Getting the tach to work - 13B-RE
 

As some of you know I've had this swap in my car for over a year now, using a 2rotor 13B-RE and a GT40R turbo. I have the PS working but have always had some problems getting the tach to work.

What I've done is taken the stock RX8 trigger wheel and mated it to the front pulley of the 13B-RE. I then took the RX8 trigger sensor and mounted it to read the wheel, then wired it to the following pins of the ECU:

The Y/B ( Yellow Black) to ecu pin 2U And Y/R (Yellow Red) to ecu pin 2X And the shield wire (Bare Wire) to ecu pin 2H And grounded pins 5D, 5T, 5O, 5R.

I always thought the problem with the tach was that I had mounted the sensor incorrectly, but recently I had it remounted very accurately and the tach still does not work (PS works fine though).

Does anyone have any ideas?

Hey Demon that's exactly what I'm doing right now (13bre with a GT40!)-just rebuilding the engine right now, could you tell me what other problems you ran into doing this project please thanks! I thought if you leave everything intact with the original pcm and do what you did mounting the stock trigger wheel everything works fine. Why would you have rewire the wires you mentioned? Perhaps you have a damaged sensor or it's picking up interference from something else closeby? BTW could you please post some pics of your setup or send some to my email spyrstas@yahoo.com

Well, the tach works perfectly now for about 2 seconds on startup then shuts off down to 0 rpm.

What is going on!

Not too familar with workings on the rx8 but on many imports when that happens especially when doing stand alone ecu's or ignition upgrades on the newer cars it's the ecu not seeing the feedback signal from the coils. Once the car is running just after crank up the factory igniter sends a signal back to the ecu to basically tell it that it's runnning. If the signal is interupted in anyway the symptoms you describe is exactly what happens. Also happens when you place an ignition box between the coils and the igniter. The fix for it is to use one of the many tach adapters from MSD. It basically puts a load on the ignition output to fool the ecu into believing the coils are still running.
Does the RX8 ecu have or throw codes/CEL for the coils?

Very interesting, this seems to be exactly what is happening. It's like the ECU realizes the car isn't really running and shuts the tach down.

I assume this is the correct adapter: http://www.msdignition.com/sci_12.htm

Now I just need to figure out how I would wire it...any help would be appreciated!

Thanks so much for this input, very insightful!

I don't see that being of any help crispeed towards demon, that would be the case let's say on the fd where the tach gets the waste signal from the coil(light green wire) which you could send directly to the tach. On the RX8 the tachometer the the pcm gets the signal directly from crank trigger wheel from what I know which is also needed for the p/s. Demon, did you try using a new sensor?

If that was the case...the IntX wouldn't work...no coil feedback with that...and the tach works.....

I just replaced the sensor with a brand new OEM last week, still no change. The power steering is also activated by this same sensor, which works fine.

I got these instructions directly from rgonza who has done this in his 20B car, but for some reason I'm having trouble. I would be happy to throw the tach out and use something aftermarket if it wasn't the fact that the speedo is incorporated!

Aftermarket Speedo then!

Trying to not get off topic but how does you RE fit in the 8's engine bay? Did you use the stock intake manifold? I'm asking because we have tried to fit an RE into the stock location and it wont work, the intake manifold hits the firewall by about 2in. The only solution is to move the tranny forward.

Don't want to get too far away from the topic at hand, but you need a custom lower intake manifold then the rest is fairly obvious!

I think I've stumbled upon something which may be causing this - the dash shows that there is low battery voltage (even though there isn't) - what is it that provides the ECU/dash with the battery signal?

I think when we did the engine swap we accidentally removed the stock battery harness (battery is in the trunk now) so it's possible the ECU isn't getting +12v which may be affecting it?

Did you ever get it sorted out?
Might be a grounding problem.