Road Tuning: Idle Mixture
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Idle Mixture
01.46
| 00:00 | Once we have the idle timing sorted, we can look at the mixture. |
| 00:05 | The air/fuel ratio you choose will depend to a degree on the engine you are tuning and how modified it is. |
| 00:11 | All factory engines are tuned to run at a stoichiometric air/fuel ratio idle to meet emissions targets. |
| 00:18 | This also happens to produce a good idle quality and good fuel economy so it isn't a bad place to be. |
| 00:25 | You'll find with heavily-cammed engines though that the engine will struggle to idle cleanly at stoichiometric. |
| 00:31 | These engines will run smoother with a slightly richer AFR target so we need to consider this when choosing our mixture. |
| 00:39 | As a guideline for a stock engine, we'd normally be aiming for an idle mixture of lambda 0.95 to lambda one. |
| 00:48 | On a modified engine I generally target an idle mixture of around to 0.95 lambda. |
| 00:56 | If you consistently run much richer than around 0.85 lambda, you risk failing spark plugs over time. |
| 01:04 | When you're tuning the idle mixture, it's important to make sure the engine is up to normal operating temperatures and no compensations are being applied that could affect your mixture. |
| 01:14 | We would now adjust our VE map or main fuel table until our measured AFR matches our target. |
| 01:21 | A tip here is to target slightly on the richer side of the ranges I've suggested. |
| 01:27 | The reason for this is that after a hot restart it's normal for an engine to run slightly leaner for a minute or so. |
| 01:34 | While there are tables in the ECU that can help smooth this out, if your engine runs lean after a hot restart, it will feel erratic and rough. |
