have 91 civic hatch dx. stock ecu is pm5. i am converting to an obd1 po6.
i just got the conversion harness in the mail and the three big plugs match up fine, however there is a fourth plug on the new harness with 12 pins and im not sure what it goes to. the packaging said tht the harness fit multiple vehicles so is it possible tht i dont need the 12 pin plug?

 

Should be VTEC wires (if needed) and wires for the O2 sensor.

Which harness did you get?

 

is it a circle or rectangular plug?

 

I hope your using an OBD1 Distributor. I just found out OBD0 don't like OBD1 electronics and vice versa.

 

The extra wires are for:
IAB wire
Vtec Switch
Vtec Pressure
2 X for the O2 heated circuit
Injector power - Leave unconnected
Injector Gnd - Leave Unconnected
Knock sensor
and several other Gnds and sensors that you probably don't even have.

Just leave them unhooked unless your using an OBD1 motor and have the connections to them.

 

http://www.ebay.com/itm/400337887755...84.m1497.l2649

this is the link to it on ebay...
i need to kno the exact purpose of the 12 pin plug

 

What I just said above, I have the exact same harness off ebay. I have yet to install it since I'm working on my bushings atm.

 

ok... got 1 more question. i am also converting from dpfi top mpfi... i kno where to run the injectors at on the ecu.. but there is another wire on each one. iv done a little looking and i saw something about a 12v (+) junction box. what and where is this or do i need one. if so, is there a way to wire it without it?

 

If you have obd0 injectors, you need the resistor box. If they are obd1, I believe you tie those 4 wires together but double check that.
The 12 pin plug is for everything your car doesn't have already, as swordofdoom mentioned. You can use that plug, or wire up it directly.

 

The 12V is what supplies power to the injectors and they all run off the same 12V+, The ecu just grounds them out when it calls for them. If your running on low impedance injectors most commonly found on stock OBD0 motors, you need to wire the 12V+ into the Resistor box and from there into the injectors for power. If you don't, expect to blow up your ECU within minutes. High impedance or OBD1 Injectors don't have that issue.

If you did the MPFI conversion correctly using the resistor box you shouldn't need to use the extra 12 wires unless your running a vtec motor or an OBD1 engine. I made a pinout of that extra 12 wires but I don't have a scanner or internet at home...

 

my engine is b16a1 (vtec) do i need to wire the Vtec Switch and Vtec Pressure ?

 

Is your P06 being converted to VTEC? Normally the B16A needs both VTEC wires and knock sensor connected plus for the P06 you'll need the extra oxygen sensor wires connected.

 

o2 sensor ground on obd1 pinouts is D22

can i connect the o2 sensor ground on ( A23 or A26 or B2 ) ?

 

Why would you even do that? just hook it up to D22 just like you know you should.


You replied to 5 threads that have been inactive for over a year and none even talk about the issue that you are working on.
Next time consider starting your own thread - just one post that directly addresses your question.