Another megasquirt question (I'm still learning - lol)

If i build the revs up then let the throttle go, as the revs slow down i get lean popping.

If i do the same, but gently let the throttle down, it's fine.

Any tips, to point me in the right direction?

Cheers

Here's a quick video of the car...

http://www.youtube.com/watch?v=cdQxN03XQzA

[Edited on 11/5/11 by David_17]

I know this does not make sence but i had my car rolling roaded and the last thing done was the popping on overun. All they did was richen the bottom line up till it stopped, i have now weakened it of a bit to make it pop a bit.

Is there anything wrong with popping on overrun?

As per MadTeg - richen up the zero load sites for the revs it's popping at...

If you have an AFR gauge then take a look at the overun readings - I bet they will be quite lean. Just bung an extra drop of fuel in and you will soon be running quiet again.

Rather than richening it and wasting a bit of fuel, just turn on the overrun fuel cut. No fuel at all = no popping

Oh, and you probably need more ignition advance at really low load as well. You can run a lot more than you'd think at really low MAP, 40-45deg isn't unusual.

I think popping on the overrun can also be caused by a minor air leak in the exhaust system or manifold.
Sounds a bit on the cool side, as people can hear you slowing down!

Overrun fuel cut kills it, but since it sounds lovely and is better than wasting extra fuel to shut it up the normal way, why would you bother doing that? Either ORFC it or leave it and enjoy it. If you get it just right you can get some lovely flameage

Agreed with the above.

You do also need to have spare fuel in the exhaust, so when you are running rich you put fuel in the exhaust which then burns (pops) when the engine is running lean.

I think the reason it doesn't do it when you are smooth with the throttle is that your map transitions gradually from rich (when blipped) to lean, and during that transition the spare fuel is blown out of the exhaust.

As the tune gets closer you may find you have less fuel in the exhaust which causes less (or more gentle) popping. I have heard that popping isn't good for catalytic converters, although I have no direct experience.


Matt

p.s. the car looks great, nice stripes. It might be the video, but do your TBI's need balancing?

Mine pops on over run and thats on the standard ecu with fuel cut
it sounds great

Mine pops if I get back on the throttle really gently, great for scaring the crap out of pedestrians

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Mine pops on over run and thats on the standard ecu with fuel cut it sounds great

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Thanks everyone for all your help/replies. Will give it a bash this weekend and see what happens.

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Originally posted by coyoteboy
Overrun fuel cut kills it, but since it sounds lovely and is better than wasting extra fuel to shut it up the normal way, why would you bother doing that? Either ORFC it or leave it and enjoy it. If you get it just right you can get some lovely flameage

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I used to get all sorts of pops, bangs and whizzes out of my exhaust, more due to a couple of air leaks in the exhaust drawing in air to burn with the excess fuel. My exhaust was a bit tatty, but it did sound pretty awesome

Used to get flames too, at night it was pretty awesome watching the hedgerows light up braking into a corner

James

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I can't understand why anyone would want flames?

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worth checking ignition timing on over run too, less ignition is more prone to pops.

we actually have some customers specifically ask for pops and bangs and even flames on over run lol.

so to stop pops and save fuel, inject less fuel on over run, but advance the timing, this will also leave a nice crisp clean cylinder ready for when you hit the throttle again

remember some manufacturers completely cut the injectors on over run to save fuel.

- colin

[Edited on 17/5/11 by atspeed racing]

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remember some manufacturers completely cut the injectors on over run to save fuel.

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I was always under the impression that fuel cut often causes popping - in fact my overun was very noisy until I increased the fuel. It also made the throttle butterflies a little easier when gently putting on the power again.

incidentally I find that if I fuel cut completely I get a nasty jerk when coming back into the fueling zone or touch the throttle again, it's much smoother to feed the fuel in slowly as you get back on teh gas, and the best way of doing that is to put it into the VE maps IMO.

yes we always make sue fuel is available at extremely light throttle openings, especially at low rpm. as obviously its going to interpolate between the two sites. it can also smooth out any transitions between idle conditions switching on/off.

- colin.