jamo240 Posted March 5, 2011 Share Posted March 5, 2011 Hey guys Does anyone have knowledge on how to drive a Z tach with an RB ignition system? As we know, the Z tach is driven off the ground side of the (single coil). The RB engine uses an igniter (a power transistor) that grounds each of the six coils in turn to fire the cylinder. The ECM controls the igniter transistors (ie switches current on and off in the coil primary cct thru the igniter), and I guess it uses this information to feed the engine speed through to the R33 Skyline tach. Each transistor in the igniter appears to ground the primary side of the coils through a common ground, so that may be the spot to hit to find a signal which would replicate the ground side of a standard single Z coil??? From what I've heard, the standard signal from the ECM will not drive a Z tach, so it seems either you have to amplify that signal into something the Z tach understands, or use the igniter ground for the six coils to pick up a signal the Z tach will respond to. Any comments? Has anyone already overcome this issue already?? CHeers Jamo Quote Link to comment Share on other sites More sharing options...
jamo240 Posted March 5, 2011 Author Share Posted March 5, 2011 OK...I think I may be wrong with the Z tach being driven off the ground side of the coil....seems like it is off the +ve side...there is also a common feed to all six coils on the RB25, so is there a consensus that this may be the spot to look??? Cheers Quote Link to comment Share on other sites More sharing options...
Wayne G Posted March 5, 2011 Share Posted March 5, 2011 I am in the process of RB swap into mine. There is a taco output wire from the factory ecm, I was thinking of putting this in to the factory taco and see what happens, after all, the taco is looking for a pulse isn't it? I do not remember the pin off the top of my head but it is listed on those pinout lists available from various sites. Quote Link to comment Share on other sites More sharing options...
jamo240 Posted March 5, 2011 Author Share Posted March 5, 2011 Thanks Wayne The pin you're talking about is pin 7 on the ECU. I don't believe this will drive a Z tach, but feel free to have a go. I think the Z tach's are driven from the +ve side of the coil, and this is quite an unusual approach by current standards. I would say that the output from the R33 ECU is a processed signal that the tach would 'read'and then display as the engine speed. The Z signal is just a raw unprocessed output from the coil. Anyway, could be worth a go. Let's see if anyone else has already faced and overcome this (potential) problem. Cheers Jamo Quote Link to comment Share on other sites More sharing options...
NZeder Posted March 5, 2011 Share Posted March 5, 2011 Most of our RHD Zed have a inductive loop off the +ve side of the coil to drive the tach. This is a licensed copy of the smith's gauge used in Jags of the same/earlier vintage. Some of the US LHD (thinking mainly 280z here aka EFI cars, so might be same for some of the JDM S31/L20e powered cars - not sure) were more standard tach setups with a -ve coil connection. The issue with the +ve setup is if the tach as a fault it can stop the spark as depending on the fault you could lose the +ve to the coil. However I have not heard of that happening to a Zed tach You can get a conversion board that you install into the back of the tach to remove the +ve inductive loop setup and change to the more modern -ve coil pulse setup. Again the Jag Smith gauge conversion will work on the zed tach Check on Hybridz there are number of different ways to drive a tach from the RB ETC -- using a modified tach as stated above, or as other have done using a different tach in the zed housing/face etc. Quote Link to comment Share on other sites More sharing options...
DevilZ Posted March 5, 2011 Share Posted March 5, 2011 Hey guys Does anyone have knowledge on how to drive a Z tach with an RB ignition system? As we know, the Z tach is driven off the ground side of the (single coil). The RB engine uses an igniter (a power transistor) that grounds each of the six coils in turn to fire the cylinder. The ECM controls the igniter transistors (ie switches current on and off in the coil primary cct thru the igniter), and I guess it uses this information to feed the engine speed through to the R33 Skyline tach. Each transistor in the igniter appears to ground the primary side of the coils through a common ground, so that may be the spot to hit to find a signal which would replicate the ground side of a standard single Z coil??? From what I've heard, the standard signal from the ECM will not drive a Z tach, so it seems either you have to amplify that signal into something the Z tach understands, or use the igniter ground for the six coils to pick up a signal the Z tach will respond to. Any comments? Has anyone already overcome this issue already?? CHeers Jamo Hi, I haven't set-up the tacho from a RB but I converted my Z to use a 3-coil direct crank ignition driven from a Wolf ECU. I had to have the origional tacho modified by a gauge expert for it to work, to be able to accept the signal comming out fom the ECU. I'm thinking yor have to do the same. The place I used is over in Ringwood in Melbourne. Think it is called Spedometer Gauges. Raj Quote Link to comment Share on other sites More sharing options...
zed240au Posted March 6, 2011 Share Posted March 6, 2011 With my LS1 conversion found the ecm feed would not drive std tacho so i ended up buying after market tacho and pulling internals from z tacho Then fitted aftermarket tacho into std z housing with std tacho face works fine now even upgraded turn signals in tacho to l.e.d work good too mick Quote Link to comment Share on other sites More sharing options...
jamo240 Posted March 6, 2011 Author Share Posted March 6, 2011 Thanks Mick How did you get the displacement of the needle to work right...ie get the angular displacement to represent the correct rpm...did it just work out lucky, or did you have to customise the displacement to work with the layout of the std Z tach fascia? Cheers Jamo Quote Link to comment Share on other sites More sharing options...
zed240au Posted March 6, 2011 Share Posted March 6, 2011 just bought a tacho which was about the same size face as the zed one think it was 3.75" face with 8000 rpm total i think from memory .Laying face over top of zed one it ie near perfect match mick Quote Link to comment Share on other sites More sharing options...
d3c0y Posted April 5, 2011 Share Posted April 5, 2011 For what it's worth i have all the components at home to build convters for inductive loop tachos so they work on electronic active ground signals. I will be making 3 or 4 if any one is interested. Quote Link to comment Share on other sites More sharing options...
Moderators Zedman240® Posted April 5, 2011 Moderators Share Posted April 5, 2011 How much will they be approx? Quote Link to comment Share on other sites More sharing options...
rb25240z Posted April 6, 2011 Share Posted April 6, 2011 I think it would be possible to run a wire from each coil +v through a diode then all meeting together to the tacho input. Diodes work kind of like a one way valve for electricity and only cost a few cents from jaycar etc. This way the coil that fires signal will get to the tacho and the diodes on each of other five wires blocks the signal from traveling back to the rest of the coils. Quote Link to comment Share on other sites More sharing options...
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