4.8 to 5.3 with mods gen3

[RicksPerf]

Been working on this for a bit now. 03 Sierra 4.8 swapped to 5.3. 10.0 to 1 CR,222/[email protected] 112LSA,TrailblazerSS intake and injectors,
LS3 90mm Throttle body using XLINK adapter, return style fuel system (no vac ref) p59 pcm.

Running better but still a few starting and idle issues
Here is a tune file as found and the latest tune file after changes. Also 2 logs from first short drive
Was hoping for someone to look over and show me where I may have messed up or not made the correct changes.
Any advice is greatly appreciated. Thanks

[blindsquirrel]

Attachment 123313

[RicksPerf]

Great I'll write that in Thanks

[blindsquirrel]

'Return' and 'returnless' are really shorthand for 'referenced' and 'non-referenced'. It has nothing to do with where the regulator is located (in the tank, in-line, on the end of the fuel rail) or whether it has a hose to dump excess fuel back into the tank.

'Return' or 'referenced' means fuel pressure goes down when manifold pressure goes down (vacuum increases) and fuel pressure increases when manifold pressure increases - the difference in pressure between the injector inlet and injector outlet is always the same, so the flow thru the injector is always the same. This type of fuel system/regulator uses one value all the way across for IFR & Offset.

'Returnless' or 'non-referenced' means the fuel pressure remains fixed no matter what the engine does, because there is no vacuum source to raise or lower the fuel pressure based on manifold pressure. In this type, flow thru the injector DOES change all the time, because the pressure in the intake manifold changes while the supply pressure does not change. This type uses sloped IFR & Offset tables.

[RicksPerf]

Hi, Thanks for the explanation.but I am still a bit confused. So this system is using a regulator which is maintaining 58 PSI..It has no vacuum line to it to lower the fuel psi at high vacuum conditions or raise the psi during low vacuum WOT conditions.It does have a return line to return excess fuel back to the tank. Would this be referred to as a return/non referenced which uses the sloped values? When I look at the IFR table (the scale goes from 0 to 80 kpa) at zero kpa the injector is flowing less fuel so the injector flow rate is lower than at 80 kpa which the flow rate will be higher because fuel is actually being sucked from the injector. The ecm sees the higher kpa (vacuum) in the manifold and reduced the pulse width . Does that make sense ? I am just a bit confused in your reply where you say returnless =non referenced ( trying not to be a pain but I need to get this straight in my head )

[blindsquirrel]

If you stick a straw in a Big Gulp, the harder you suck the more Coke you get. The straw is the injector. Yo mouf is the intake runner. Atmospheric pressure acting on the Coke in the cup is... OK, this is getting silly.

80 kPa vacuum is very low pressure, like up at the edge of outer space. 0 kPa vacuum is the air you're breathing right now. If you put a steady, constant 58psi into the fuel rail, and the intake runner where the injector tip is is at 80kPa vacuum, the injector is going to flow more than if the same injector with the same rail pressure is spraying into an intake runner at zero vacuum (or normal atmospheric pressure). Lower runner pressure (more vacuum) sucks more fuel out of the injector.

With a regulator that references fuel pressure to manifold pressure, the fuel pressure changes by the same amount as the change in manifold pressure. The difference between the inlet pressure and outlet pressure (the injector tip) is the same. You do not have this type of fuel system, even though your 'regulator' is outside the fuel tank and has a return hose. Your fuel system needs the same injector data setup as a 'returnless' system, because as I said, 'returnless' is just shorthand for 'fuel pressure is not referenced to manifold pressure'.

(side note: the "0 - 80 kPa vacuum" scale used in these tables is gauge pressure, meaning it's relative to normal atmospheric pressure. But a reading you might be more familiar with, the numbers your MAP sensor reads, are absolute pressures, which means they're relative to a perfect absolute vacuum, the lowest pressure it's possible to theoretically have. "0 kPa vacuum" just means no vacuum at all, equal to normal atmosphere, or ~100 kPa absolute. "80 kPa vacuum" equals 20 kPa absolute - this is a very deep vacuum, a very low pressure.)

[RicksPerf]

Must have a restriction in the return fuel line or tank module Checked fuel pressure at idle 65 psi, changed filter regulator same thing, tried 3 different gauges same thing, Checked pressure in return line 3 psi at idle
cant see any obvious restrictions in return line to tank. would there be anything in the fuel pump module that would cause the return line pressure?
At 65 psi fuel pressure the injector flow rate will be higher

[blindsquirrel]

It's pretty common for the Corvette filter-reg thing to be too small internally for a decent sized fuel pump. Remember that at low engine fuel demand ALL the volume of the pump has to be able to go thru the return path. The orifice inside the filter is part of that path. The Corvette filter is often not a good choice, especially because it looks so simple but has hidden drawbacks you don't find until it's too late.

[RicksPerf]

Looks like i will have to work with 64/65 psi fuel pressure . I can bump the IFR rate up a bit. Will the offset and short pulse adder remain the same? The fuel pump is the stock one

[blindsquirrel]

You can test whether the restriction is in the filter or in the rest of the return plumbing, just pull the return line off the filter and stuff on a hose going into a bucket. Key on engine off with the pump running should be enough to tell you if there's any difference.

[blindsquirrel]

If the restriction is internal to the filter I don't think you'll be able to get away with leaving it like that, because the pressure won't remain at a fixed 65psi. It'll drop to 58 as the engine uses more fuel that doesn't have to try to get through the return orifice. Sorry to say.

[RicksPerf]

Already did that, Running into bucket drops to about 62. Would like to find out where the restriction is in the return line , Looks like the filter/reg is also causing
a bit of the problem

[blindsquirrel]

Well service manual calls out 55-62psi as 'normal'.

The truck sending unit already had a return fitting, right?

[RicksPerf]

Yes

[RicksPerf]

log file. hot start, reverse over 2mph adaptive spark kicks out rpm drops. Jab throttle in P/N ok. Jab throttle in gear almost stalls.
cant seem to affect the almost stall when in gear and touch and release throttle.. What am I missing. Here is the current tune file Thanks