ED-EF Swaps 1991 and older Civics, CRXs

In Depth MPFI Swap Questions....

Old 09-21-2005, 08:23 PM
Thread Starter
Join Date: Sep 2005
Posts: 6
Default In Depth MPFI Swap Questions....

I have a 91 civic hatch, not sure on the code but it's the most bare one you can get. I had a crx Si motor in it but we got lazy and didn't wanna wire up the DPFI to MPFI swap so we just slapped the dual point manifold on there. Well, a few months ago I ran into some water in the middle of the road and hydro locked it up. I finally got a new Si motor from nippon and we decided to try to wire it up correctly. We just got done fighting with these Vague instructions off the net on my swap and now, of course, the car runs like crap and it's flashing codes non stop (mostly a TDC code)My dude said it seems like it's only runnin on 2 cylinders or something. So here's what we encountered through this....

The instuctions weren't very specific, and when they were, like the A3 and A7 wire colors, they were off! said they were supposed to be like red and yellow or something? and they weren't. So we were confused as to weather to just go with the wires in the pin #'s or find the right colors. We just went with the pin #'s and disregaurded the colors. Was that right?

The injector #'s were backwards. I got a diagram and it showed the injector order backwards from the cylinder #'s or is that normal??

Moving the orange and white wires from their spot over to B10 and B12, well it said that B12 might have a wire in it and it did, and that you could use one from B2 or B11 for B10 cause they were empty but both those had wires in them. So we took the pin and wire from B2 (think it was orange) and used it....don't know if that was right or wrong?? or if it had a purpose there or not and we just messed it up??

Finally, and what we think the problem is, the distributor wiring colors were no-where near what the diagram said. It was calling to connect all these diff color wires but all my harness AND the distributor had were like a few whites with diff color tracers and 2 plain whites. Now both the harness and dist. wires were identical so we just conected them color to color with the exception of the 2 plain white ones, we just left those loose so we could change them back and forth since we didn't know which white went to which white. Don't know if that was right either or if we should've tried to follow the diagram better. But I don't see how cause like I said the colors weren't right.....

Thanks in advance for any help or advice you guys have. I posted this on honda-tech.com and didn't get any answers other than some guy e-mailed me some better instructions that basically confirmed the moves we made. Gettin a little agrivated not to have my Honda when gas is so much and I drive 50 min to work each day........
Old 10-08-2005, 11:10 AM
Join Date: Oct 2005
Posts: 13
Default RE: In Depth MPFI Swap Questions....

where did you get your wiring info, i would grab a chiltons and look at the wiring for a mpfi the colors are not as important as them being in the right connector and if you want to see if your missing just pull plug wires one at a time if mothing changes your car is missing on that cylinder. just think a circuit needs power and ground use a test light and get hunting
Old 11-22-2005, 04:47 PM
Senior Member
Join Date: Nov 2005
Posts: 2,667
Default RE: In Depth MPFI Swap Questions....

if you didn't mod the wires yet, buy a coversion harness through www.boomslang.us it is like 100 dolars and there is no cutting just connect a few wires your done
Old 11-24-2005, 02:35 AM
Senior Member
Join Date: Dec 2004
Posts: 3,095
Default RE: In Depth MPFI Swap Questions....

TDC code is because you didn't switch the wires.

Are these the instructions you got?:


The following are the modifications needed to convert an 91 Civic/CRX 1.5l DX wiring harness (manual transmission only) to an 91 ZC motor.

The first area of modification is at the ECU. A DX model will not have any connection at pins B10 and B12 on plug C452 (The middle ECU plug). Therefore, to connect wires at this point you will need extra connector pins to add to the DX plug. These connectors can be carefully grafted from unused pins. Some models will already have wires at B12, in this case you will cut the existing wire off and use that terminal directly. B10 will be empty, a wire for this space can be grafted from unused pins such as B2 or B11. Once you have a place to connect wires at B10 and B12 you will cut the orange and white wires off of pins C1 and C2 on connector C453 and connect them to B10 and B12. NOTE: These wires can be connected in any order because the measurement is resistance, but the book says orange to B10 and white to B12. Be sure to leave enough wire on C1 and C2 for the next step! The next connection is to run wires from C1 and C2 to the engine compartment for later use, label them C1 and C2. The last modifica 89 Acura Integra (RS, LS or GS) ECU or an 91 Honda Civic/CRX Si ECU.

Part two of the wiring modification is in the engine compartment. With the DX motor out of the car and the ZC motor next to it, carefully transfer the DX wiring harness over to the ZC. You should be able to make all the connections. If a wire is too short (TPS and EACV usually), remove some of the flex loom and it ll fit. You will end up with three extra plugs, C117 and C118 which are DX injector plugs and C115 which is the DX s Tandem Valve Control Solenoid Valve. Install the motor into the car and continue.

To make the rest of the connections, the ZC motor must have plugs and excess wire on the injectors as well as the Cylinder Sensor which is on the end of the exhaust cam. To wire the ZC s fuel injectors you will need the yellow and red wires from C117 and C118 respectively and the two wires you ran from the ECU labeled A3 and A7. Assuming the ZC s injector wires are intact with excess wire make the following connections: [Connect the yellow wire from C117 to the ZC s #1 injector which should be a brown wire. Connect the red wire from C118 to the #3 injector which should be a light blue wire. Connect the wire you labeled A3 to the #2 injector which should be a red wire. Then, connect the wire you labeled A7 to the #4 injector which should be a yellow wire.] With all of these connections in place you will need to connect the power leads to each injector. These leads MUST be wires through an injector resistor, which is basically a 6 ohm resistor for each injector to reduce the switching load on the ECU. You may use any Honda injector resistor, as they are all 6 ohms. As old as a first generation CRX Si or as new as a 97 Accord. For my application I used one out of an 87 Acura Integra. The resistor is a small aluminum box, usually with a heatsink, that has five wires coming from it. Four of these wires will be the same color, connect one of these to each . injector, and the fifth wire needs to be connected to the two yellow/black wires from C117 and C118. Now that you have completed the injector wiring you need to hook up the Cylinder Sensor. This is simple, just connect the wires you marked C1 and C2 to the blue/green and blue/yellow wires on the Sensor. The last modification is VERY important! You must reverse the green/white and yellow/white wires on the Throttle Position Sensor, because the DX s turns backwards.


I know these instructions are correct, so assuming you followed/follow them to the letter, it should work (even though these are instructions for a ZC and not an SI swap).

Here are some pretty complex ECU pin maps, so I hope you can decode them. I had to convert them to txt files, so they might be tough to follow. If not, send me an email and I can send you the real things (Excel format).


1990/1991 Honda MPFI CRX ECU Wiring reference

"The colors are ordered with the "primary" color of the wire listed first and the "stripe" color is listed second"
Last Updated on 25-Sept-2000 by David Moore * http://www.dmoore.com

C451 (Shown from WIRE side of FEMALE connections)
Numbers inside corrospond to those in the Hnda Electrical Service Manual
Letters/Numbers on the outside corrospond to the Chilton/Standard Service Manual
Bold number connectors are heavy gauge wire

Brown Red Lt Blue Yellow Key Blu/Yel Yel/Blk Yel/Blk Not Used
A1 A3 A5 A7 (A9) A11 A13 A15 A17
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16 17
A2 A4 A6 A8 A10 A12 A14 A16 A18
Black Black Green Not Used Not Used Grn/Blk Grn/Blk Brn/Blk Blk/Red

Pinout Cross Reference and Function
A1 / 1 - Injector #1
A3 / 2 - Injector #2
A5 / 3 - Injector #3
A7 / 4 - Injector #4
A11 / 5 - EACV (Electronic Air Control Vavle) - Si Only
A13 & A15 / 6 & 7 - Power Input to Fuel Injector Box (connected later in the harness)
A2 & A4 / 9 & 10 - Ground (to main relay - connected later in the harness)
A6 / 11 - Purge Cut-Off Solenoid Vavle (Si Only)
A12 & A14 / 14 & 15 - Fuel Pump Control (Main Relay)
A16 & A18 / 16 & 17 - Ground (for shields on CYL/TDC/Crank Wiring)

C452 (Shown from WIRE side of FEMALE connections)
Numbers inside corrospond to those in the Hnda Electrical Service Manual
Letters/Numbers on the outside corrospond to the Chilton/Standard Service Manual
Bold number connectors are heavy gauge wire

Wht/Grn Yellow Wht/Yel (HF only) Grn (HF only) Grn/Blk (HF only) Green Blu/Wht White White Grn/Red
B1 B3 B5 B7 B9 B11 B13 B15 B17 B19
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
B2 B4 B6 B8 B10 B12 B14 B16 B18 B20
Blue Yel/Grn Grn/Orn Blu/Red Orange White Blue Yel/Red Not Used Brown

Pinout Cross Reference and Function
B1 / 1 - Battery (+12) Input (hot at all times - fuse #34 under hood)
B3 / 2 - A/C compressor Clutch Relay Control
B5 / 3 - Alternator RF Signal
B7 / 4 - A/C on Input (HF Only - wire not present on Si)
B9 / 5 - Back up Lights Switch (HF Only - wire not present on Si)
B11 / 6 - Clutch Input Switch - reports when clutch petal pressed (HF Only - wire not present on Si)
B13 / 7 - Starting input (hot when starting - also goes to main realy)
B15 & B17 / 8 & 9 - Ignition output signal (to ignitor unit in distributor) connected later in the harness)
B19 / 10 - Electric Load Detector (ELD) input
B2 / 11 - Fast Idle Control Solienoid Vavle Control (Si Only - not present on 88 Si)
B4 / 12 - A/C on input
B6 / 13 - Check Engine Warning Light Control
B8 / 14 - Radiator fan and Condensor Fan Control
B10 & B12 / 15 & 16 - Crank Sensor (in Distributor)
B14 / 17 - Alternator Output Signal
B16 / 18 - From Speed pulser in Dash Cluster (speed sensor)
B18 / 19 - Not Used in Si/HF
B20 / 20 - Ignition Timing Adjustment Connector Input (jumper for setting timing)

C453 (Shown from WIRE side of FEMALE connections)
Numbers inside corrospond to those in the Hnda Electrical Service Manual
Letters/Numbers on the outside corrospond to the Chilton/Standard Service Manual
Bold number connectors
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