driftz240 Posted April 14, 2008 Share Posted April 14, 2008 i have a rb20det and im trying to install a aftermarket tach, i know the tach signal wire off the ecu or dash harness is where to pick up the signal, but it will not work a tach, i have heard alot of ways that are saposed to work, ive never installed a tach on a distributorless ign system, they sell coil on plug adapters made by msd, but im not sure if they will work eigher. anyone have a aftermarket tach working on there rb20? Quote Link to comment Share on other sites More sharing options...
chrism Posted April 15, 2008 Share Posted April 15, 2008 I'm getting a new tach in the mail. I'm going to pull signal from the loop located on the transistor pack. I saw someone at a tuner shop use it with the Dyno to get a tack signal. Strange thing is, I don't see this loop in the FSM but it's in the harness connected to the transistor pack. You might want to wait on using this until I give it a go. I'm gonna measure the voltage before making any connections though. I'll keep you posted. I' Quote Link to comment Share on other sites More sharing options...
driftz240 Posted April 15, 2008 Author Share Posted April 15, 2008 keep me posted, i found a thread on a r31 rb20det swap, it said use a 10k resistor between the ecu power and tach signal and it will work. but im not so sure about splicing a tach signal into exc power, sounds like it would cause bad things to happen to the ecu... Quote Link to comment Share on other sites More sharing options...
chrism Posted April 16, 2008 Share Posted April 16, 2008 Sounds like he is trying to pull up the signal. I wouldn't try that. Hope to have the tach soon. Can't wait to try it out. I have the wire ran to the driver side already just waiting for the tach to show up. Quote Link to comment Share on other sites More sharing options...
driftz240 Posted April 16, 2008 Author Share Posted April 16, 2008 ive thought of using a gm hei 4 module to run it also, maybe it would covnvert the signal to somthing usable...worst case i buy a apexi safc and keep it on the tach setting. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted April 16, 2008 Share Posted April 16, 2008 I didn't know there was a problem running an aftermarket tach on an RB. My stock 240sx tach works fine. Evan Quote Link to comment Share on other sites More sharing options...
driftz240 Posted April 17, 2008 Author Share Posted April 17, 2008 how can a 4cyl 240sx tach work with a 6 cyl rb? how did you do that? Quote Link to comment Share on other sites More sharing options...
driftz240 Posted April 18, 2008 Author Share Posted April 18, 2008 I HAVE A WORKING TACH . YEAAAAAAY The 10k 1/4 resistor trick worked awesome.... http://wiki.r31skylineclub.com/index.php?title=Wiring_a_Silvertop_RB20DET_into_an_R31 use the wiring diagram under the tach section....worked for me, i bought a 29$ 2 1/2 dia tach from Oriley auto parts and some 10k 1/4 wt resistors for 1$ "5 resistors" at radio shack. sure beats a 150$ skyline dash, and hours modifying that to work. i tried it to the stock 240 tach and it went ape ♥♥♥♥, obiously way off...so you have to use a aftermarket tach. problem solved. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted April 18, 2008 Share Posted April 18, 2008 how can a 4cyl 240sx tach work with a 6 cyl rb? how did you do that? Its not accurate throughout the RPM band. I could swap in a 300zx gauge to my cluster if I needed perfection. I dialed it in so rev limiter is at redline. I certainly don't need it to drive, so it does the trick. Evan Quote Link to comment Share on other sites More sharing options...
chrism Posted September 6, 2008 Share Posted September 6, 2008 Got my Autometer tach to work using a 470 ohm resistor. Below is a diagram of how I connected it to the tach. Hope this helps. I drove around with this and had no problems. Quote Link to comment Share on other sites More sharing options...
falkhen Posted April 13, 2009 Share Posted April 13, 2009 how do you figure the resistor value for the particular brand tach? Quote Link to comment Share on other sites More sharing options...
chrism Posted April 15, 2009 Share Posted April 15, 2009 Any Tach that is 12v will use this resistor. The resistor is only to pull a 5v signal up to 12v. It is a connection between the signal input and 12v. Its value is set to 470 ohm as a minimum so that the resistor will not heat up and open. Some guys use 10k. This value was used by others on Skylinedownunder. There is no formula needed to get the exact resistor needed. Quote Link to comment Share on other sites More sharing options...
falkhen Posted April 21, 2009 Share Posted April 21, 2009 ok this make take the thread in new direction but its related. pin 7 might work but im missing it = ( Pin 41 120° signal from ECU does not need resistor and tach reads directly. Pin 42 1° signal need power bump up to work Next problem my tach reads off like its reading a 4 cylinders. started of my issue Blitz Tach with Live unit. oringinal jumped from Pin 41 with out any resistor or mod this worked but it was reading off. same or similar symtoms run like a 4 cyclinder with many attempts to reset the Gauge and live unit I as per document: http://www.blitzperformancesales.com/techsupport/pdf/rm-dc2.pdf since my harness does not have Tach (pin7) i just used 180° signal (word usage told to me?) that was wired in previosly by some else(I didn't make or mod harness). or use another pin from unused location like speed sig(pin 53) to insert into pin 7 see if that works. (im having problems submiting post on this forum?) Quote Link to comment Share on other sites More sharing options...
chrism Posted April 22, 2009 Share Posted April 22, 2009 Just go directly to the tach signal pin on your ECU and pull the signal from there. If you don't have a wire then solder one in or put a terminal lug on the end and insert it onto the correct pin. If the pin is broken, then open the unit and solder directly to internal side of connector. Look up the pin assignment for your ECU. Don't use Speed sensor. I don't think that is the same signal as tach. Cam angle uses 5 v signal. Never tried that one. Your tach is set to 4 piston from factory and you have to reset to 6 piston. That also means there should be a memory wire so when the car is turned off, the tach stays at the correct setting and maintains calibration. Assumption is that you follow the calibration instructions. If that is not connected, you will always have to reset and recallibrate everytime you turn the car on. Quote Link to comment Share on other sites More sharing options...
falkhen Posted April 23, 2009 Share Posted April 23, 2009 i well im a idiot i missed counted >.< traced the tach signal wire up the wiring harness with it T's off and jumped it there. as for the blitz tach its sucks its just not sensitive enough. so i put my Jumbo Apexi tach that I had sitting in the closet for who knows how many years(so old the can't find online docs for it any more). soldered in a resistor from the main power to tach line. set it to 6 cylinder and it shows that car idling under 1000rpms. blitz when i finaly got set still showed 1200rpms or more... Hey thanx.. ^.^ Quote Link to comment Share on other sites More sharing options...
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