If you have a programmable management system fitted to your car, can you tune it on the road? The answer is that yes, you can – with some caveats.
Firstly, the car cannot be immensely powerful. It’s just too dangerous if full throttle results in mass wheel-spin, or tuning at higher rpm in fourth, fifth or sixth gears results in warp speed.
Secondly, you need a mix of roads – heavy urban traffic, all the way through to near-empty blacktop.
You’ll also need some things organised before you begin, so let’s start there.
1. Wide band air/fuel ratio meter
A wide-band air fuel ratio meter is a must-have. These days, you can buy good quality instruments of this type fairly cheaply, so there’s no excuse for not using one. Without one, you’re very much risking blowing up your engine through overly lean mixtures, and at minimum, without one you’ll chase your tail a lot when tuning.
It is far better if the sensor is screwed into the exhaust close to the engine. Yes, you can tune with it up the tail pipe, but response will be slower (important when setting things like acceleration enrichment) and the reading will be a little less accurate if the sensor is located after the cat converter.
2. Knock detection system
Unless you are using software that works with the factory engine management and can therefore monitor the factory knock sensor (and work with the factory ECU knock sensor logic), you need a way of detecting engine knock (detonation).
The cheapest, most effective and simplest way of doing this is to use a remote-mounted microphone in the engine bay, connected to an adjustable in-cabin amplifier. The person listening to the engine should wear fully-enclosed headphones – and that’s especially the case if the car has a loud exhaust.
It’s easy to make your own listening system, starting with a cheap eBay amplifier and then extending the microphone wiring and adding good quality headphones. See Hearing Detonation for more details.
Note that in real world tuning, being able to hear the engine is very useful in other ways as well. You can hear when the radiator fan is running (useful when setting up idle speed control), in a turbo car you can hear the operation of a plumbed-back blow-off valve, and you can hear slight engine staggers (eg when engaging the clutch and moving away from a standstill) that may not be obvious in normal circumstances.
3. Spark plug spanner
Periodically when tuning you should pull a spark plug and inspect it closely. Plenty of charts exist on the web that will show you what spark plugs look like when the engine is detonating (for example, tiny globules of aluminium deposited on the porcelain insulator), when the plugs are overheating (erosion of electrodes), when the mixtures are rich or lean – and so on.
‘Reading’ spark plugs is probably amongst the oldest of engine tuning techniques – and is still quite valid.
4. An assistant
You also need an assistant – either to drive the car or listen to the engine and operate the laptop.
Note that the assistant doesn’t actually need to know a lot about tuning!
My approach is to drive the car, feeling its behaviour and watching the air/fuel ratio display while my wife (or 10 year old son) operates the laptop. Based on what I can see, hear and feel, I ask for specific tuning changes.
Taking this approach, the assistant obviously needs to be able to find their ways through the maps and make the required changes, but a detailed knowledge of tuning isn’t needed.
Having a plan of attack is vital. Whether you’re starting with a base map tune or tuning from scratch, there is a series of stages that the tune should pass through.
The hardest areas to tune really well in a road car are idle and light loads. That surprises many people but in comparison, high loads are basically just a case of running reasonably conservative ignition timing and lots of fuel! The differences in tuning between (say) 100 per cent throttle at 6000 rpm, and 80 per cent throttle at 5000 rpm, are relatively slight.
Therefore, if you have access to (say) an empty road or racetrack for a limited time, schedule that for later in the tuning process and then spend that time on high loads – the lower loads may well take ten times as long, but they can be more easily done on populated roads.
So what sort of tuning steps should you go through?
1. Start with the engine warm. (Before tuning the idle, you may have to apply throttle to keep it revving so that it gets warm.)
2. Ensure that the system is set up as simply as possible – no EGR, no closed loop feedback, no warm-up enrichment running.
3. Ensure that the sites at and around idle are all at the same values, both for fuel and ignition - then when you do make changes, change all these sites together. (If the active site is swapping back and forth across different values, oscillations in idle behaviour can occur as the engine is altering in fuel or timing.)
4. Without having any active idle speed control activated (ie turn off PID loops, etc), see how well you can get the idle speed to work, tuning just the opening of the idle speed control valve.
5. Activate control loops only one parameter at a time, assessing the action of altering that one parameter. (Many people try to change all three PID parameters at once, and can lose themselves in their own control loop!)
5. Switch loads (eg air con or power steer) on and off and then use the various ECU corrections to keep idle stable when these loads are occurring.
6. Optimise fuel and ignition at the stable idle setting. Idle air/fuel ratio on petrol will typically be at 14.7:1 AFR, and ignition timing as specified for idle in the workshop manual.
7. Wait until the next day and then start the engine from cold, ensuring that fast idle settings and fuel enrichment are correct for idle warm-up. Don’t change the settings that you optimised the day before for normal, warmed-up idle!
8. Expect to make minor ongoing tweaks to idle speed control – it’s hard to get it perfect straight out of the box.
1. Again the engine should be fully warmed. At this stage don’t use closed loop feedback, acceleration enrichment or any other corrections of that sort. In a turbo car, you are at this stage tuning in the area of the map that is off boost.
2. Drive the car at the smallest possible throttle angles consistent with normal driving, starting at low revs first.
3. Advance the timing until detonation is just heard when the throttle is opened further then retard the timing so that it doesn’t occur, even with further throttle openings. As the load is reduced, timing is increased, and as the revs are increased, timing is advanced. Therefore, the most advanced parts of the timing map will be at high revs, very low loads. You are almost certain to do no engine damage if the engine can be heard lightly detonating (through the proper listening system, not just by bare ears) at light loads. Taking this approach allows you to (1) hear what detonation on your engine actually sounds like, and (2) get some initial timing figures to then work outwards from.
4. Tune the air/fuel ratio. At light loads it will be stoichiometric (as at idle) or even leaner (higher AFR numbers).
5. When tuning light loads for good driveability and economy, the juggling act is between going too lean for good driveability (flat spots, doughy response), or on the other hand using too much fuel or having poor combustion behaviour.
1. The process is very much the same as for light loads, except this time you should be able to recognise the sound of detonation, and also be able to hear through the listening system when the engine is changing a fraction in combustion note, indicating it is getting close to detonation.
2. Based on the pattern of fuel and ignition numbers developed in light loads, you should be able to pre-fill the medium load areas with ‘best guess’ numbers – road testing then becomes a case of seeing whether those numbers give the AFR and ignition timing behaviour that you had expected.
3. In a turbo car you’ll now be working in the area of low boost, so you should also watch intake air temperature – a higher intake air temp is more likely to cause detonation.
4. Ignition timing is going to more retarded (lower numbers) than at lighter loads, while the AFR should still be stoichiometric or just going into slightly richer (lower) numbers on the meter.
1. The process is an extension of the tuning you did at light and medium loads. The complete high load tables for fuel and ignition should be pre-filled with numbers based on the changing pattern you have developed so far. For example, ignition timing will continue to be more retarded (numbers getting smaller) and AFR continue to get richer (again numbers getting smaller on the meter). If in doubt, make both sets of numbers more conservative than you actually expect will be needed.
2. Do quick bursts of power into the high load area, ensuring that there is no detonation and that the AFR is suitably rich. In most cars, mid-12s in AFR at high loads are safe. Make only small adjustments if you are going leaner in AFR or more advanced in ignition timing.
3. Any stutters – no matter how minor – indicate a problem; don’t try to ‘drive through’ these. Instead, back off and look carefully at the tuning maps to ensure that you don’t have a rogue number that is causing the problem.
4. In a turbo car, carefully watch boost and intake air temp numbers. Start with the lowest full-throttle boost that you can run and build up slowly from there. For example, start by using the default wastegate value (eg 4 psi) rather than using electronic control of boost to give higher values.
5. Pull out spark plugs and assess that their appearance is indicative of appropriate combustion behaviour. If you don’t know what to look for, do a web search under ‘reading spark plugs’.
6. Place the car in a condition where gradually you spend a longer period in high load areas – eg a long country road hill, retarding the car using brakes, or a long full-throttle burst in 3rd or 4th gears. You are especially looking for detonation – the AFR is unlikely to change but holding the car at a high load point can indicate the need for timing that is more retarded than you found when the engine was only briefly at that load site.
7. Go back over the loads between peak torque and peak power, seeing if you can add more timing in this area without getting the hash engine ‘edge’ sound characteristic of an engine nearing detonation. If you can add more timing, you’ll probably also need to then add more fuel.
8. Drive at high revs, low load – and then go straight to full throttle from this point. This driving behaviour requires probably the fastest change in ignition timing, so listen carefully for detonation.
9. If you have a turbo car where you can easily change peak boost, set the peak boost to varying levels (eg changing in 2 psi increments) and then check that the fuel and ignition are correct right through the rev range for this boost level.
10. The use of a video camera (eg phone) recording AFR numbers, rpm and manifold pressure during acceleration runs allows you to watch the numbers later at your leisure. You can then make appropriate map tuning changes.
Ensure that the air/fuel ratio reflects the numbers that you are putting in the charts. If for example, the fuel pump or fuel lines is inadequate, or the fuel pressure regulator in a turbo car isn’t coping with the boost, air/fuel ratios may be much leaner than the table numbers suggest. Never assume that ‘rich’ numbers on the chart will automatically give a rich AFR.
With the right tools, some empty road and – it must be said – plenty of patience, you can get a car running really well on programmable management… even if you are programming it from scratch.
That’s enough for this issue – next issue, sorting acceleration enrichment, fuel injector cut-off, EGR and turbo boost control.