Lean spike during steady state, injection timing?

[kbuhovecky]

Hi Everyone,

I've gotten a bit stumped on a small issue I'm having and wondered if anyone has some input on this one. Basically, lean spike that happens about 2 seconds after you are in a steady part throttle load. Runs great Wide open. I'm left thinking this is in the injection timing...

injection timing.png

As for the build...

1. 4.3L GM Vortec
2. Marine intake
3. GM LS fuel injectors with custom fuel rails
4. 224/230 @ 0.050 duration
5. Yukon fuel pump
6. Corvette return style fuel filter
7. Injection timing changes...Boundary 6.42/Normal 5.31 and Make-up 5.69
8. Gen 3 ECU

4.4L V6 224_330 110lsa.hpt

[blackwidowvette]

i am also having a similar issue where it is idling great and then all of a sudden it will lean out and then the computer will try and enrich it and it will bounce to being rich and then level out. I was actually just in the process of typing something up to see what everyone thought. I can feel and see it doing it while driving normally, but when i get on it, it doesn't do it.

[kbuhovecky]

Update: changed Injection timing Normal to 4.76 and Make-up to 5.34.

Now there is a lean spike on tip on, lol.

[kbuhovecky]

Blackwidowvette, Sounds like we are looking at the same thing...Might learn something new

[kbuhovecky]

Boundary 6.5/Make-up 5.55/normal 5.55

This made it a little lean at idle and had to add fuel but no more tip in lean spot. Ran well but still has lean spike at 2 second mark

[anniversaryss]

Post your file whats the LSA and centerline.

[kbuhovecky]

110 LSA 105 Intake CL (IV 7/37 AND EV 50/0 @ 0.050)

4.4L V6 224_330 110lsa.hpt

[anniversaryss]

Do you happen to know stock cam specs? If I run this with all your numbers on a gen 3 ls1 format I get your EVC event at 360. So using your tune and logged IPW if you leave your boundary at 6.5 and raise your normal/makeup to that would get your injectors to spray after the EVC happens. But again not sure how yours differs being a v6.

if done right your wideband should get more rich.

[kbuhovecky]

Stock injection timing 5.33/4.25/3.67 cam is 195/191 111LSA

[kbuhovecky]

Any suggested values for the Normal/makeup that is beyond EVC event? I figured the EVC was at "4" or 360 @ 0.050, from what I've read.

I got 6.42 for IVC @ .050 then minus 1.11 (1.11 x 90) to get the 5.31 Normal.

With the Injection timing at 6.5/5.5, the lean spike was weirdly enough worst and making me think going past 6.42 was just pushing fuel out the tail pipe on the next cycle.

Thanks for the input!

[blackwidowvette]

Yes I am wanting to learn how to fix this. Its frustrating. I posted a video on YouTube of my problem.

[85K5Jake]

You guys should read through the transient fuel sticky at the top of the forum it helps alot for throttle transition tuning for rich/lean spikes. It's under the how to sticky.

[kbuhovecky]

85K5Jake, transient is considered to be with-in 400ms from tip in? This happens 2 seconds into a steady load, like climbing a hill.

[kbuhovecky]

Hi, Cranked up and left for work today when I noticed that the issue was not there. While I was sitting at the light, temperatures flipped the system to closed loop. Light turns green, short shift to third and apply +40% throttle and count 1 Mississippi...2 Mississippi and then lean spike. Even did it with PE kicked (wide band swings from 12.2 to 15 back to 12.2) you can see it in the log.

Is the issue not present during open loop? So I tried again after work, purposefully trying to induce it and couldn't. Right after the system flipped to closed loop...issue returned.

( It is in SD mode)

[anniversaryss]

Did you change anything?

[kbuhovecky]

nothing that should matter (Leaned out Primary table 100 and 95 Kpa)

Any ideas? Im about to leave and will log it again to see if i can reproduce it again.
Thanks!

[kbuhovecky]

Fixed it! Runs really good and grunts down low too.

Redone injection timing. My math was a little fuzzy, lol. I set the "Boundary" to IVC @ .050 and computed the "Normal" value 2 degrees after EVC. (6.42 and 6.60)

The Normal value was too low, causing the injection timing to able to start when exhaust valve was open still.

[kbuhovecky]

Thanks for the input "anniversaryss". This pushed me to revisit my thoughts

[anniversaryss]

No problem man. I am having the exact same issue last year, the car is in storage so as soon as its out injection timing is the first thing im changing.

This is the second time someone has had this issue with a 24x swap pcm and the second time this was fixed with injection timing.

I am 100% certain any cam with overlap (especially SBC or non ls1 motors) the way the ls1 motors injection timing will absolutely not work well by spraying the back of the intake valve.

[anniversaryss]

Hows it run? From my research you could further those numbers and get injection to happen at PPV for better mixture.