Starter cranking slowly - low voltage from starter trigger wire

[LTDScott]

Ever since I swapped a '92 M50NV into my race car, I've had problems with the starter. Occasionally it'll crank at full speed, and every once in a while it won't crank at all, but the vast majority of the time it just cranks slowly. After a few revolutions of the engine, it fires right up every time, so it's a problem with the starter.

I decided to pull all of the electrical connections off the starter and clean them, along with the ground cable from the chassis to the engine. I put it all back together and nothing changed.





Note that I do not have the unloader relay connected to the starter. This is a gutted race car so there's no A/C or power windows to worry about.

The battery tested at 12.6V and I'm getting 12V+ to the starter at the big terminal (battery/alternator connection). I used a starter bypass switch to jump the big terminal to the small one with the starter trigger wire, and it cranked at the proper normal speed. Tried again at the start switch in the car, and it was back to cranking slowly.

I checked the voltage at the smaller terminal with the starter trigger wire, and when using the starter bypass switch I'm getting 10+ volts. I figure that's a normal voltage drop from 12+V when cranking. When I use the normal starter switch in the car, it only gets 7V. That would explain the slow cranking.

Here's a video. You can hear the difference in starting speed and see the voltage difference: http://www.youtube.com/watch?v=PNhO-LfIlII

Where does the starter trigger wire get its signal from, and what determines how much voltage it gets? I looked at the wiring diagram and I'm confused. For what it's worth, the car has a new main relay. Any help is appreciated.

[LTDScott]

Upon further thought, it was brought to my attention that, hey, this is a race car, so I can just bypass the factory wiring altogether and wire the starter switch straight to the trigger on the starter, so that's what I'll probably do. I still wonder why the factory wiring is having this issue, though.

[kbeefy]

Low voltage on the trigger wire shouldn't make it crank slow, if it's enough to trigger the solenoid it should get full battery voltage.

it sounds like maybe there's another load or short in the ignition circuit.

[Wanganstyle]

are you following the diagram for the longacre wiring start button? the starter and all of its components are grounded to the block physically. the signal wire is sent power from the start button to trigger it to engage the pinon + the flywheel ring gear.

since its prickstine/the homer its full race and you need to just bypass the entire OEM setup

make sure the starter always has power and is not going through the kill switch; it should be powered all the time just like the OEM e36 and e30 starter is.

if you have a slow cranking it would be likely due to the power having to go through something; the power path should be:

battery ---(big guage wire)--->starter

start button -->small trigger terminal to engage starter solinoid

also make sure the kill switch shuts off the power path to the DME; the Alternator output power wire needs to go directly to the Battery and bypass the DME cross branch from starter; the e36 engine wiring setup daisy chains the starter power->alternator->dme block; we had this issue and initially our kill switch would not shut off the engine!