Fuel System
The best SM4 installation will yield poor result if the fuel system does not meet the
demands of the engine. Insufficient fuel flow can lead to engine lean out and detonation
that could destroy you engine. For the best of your engine, we urge you to check that
your fuel system’s capacity and ensure that there will be sufficient supply at all loads and
RPMs. A fuel pressure meter should be used during testing and tuning to ensure the fuel
pressure does not fall pout of regulation, meaning pressure drop or oscillate. The SM4
can use an external pressure transducer connected to analog I/P and be logged and
displayed in the ECU Error History.
This manual offers guidelines to testing your fuel system and suggests some solutions, if
there are supply problems. If you find you need to modify your fuel system and are
unsure what to do, contact your Autronic dealer.
Flow Estimation
If you can estimate the power output of a gasoline engine, you can make a reasonable
guess at the fuel flow requirement. A simple rule of thumb may be expressed in metric or
imperial units.
T
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This assumes a brake specific fuel consumption of 1.50. The actual fuel flow necessary
by injectors and pump are likely to exceed a figure derived this way. This is due to the
overheads in injector dead time and pumping return fuel to maintain regulation.
A nice help program called Injector Size.exe can be downloaded from
http://www.autronic.com
Injector Flow Capacity
If you are using second hand injectors, or have removed the current injectors while doing
work on the engine, we strongly recommend that you clean and flow test them.
Your total injector flow capability is given by the sum of the injector flow rate. Injectors
are specified in either cc/min or lb/hr. Check that you have enough injector flow to match
the estimated power output. Keep in mind that you do not want to exceed 85-90% duty
cycle injection on time, and that at high rpm, injector dead time can consume a significant
amount of available injection time, thus Autronic is fully sequential and minimize the dead
time.
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