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S1 RB25 tach/rpm signal

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14K views 6 replies 4 participants last post by  ANV1L  
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#1 ·
Hi guys, I've got a pretty frustrating problem that i've tolerated up til now. As with all RB swaps, my tach is way off, I believe it's about 50% over what it really should be( ie: 1000 reads as 1500 and 6000 is pegged against the hour/minute knob.) To completely avoid ripping out the cluster and sending it out to Carl H or using an r33 speedo/tach assembly, I bought an HKS turbo timer type 1. It can display speed or rpms along with its other basic functions. I find the ECU pinout, i wire all successfully and to my dismay the tach signal reads exactly what the dash tach does. The only two options I have from here are to look more into the 5v/12v digital/analog discrepancy(which hks has an adaptor or something for) or to find somewhere else to wire the rpm signal wire to. Any suggestions?

I've also heard of someone using a resistor? I can't find any other info on this either.

I've searched a ton I promise! So be nice.. D:

Btw, Its a DOHC cluster, 93 hatch. Thanks in advance!
 
#2 ·
Autometer makes a tach adapter for distributor less motors that I believe would work. What I did however was the resistor trick. Not sure if its exact or not though. Basically what I did was get a 12 V source and add I believe it was a 10k ohm resistor (i can't remember if it was 1k or 10k but they're cheap and just try it first if you can't find the info). And run the 12 V to the tach signal wire. If you need me to clarify i can try to draw a pic of it.

That was my solution if i remember correctly but if anyone wants to point out an error please do so...its been a while since i wired it up.
 
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#3 ·
http://paulr33.skylinesaustralia.com/diagrams/rb25det-pinout.pdf

this is the ecu pinout diagram i used. i still have my tach on the dash installed, i'm not sure if that affects anything or not. I used pin #7. checked and double checked. I'd rather just get the turbo timer to be accurate and i'd be happy. D:

I looked into that tach signal adapter, there seems to be a delay with that setup. I'm really unsure about using resistors and all that jazz but i will do it if I cant resolve this soon.
 
#4 ·
Yea that's the right wire...the only things i've heard of working are the resistor or the adapter. Try to make sure the timer is set for 6 cyl though. Worth a shot. Carl H might have a better idea too.
 
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#5 ·
i know you said you dont want to rip out ur cluster but u might want to think about getting a j30 tach. its almost a perfect fit in the s13 cluster and has pretty much the same redline as rb25. i picked up a full j30 cluster from ebay for $20 shipped (to alaska) and only used the tach and threw the rest away.
 
#6 ·
I had a resistor setup on my RB20DET and the tach was somewhat accurate. I now have an AEM EMS on a S1 RB25DET and it does the work for me. The funny thing is that my AEM EMS reports a very accurate tach reading, the HKS is off by about 400rpm, and the tach is off on the low end by about 200rpm. So, I don't know what the HKS has such a weird reading...
 
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