# Datsun Pickup 4X4 Tacho Problem



## Muzzman (Sep 22, 2010)

Hi All, I have Datsun Pickup 4X4 that "i think" is a Jap import, i'm not sure as the compliance plate was changed by a previous owner. I know it was changed as the Transport department and police were kind enough to tell me someone was trying to register a Nissan Navara D21 with my VIN number and proceeded to check my ute to see if it was stolen lol. 

When i bought it it was pretty tired, the original parts were a Z20S motor, 4 spark plugs, pionts dizzy, single hose to the Air Induction Valve on the air cleaner(like the non calafornia models) and self locking hubs. I have since put a little bit of life back into it with a sports grind on the cam, piston rings, 2 1/4 exhaust with wild cat extractors, 32/36 weber carby and an after market electronic dizzy and coil. 

The problem is since installing the electronic dizzy the tacho has played up. It works when it's under load as in when you put your foot down and the more you do put it down the more steady it reads. Even on the highway if you back off the accelerator gradually it will start to twitch up and down and if you only just have your foot on it the needle flicks up and down badly, if you take your foot off it drops to 0 revs. If you slowly increase revs when it's parked the tacho flicks around the lower rev range right up till the motors at higher revs, but if you floor it it reacts normally. 

I know the original points dizzy had a ballast resistor to bring the volts down to about 8-9 volts and the new electronic dizzy needs 12v to work properly so i bypassed the resistor. I'm also pretty sure the signal from the points dizzy would be a longer duration (i think dwell time?) compared to the electronic which would be a lot faster. These are the only two things i can think of that may be causing the erratic tacho readings but the fact that under load it opperates well is a mystery to me. Are there any ideas as to how i can fix this without replacing the tacho? I have thought about taking the original negative feed from the loom to the coil off, and running a new line to the tacho with the original ballast resistor in series to bring the voltage back to 8-9v but was hoping there might be something simple i'm missing.

Any Ideas??


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