Fuel pump voltage correction and heated O2 - Third Generation F-Body Message Boards

Aaron's 87 · 02-10-2001, 08:35 AM

A lot of people tap their heated O2 into the fuel pump power. Will this draw down fuel pump voltage and in turn raise the injector pulse width due to the correction table?

Grim Reaper · 02-10-2001, 12:07 PM

With my Diacom, I can monitor my fuel pump's voltage along with my battery's voltage. The fuel pump is always .2 volts higher than the battery's. If I turn on my headlights or rear window defroster, it takes voltage from my total system and affects my fuel pumps voltage anyways, so I think its a non issue.

Besides, I think the draw from the O2 sensor is neglgible.

Grumpy · 02-10-2001, 10:59 PM

Quote:

<font face="Verdana, Arial" size="2">Originally posted by Aaron's 87:
A lot of people tap their heated O2 into the fuel pump power. Will this draw down fuel pump voltage and in turn raise the injector pulse width due to the correction table?</font>

And the problem is?.
That's why there is a voltage corection for the injectors, if the pump v drops then you need a longer correction.
The fuel pump needs checked anyway.
I have a relay mounted right near the pump, with a Heavy Fused wire directly to the battery to make sure the fuel pump gets battery voltage. On my car you can hear the difference when you switch the aux pump power on.

Aaron's 87 · 02-11-2001, 10:06 AM

I've just heard of cars running way rich when the fp loses too much voltage.

Grim Reaper · 02-11-2001, 10:48 AM

As Grumpy said, there is an Injector/Battery Voltage correction table. Assuming 14.2-14.4 is normal voltage, any voltage under 14.2 will tend to lean an engine due to and above will richen it. The correction table actually adds more fuel at the lower voltage readings and decreases fuel at the higher voltage readings (within certain limits).

I have found these correction factors very good and have not yet had to "improve" them. I have an underdrive crank pulley and I am still able to maintain my BLM/INT values when I have ALL the accessories on while idling and my voltage drops below 12 volts.

NickG · 02-11-2001, 05:06 PM

Quote:

<font face="Verdana, Arial" size="2">Originally posted by Glenn91L98GTA:
As Grumpy said, there is an Injector/Battery Voltage correction table. Assuming 14.2-14.4 is normal voltage, any voltage under 14.2 will tend to lean an engine due to and above will richen it. The correction table actually adds more fuel at the lower voltage readings and decreases fuel at the higher voltage readings (within certain limits).</font>

Actually, the purpose of that table is not to richen or lean the mixture, but to compensate for the injectors open and close response time due to voltage changes. An injector will be slower to open if its voltage is lower than spec. Hence, if the pulsewidth isn't increased to compensate for the lower voltage, there won't be enough fuel sprayed (cause the actual on time of the injector will be less), causing a lean mixture. Increasing the pulsewidth with lower voltage keeps the actual fuel flow correct, resulting in the correct mixture.

Nick