ECU on carburated engine ???

Did the carbureted engine, say, for Civic or CRX from early 80s to early 90s
have any sort of ECU or its alternative (control box)???

For some reason I convinced myself that only vehicle with fuel injection
(read: it has fuel injectors, not carburetor) will and can have ECU.

Tell me that I am wrong. What specifically can ECU do on carbureted engine
if everything is manual or vacuum driven, as far as fuel mixture, and ECU
has no way to adjust it?

TNX

 

My old 1981 Camaro Z-28 had an ECU and a carb. The carb was basically a
modified 4 barrel Quadrajet. If I recall, as Im going back to my high-school
days here...the ECU controlled the accelerator pump on the carb. The car
also has a MAP (manifold pressure sensor) and an 02 sensor. On-board
diagnostics were part ofthe ECU as well. 1981 was the first year GM put ECUs
on board.

 

Now, please, try to recall WHAT would that ECU do to the accel pump to
change, say, fuel mixture, HOW would it interpret data from MAP and O2
sensor, what would it do with all the "data". I mean, what were the
mechanics involved? Did the ECU "alter" the engine management through vacuum
lines, solenoids, electric motors, cables?

With MPFI it is easy - a matter of simply sending a signal, change in the
voltage, whatever.
Really interesting!

 

Lots of cars with carburetors used ECUs in the late 70's and early 80's.
These were often refereed to as "feedback carburetors" and doing a
google search will give you a lot of hits (mostly useless ones, though).

I know some used a stepper motor to control an auxiliary air valve that
led extra air in after the venturi.

 

My '85 Escort (carburated of course) had something that the mechanic
referred to as "brain box". I suspect that's what they called an ECU back
then. Unfortunately, I don't know exactly what its function was, but it did
break once and had to be replaced.

Cheers,

Pete

 

Carburetor is called Emission Control Unit not ECU. Fuel injection is
called ECU or Electronic Control Unit to avoid confusion.

The Emission Control Unit controls vacuum flow by blocking or
unblocking solenoids. For instance, it could cut-off fuel under
deceleration. It has a variety of jobs.

Voltages from O2 are converted to digital at which it activates a
preprogrammed instruction. The instructions triggers a transistor to
open the mixture solenoid valve to increase air ratio only if O2 says
0.9V or higher, for example.

No cables, or motors as I recall.

 

OK...now youre pushing it....

I think, basically, you got it right. The ECU used data from the MAP and O2
sensor to adjust the fuel mixture through the accelerator pump. It was
pretty rudimentary.

 

Correction, it should read. The Emission Control Unit controls vacuum
flow by blocking or unblocking flow using solenoids.

 

I have a 1987 Accord DX (Carb, Sedan, US model)
I know with a fuel injected car, while decelerating, the injectors are
typically shut off to increase fuel economy.
So, on my carb model, does the fuel get cut off during decel? Or would
shifting to neutral during deceleration be better for fuel economy?

 

[Would fuel cut off during deceleration & in gear on Carb?]

Yes. I'd been waiting for someone to ask this question. Shifting to
nuetral will not save gas as fuel is used for idling. On the the DX,
fuel will shut off during decelerating while in gear and over 1200
rpm. Hint: Cruising at 30-40mph on 5ft gear will use almost about the
same gas as idling, (as surveyed on my test jig).
K

 

[Would fuel cut off during deceleration & in gear on Carb?]

Yes. I'd been waiting for someone to ask this question. Shifting to
nuetral will not save gas as fuel is used for idling. On the the DX,
fuel will shut off during decelerating while in gear and over 1200
rpm. Hint: Cruising at 30-40mph on 5ft gear will use almost about the
same gas as idling, (as surveyed on my test jig).
K

 

[Would fuel cut off during deceleration & in gear on Carb?]

Yes. I'd been waiting for someone to ask this question. Shifting to
nuetral will not save gas as fuel is used for idling. On the the DX,
fuel will shut off during decelerating while in gear and over 1200
rpm. Hint: Cruising at 30-40mph on 5ft gear will use almost about the
same gas as idling, (as surveyed on my test jig).
K

 

Interesting.
I've been shifting to neutral to coast down hills for a few weeks now, and I
did notice my fuel economy worsen, but I assumed it was just the commute to
my new job...I'll stop using nuetral, and see what happens.

--Peter

 

Do you have a website with this information you've compiled, and what's
your test jig. I'm curious about any technical data you've got compiled on
these models regarding fuel usage and the like.


--Peter

 

First... the previous multiple posts was unplanned.

Second... Been waiting for someone to ask this question. I noticed few
folks forget about the joy of fuel efficiency, it`s more than just
saving money. Also, I noticed you have a Civic before. If you still
own a Civic the device below may inaccurate due to the fuel return
line but works well on carbs. I use to gauge my boat engine`s fuel
economy to see whether it`s running top shape. The same principle is
use virtually on many equipment. Here is a site that sells one.

http://www.measureanything.com/products/exoflow/datasheet_fuel_flow_system.asp

Third... Due to my crafty skills, I make my own fuel meter. I also
turn the dash light dimmer to control the fuel pump`s currents, and
thus pressures. The output of the dimmer is used to trigger an FET,
which controls the speed of the fuel pump. At high speed, 45-mph and
above, low fuel pressures can achieve greater fuel mileage. This is
already done with the fuel return line - so very little you can do by
dropping the pressure further. This only applies to fuel injection
cars.

The end result is a bit more mileage, reduced passing power, bad air
for environment, and an occasional premature engine heating, which is
easily solved with a sensitive engine temperature sensor. Not
recommended for novice drivers as I've noticed the dangers involved
with no passing power. I have no problems with it.

Fouth... Datas are compiled from service manuals. The data regarding
the fuel shut-off above 1200 rpm can easily be determined by
connecting a light bulb in series to fuel cut-off solenoid valve's
green/red and ground (on Carb only.)

Etc... I don't keep datas but I keep in mind that the FI Accords gets
31 Hwy avrg. FI Civic gets 36-40 Hwy. No datas on street as driving
style changes too often.
K

 

My last car was a 94 Civic CX (Fuel Injected). I got about 45MPG on that
car, and about 50MPG during the summer months.
I actually observed with that car that it was more efficient, if I
accelerated briskly (not tire spinning fast, but just briskly...not that you
could spin the tires on that car anyhow. ;-) from stops, and to never shift
too soon (always kept the revs above 1500) Shifting into 5th at about 35-40
would leave me needing to really press the throttle pedal to get any more
speed. And so on that car I determined that it was more efficient at higher
revs, than in a higher gear with my foot buried in the throttle trying to
get some power.
With my 87 Accord, carbureted I'm not entirely sure how to best drive it,
but I do know it doesn't behave well below 2000 RPM.

BTW, where does it mention the fuel cut-off solenoid in the service manual?
Thanks for the info Koji San

--Peter

 

45-50? Wow.

The Primary Slow Mixture Cut-off Solenoid Valve is explained on page
11-92 of the 1988 Accord SM. The wire output pin is on p 11-85. To be
exact on when fuel cuts off it must meet these criteria.

Clutch switch on
warm engine
above 12.5 mph
Vac switch a off
Vac switch B on
rpm above 1500 not 1200. 1200 is for FI cars only.
K