MSefi.com read only forum (Jan.15,2018)

Hello;

I am planning to use a Honda TBI throttle body in my 1982 4WD Subaru
stat wagon (1.8l), with ms-I, a version 3.0 board and a relay
board that I've almost finished assembling. Pictures of the tb here:

http://jimulco.autonoma.edu.co/fotos/tbi/

Unfortunately, I have not been able to find much info on this
throttle body. It has two injectors; one of them seems to be
some kind of auxiliary injector (for starting? enrichment
with cold engine?) and has a DC resistance of roughly 1 ohm.
The other one is probably the normal injector and has a DC
resistance of 8.2 ohm . I have no info whatsoever on the
lbs/hour rating of either injector, or the operating pressure
for the fuel (it does have a fuel pressure regulator attached).
I've figured out the following tubing/hose connections in the
tbi:

- fuel line/fuel return/fuel pressure regulator vacuum
- vacuum line to top butterfly diaphragm, with solenoid
valve for disabling its operation - normally even a very light
vacuum will open the top butterfly completely
- vacuum line to another diaphragm that will close the
main butterfly further when idling. This one does not have a
solenoid valve.
- vacuum port, samples MAP just in the intersection of the
throttle body and the intake manifold (hole and channel can
be seen in the picture labeled 'bottom')

This leaves me with three hoses that I am not sure about;
they can be seen in the picture labeled "south";
one is at bottom left, protruding left; another is at bottom
center, protruding normal to the picture, then turning down;
and the last one is the one protruding from the center, immediately
right of the solenoid valve; it's got a hose with a reddish jacket
attached. The first two hoses here seem to be connected
internally (what for? engine coolant or something to warm up
the throttle body bore?), while the last (the one with the
jacket) leads to a small hole in the center of the throttle bore,
between the two butterflies (EGR?).

This tb apparently belonged in a 1991 Honda Civic originally, 1.5l .
The bore diameter is 44mm. So here are my questions:

1) What is the top (auxiliary) injector for? What size resistor should
I use for it (it has ~1ohm resistance) What is its capacity?
2) What is the rating for the bottom injector? (it has 8.2 ohm
resistance and I assume that it is the main injector here)
3) What are the three remaining hoses described above for?
4) The diaphragm without a solenoid valve -- where do I connect
its vacuum line? Normal MAP? Or is it supposed to come from
elsewhere?

Any help will be greatly appreciated as I haven't found much info
yet. The idea is to make an adapter to attach this right
in the original carburator seat.

Regards,

cmurillo

According to ALLDATA and Chilton's the top injector is the Main injector with specs of 0.6 to 1.6 ohms and the bottom injector is the Auxilary injector with specs of 6 to 10 ohms.

Fuel pressure specs are 35-36psi with vacuum hose connected to fuel pressure regulator and 40-50psi with vacuum hose disconnected.

I would recommend getting a factory service manual. This is the service manual used by techs at the Honda dealerships. These type of service manuals have so much more info than ALLDATA or Chiltons or Haynes. You can get them on eBay usually.

The main reason I recommend this is that just because the top one is call main and bottom one auxuilary, you shouldn't make any assumptions as to how they show be controlled. I remember testing these injectors on these Civics and the bottom auxuillary injector operated at idle and with throttle depressed, while the top main injector operated only when throttle was depressed.

I do believe two of the hoses should be for coolant to keep the throttle body from icing. The third I do not remember, and my manuals don't tell me (get the factory service manual). It could be for egr, but only the Civics built for California had that during that year, so maybe.

The diaphragm without a solenoid is called the Dashpot Diaphragm. It's hose just goes to manifold vacuum. ALLDATA says the vacuum at idle pulls the throttle to the idle position, and during cranking the spring in the diaphragm holds the throttle open a certain amount to help with starting. Chilton's adds that the diaphragm also slows the throttle as it approaches the closed position.

That's all the info I have. Good luck. I've made an adapter for my dual carb Volvo. I made it go from two carb mounts into one throttle body mount. You can make anything you want, with enough time and money.

It looks like that center hose between the two throttle plates is for evap purge from the charcoal canister.

[img][/img]

Whoops. I think the vacuum hose diagram image will post this time.

Thank you alienbush! This is a whole lot more info than what I had. Now I
know where all the hoses go, and something important about the
operation of the injectors; it seems that the best way to operate
the two injectors is to use the "staged injection" feature in the
ms-extra code, with the auxiliary injector as "bank 1" and the main injector
as "bank 2". And the difference in DC resistance calls for using a
resistor in series with the low-impedance one.

Buying things on eBay is a little difficult from Colombia and Honda models
from that era are not very common either, so my chances of obtaining
a factory service manual for a '91 Civic here are slim. I would have
to wait until the fall, when I plan to spend a couple of months in the U.S...

But really, thanks to your help, at this point I think that the only missing info is
the flow rating for the injectors. I plan to use an LC1 for EGO (which I bought
last year) and a second MAP sensor for appropriate barometric
correction. This is a must here in the Andes, where some paved roads climb
from 2600 ft all the way to 13500 ft in as little as 28 miles, and if you
venture into this natural park which is close by, there is an unpaved road
that takes you to 15420 ft, almost as high as Mont Blanc. I've been there
with my carburetted Subaru several times - worked fine, loses a lot of power,
though I thought that other cars lost a larger percentage, and many simply stall.