Throttle Cracker and Follower

[DaddySS]

Todays dumb question:

The VE table tells the PCM how much air the engine is using at RPM and MAP and therefor how much fuel it it should add.

The throttle cracker adds to that based RPM and Speed and the throttle cracker adds based on TPS (and multiplied by the RPM multiplier).

So, are the throttle cracker and follower an additional airflow/fueling signal to the PCM that in effect would be same as adding to the VE if all conditions were static or do they do something different?

I ask because I am running lean at like 7% to 10% throttle in the 1400 to 2400 rpm range and trying to figure out the best strategy to solve it. All other conditions - idle, higher RPM and throttle, deceleration, etc. are nearly perfect so I don't want to affect anything except the problem area.

Thanks!

[dfe1]

Under the conditions you're describing, (assuming steady state operation at the throttle position and rpm you mention) throttle follower and cracker should be pretty well out of the picture. Under the idle folder, look at the follower and cracker descriptions and see if that makes sense. Sounds like you need to adjust your VE table or you're running into DFCO.

[SSpdDmon]

Throttle cracker and throttle follower do allow air into the engine via the IAC. However, it's post MAF air that's already metered. Therefore, fueling should have already been calculated (even if you're running SD). They are for driveability alone.

If you're running lean, you need to add fuel via the VE or MAF tables (or if you're old school, the Injector Flow Rate table or Commanded Fueling in Open Loop Table).

[WiseGuyZ06]

Listen to this guy he knows what he's talking about!!!!

[WiseGuyZ06]

Throttle cracker and throttle follower do allow air into the engine via the IAC. However, it's post MAF air that's already metered. Therefore, fueling should have already been calculated (even if you're running SD). They are for driveability alone.

If you're running lean, you need to add fuel via the VE or MAF tables (or if you're old school, the Injector Flow Rate table or Commanded Fueling in Open Loop Table).

Listen to this guy he knows what he's talking about!!!

[DaddySS]

Thanks for the replies gang, so looking at my log and tune, even though my VE table seems high alredy in that range I should add more to bring the fueling up?

I would also appreciate it if you had a look to see if there is anything else I'm missing?

[SSpdDmon]

Doesn't look too high to me...

Here's what my VE looks like with my setup.

[ViolatorTA]

Wow!!!!! How do you get such a nice smooth table and keep fueling right? I'm figuring you're cammed with the hp in your sig. Here's mine and it still isn't dialed in.

http://img.photobucket.com/albums/v696/Violatorno1/VE.jpg

[SSpdDmon]

Wow!!!!! How do you get such a nice smooth table and keep fueling right? I'm figuring you're cammed with the hp in your sig. Here's mine and it still isn't dialed in.

That's just it. You can dial it in for the cell at a given rpm/kpa. But, once you stray from the center of that cell and the pcm starts interpolating the fueling is going to be off a little - usually up to 3~4% in some instances. I'm still tweaking mine a bit here and there. Once I'm done, I plan on increasing it 2% so that the variance is -2~2% instead of 0~4%.

[DaddySS]

So as to compare, mine is in % and yours is in units kelvin, how do I change the units - it's not imperial versus metric......???

[SSpdDmon]

So as to compare, mine is in % and yours is in units kelvin, how do I change the units - it's not imperial versus metric......???
Edit>Properties

Volumetric Efficiency values:
Display in: "default units (g*K/kPa)"

[DaddySS]

Oh yeah, forgot, thanks!!!

[SSpdDmon]

np.... :)

[DaddySS]

OK, I first tried using the throttle cracker table from the original tune since it was almost double in the area where the lean condition is occuring but it affected drivability more than it helped the lean condition. Adjusted the main VE per SSpDmon's recommendation and that seems to be doing it, I'll continue to tweak that and see where I am from there.

Thanks!

[DaddySS]

Another question - when moving from a stop, is the throttle response controlled or affected by the cracker or the follower - mine seems a bit sluggish for instance when backing out of the driveway which is on a very slight incline.

[SSpdDmon]

Another question - when moving from a stop, is the throttle response controlled or affected by the cracker or the follower - mine seems a bit sluggish for instance when backing out of the driveway which is on a very slight incline.
Yes...sort of...

This is my take on things. How accurate it is, well, IDK for sure. But, it seems to make sense to me...

An engine's 'eagerness' to go is determined primarily by two things: air and timing. Fueling is the easy-to-set variable when working with a WBO2. So, we can kinda discount that based on the assumption that fueling is accurate. Obviously, giving the motor more air will allow it to make more power as it will be matched with more fuel and a stronger explosion in the cylinders. The more timing you throw at the motor, the more it will want to get ahead of itself (to a point). That's one reason why tuners throw more timing at a cam'd car. Instead of futzing with the IAC, they can compensate by adding more timing. The problem is, too much timing will cause surging when you're coasting down the road. That's why you need to find the right medium. I don't need 30* of timing at idle to get my 232/238 cam to stay running. I'm actually working on dropping it down (currently under 24*), which is allowing me to get rid of that last 5% of surging I have left every once in a while.

Anyway, back on topic. If it feels sluggish you can try one of two things: get the IAC to add more air via the cracker or follower or try a little more timing.

The other thing you should keep in the back of your mind is the cam's efficiency. The stock cam (according to the stock VE table) was much more 'efficient' at lower rpms than your aftermarket cam. That might be what you're feeling - that loss of efficiency - if you were used to the stock cam for so long.

[ViolatorTA]

Don't mean to hijack daddyss's thread but I have a Q for spddmon.

Is that 232/238 cam the Lunati Voodoo cam?

[DaddySS]

OK, spent the last two nights dialing in the VE and I now have it close to....well excellent anyway. The lean condition is just about completely clear, virtually no bucking, good idle, deceleration and power. I am going to play with the timing correction later but for now I just want to drive and enjoy!

Thanks again for all the help!

[SSpdDmon]

Don't mean to hijack daddyss's thread but I have a Q for spddmon.

Is that 232/238 cam the Lunati Voodoo cam?
No, I don't think so. I think it's just a rare Comp grind. Don't know for sure though given the previous owner didn't pass on too much info.