Idle question

[BBR]

I messed around with the BBR on Sunday and worked out some little bugs with great success.

You can blip the throttle and the idle will come up 3-400 rpm then after a few secs it will drop back to 1000rpm like it is supposed to.

Is there a way to tune this out or just leave it alone?

[dieselgeek]

Re: Idle question

I messed around with the BBR on Sunday and worked out some little bugs with great success.

You can blip the throttle and the idle will come up 3-400 rpm then after a few secs it will drop back to 1000rpm like it is supposed to.

Is there a way to tune this out or just leave it alone?

Although that's a common issue with "huge cam" like yours, it can also be an indication of a throttle body leak or an intake manifold leak. Make sure there's not one or two cylinders whose spark plugs look different than the rest.

For idle tuning you'll have to do it "by feel" but a good way for me to help is to take a datalog of a throttle blip where it does this, then send it to me. What I look for is what your pulsewidth is at the "hang up" point, also your manifold pressure (might indicate the leak). It may be that your idle is too lean and it wants more fuel to idle a little faster (in which case you tune for that, then you close down the throttle blades a little to get the idle back down where you want it).

SEnd me a datalog again if you can,
-scott

[email protected]

[shaun callaway]

Re: Idle question

What is your target AFR at idle?

What is your TPS set at, at idle?

[BBR]

Re: Idle question

I've just been shooting for around 14.7 at idle.

I've had other EFI engines that did the same thing and was just curious what makes them do that.

If I think about it next time I am in the shop I will try to log it.

[shaun callaway]

Re: Idle question

if it runs good there great but i usually shoot a little fatter at idle like 13.8-14 to 1

[dieselgeek]

Re: Idle question

I've just been shooting for around 14.7 at idle.

I've had other EFI engines that did the same thing and was just curious what makes them do that.

If I think about it next time I am in the shop I will try to log it.

usually on OEM EFI engines, it's the Idle Controller that's holding RPM after you blip the throttle (for coasting while in gear). but on something with an aggressive cam, it just means that your idle can be tuned up a little better. It might mean that your accel enrichments are putting in too much fuel, and the idle happens to like more fuel, so it runs a little faster until the extra fuel is burnt off - 1-2 seconds, etc.

I don't think you're going to get any kind of useful, accurate Idle AFRs, I'd try it richer, then leaner, and decide where the motor pulls the most RPM and vacuum. Remember to play with timing too. I wouldn't be surprised to see 36 degrees of ignition advance at idle to make it run the most RPM/vacuum. Tune it for that first, then reset the idle screw to the RPM you like.

Don't forget that datalog, I can tell a lot from those.

-scott

[shaun callaway]

Re: Idle question

i think you could get it to idle lower maybe 850-900 with enough time invested. i am a weirdo on this stuff and idle is where i spend most of my time tuning, and then there is the parking lot tune. its nice when you dont have to give a manual trans car gas to lug through a parking lot. ask scott

[BBR]

Re: Idle question

It will idle lower, no sweat. I have been told 1000 probably provides better lubrication for the roller cam/lifters and I am all about keeping those thing lubed up.

Agressive cam... hmmm does 278? at 0.050" qualify? lol ;D ;D ;D

[shaun callaway]

Re: Idle question

ok cool

[BBR]

Re: Idle question

I made a vid

It wasn't doing it as bad as the other day. I can live with this. Still a little lean at idle I think. I didn't have much time to fiddle, as I had to put the Durango in the shop to replace the radiator.

http://tinypic.com/r/34xlzcz/5

[shaun callaway]

Re: Idle question

dude thats bad ass

[CDMBill]

Re: Idle question

My motor which is similar to yours likes an indicated 13.8 AFR at idle and exhibts that same gradual fall back as the accel enrichments that were neccessary to get the car moving out of the gate are the carb'd equivelent of dual 50 CC accelerator pumps on a Dominator, all that fuel doesn't really get used under no load RPM blips.

You have my last .msq, but back when we were tuning it for darg strip performance we ended up adding a top of fuel and changing accel enrichment timing around to get the best leave.

My new refreash is finally getting finished and the new cam is similar to yours, 275/279 @ .050 109 LSA and .798 lift. I bumped the compression to 11:1 so we'll see if runs as nice as yours.