Hopefully I can get somewhere on here on finding a fix to this problem.

The car is a 99 Civic SI (EM1), the car has it's stock ODB2B ecu, everything works fine at this stage.

I have a P06 chipped to work as a P28, but whenever I install it into the car, the tach does not work.
So because the tach works without the odb1 ecu I know it's either the ecu or the odb2b to odb1 harness, and since my chipper/tuner is legit, I will give him the benefit of a doubt. So my only conclusion is the harness.

Is anyone familiar with this issue or the set up in general?
I keep double checking the harness according to diagrams online and everything looks fine. it even has the "ODB2B A19 wire spliced with B13 ... going to OBD1 A21."

The harness is a generic harness, all black wires, odb2b side is red.
I came across a post on here saying "tap a 1k ohm resistor between pin numbers a21 and a25 wires" and before I try that, i want to know why for i don't screw things up.

 

The OBD2b ECU sends the rpm signal to the tach. As the OBD1 ECU does not, you need to get your tach signal from the blue wire from the igniter unit in the distributor.

 

If the OBD2b ECU sends the rpm signal to the tach ... that means the ODB2b ECU gets the rpm signal from the igniter right? So that would mean I should be able to jump that wire on the harness side back to the pin that would go to the tach?

 

No, the OBD2b ECU gets the rpm signal from the CKP sensor in the distributor, not the igniter unit/ICM.

 

So I find which pin on the ODB2B harness runs back to the tach, and tap that into a wire which goes through the firewall then goes to the igniter unit? Is that correct or is there an easier way? I don't have any wiring diagrams on me or do I know which ecu pins are ins/out.
On the OBD2B harness, the B13 says its the ICM. would this be the wire I need to tap into or something different? and i'm unsure which pin goes to the tach.

 

Don't mess with any ECU wires. B13 is the ECU wire that tells the ICM when to generate spark. It's not an rpm signal wire.

You need to connect the blue wire to the igniter unit inside the distributor and run that wire into the cabin and splice it to the blue tach wire at the rear of the cluster.

 

The blue wire coming from the distributor then? Or do I actually have to run a new wire into it? Because I think there should be a wire for every part coming from the distributor, and I think all those wires have to be going somewhere... someone had pointed to me a blue wire with a test plug on it in the engine bay on the driver side corner next the window, can't I use this wire? is this the rpm input then from the distributor?

 

Please read my posts so I don't need to repeat myself. No rpm signal comes from the distributor in an OBD2b Civic. Both the tach test plug and the tach in the cluster get their rpm signal from the ECU in an OBD2b Civic. If you want the tach to work with your OBD1 ECU installed, you need to connect a wire to the ICM rpm terminal in the distributor and run it to the blue tach wire at the test plug or at the rear of the cluster.

 

My apologies RonJ, I was having problems following along with the concept you laid out, that was until I just went outside took your information and actually looked at the distributor plug and saw there was no wire coming from pin 9 (I assumed everything was there, and one of my friend's kept asking if I am sure cause his odb2b car doesn't have this problem)

 

No problem. You should be able to get the tach working now that you understand the problem.

 

well I was taking the distributor apart, routed the wire through, keeping it away moving components, routing it with the other wire... decided to test out the car first before hooking up the wire... and it looks like I messed up... CEL 1381 ... won't go away. Cylinder Position Sensor... I don't know how I messed up the sensor...

 

firejackel did you get your tach to work

 

did you bother reading what the fix was?

 

3 year old thread

Vi Nation, don't do that. Ever. You've been around to know better. Read the rules, and unfuck yourself.