Help with 1JZ a340e speedo in a GZ20

[gztwenty]

Okay, I'm not sure if posted this up once before, but everyone I ask seems to either have no clue, or end up going off on a tangent that heads in the wrong direction, haha.

My dilemma is I have a GZ20 Soarer, and have had a 1JZ auto in her from a JZZ30, for quite some time now. Ever since the conversion, the speedo and dash worked, but the speedo read 1/4 of my true speed. Ie I would be driving at 60kph and my digidash would say 15kph.

I thought I had the problem fixed when I purchased a 2nd hand 'z20 speedo' and it didn't even fit in the trans tunnel (it does now hahahahah). But now my dash power is gone and my speedo is non existant.

Has anybody got a solution for getting the dash power back and my speedo reading true again?

-side note- My car can start in gear, does this mean the neutral start switch is shagged?

[CrUZida]

Firstly the sensor on the JZZ30 box is a 4 pulse/rev, and going by the amount your speedo is out, I'd say the GZ20 is a 20pulse/rev.
There are a few Toyota's around this era that are 20pulse/rev.

I'm pretty sure the JZZ30 speedo sensor bolts on, where as the GZ20 screws on.
You need to convert the box to a screw on system (requires some old parts and a little brackeering).

But it sounds like you've already done that.


If the dash is dead (ie, it doesn't even read 0) then its either a fuse blown, or the dash/instruments are dead.
I've worked on a car that was dead before (just died one day), swapped over to another one, and it all worked.

It could be that when you put the GZ20 sensor on there you blew the dash up.

Fix the dash (and the wiring assuming that caused it) and your speedo should be much closer.


As for the car starting in gear, that is most likely due to dodgy wiring by the person who wired the 1JZ in.

[gztwenty]

I've done so much work to the car it's hard to find the faults now, haha.

The speedo sensor I have in there now simply slipped in and bolted in place with a little tab/key thingo. I matched up the wire colours best I could (red to red, cream to cream, and green to blue/red). They each have continuity and such.

Now the dash... Nothing on it shows. BUT... When in reverse sometimes... The speedo and only the speedo shows up. Just 0kph. So I go no friggin idea. Might need a trip to the auto sparky

[CrUZida]

If its showing 0kph then the dash is still working, but your wiring is wrong (at the sensor, the bit you modified)

[gztwenty]

Ok well I been fiddling today and it's better, but still not great. I fiddled with the neutral start switch, because what was happening was if a manual changed it, L-2-D, it would go 1, 2-3, 2-3. As in L would be 1st, 2 would be drive (it would jump into 2 then snap into 3). Then as you change from 2 to D, it would drop into 2 then go into 3. WTF man?! haha.

So I adjusted how the neutral start unit sat and she shifts great now.

I have the odometer working and trip meter, so the speedo must be fine, but no dash power. But get this, the speedo comes up (and only the speedo) when it's in reverse, and only reads 0kph. (dont think i tested driving in reverse though).

The 'gauge' fuse is fine. So maybe its a busted dash, no idea. Any way of testing this? I'll also ask the peeps on our z20 website.