Lift off popping

[dodd1980]

I'm running MS2 V3 Firmware 2.891

My car drives pretty well and accelerates very well.

But when i lift off then put my foot down again i get a loud pop, Generally this is always low down the rev range any suggestions on where to look to stop this?

[Bernard Fife]

d1980,

If the popping occurs through the exhaust, then this is likely the overrun fuel burning in the exhaust, and if you are using standard accel enrichments I would decrease the decel fuel amount: http://www.megamanual.com/mt29.htm#tl If you are running X-Tau exclusively, you would need to reduce the Puddling Factors (decel): http://www.megamanual.com/mt29.htm#ud

If the popping occurs when you get back on the gas and the occurs in the intake, it is very likely that the mixture is too lean, and you need to increase the Acceleration Enrichment Bins (ms) amounts and/or the Accel Time (sec): http://www.megamanual.com/mt29.htm#tl With X-Tau you need to work with the Puddling Factors (Accel) and Time Factors (Accel): http://www.megamanual.com/mt29.htm#ua to increase the fuel.

Lance.

[dodd1980]

is it possible to get both popping, i think i get a popping in the exhaust and the inlet?

[Bernard Fife]

dodd1980,

Yes, it is certainly possible to get popping in both the intake and exhaust, but it would be for different reasons. In that case you need to do both of the above fixes.

These assume that your ignition and cam timing aren't totally messed up, but the car would run poorly in general then, not just under specific conditions.

Lance.

[dodd1980]

ah i see, i think it is more exhaust popping so will start there and see how it goes,

Thank you very much

[autosportnorth]

A little inlet manifold air leak can sometimes also cause some pretty impressive pops when you are on transitional throttle, so maybe worth a quick check there too

[dodd1980]

what's the best way to find an inlet leak?

[Bernard Fife]

dodd1980,

An inlet leak on a carb'd vehicle, or downstream of a MAF will cause lean popping. If you are using MAP, and inlet leak will only cause a high idle, not a rich or lean mixture (because the MAP adjusts for the leak).

If you are running MAF, one way to check for a leak is to hold an unlit but open propane torch near where you think the leak is. If the engine speeds up and smooths out, the propane is getting into the manifold through a leak near where you have the tip of the torch. You can also use WD-40, starter fluid, or other flammable liquids for this, but you must be more careful, and it can make a mess.

Lance.