Practical Standalone Tuning: Step 4: Base Ignition Timing/Fuel Pressure
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Step 4: Base Ignition Timing/Fuel Pressure
05.57
| 00:00 | - The next step of our process is to check and set our base ignition timing as well as our base fuel pressure. |
| 00:06 | The base ignition timing in particular is critical because this aligns the timing values for our ignition angle that we're seeing on our laptop screen with the actual ignition timing the engine is receiving. |
| 00:18 | In order to do this and set our base timing, we need to actually physically fit a timing light to number one coil on the engine. |
| 00:26 | The fuel pressure on the other hand in the case of our Subaru STi is not adjustable, this runs a factory fuel system with a factory fuel pressure regulator. |
| 00:35 | This is manifold pressure reference which means that the fuel pressure will rise and drop based on manifold pressure. |
| 00:43 | Even though we can't adjust it, we do have that fuel pressure sensor fitted that we already looked at so we can check and make sure our fuel pressure is where we'd expect it to be. |
| 00:53 | In order to do this, what we can do is take note of our fuel pressure, we've got that sitting right here and there's a couple of ways we can test this. |
| 01:01 | Once we've got the engine up and running, we can physically disconnect the manifold pressure line to the regulator and in most instances with a factory system like this, we should be expecting to see about three bar or 43.5 psi. |
| 01:15 | We can also test this, if we go to our outputs here, as we already saw, we'll come down to our fuel pump and we will unclick the invert output, that will run the fuel pump and we can see at the moment it sits at 2.81 bar so a little bit lower than where we are expecting it to be however it's important to understand that right now we don't have the engine running so the alternator isn't charging, our battery voltage is lower than normal so it's quite likely we would see that pick up. |
| 01:45 | We'll disable that for the moment though, that is something we can come back and recheck once we've actually got the engine running. |
| 01:52 | In our case again, we've got no ability to change this but it is a parameter that is worth monitoring because we have a fuel pressure sensor fitted to the engine, this also gives us the opportunity to monitor the fuel pressure at higher boost and high RPM and just make sure that the fuel pressure isn't dropping away due to a fuel pump that can't keep up. |
| 02:11 | Let's move on and we'll have a look at our base ignition timing setup. |
| 02:15 | And the way we go through this, as we've discussed briefly already, is we're going to use our ignition angle lock feature, we'll click on that and we can see that brings up a new parameter here which is our locked angle. |
| 02:27 | Currently set to 10° so what this means is that when the ignition lock angle lock is on, the ignition timing output will be 10°, irrespective of the table values or any corrections that are present. |
| 02:40 | What we want to choose, ideally here, is an ignition timing value that will let the engine idle adequately and also one that's easy to see on our crankshaft pulley and the reference markings on the front cover of the engine. |
| 02:53 | In this case there's a range of markings on the front cover of the Subaru engine, 10° is a fairly easy one to spot so that's pretty easy to get us up and running there. |
| 03:03 | What we're going to do here is set our timing in two ways. |
| 03:07 | We need to at least get our base ignition timing into the ballpark before we can expect our engine to start for the first time. |
| 03:14 | However at this point of course we can't really expect the engine to run particularly smoothly so there's two ways we can go about this. |
| 03:21 | We can start by disabling our ignition outputs and we can crank the engine using the benefit of our helper and use our timing light to get our ignition timing broadly into the ballpark. |
| 03:33 | We should be able to get that within about two or three degrees of our mark. |
| 03:36 | Once we've done this we can then come back and revisit this step once we've got our idle control sorted out, our engine is idling happily with a sensible air/fuel ratio and more accurately dial this in. |
| 03:49 | It's very important we do get this accurate. |
| 03:51 | The reason we can't expect to get perfect results at cranking speed is that depending on the trigger input we're seeing, we may see the timing shift around a little bit due to the oscillations in engine RPM at cranking speed. |
| 04:04 | Anyway, let's see how we'll go about doing this. |
| 04:07 | As we've already mentioned, the two parameters that we are using here are our first trigger tooth and our trigger angle, there's an interaction between the two. |
| 04:15 | We're trying to choose a first trigger tooth value so that our trigger angle ends up in a sensible range defining our maximum ignition timing value. |
| 04:26 | In this case again, 69°, a little bit more advanced than we're every likely to choose but what we're going to do is crank the engine, we've got our timing light set up on number one coil. |
| 04:37 | Awkwardly on the Subaru STi, this actually requires us to remove the air box to get access to the wiring harness for number one coil but once that's on there, we can then point the timing light at the crank pulley, get our helper to crank the engine and just take note of exactly where the timing is occurring. |
| 04:56 | And then using our little up and down arrow keys here, we can advance or retard the timing until we've got it as close to our locked angle as we possibly can. |
| 05:05 | Once we've done that, we can then untick our ignition angle lock, that'll revert back to our timing values, really important we remember to do that, otherwise you can waste a lot of time wondering why the engine isn't responding to ignition values that you're changing when we get to that step and we can also make those changes permanent in the ECU. |
| 05:27 | Remembering again, this has only broadly set our timing in the ballpark and we will want to come back and fine tune this once we get the engine actually at a point where it's running comfortably. |
| 05:38 | So by this point we should have our ignition timing dialled in close enough to get the engine up and running, we should also have our based fuel pressure set to our desired target, or alternatively, at least know where our base fuel pressure is. |
| 05:51 | And at this point we're ready to move on with the next step of our process. |
