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Practical Standalone Tuning: Step 6: Idle Tuning

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Step 6: Idle Tuning

05.20

00:00 -Now that we've got our engine into a situation where we can actually start it and make it run, one of our first tasks is to get the engine to idle smoothly and consistently.
00:11 Remember, this can give us a lot of information that can help prevent wasting a lot of time and potentially damaging the engine.
00:21 What we want to do is make sure that we can get the engine to maintain a stable and sensible idle, that we are getting a reasonable manifold absolute pressure signal that indicates that the engine is mechanically healthy.
00:38 We can often find particularly if there are inlet manifold leaks for example, or perhaps the cam timing is not correct on the engine.
00:48 It can be easy to get into a situation where we've wasted a lot of time on the dyno doing full load tuning and then we need to go and correct whatever the mechanical issue is.
01:00 Now, we can often see the air idle because the engine won't maintain what we consider to be a sensible idle speed.
01:09 In this case our VQ-35 engine is essentially a hundred percent stock standard including factory cam shafts so I would expect it to be able to idle at a normal speed of something like perhaps 800 RPM once it's up to operating temperature.
01:27 We'd also expect it to be able to pull a relatively high manifold vacuum.
01:32 So all of these are good signs that everything is mechanically healthy.
01:36 So let's start by looking at our idle speed control tab and there's a couple of parameters here we're going to be looking at.
01:43 First of all, we have our idle target table.
01:47 So this is simply a 2-D table of our target idle speed versus our engine coolant temperature.
01:53 What we're going to be looking at at this point is particularly, once the engine is up to a normal operating temperature between 70 and 90 degrees Centigrade, you can see the target idle speed in these regions is 800 RPM.
02:10 We've also got our idle base position which defines, to some degree, the amount of throttle opening that's going to be used to control our idle speed.
02:20 So this all looks relatively sensible at this stage.
02:24 Now what we're going to do is start our engine and we're going to allow it to maintain an idle speed and we can come back to our VE table at the same time, and now what we're going to do is make some finer changes to our volumetric efficiency numbers around the idle speed.
02:47 Again, you can see that our target lambda is displayed here versus our measured lambda, and you can see that our guess of 50% as a starting point actually turns out to be pretty much perfect, so there's not really any work to do to this table at the moment.
03:06 We're currently idling at a coolant temperature of 50 degrees and our lambda is almost perfectly on target.
03:16 What we want to do is allow the engine to come up to a normal operating temperature, and once the engine operating temperature is normal then we can make any adjustments as we need to to our VE numbers.
03:31 At this point we're not going to be considering cold start enrichment or warm-up enrichment, we're going to be looking at all of our tuning with the engine at a normal operating temperature.
03:42 You can see that now that the coolant temperature is coming up to 55 degrees we are approaching our normal target lambda at operating temperature of lambda 1.0.
03:54 You can see that our two lambda inputs are sitting just very slightly rich.
04:00 So what we can do there in the cells that the ECU is currently accessing, which I'm going to adjust both 750 and 1000 RPM and you can see how manifold pressure at the moment is 32 kPa, which puts us between those two zones.
04:20 What we can do is we can just remove 1% fuel and you can see that's brought us right back on to our target.
04:29 So everything's looking good at the moment for us we've got good manifold vacuum, our idle is achieving our target.
04:36 We can see now we're dropping a little bit to 900 RPM as the engine is warming up, and we can also adjust our idle speed parameters based on the idle speed feedback.
04:54 So what the ECU is doing to the idle speed control in order to make or achieve our target idle speed.
05:03 Okay, so now we've achieved correct target idle speed.
05:06 We know that the engine's mechanically healthy, we've got good control over our air/fuel ratio.