Just recently went with Low Impedence injectors 1 bar map and speed desnsity, I am running a 383, 15psi boost ATI and decent cam, 75 lb injectors, 210 afr heads etc.

If I blimp the throttle too quickly I get a sucking noise from intake (lean) starving for fuel, I've messed around with many tables, it is a 97 TA with OBDI computer. There is no acceleration anticipate / bump shot table in tunercat, so I tried even messing with VE and bringing down the injector constant lower to simulate smaller injectors than correct for too rich condition with VE to help lean tip in, but although it helps slightly it messes with everything else like start tables etc.. I know all which I can correct, but it's still there no matter what.

My question being, I've read many threads on here to see what the solutioncould be and one area I'm not 100% clear on is the :

Low pulse width injector offset adder vs. BPW

Now I know its to do with altering the base pulse width, but how does that table translate or help with lean tip in? I know Datamaster reads injector pulse with in MS while its tunercat it's in Nano seconds, so no problem translating that.

However how does that help Tip In, from what I can see it's basically just going to add a small amount of fuel while running small pulse width up to 1.9 ms? Or am I reading it wrong, anyone with any experience let me know.

Thank you.

 

Low pulse width injector offset adder vs. BPW = just that... LOW PULSE WIDTH...

When you hit the gas your no longer in the "LOW PULSE WIDTH" area.

I tried the above and everything else. Nothing made a difference.

I would suggest lowering your INjector SIZE even more.. lower it ALOT... then lean out everything else and see what that does.

Your saying you see improvement... that means keep doing it but you have to compensate the other tables so it still runs good or you may see new problems which mask this. If SD tables are too lean then this will also contribute to this.

Curious what your Injector Size is. I actually lowered my 82lb/hr (with severe tip in stumble) to ~60 from 82. (mine is 2 bar MAP so it says 30lb/hr) and the problem was immediately fixed, leaning out the other tables makes it run perfect. Occasinally with a fresh flash (or battery disconnect) I might get one or two stumbles until Closed loop takes over the first time but that's it... after a ~10 min run in closed loop then all following open/closed loop runs are good.

 

Yeah I tried quite a bit, even lowered my 75 LB injectors to 16lb when I tried 2 bar, but it's still there once VE tables adjust and thats the whole problem, when you say SD tables too lean, you mean all tables relating to speed density like VE etc.. right?

I went back to 1 bar to try to correct this than once fixed go over to 2 bar again. I have 2 connectors for MAP wired in, so I just replace the MAP and throw in the other tune.

I was thinking that maybe the "Low pulse width injector offset adder vs. BPW" could be adjusted to be leaner so that when the throttle is pressed right away instead of leaning out it richens up. What I mean by that is bigger injectors run rich at low pulse width only as they are not as accurate, and than once PW goes up, they lean out, now that depends on the brand of injectors, some have a more linear transition from low to higher PW thus less of a problem.

Hopefully this weekend I'll try that as well see where I get with that. The other trick I'm thinking of doing is adjusting the idle & off idle cylinder balance, scale all readings down 10% and than set cylinder balance off feature to 30% TPS, what that will do is when I blimp the throttle past 30%, it will be like a 10% pump shot if you know what I mean, as it will go from .90 to 1.00 (90-100%).

I do understand that with that I will need to alter the VE tables some more, but you're not often past 30% TPS cruising, and if there are cells that are lean, they will get richer, and those that are rich, VE master should lean out, I think making a more accurate trasition, I'd rather get a sudden overfuel than underfuel to help tip in.

Another thing maybe try to hook up the power on the Converter box to the alternator as the Power source since if I get even another volt out of it, that will help to drive the injectors that much quicker to open/close, can't hurt, although these peak/hold injectors should be faster than saturated high Z injectors, when we deal with big flow rates, I'm sure they are less accurate.

But before all that, I will also try a different size/brand injectors I have laying around (50 lb) see if they help.

As you can see I've done a lot of thinking by now lol as it's driving me nuts, thus can't wait till the weekend rolls around.

 

"Hopefully this weekend I'll try that as well see where I get with that. The other trick I'm thinking of doing is adjusting the idle & off idle cylinder balance, scale all readings down 10% and than set cylinder balance off feature to 30% TPS, what that will do is when I blimp the throttle past 30%, it will be like a 10% pump shot if you know what I mean, as it will go from .90 to 1.00 (90-100%)."

I dont think that will work since these mods will only affect idle fuel relative to off idle fuel.. once your off idle everything will be richer according to the VE tables... I mean if you increase Cylinder balance values off idle then your increasing fuel flow off idle everywhere... the only way I know how is to lower injector flow and lean out VE tables. It's worked for a bunch of people, should work for you as well. Are you running injector driver for those injectors? I have AEM

Wondering if you have other problems, such as Fuel pressure? I have my stock regulator hooked up.. with it plugged into manifold I have ~43psi, when I blip throttle or put under a little load it goes to ~51psi, is your working like that?

 

Yeah the regular seems to work fine as well, but the off idle tables stock are only affective up to 14% TPS, after that the "off idle correction" no longer applies, check in tunercat you will see in the constants a variable called "TPS turn off correction" if you bump it to 30% and you have 90% for value, correction 10% lower I mean, than after 30% pcm just goes to 1-1.

So basically afte 14% TPS stock the Off Idle table means nothing anymore, so lean it out and set the TPS off idle correction ignore setting to 30% TPS.

 

I'm with dookie. I lived with a lean tip-in for years with my 84 lb/hr injectors. Finally switched to his 2 bar SD tune and, after some tweaking, my response is great. I had to add a whole butt-load of VE in the 50 and 55 kPa range (equates to 100 kPa on a 1 bar setup) up to 2000 rpm. I wish I had done this years ago. I did also have to monkey with the startup fuel tables a bit too, but my car was already pig rich on crank so it needed fixing anyway.

Mike

 

Have you tried the injector offset vs. voltage table? That can make a noticeable difference with SVO injectors. Perhaps it could help with your issue. Sounds like you might want to start with lowering the values, so the injectors fire sooner than normal.

Just one more thought to try...