The wiki is filled (if you can find them) with errors caused by modified trigger wheels.
The pull-up/down resistors may get you some of the way towards a usuable signal.
The way the LM1815 works (
http://www.ee.washington.edu/stores/DataSheets/linear/lm1815.pdf ) is that it produces a trigger when the signal voltage crosses zero from positive. So if during the missing tooth, a noise spike occurs the chip will trigger and the gap will not be identified...
Basically a pull-down reduces the total voltage seen by the LM1815 so noise gets dampened out and it won't false trigger.
A Pull-up increases the 'zero' voltage so that noise spikes can't rise above the zero voltage so they can't fall below it.
On the Toyota 24+4 (4A-GE) setup we tested we found that the ground voltage was 0.6v, which went to show that they were expecting a very noisy trigger, it turned out that they had put a load of filtering in the ECU, the reason transpired - they'd not used shielded wire on the stock looms.
