[Diy_efi] RE: Dropping Subaru injectors for economy

Michael Richards michael
Wed Feb 1 17:07:09 UTC 2006


Hi,

These two are absolutely correct. The ECU has pretty good knock and
misfire detection. It is highly unlikely that you will find a way to
bypass this. It is also doubtful that you would gain any fuel economy.

There are a few to know about the gas mileage.
-Subaru engines do not get good mileage when they are new. In my
experience it takes about 8000km before they start loosening up. My
Impreza got 490km/tank on the highway when new. After 10,000km it got
560 (same trip cruise set the same).
-A performance exhuast will help if you can stand the noise. On my car
it went from 560 to 610 on that same trip after I put on headers and
exhaust.
-A reflash of the ECU can help but may also run into warrantee issues.
This also depends on the tuner as the tune can be biased toward fuel
economy.
-Subaru engines like to be run very rich. They are insanely rich in
factory tune under boost. Not sure about your legacy but the WRX has a
cat before the turbo... this doesn't help fuel economy under boost as
they need to dump a lot of fuel to keep it from burning up and
destroying the turbo.
-Performance air filter will help as well.
-Regapping your plugs to 0.032 will help as well.

-Michael

> He's going to have a MIL on anyway, when the PCM's
> misfire monitor notices that the engine doesn't speed up 
> appropriately when the cylinder in question comes around in the 
> firing order.  The only way around this issue will be to ensure that
> the misfire monitor's enabling criteria are not met.  IDK what 
> those are for this particular vehicle; a Subie tech could look it up.

>> Ideally you would have some sort of vavletrain control to minmize 
>> pumping losses on the inactive cylinders. Since nothing short of
>> electronic valve actuation does, those dead cylinders will be like 
>> driving an air compressor. I think the resulting economy gain would
>> not be worth the trouble. If your  Legacy is turbocharged, this could
>> actually be a dangerous thing to do if you lean out a cylinder under
>> boost. If you did do it, you would also need to simulate the unused
>> injectors or you will get a check engine light.

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