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Old 08-09-2017, 12:15 AM   #43 (permalink)
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Join Date: Apr 2017
Location: Canada
Posts: 17

Terky - '99 Toyota Tercel CE
90 day: 55.71 mpg (US)
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Originally Posted by BLSTIC View Post
That... won't work. Your fuel pressure has nothing to do with your pump voltage (unless you have a pump that's too small), it's all your fuel pressure regulator. Even returnless systems have one, it's just 2" away from the in-tank pump, still inside the housing.

Increasing voltage to the injectors will decrease open time, improving flow linearity ever-so-slightly but ultimately injecting more fuel. However the air pressure over the course of the day will vary the mixtures more than this, so I wouldn't bother.

Increasing voltage to the ignition won't help much unless you are bordering on misfiring due to cylinder pressures or have a faulty coil. Side-gapping your plugs will improve burn ever-so-slightly though.
Thank you for your comments

Just to be clear, my plan is only to increase to the voltage of the fuel pump to help maintain fuel pressure to its factory spec. As it stands without the alternator I am running about 2.5-3v less than spec (roughly 12.0v under load when fully charged). I theorize that this reduced voltage reduces the available pressure - though to confirm for sure would necessitate a fuel gauge, and I don't have one in the toolbox.

Fuel injector opening time is admittedly a minor concern but if I'm going the route of messing with bus voltage this one is a relatively easy "while I'm there" mod. Ditto with the spark.

If nothing else, it will get my MPGuino back in calibration, as it gets thrown off when I switch the alternator on/off.

Off topic, I'd like to take this moment to say

Wahoo! I made the top ten list on the front page

Last edited by jonzobot; 08-09-2017 at 12:38 AM..
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