LM1815 + VR == timing jitter?

Hey gang,

So I resurrected my hooptay earlier today, and am having some big misfire issues. I'm using a RSI flywheel with the 60-2 drilling, and a stock VR sensor.

Hitting #1 with a timing light, the mark jumps around a ton - usually it's right on idle timing (~14deg), but about 20% of the time it jumps to what looks to be about 90* before or after target timing.

I've cranked open the idle screw to get it up to ~1200 so it'll stay alive.

I'm using an old MS2.2 with the Zeal daughtercard (which uses LM1815s).

Idle on a datalog looks pretty smooth. No sync loss once it's running.

Anybody got any brilliant ideas? Maybe I've got the VR backwards, would these be that kinda symptoms? Noise on the line? It's shielded the whole way in, but runs kinda close to a bunch of other stuff through the firewall.

Potentially related, cranking is still pretty un-dialed in. I'm getting some kickback, but if I baby it enough (ride ye old flood clear) it'll light up okay.
Cranking timing is trigger return, 10* advance.

All that said, I've got everything I need here to swap to a hall sensor, but it requires a slight rewire and if I can avoid it just to get running and start tuning, that would be bitchin'.

somewhere in the megamanuals there is an explanation of the difference between ms 1 vs ms 2 and how they read the teeth of a trigger wheel but basically ms1 will run like a distributor by only reading 2 of the 58 teeth, compaired to ms2 that actually reads information from every tooth.

so yea if your motor runs lumpy the timing can get off quite a bit om ms1 but if it is turning over smoothly the timing will be dead on. you might try tuning your afr at idle just get it to be smooth and not slow unexpectedly and the timing will be smooth.

but the ms2 or 3 ecus are pretty sweet also.

any kind of fouled plugs or flooding and general un tunedness will make it jump timing all around too exacerbating the issue lean it out and tune the cranking and idle fresh plugs and go from there.

Using a missing tooth wheel with an LM1815 you'll want to disable the adaptive hysteresis on the chip. By applying 5V to pin 5 on the LM1815 you disable adaptive hysteresis and the chip will trigger at a fixed hysteresis of 200mv.

The LM1815 is known to create "false" triggers when adaptive hysteresis is enabled with missing tooth wheels.

gross polluter said:

Using a missing tooth wheel with an LM1815 you'll want to disable the adaptive hysteresis on the chip. By applying 5V to pin 5 on the LM1815 you disable adaptive hysteresis and the chip will trigger at a fixed hysteresis of 200mv.

The LM1815 is known to create "false" triggers when adaptive hysteresis is enabled with missing tooth wheels.

Click to expand...

I thought this was a known thing, it's been discussed a number of times but not very recently I guess. didn't know anyone was really using an 1815 setup anymore...

I suppose since nobody is running them anymore it's not as well known as it used to be.

yep. So there's your real answer, Pike. Update your junk!