1978 Porsche 928 body
1989 5.0L 32V V8 engine
78 2.75 drive ratio rear mounted transmission
V-1 Vortech Supercharger
Engine Build:
Swaintech www.swaintech.com coated pistons, ARP Rod bolts,
ARP head studs switched from OEM head bolts
Cometic Headgasket
Forged early 928 rods
944S2 valve springs
928 S3 (928 from 85-86) Cams (Shortened and bearing surface moved by Elgin Cams)
Planned: Side plates on dual resonance intake for more volume
VEMS Process:
IGNITION: Porsche Cayenne Coils fit PERFECTLY into the 928 32V heads, almost as if they were meant to there.
PNA- 721 043 00 430 “Car Tool 9” 26.01 and this is a pack with two male plugs for the coils. They are without wires, and you would need 4
948 602 104 03 “Pencil Coil” 12.21(!) dollars
PNA 721 043 00 504 “Harness Re” 67.44. Its enough terminated wires for two plugs, so you need 4. They are crimped onto the metal female receivers that slide into the plug itself, and have rubber gromits and about 12 inches of wire.
Partial Description of Wiring diagrams for Coils:
I took some time to analyze the drawing. It's almost illegible, but I did figure out some useful info. The coil plug has 4 wires and they are labeled A1, A2, A3, A4. On the drawing, the wires come out of the plug, left to right, A1, A4, A3, A2. A1 is ground. A4 is the pulse input. A3 is +12 volts. the function of A2 is sort of a mystery. It's a small wire only 1mm in diameter. The color as near as I can tell is brown/black. It goes to something called MM1 as near as I can read the drawing. Four coils go to MM1 and 4 coils go to MM2. Since this wire appears to be connected through a diode internally in the coil to the low side of the secondary winding, it may be a sense line to feed back some spark signal characteristic to a "black box" ignition control unit. I know some ignition units sense the ionization characteristics of the spark to determine if detonation is occuring. I don't know enough about the Cayenne to know if this is the way the detonation detector works or not. The drawing if the coil internals is quite basic with not enough detail to know what's really going on in there.
- It is possible the coil would work with only 3 of the 4 wires used? That is ground, + 12 volts and a trigger pulse. The dwell either being controlled by the trigger pulse length or through feedback from the A2 line. If the latter, then the A2 line is probably necessary and should only be used with the Cayenne control unit. Some experimentation may be necessary.
- it is very common nowadays with non-logic-level (but power input CDI capable) ignition transformers that the secondary has a return signal. This return signal is suitable for IonSense current measurement (when connected to a 100V supply). You can simply connect the return signal to ground (secondary current is small, 0.5mm2 wire is more than enough).
I am trying to get the PDFs of the wiring diagrams up on photobucket so I can post here. Also, measure resistance between all pin-pairs, in both direction.
I have posted the PDF of the wiring diagrams of the coils on my coils question on the VEMS forum for the UK. The URL is: ...
The v3harness is for 4cyl (4 injectors) by default (though more ignition and misc channels, suitable for upto 8 cyl). Regardless of the VEMS assembled controller options, you have to write an order note to request 6 or 8-injector version loom. The 6 cyl is suitable for 5 as well. The 8-injector is split to 2x4.
I have EV6 plugs here, but that limits my injector choices.