Practical Standalone Tuning: Idle Mixture
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Idle Mixture
01.38
| 00:00 | Once we have the idle timing sorted out, we can look at the mixture. |
| 00:04 | The air/fuel ratio you choose will depend to a degree on the engine you are tuning and how modified it is. |
| 00:10 | All factory engines are tuned to run at stoichiometric air/fuel ratio or idle to meet admissions targets. |
| 00:17 | This also happens to produce a good idle quality and good fuel economy so it isn't a bad place to be. |
| 00:23 | You will find with a heavily-cammed engine though that the engine will struggle to idle cleanly at a stoichiometric ratio. |
| 00:30 | These engines will run smoother with a slightly richer AFR target so we need to consider this when choosing the mixture. |
| 00:37 | As a guideline for a stock engine, then we would normally be aiming for an idle mixture of lambda .95 to 1.0. |
| 00:45 | On a modified engine, I would generally target an idle mixture of around .90 to .95. |
| 00:52 | If you consistently run much richer than .85, you risk failing spark plugs over time. |
| 00:58 | When you're tuning the idle mixture, it's important to make sure the engine is up to normal operating temperature and no compensations are being applied that could affect your mixture. |
| 01:08 | We would now adjust our VE map or our main fuel table until our measured AFR matches our target. |
| 01:15 | A tip here is to target slightly on the richer sides of the ranges I've suggested. |
| 01:20 | The reason for this is after a hot restart, it's normal for an engine to run slightly leaner for a minute or so. |
| 01:27 | While there are tables in the ECU that can help smooth this out, if your engine runs leaner after a hot restart, it will feel erratic and rough. |
