Tachometer driver

Newbie here that needs help. I have a ford factory tach from a pickup and i have installed it in a van, now i need to calibrate it. The ecm outputs are different. Tach sig comes from a hall sensor and is sq wave 6volt dc.
Pickup output from ecm to tach.
650rpm=43hz/+-10hz 6volt
3000rpm=200hz/+-10hz 6volt
Van output from ecm
650rpm=130hz/+-10hz 6volt
3000rpm=600hz/+-10hz 6volt
I need to convert the 130hz@650 to 43hz@650.
I have nat LM2917N-8 for hz to volt and nat LM231N for the convert back from volt to hz. Seems so far i cannot get the hz out to the spec of 43hz@650rpm with 6volts.
LM2917---vtp=7.56xfreq.inxc1xr1////vtp=7.56x130x.02ufx62k
LM231---freq.out=v.in/2.09xrs/rlx1/rtxct////fout=1.9/2x8k/100kx1/6.8kx0.1uf.
My output is .44volt/3.7hz@650rpm
What did i do wrong I'am stumped, Is there another way to change the hz
any help would be greatly appreicated.
BILL

Hi Madvan,
Instead of F to V then V back to F, how about simply using a divide-by-3 counter, made from a 4018 and 2 mickey-mouse diodes for an AND gate, that is powered from 6V? Its output isn't a symmetrical square wave, but neither is your LM231, so maybe the tach doesn't care.

audioguru
I have looked at sticky's data sheets for cd4017 fairchild. I cannot see how to wire this to divide by three.

BILL

audioguru said to use a 4018 device -- which is a "divide-by-n" chip. The 4017 is a divide-by-10 device.

**broken link removed** is a datasheet for the TI CD4018B series.

audioguru said to use a 4018 device -- which is a "divide-by-n" chip. The 4017 is a divide-by-10 device.

**broken link removed** is a datasheet for the TI CD4018B series.

Thanks for the help
Bill

Looks like alot less work this way. Excellent!!!

Going to try the CD4018b with the CD4011b @q1 and q2 for the division of three. Feed to clock is 6v @130hz, my cl out should be 43hz. My question is what voltage will the cl be? Do i have to supply the vdd with 6v so that the vss has a 6v output to feed the cl with a diode? Then i will have my 6v@43hz.

Bill