Just completed the MPFI swap on my 91 STD HB.
Have some comments on the instructions I found on the web for this mod.
The best info/instructions I found are on
http://www.50mod.com/fourthgenhatch/mpfi.html
My notes when using these instructions:
- If your new MPFI manifold has a FITV (fast idle thermal valve) and you want to hook this up (why not), you CANNOT use the pin from the B2 ECU connector and use it for something else. B2 is the ECU wire for the FITV. My advise is to get a couple of 88-91 Civic/CRX ECU connectors from a junk yard and take the extra pins you need out of these connectors.
To hook up the FITV use the wires from the DPFI Tandem Control Solenoid Valve (orange & black/yellow). MPFI does not use this valve and it uses the same ECU connection (B2) as the FITV. You will need the orginal plug from the SI harness, solder the blue wire from the plug to the orange wire on the old DPFI harness (and the black to the black).
- None of the MPFI instructions I found on the web mention anything about this difference in wiring between a DPFI and MPFI car:
the Purge cut-off solenoid valve is wired differently!
This valve sits on the firewall and has 2 wires going into it.
DPFI: Green (-) and Black/Yellow (+). Black/Yellow is wired to the main relay and fuse nr. 14. Green is a direct connection to the ECU.
MPFI: Green (+) and Black (-). Green is a direct connection to the ECU and Black is a ground wire.
If you don't change the wiring for this valve you have 2 wires with +12V hooked up to the valve wich will result in an ECU error code with 20 flashes.
To fix it simply cut the yellow/black wire about 3-4 inches from the valve and take the wire from the valve and ground the it to the firewall. There is a hole in the firewall right by the valve where you can screw a bolt in to hold the wire.
Finding the reason for the ECU error 20 and this difference in wiring took me quite some time. Hope this information will save you from the same fate.
Here are some pics of the swap process:
Before swap:
During:
PM6 ECU Wiring:
Injector Resistor Box:
Purge Valve Wiring:
Swap Completed!:
