985 – 1986) also was a 25 pin module, however it used an earlier generation Intel 8039 microcontroller and obtained engine load information via a vacuum line from the intake manifold. The EZF did not have spark knock detect.

Conclusion:
After further inspection of the Holbert EZ 121 spark controller, I believe it uses the same printed circuit board as the EZK 117 used in Volvo 740s with engines B234F or B230F/FT. In the Volvo application, the (single) knock sensor is connected to pin 13. What I don’t know is what kind of tricks Bosch and Porsche played to get this spark module that was designed for a 4-cylinder application to run on an 8-cylinder engine. We would need to evaluate the original wiring harness and final stage spark system to understand the implementation.

I currently do not have time to evaluate the circuit changes made with the jumpers or to disassemble the EPROM code.

Current Implementation:
I have not heard from Mark what kind of spark controller is now in the Holbert-Kibort 928. I would guess that the original 25 pin wiring harness has been removed and replace with a standard 35 pin Porsche EZK controller and associated 35 pin wiring harness (and with the associated knock detectors). Mark, can you tell us what is in there?

Conclusions and theory?
- Speeds are high on the Bonneville Salt Flats, so a Volvo part was used for safety
- The Porsche EZK spark system was not available at the time of the speed record attempt, so the engineers from Porsche and Bosch pulled something from the parts bin and made it work well enough to set a land speed record

We have a group of wise Rennlisters, so do you have other ideas from this data? To assist you all, photographs are provided.

mark kibort

WOW Rich, Nice work.

I thought i mentioned it, but yes, the spark box in the car now and from my beginnings with the car, is the stock 35 pin EZK. (came from 928intl originally to the previous owner along with then stock S4 wiring harness) And, from the paperwork, yet i have not verified, the stock LH box , with 35 pin was always used. so, someone did re wire by using the S4 harness, and it looks like there is even a knock sensor wire on the engine, but i still dont know for sure that is what the connector and wire leading deep to the engine valley is.

Thanks for the digging. thought we might find some super algorithms on the chip to give us all 50hp and 30 mpg!!

Mark

Rich9928p

Well, driving a Volvo can get you 30 MPH! We're half the way there.

I forwarded this information to some buddies that live in Germany and are members of the Porsche Club 928 Germany. They may be able to get some information from Porsche employees at that time.

heinrich

ultra-cool, thaks Rich. Maybe this could help us use the Volvo units for possible future replacement/ improvement?

Rich9928p

Heinrich,

The only improvement to be made by using a Volvo module would be to put in a 4 cylinder motor into the 928!!

I think you're confusing things. The topic of this post is not the LH fuel injection system. There are no problems with the 928's EZK spark system, it is very reliable. Most ignition problems are with coils, spark plug wires - rotors and caps, sensors (engine RPM and knock) or with connections at the ignition final stage.

If Mark had access to the original Holbert prototype EZ wiring harness or some pictures, we might figure out how Porsche configured the system (this Volvo spark system isn't made to support two spark systems or two knock detectors like the EZK is). I have some guesses how they did it, but they are just guesses.

heinrich

What can be won here Rich is that the Volvo units are plentiful, the Porsche LH is not.

heinrich

Oh I see, not the LH - just the EZK?

Rich9928p

Yes, just the SPARK module.

You also need to appreciate that the 928 LH fuel injection controller is quite a custom design. Not many other cars of that period (or even today) have a resonance valve (aka flappy). Not that many cars have a separate fuel and spark system. So the odds of "lucking" into something else that will plug in are zero. Also, many (not all) of the Saabs and Volvos with LH also have a hybrid circuit that fails!! And no, the modules are not interchangable.

drnick

will the eprom codes provide any usefull info?