Modified electrical/starting problem..., ... Found the problem. Need a solution. Options

[BMXerror]

Calling all racers. I haven't had much time to mess with the 914 since finishing the SDS install nearly a year and a half ago. It's got a pretty decent baseline map in it (street tune, no dyno), but it's always been a hard cold starter. It will crank and crank and nothing, but as soon as you let go of the starter it stumbles and tries to fire. Keep doing this and it will eventually start. Just this past few weeks I've gotten back into it and am trying to resolve this issue. And after successfully testing one of my father's theories, I've found the problem. The starter is robbing too much power from the coils, and they're not firing while the starter is engaged. I confirmed this with an inductive timing light. So the question is what to do about it.

Some background info:
*The starter is an ebay high torque starter and has been installed for some time. It started just fine with the D-Jet system.
*The injection is an SDS EM-4F, meaning it's crank fired with two coil packs(batch fire). Supposedly it's a pretty hot spark.
*Part of my SDS install was relocating the Battery to the front. Currently I have the secondary lead on the starter running through the tunnel, and the hot lead that runs the injectors and coils pulled off of the starter pole. However, in my testing I ran a test lead direct from the battery to the coils, and it didn't seem to help the situation.
*I'm seeing a voltage drop at the battery to 8.5V when I hit the starter.
*The battery is fairly new and seems strong, reading 13V at rest.

Any recommendations on how to resolve this problem. It just seems to me like those coils and that starter are too much for that system. Input appreciated.
Mark D.

[Mike Bellis]

It sounds to me like the "Hot While Cranking" wire is either not working or you have the wrong wire connected to the coil.

I think your either connected wrong or the ignition switch is bad or you need a larger battery cable. While in theory it is possible to have such a voltage drop normally, this would mean you wiring system is too corroded to function properly. You could test by adding a diode between the starter wire and the ignition wire. Make sure you connect the polarity correct. On way will allow starter (cranking) power to energize the ignition wire, the other way will cause the run position to crank the starter (you do not want this). If this works, the ignition switch is bad. If it does nothing, the electrical system needs a look see.

What size battery primary cable are you running? Where is the battery grounded?

I run a 4/0 power and ground from the front trunk. Ground lead bolted to the engine block. I have no issues cranking or starting.