boost with returnless fuel system

Anyone running boost with a returnless fuel system. I don't understand how you can tune any of these GM vehicles if it is fixed fuel pressure and the IFR table doesn't go into the boosted range?

Does everyone that runs boost install a return line and a fuel pressure regulator referenced to manifold like the old days?

I'm knee deep in fitting a supercharger to an 06 gm I6 4.2. I've been trying to learn all I can so I can tune this thing when I complete the hardware. I hadn't originally planned on changing the fuel system but from what I've come to understand, I don't see how the PCM can get an accurate fuel calculation with a fixed rail pressure and the way the IFR table is laid out.

Anyone help out?

Somebody with actual experience I'm sure will chime in, BUT I thought that you do that via the airflow tables- the computer may not know how much boost, but it does know how much airflow if you've dialed in the MAF and VE correctly.

I understand you have to give the pcm an accurate model of the airflow by tuning the maf and VE, but the PCM still needs to be able to calculate the required fuel mass by referencing the IFR table.

If the IFR table doesn't extend into the boosted region, does it carry the 0 KPa value out into the boosted region? That would make it go leaner and leaner.

I guess this question is only applicable if you are not running a SD tune and are sticking with MAF. HP tuners doesn't have a SD option available for an I6 engine, so I'm thinking I'm going to have to add a return and Boost referenced regulator.

Couldn't you scale it? You'd lose resolution, but you'd at least be able to tune for boost?

Our TB is SD from the factory- I don't care for it myself. But that's my opinion.

I'm planning on a turbo next year for our Colorado (same controller I believe as yours- might have better luck in the I4/5/6 section), and will have to fight the same issues, so I'm keeping an eye on what's posted for you.

The E38 goes into Negative Manifold Vac. which equals boost. i have also logged IFR and watched it go into the boosted region.

-Carl

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That would solve the problem...too bad I don't have that. I've found many tunes that are for supercharged vehicles and use returnless fuel systems and don't have IFR tables that go into the boosted region.

What does the PCM do if the IFR table doesn't extend into the boosted region and it is seeing boost?

it will just hold the 0kpa vacuum value.

the net result is the MAF curve needs to jump up a bit or the VE tables values are higher. It works either way but most serious setups would include a vac ref'd reg.

Remember if you do fit a return line & reg to make your IFR table flat.

Chris...

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Originally Posted by Chris@HPTuners

Remember if you do fit a return line & reg to make your IFR table flat.

Chris...

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Chris I have seen that posted many times , can you explain why to make it flat in a return system ? and why at least some GM sc'ed cars with return systems arent flat from the factory ? (3800 L67 SC)

the regulator changes the fuel pressure in a 1:1 ratio to boost or vacuum which gives you close to a constant injector flow rate at all times. In a constant pressure fuel system the PCM needs to know how the IFR varies with vac/boost.

The added benefit of a vac ref'd reg is you can run a lower fuel pressure at idle which helps avoid short pulse widths with big injectors, and higher fuel pressure under boost which reduces the injector duty cycle and possibly the requirement for larger injectors.

I like to think about it in terms of differential pressure. A returnless system stays the same absolute pressure, therefore the differential pressure between rail and manifold varies depending on the pressure in the manifold. A manifold referenced rail pressure with a regulator will keep the same differential between the rail and the manifold. The flow rate of the injector will not change if the differential pressure(rail to manifold) stays the same.

Just another way to explain it.

08 chevy Colorado 3.7 here. So switching to a return style would be easier when I put my turbo on? Not sure if a return style would just add to the "to do" list rather than sticking with the returnless setup.

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Originally Posted by emaxxer

08 chevy Colorado 3.7 here. So switching to a return style would be easier when I put my turbo on? Not sure if a return style would just add to the "to do" list rather than sticking with the returnless setup.

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You have the E67 and the ability to tune for boost pretty easily the way it is.

FWIW, the regulator on the 2005 3.5L is capable of adjusting for vacum and pressure :D

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Originally Posted by HawkZ28

You have the E67 and the ability to tune for boost pretty easily the way it is.

FWIW, the regulator on the 2005 3.5L is capable of adjusting for vacum and pressure :D

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Yeah I know and I'm looking around for a 3.5L fuel rail. There's a couple guys that swapped out their 3.5's for the 3.7 and have parts available. I plan on running a rear mounted he351 holset, e85, and water/meth non intercooled on 10 psi.

I've got the tank out and the aeromotive pump going in and I've added a return line and regulator. I need to bypass the intank regulator but it is part of the jet pump assembly. If I bypass it, I will lose the jet pump scavenging that fills the fuel pump assembly basket! How the heck do you do this?