My MPFI swap experience

[ElbertR]

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!:

[turtlecrxsi]

Good job man!

This should be stickied or something.

[FrodoGT]

Wow man, that intake is friggin HUGE! I know it's stock, but if it were on my b16 that sits much farther toward the firewall...I don't think it would fit! The runners just stick so far out...

[ElbertR]

Originally Posted by FrodoGT

Wow man, that intake is friggin HUGE! I know it's stock, but if it were on my b16 that sits much farther toward the firewall...I don't think it would fit! The runners just stick so far out...

The first MPFI intake I found was in a u-pull-it junkyard sitting in a '90 Civic Wagon. The engine bay is shorter in a Wagon and I found out that the only way to get the intake off was to lift the whole engine out.

A little too much work for me. Did take all the other MPFI parts out of there I could get my hands on (wiring, trottle body, resistor box, EACV, FITV, fuel rail, injectors).

The distributor and plug were already gone. Looked in about 5 different junkyards and could not find a SI distributor. For some reason these are very popular.

I finally found the actual intake by doing an internet parts search and calling junkyards all over the western U.S. I had it shipped to me in FL from a yard in NC.

I cleaned it, inside and out, painted it and used new gasgets for the trottle body and the actual intake.

Also had to get a new hose and vacuum valve from the Honda dealer. The dizzie and PM6 ECU I bought on Ebay.

Couldn't find the female side (wire harness side) for the SI distributor connector (8 pin) so I attached a bigger (12 pin) connector to both sides. There are 2 white wires coming out of the dizzie for different functions and had to figure out which is which.

[FrodoGT]

eah, nice work though man, I just found a crx hf today and promptly took the engine harness, Ive had an SI interior harness lying in a box for about 3 weeks and I was really hating the fact that I was gonna have to pay a ton of money for a mpfi engine harness...I got it for $25 HA! Oddly enough, I went to the junkyard looking for an SI (civic or crx...I needed the seat brackets), and came home with a wiring harness...and a trunk latch for an accord for my buddy lol.

[91hbcivicdx]

so after the swap, do you feel a difference from before? hows the gas mileage?

[ElbertR]

Originally Posted by 91hbcivicdx

so after the swap, do you feel a difference from before? hows the gas mileage?

Definitely better acceleration, now I can actually gain speed while in 5th gear. Really feels like it has more power. Using the short air intake makes the engine 'roar' more.

Can't tell about the gas mileage yet. Still haven't driven my tank empty yet. Don't think it will be much less then what it was.

[FrodoGT]

Cant be all too bad...Im getting 28....and my wiring is jacked up until I swap it..

[ElbertR]

After the swap my average fuel milage is still between 30 to 35 mpg.

Not much difference from my old DPFI / 4-speed setup.