injector duty

[04silverado6.0]

I have a 04 silverado 6.0 swapped. Stage 3 v2 btr truck cam, .020 over with flat tops, 243 heads, gen 4 intake, headers, 12587269 injectors. I just got finished tuning ve, my injector duty seems about 10% higher than expected. What is going on? It also has a new factory GM fuel pump put in about 2 years ago with maybe 20k miles on it. Could my injection timing be way off? The sd edit file was made after the log but is pretty much identical. The non edit was used during the log.

[04silverado6.0]

Also may be unrelated but i swapped plugs before swapping the intake. 16k miles on a set of tr55gp plugs and the gap had grew 10-15 thou since new. Plugs had good color (light brown). No oil or anything concerning beside the gap spreading.

[RDF1]

Did you check fuel pressure?

[Matt Vardaman]

In my experience Fuel pumps that are AC Delco, Delphi, or any name brand are better than the cheap ones but are not the quality they used to be. I've had brand new ones fail a month after install. Always check fuel pressure. These days I just buy the rail mounted pressure gauge and put them on everything.

[04silverado6.0]

I have checked it at idle and it was fine. The 8.1 truck injectors ran around 90-95% before swapping the intake. Is this pretty normal for a build like this?

[GHuggins]

Verify pressure under load. Then you can try changing boundary to 6.7 or 6.3 and then go wot with each and see what your afr does whether it be richer, leaner or no change.

[04silverado6.0]

Still not checked fuel pressure. Did manage a log with the injection boundary set at 6.3. No noticeable change on wideband. Can probably ignore the stft change since the first log was started on a cold engine.

[04silverado6.0]

I have read nearly every eoit forum i can find. I am still not certain how the boundary number works. I have read its a limit and also that it is the total window of spray and several other explanations. What does this do on gen 3 exactly? What changes in the wideband would tell whether i am going in the right or wrong direction?

[GHuggins]

Boundary is the wall - can't spray paste this point. All of the other numbers including ms of injector spray time are then taken from that number. You're looking for your AFR to richen up, but with DC's that high you may not notice anything. Raising it in your case may be the better way to go - just depends on your backpressure and cam overlap. Wouldn't go past 7 either as cruise fueling can start to suffer.

[Fast4.7]

Verify pressure under load. Then you can try changing boundary to 6.7 or 6.3 and then go wot with each and see what your afr does whether it be richer, leaner or no change.

I have messed with several different combinations. SBC, LS and 8.1L and they all seem to really like a 6.1-6.5 boundary. IIRC 6.5 is very close to BDC anyway. Anything higher than that is spraying fuel into the reversion pulse during overlap period of the piston starting to ascend in the bore with the intake valve still open. The only difference I have noticed is with the MAP below about 60KPA and at lower rpm changing the injection timing. The biggest difference I have observed is around idle.

[GHuggins]

I've had a few of the 6.0's do good around 7 - much more responsive with transients for example. Boosted setups really benefit the best from changing the inj timing and as far as that goes torque is usually gained on the NA setups. I don't care too much for the gen3's though as they are too "globally" adjusted and you can't change it for varying rpm levels. Gen3's are a lot of give and take for what you most prefer.

[04silverado6.0]

I went out today and it was on the lean side with the boundary at 6.30. I set it back to stock and delayed the normal table about 8-9 more degrees and it was slightly richer and seemed to be a little more powerful.

[04silverado6.0]

I believe I understand what the boundary does now. I still do not understand why to change the boundary vs changing the normal table. It seems like you will still end up with the same eoit target after all said and done. If I make the boundary earlier and delay the normal table would that give me more total time for injection, lowering duty cycle theoretically?

[GHuggins]

By changing the boundary vs the others you're changing how late it'll spray. Yes changing all of them will do essentially the same, however only the boundary defines the wall. The only thing that will lower DC is if it goes richer and you have to pull fuel to re-obtain your commanded afr... You would need to raise boundary and raise normal so everything stays in the predefined calibration windows then re-evaluate to see if it goes richer and you need to remove fuel.

[04silverado6.0]

I will play with it some more when I have a couple nights off again. Still need to hook up the fuel pressure gauge as well. I did go back and find the formula for eoit calculation so I will be able to adjust both boundary and normal tables and actually know what the new target is. Right now eoit should be right at evc so I will delay another 3-5* and see what happens.