05 STS fuel pump noise

[kevm14]

It turns out I was completely wrong about the fuel system theory (dual tanks/transfer situation).

I have attached an FSM excerpt.

This finally occurred to me last night while I was watching Sloppy Mechanics. His G35 (with 4.8 and LSA blower) has saddle tanks like my Sigma cars. He mentioned some kind of venturi transfer mechanism and that's when I was like....wait, maybe I don't actually have two pumps and I've been running with that bad information this entire time.

I could look it up but I am sure the SRX and my CTS-V work the same way.

And yeah, look at the FSM. It does not have dual pumps. It has dual level senders but the transfer action is mechanical. This explains everything including why there is no Tech II control for the "transfer pump." It also means that noise is probably something else entirely (which I haven't been hearing lately anyway). I almost wonder if it is coming from the audio amp and the noise is coming from my seat speakers in those times, and it just makes my brain think it is coming from the back seat. Ha.

Other fun facts about the fuel system is the fuel filter and regulator approach. The filter has a return line on it and I THOUGHT originally that it was also the regulator like on some Corvettes and stuff. It is not. There is a short loop of fuel that goes from the pump, to the filter, and excess fuel not consumed by the injectors/engine is returned to the tank via that line and the regulator is actually in the tank on the pump assembly, right at the return outlet. This may be so they don't continuously circulate fuel through the (hot as hell) engine bay and just warm up all the gas. It is also a fixed 55-60 psi and is obviously NOT vacuum referenced. Definitely different than the older GM stuff I'm used to.

I like all this theory/design stuff but it's better when the details are correct...