Fuel Pump Control

[NateD4]

Does any one know how modern fuel pumps control pressure (3900 VVT)? I only see one line on my fuel system so I assume the pressure is controlled at the pump. Is it electronically controlled?

[robertisaar]

according to alldata, an 07 impala with 3900 has a supply and return line.

it's also a normal 4 pin plug for the fuel sending unit/pump, the important parts being a normal relay driven(by the PCM) +12V and ground for the pump.

i also see a FPR.



sounds like the classic 660. if you get into the 3.6 or other newer DOHC stuff, then it's probably different.

[NateD4]

I'm working with a 2008 LZG from an Impala. It appears to only have a single fuel line.

Do the newer pumps have a FPR built into them.

[pocket-rocket]

From what I've read about the returnless style systems the PCM does control fuel pump RPM to control fuel pressure. If you want, I can scan the section of my computer tuning book where it says that.

The one thing I like about the thought of returnless is you don't have more fuel than you need going to the engine, getting heated up and returning to the tank. Only what's needed is sent to the engine, so you don't get the whole tank hot from running it to the engine and back.

[rooster5333]

From what I've read about the returnless style systems the PCM does control fuel pump RPM to control fuel pressure. If you want, I can scan the section of my computer tuning book where it says that.

The one thing I like about the thought of returnless is you don't have more fuel than you need going to the engine, getting heated up and returning to the tank. Only what's needed is sent to the engine, so you don't get the whole tank hot from running it to the engine and back.

i think rocket has hit on something. why run a loop onto a hot engine, to heat up the fuel? why couldn't you put in a fpr just after the filter, and loop back from there? you would still get full pressure to the rail, and any excess fuel would simply be looped back to the tank from the cooler filter area, instead of the hot engine area. leave the original fpr in place with no vacuum line, that way, there is no chance of too much pressure. hmmm, just a thought. what you guys think. possible? or am i thinking outside of my pay grade?

[pocket-rocket]

i think rocket has hit on something. why run a loop onto a hot engine, to heat up the fuel? why couldn't you put in a fpr just after the filter, and loop back from there? you would still get full pressure to the rail, and any excess fuel would simply be looped back to the tank from the cooler filter area, instead of the hot engine area. leave the original fpr in place with no vacuum line, that way, there is no chance of too much pressure. hmmm, just a thought. what you guys think. possible? or am i thinking outside of my pay grade?

I've considered putting a FPR back at the tank, but then I also think of the length of vacuum hose to run it clear back there. My concern with that is in turbo systems, you want the vacuum lines for the BOV and wastegate as short as possible to avoid lag in these things activating too late. I compare it to the lag in air brake systems on a semi, so carrying that over to a fuel system doesn't really appeal to me, unless the variable speed fuel pump was adopted to control fuel pressure. One of the turbo guys said it wouldn't hurt, but I don't want to run my engine lean for even .01 second. A few hundred times of that happening will cause a failure, and just think how many times your engine load (vacuum) changes during the course of 1 trip somewhere. Other than that, I like the idea

[CNCguy]

On LX9 and LZ conversions, we mount an AFPR on the fenderwell or firewall and run the return from there. I'm sure it probably picks up some heat from the engine bay but it can't be anywhere near as much as passing the fuel through an aluminum fuel rail sandwiched between hot upper and lower intake manifolds.

[pocket-rocket]

On LX9 and LZ conversions, we mount an AFPR on the fenderwell or firewall and run the return from there. I'm sure it probably picks up some heat from the engine bay but it can't be anywhere near as much as passing the fuel through an aluminum fuel rail sandwiched between hot upper and lower intake manifolds.

Marc, I like your thinking

[rooster5333]

hey pocket rocket, i was thinking about closer to the front, after the filter. leaving the stock one in place without vac line attached, sorta as a back up. use a piece of small diameter vac tubing, maybe a few extra feet. using the big rig air line as example, i would think would be the reverse. the lag in building vac upon throttle closing would retard lowering rail pressure. helping prevent lean out. when opening throttle, i can't see the extra vac tubing storing enough extra vacuum to retard raising the pressure. and yes when driving the are hundreds of load (vacuum) changes. but it seems to me ( i am no engineer or anything, just thinking here) the lag time in building vac( lowering rail pressure), and lowering vac ( increasing rail pressure), would be a minor event, as compared to the variable pressure fuel pump, constantly trying to spin up to increase, and slow down to reduce rail pressure. just a thought. maybe too much ehh. am i thinking outside my paygrade? or i know, maybe we could... nawwww never mind! no evap core from a/c system to lower fuel temps. what was i thinkin???