Where does the ECM sense the fuel pump voltage?

Also, other than using that voltage sense for calculating injector offsets (when the switch isn't activated for using battery voltage), what does that voltage sense get used for?

The fuel pump voltage on the ALDL stream is showing about a volt lower than the battery voltage in the same data stream.

I currently have the switch activated for using battery voltage for injector offsets, so I was wondering if I should go through the effort to beef up the fuel pump wiring.

I currently do not have any fuel pressure issues, so the pump itself appears to be happy. But I don't know if the fuel pump voltage sense is being used for any calculations in the ECM or where the ECM is sensing that voltage to begin with (i.e., what wiring do I go after to minimize that voltage drop).

 

Also, one more question...

For a given set of injector offset vs battery voltage values.... assume for the moment they're not correct for the injectors I'm running.

If I have a BLM of 128 for a given operating condition, does that mean I'm at ~14.7:1 in spite of the incorrect offset values? that is to say, I've compensated for the offset values through tuning the VE tables?

Or is it the case that the ECM is displaying a BLM of 128, but in reality, it's making an "assumption" of 128 based on the offset values and in reality I'm actually getting a different resultant AFR at the O2 sensor?

I should probably invest in a wideband at some point, I know. But I'm also curious about how the system operates.

 

The 'battery' voltage is from the ignition switch feed. The ECM reads the ignition input for this value as it is also used to know when the ignition has been turned off.

The fuel pump voltage is going to be harness dependent. It is supposed to be from the relay that feeds power to the fuel pump itself. That is the fuel pump side of the relay so that it may also be used for the fuel pump relay malfunction logic.

As such this is usually picked up under the hood and then fed to the ECM.

As for the BLM of 128, that takes into account all and any fuel that gets injected. If the injector offsets are changed in the common voltage range, the BLMs will change.

RBob.

 

Thanks RBob. So then on the injector offsets, if I've achieved BLM's of 128, there's no real value to be had by changing the offset values and retuning to 128 again? Reason I ask is I found the offset values for the SVO 24# injectors (which is what I'm pretty sure I have). Before I go through the hassle of a re-tune, just wanted to see if any value in the effort.

Curious that the ECM should detect such a significant voltage drop at the fuel pump with the sense location actually not that far away.

 

If it were me, I'd make the injector compensation changes. Then tweak the VE back in to correct values.

RBob.

 

Ok, I'll do that and let you know what results I get.