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Gasoline Fumes 01-17-2010 07:08 AM

Does the MPGuino work with the 1988-91 Honda Civic/CRX TBI? There's a main and auxiliary injector in the throttle body.

Christ 01-17-2010 02:27 PM

You'd hook it up to the main injector, but as far as whether it would give accurate readings, that'd be based on your calibration, I'd think.

The aux injector doesn't do much, I never even had one while I had DPFI on my Civic.

Gasoline Fumes 10-08-2010 02:28 AM


Has anybody tried the MPGuino on a Honda with the DPFI? My concern is that the aux injector would be unmonitored, making the displayed MPG inaccurate.

Gasoline Fumes 10-08-2010 09:39 AM

I haven't done any testing of the injectors myself, but I found a little more info about the Honda DPFI here:
90 model civic dx injection operation from factory manual - Car Forums and Automotive Chat


While trying to find a way to monitor the FI on time tobe able
to monitor fule use real time I had a dual channel oscillsocpe
connected to botht eh main adn aux FI.

There is no simple way to discribe the "firing" events.
The main cylcled pretty much the way I expected.
But the aux didn't behave in what I would consider to be
any logical manor. During cold starts the main and aux are
both one about the same times. As the engine warms up the
aux on cycles are reduced except for odd cyles that do not
relate to acceration or engine speed. For instgance,
while driving on a level stretch of highway, keeping speed
and throttle postion constant, the main chugss away more or
less like I expected. But at odd intervals the aux would cyle
on for no apparent reason.

In general any demand for increased engine RPM, ie opening
the throttle, will result in the aux opening for variable
periods. Deceleration using the engine had the aux cycling
more then the main. I finally found this link,
<>;, and I use 2 of them
to monitor both main and aux. I had thought about trying to
combine the outputs so I only had to deal with one disply,
but after some practice I can now minmise my fuel consumption.

I was intrigued by the lowest intake manifold vacuum does
not translate to best fuel economy.

I am sure that a real micro computer whiz could read the data
from the ECM EPROMS and build a table that shows on ratio for
engine temp, MAP, O2, RPM and BAR but this is way beyond my
skill set.

My 1991 Civic has been a test bed since last fall.
I have played around with lots of odd stuff trying
to understand the ECM better. You can fool the ECM
into thinking the secondary injector is present and
the car will start, if the enigine is "warm". I didn't
try too long but my car starts within 3 or 4 secs
worst case with both injectors. But with onlh the
primary I cranked a cold enigne for 15 sec. I don't
think the primary alone can get the mix rich enough
to start when cold.

However drivibility will be really, and I mean *REALLY*
bad. Jerky take offs with odd surges in acceration.

And during downshifting you will experience mild back
firing, more of a back burping.

I have not been able to understand why under steady load,
steady speed on a very level 5 mile stretch of road, the
primary just toggles like I expect, but the aux/secondary
opens at what certainly appear to be random events.

During downshifts it is clear. The primary shuts down and
the aux fires as determined by engine speed and presence of
breaking, ie the brake light also feeds the ECM. This is way
you are better off using the engine to slow down then to
shift into nuetral or hold the clutch in. At idle the primary
is just chugging away, during downshift only the aux is firing
and then only enough to, I think, keep the engine alive.

If you monitor the O2 sensor you will see the mix has become
rather lean.

dcb 10-08-2010 10:00 AM

conceptually, you could use two "guinos" but I don't know how you would calibrate them. Maybe drive for a tank with the aux unplugged and calibrate the main injector to the gas pump, then you would be able to calibrate the aux to the pump by the difference of the fillup to the usage on the main injector.

Also, I saw something curious online. Is the main injector peak and hold but the aux is saturated? What are their ohm readings?

Gasoline Fumes 10-08-2010 09:17 PM

From the factory manual:

Main injector = 0.6 - 1.6 ohms
Aux injector = 6 - 10 ohms

bobski 11-02-2010 03:28 PM

IIRC, the main injector is 500cc/min while the aux is 450 cc/min.

I haven't taken the time to fully examine the MPGuino code, but I assume it uses an interrupt routine to watch the injector input. The Arduino has two interrupt channels... for some reason, that injector input is wired to both. I don't see why you couldn't break that up and create two injector input channels, with different scaling values. That would be a hardware tweak and possibly a fair chunk of code. As I recall, storage space is already tight on the '168-based units. Maybe use a '328?

SVOboy 11-03-2010 10:33 AM

The 88-91 doesn't have an electronic speedo, which is another issue I just wanted to throw out there :)

bobski 11-03-2010 11:56 AM


Originally Posted by SVOboy (Post 202280)
The 88-91 doesn't have an electronic speedo, which is another issue I just wanted to throw out there :)

The speedo itself isn't electronic, but it does in fact have a VSS. The confusion comes from later generations that have the VSS mounted on the transmission. '88-91 models have a cable drive from the transmission to the speedo, and the VSS built into the speedo/odometer assembly. The signal should be fully compatible with the MPGuino.

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