How the Knock Detection System Works in the Ecoboost

The Ford Ecoboost knock detection system is one of the more complex systems out there. A lot of the vehicles using the Ecoboost engine are rated to use fuel that ranges in octane from 87 to 93 octane. Because of this, Ford built a system that is very powerful and adaptive. It actually learns your fuel quality while you drive. All the EB engines we work with use this adaptive timing system. This is great for us calibrators as we can build failsafes and adaptability into the tunes – but it has to be setup correctly.

The knock detection system starts with the sensors (microphones) that pick up engine noise and are mounted to the engine block. If the engine noise falls within the correct frequency and window of operation (around the time the spark plug fires), the ECU registers this as knock. When knock is registered, the ECU looks at the Knock Response table pictured below. Based on the intensity of the knock it subtracts timing advance from the Ign. Corr. Cyl X Parameter (which you can view and datalog) on a per cylinder basis. On each knock events it also increments the Knock Count Cyl X parameter which can also be viewed. Both of these parameters are reset to 0 once you let off the throttle, shift gears, or experience a throttle closure.

Keep in mind that the following ECU tables shown have OEM values. We adjust these to better suit our performance criteria, but the principles remain the same.

ignition-reduction-table

The amount of timing being pulled for each knock intensity and engine speed is completely under the control of the tuner who builds the tune. You want to make sure that you pull enough timing per knock event to maintain engine safety and stop the knocking. Here’s how this looks in a graphed datalog of a single cylinder during a pull.

ecoboost-knock-count-and-ignition-correction

These negative ignition values are always subtracted from the current Ign Corr. Cyl X variable for each cylinder. This is important to understand because the Ign Corr. Cyl X variable also ADDS timing when the system does not “hear” any knock and you are on the throttle.

The rate at which timing is added and how much total timing is being added is also adjustable in the tune. Ideally the tune should walk timing up at a reasonable rate that is not so fast such that knock is induced and not too slow such that performance is left on the table.

One thing that has to be understood is that all engines will knock at some point regardless of tune and fuel used. The combustion process is a chaotic process and sometimes you get some irregularities. This is inevitable. You want to tune out heavy and sustained knocking, but completely eliminating all knock is not something that is realistic – especially in a street engine. Handling knock correctly is the key. Light knock will NOT damage an engine especially if timing is reduced via a reduction in Ignition Corrections when it happens. LSPI (Super Knock) and bouncing off a Rev Limiter have a MUCH more damaging effect on the pistons and rods.

The beauty behind this knock control system that both adds and subtracts timing is that it also LEARNS the quality of your fuel over time. The learning variable is called OAR (Octane Adjust Ratio). This variable is like a fuel trim but used for ignition and load/boost targets. It can range from -1 to 1. Below is the table that allows the ECU to learn and adjust OAR. You can see from this table that in order for this system to work, ignition timing and the Knock Response table must be set such that the ECU can ADD and SUBTRACT enough timing to make the Ign. Corr. Cyl X parameters positive as well as negative during a pull. With an adaptable tune you are likely to see Ign. Correction numbers that are both positive and negative at times.

how-oar-learning-works-ecoboost

Finally, this OAR number is not just another pretty face. It affects the timing AND load/boost tables the car will be targeting. An OAR that is closer to 1 will remove both timing and boost reducing future knocking. An OAR closer to -1 will add timing and boost due to good quality fuel and increase performance. It is normal for OAR to fluctuate slightly depending on your fuel quality and driving conditions (5th gear pulls are more likely to knock compared to 3rd gear pulls and OAR will adjust to reflect this). Below is the timing table that is multiplied by OAR in the OEM calibration and added to the overall ignition timing the ECU runs. In this case an OAR of -1 will add 4* timing and an OAR of 1 will remove 4* of timing near redline. OAR dependent boost/load limits are setup via a blend of several tables not shown here.

oar-multiplication-table-ford-ecoboost

It should be clear now that NEVER seeing any negative corrections is an indication of a tune not setup to use this learning system to its full potential. This is not ideal on a street driven car as it means that it will not adapt to keep the engine safe when fuel quality or driving conditions change nor will it extract more performance when the situation allows. 

Keep in mind that these knock detection systems are extremely fast to react. If knock is detected, if setup correctly, the system will very quickly pull timing to stop the knocking during that pull and adjust the tune for future pulls. Excessive repeatable knock or only positive ignition corrections are something that should be addressed in the tune – and can only be done by the person that has set the tune up. More on knock in this article. 

Now let’s have a look at a set of logs see this in action across four cylinders.

Here’s a normal 3rd gear pull with all 4 cylinder Ign Corrections and Knock Counts graphed. As you can see, ignition timing walks up when there is no knock in a step-wise fashion. When there is knock it drops down stopping further knock. If the knock events happened earlier in the pull or were of a higher intensity, Ign Correction could have become negative.

ecoboost-knock-count-and-ignition-correction-2

Here is how we can setup the same knock detection system in a less ideal manner. At first glance, it looks like this engine is basically not knocking at all. However if you look carefully, you can see that there were 4 knock events. The amount of timing pulled for each event is very little. This does two things. One, not enough timing is being pulled to stop the occurrence of further knock. Secondly, pulling so little timing will mean Ign Correction values will not be negative even though the engine could be knocking heavily and continuously. This in turn will mean the OAR will not adjust and the tune will not adapt to the fuel quality used.

ecoboost-poor-knock-handling

For this reason, watching Min/Max Ign Correction on the AP can be very misleading. Not only does it not show you how many times the engine knocked, it also doesn’t show you how intense the knock was. To determine the performance of the tune, a full datalog is always necessary or at least a good understanding of HOW the tune handles knock events. 

Happy Tuning,

The Stratified Team

Misfires and the Ecoboost, when should you worry?

I’ve seen a number of recent inquiries regarding the misfire count on Ford Ecoboost cars and I wanted to explain a little bit more about what it means, how the ECU determines when the car misfires, and when you should worry about it.

What are Misfire Counts?

First of all, the Misfire Count as a live parameter or datalogged represents the number of misfires detected by the ECU since the last engine start. ecoboost-misfire-count

In the case shown above, the COBB Accessport monitor shows that there have been a total of 8 misfires since the engine has been running WITH THE COBB AP turned on.

 What is a Misfire?

Combustion is a complex process. The power generated by an engine comes from the “power” stroke of the 4 stroke cycle. The power stroke is where the spark plug lights the air-fuel mixture inside the cylinder and you get a propagating flame front that evenly pushes the piston down. This is of course the ideal scenario. However sometimes, for a variety of reasons discussed below, the spark plug does not effectively ignite the mixture inside the cylinder. This causes what is known as a misfire. For that one cylinder, power is either low or not made at all during that one cycle and you will feel it as a short hiccup in what is otherwise smooth engine running and power delivery.

How is a Misfire Detected by the ECU?

Modern cars have a high resolution crank position sensor and multi toothed wheels. This is attached to the crank where the accessory pulley is and looks like this.

ecoboost-crank-wheel

The ECU knows when the spark plug fires for each cylinder with respect to the position of the crank wheel and expects the engine to be accelerated during the power stroke. If the crank teeth are not accelerated during the power stroke (you can also feel this sitting in the car) it will determine that the particular cylinder has misfired.

Why does a Misfire Happen?

The engine needs a few elements for good combustion. These are air, the correct amount of fuel, effective mixing between the air and the fuel in the combustion chamber, a strong enough spark, and good compression.

During NORMAL and HEALTHY engine operation misfires do happen but they are random and intermittent. For example, the Ecoboost engine tends to misfires at idle. This is because sometimes the air and fuel do not effectively mix and light off. This is a common issue with direct injection engines where the fuel and air are injected directly in the cylinder with poorer mixing characteristics. Engine designers and engineers get around this in multiple ways – sometimes with tumble flaps that increase air velocity (which the Ford does not have) – and through extensive internal combustion chamber and injection designs. These random idle misfires are undesirable for smooth running and emissions; however they do still happen even in healthy engines. The Misfire Count will pick these up and increment but a Check Engine Light (CEL) will not necessarily be triggered.

Another common reason for misfire is spark plug gap. This happens at high load under wide open throttle operation. A gap that is too large may prevent the plug from lighting when there is a dense mixture in the chamber under boost. We recommend a 0.026 inch spark plug gap to avoid these. You can feel these as small intermittent losses of power at wide open throttle but they are a simple fix.Spark Plug Gap

Other failures of the ignition, injection, or air induction system can cause misfires (including carbon buildup) but the above two causes are the most common in healthy engines.

If there is internal damage to the engine such as a damaged ringland and associated loss of compression this can trigger a continuous misfire for that cylinder. The misfire count will increment much faster and eventually it will trigger a check engine light. This constant misfire is something you will FEEL and HEAR with the car at idle and it will be outside of the norm. A quick compression test will verify the internal health of the engine so there is no guesswork in this diagnosis.

Ecoboost Compression Test

When are the Misfires Codes (P0300, P030X for each cylinder) Triggered

The OEM ECU has a complex mechanism for determining when a misfire is part of normal operation, or when it means there is something that needs to be addressed. When it determines that something needs to be addressed; it will illuminate the Check Engine Light (CEL) and usually indicate which cylinder the issue occurred in (P0301 indicates cylinder 1, P0302 indicates cylinder 2, and so on).

There are two programs built into the ECU for determining two different types of failures. We will call these Type A and Type B.

Type A detects a failure that has recently happened or is sudden in nature (failed coil pack for example). This detects failures over a period of 200 revolutions. If the engine misfires in excess of 23% of the time (46 misfires per 200 engine revolutions) at low RPM or in excess of 5% at high RPM it will trigger the fault code under this condition.

Type B detects a condition that is progressing over time. This has a detection period of 1000 engine revolutions. For example in the Focus RS it triggers if 1.2% of revolutions  result in misfires (12 misfires per 1000 engine revolutions). This is designed to catch progressing conditions such as worn spark plugs.

For the sake of simplicity, assume that your car is idling at 1000RPM. This means that for you to have enough misfires to indicate an out of tolerance condition, you will need to have at least 12 misfires during 1 minute of running at idle.

When should you worry and what should you do?

check-engine-light-ecoboost

Because the ECU is keeping track of the misfires, you don’t need to! When a fault code is triggered for a misfire, this is when you want to investigate and look for an issue. Otherwise, keep spark plugs fresh and gapped correctly and keep in mind that misfires can and do happen on perfectly healthy engines!

The Stratified Team

MK7 GTI Step Colder Spark Plugs and Compression Test

When turning up the power on a vehicle such as we are doing via the COBB Accessport, inevitably more heat is generated. With more heat in the combustion chamber, you may start to move outside the optimal heat range of the OEM plugs and thus have an increased risk of pre-ignition. For more in-depth spark plug tech check out our spark plug article here. Because of this our red development MK7 GTI is getting a fresh set of plugs.

Knock, Pre-Ignition and Heat Range

Do not confuse pre-ignition and detonation (or knock). Knock is what the knock sensor picks up and you can datalog this as ignition corrections during a pull. Knock is caused by multiple flame fronts starting AFTER the initial flame front was started by the spark plug. Replacing the spark plugs with a step colder will not prevent knock – knock is a result of fuel used, tune, and temperatures – and I mention this because we get asked all the time if replacing the plugs will reduce knock. It will not. However it will reduce the CHANCE for pre-ignition and pre-ignition is much more serious than knock and more damaging should it occur. The knock sensors can’t pick up pre-ignition because pre-ignition happens when the air-fuel mixtures ignites BEFORE the spark event and will usually result in a hole in a piston or broken rod. A colder spark plug helps this because it pulls more heat into the head of the engine from the combustion chamber and is less likely to act as a point of ignition before it is triggered by the ECU.

Generally speaking when starting to tune a car, we go for a step colder plug than factory to avoid pre-ignition. Going too cold can prevent the plug getting hot enough to burn off deposits in daily driving and can result in fouling and misfire – so a compromise must be struck for a street car. For the MK7 GTI we chose the popular Denso IKH24KT.mk7-gti-stratified-spark-plugs-compression-1The Install

Installing the spark plugs is fairly straightforward. You will need to remove the engine cover, the coil pack harness, and then pull each individual coil pack. 
mk7-gti-stratified-spark-plugs-compression-3

mk7-gti-stratified-spark-plugs-compression-4

Once the spark plugs have been pulled it’s a good time to give them a look-over. Our plugs were very clean with no speckles or excessive deposits. They were burning cleanly without obvious evidence or oil consumption or knock. The orange deposit is due to running some race fuel additive (and normal if doing so). You can see that the new step colder plugs have a slightly recessed tip which is a feature of colder plugs.

mk7-gti-stratified-spark-plugs-compression-14mk7-gti-stratified-spark-plugs-compression-9

Compression Test (while the plugs are out)

If you have a compression tester handy, this is a great time to perform a quick compression test of your GTI. Very little is required to do so. You simply plug the compression tester in each spark plug hole and crank the engine while holding the accelerator pedal to the floor. I crank until the compression tester needle stops rising and this is around 12-15 cranks per cylinder.

mk7-gti-stratified-spark-plugs-compression-15

What you are looking for in terms of the compression test results is consistency across all the cylinders. The absolute number will depend on the tester used and altitude above sea level. Our development vehicle was very healthy with a 190psi reading across all four cylinders.

mk7-gti-stratified-spark-plugs-compression-17

Before putting the new spark plugs in and torquing them down to 18-20ft/lb it is worth checking their gap using a feeler gauge. We recommend 0.024-0.026″ (0.60-0.66mm) to prevent misfiring under heavy load. The gap will naturally open up over time as they wear out and heat cycle. The new Densos did not require any adjustment of the gap.

mk7-gti-stratified-spark-plugs-compression-7

Once the plugs are back in along with the coil packs and harness, you’re done! You’ve now checked the health of your motor with a quick compression test, looked at how clean it is running via inspecting the old plugs, and freshened up the ignition system with new plugs that are more tolerant to tuned, higher performance driving.

The Stratified Team

Does a leaner Air-Fuel Ratio result in more power on the MK7 GTI?

Calibrating an engine revolves around solid data analysis and testing of any hypotheses. In the case of the MK7 GTI, the OEM ECU calibration commands a relatively lean air-fuel ratio (AFR) target during wide open throttle operation. For the majority of a pull, unless one of the temperature failsafe thresholds are triggered, the ECU will command a 14.7 AFR tapering to mid 13s by redline.
vw-gti-mk7-oem-air-fuel-ratios
It has to be understood that these targets are within the context of the OEM tune. The boost pressure targets, ignition timing targets, and variable timing targets are all taken into consideration when selecting the appropriate air fuel ratio. On top of this, economical operation is a strong requirement for the OEM.

 

When pushing the car beyond the factory setup in order extract maximum effort from the engine, all variables including the air-fuel ratio must be reconsidered and retested.
When commanding a higher output the engine requires more in-cylinder cooling in order to avoid detonation (knock) while maintaining maximum performance. This is the case with other internal combustion engines we have worked with but we had to put the hypothesis to the test for the EA888 Gen3 as well.

 

The COBB Accessport gives us a very powerful analysis and datalogging tool at a high sample rate of 12hz (that means we get 12 datapoints per second for each sensor or actuator signal we log)
vw-gti-mk7-cobb-accessport
We tested this hypothesis in a controlled environment where we only varied air-fuel ratios. We made sure that this was done on a hot day with 91 octane fuel that is knock prone. This was done such that we can clearly see the effect of the air-fuel ratio without any other variables interfering.
vw-gti-mk7-stratified-tune-dyno
Here you can see that the richer run did produce more power. The question now is why? We looked at the knock traces from both runs for to get an answer to this as boost and temperatures were identical. The graph below answers this question.
vw-gti-mk7-stratified-tune-dyno-knock
As you can see, the leaner AFRs do not offer the necessary in-cylinder cooling to prevent the engine from knocking. Yes, the engine knocks in both runs because we have setup the test as such to ensure we see a contrast between the two sets of data. However you can see that the richer air-fuel ratios result in a diminishing knock trend which in turn results in the engine making more power and staying safer!

 

Finally, we have to ensure the data is repeatable. For this we have two back to back runs of the richer tune. You can see that the data is repeatable within 2-3whp which gives us further confidence in the test results
vw-gti-mk7-stratified-tune-dyno-repeatableThe conclusion to all this – when calibrating a vehicle outside of the OEM parameters, all variables and hypotheses need testing in order to optimize the new set up.
Happy Tuning,
The Stratified Team

So you got a bad tank of gas … now what?

It happens. You are travelling, you don’t use your regular gas station, they change the fuel quality in your area. So now you are stuck with a bad tank of gas (and what I mean by this is fuel with lower actual octane than what you usually use) in your pride and joy and your heart sinks at the thought. Here’s what that looks like, means, and how to address it.

First of all, keep in mind that your car has modern reactive knock sensors and these will pick up the knock from the poorer gas and pull back timing to keep the engine safe. This applies to all modern vehicle platforms. On an Ecoboost for example, the car will LEARN the fuel octane you are using. The OAR (octane adjust ratio) parameter is used to do this. It will adjust closer to positive 1 and timing will be pulled preemptively from the tune to prevent the knock from occurring.

The engine won’t all of a sudden explode because of knock from a bad tank of gas if the tune is setup to make use of these safety features. It is not ideal, and if the fuel quality in your area has permanently changed you should have the tune adjusted. However, this NON-LSPI poor fuel quality knock can be handled quite well by the knock sensors to ensure engine safety.

Keeping an eye on your datalogs and live monitors will tell you if something is out of the norm. Here’s how our 3rd gear pull corrections look like with a bad tank of gas.

focus-rs-bad-gas-knockYou can see that the timing additions in this 3rd gear pull stop after adding about 1.5* and then drop due to knock ending up in the -2.5* region.

Here’s how our usual “good gas” behaves. These pulls are taken on the same road, same modifications, and same temperatures but with better fuel.

focus-rs-bad-good-gas-no-knock

Notice that there are much fewer “drops” as the ECU is adding timing during the pull. Most cylinders are adding 1.5-2* near the end of the pull instead of pulling -2.5*.

Aside from the engine safety concern, this loss of timing advance does hurt performance. How much? In the case of our Focus RS the timing difference is worth a solid 16whp and 10 ftlb of torque. A ballpark figure is that 1* of timing accounts for around 3whp on the Ecoboost 2.0 and 2.3 engines.

focus-rs-gas-quality-comparison-pull-stratified

So what can be done if you run into bad gas? Here are some tips:

  • Wait it out if you know it’s a poor tank. Unless the gas is VERY bad the car will rely on its sensors to adjust timing dynamically. If you are seeing consistent corrections take it a bit easier until the tank runs out.
  • Run a low boost map – we include this with all of our tunes.
  • Add some octane booster to the tank. A bottle of the over the counter stuff will make a 2-4* timing advance difference. More expensive Race Gas or Boostane brands will have a bigger impact but they can’t be found everywhere.
  • Add 1-2 gallons of E85 to the tank and top up with premium. Adding a splash of E85 increase the octane enough to ride a bad tank out and does not require a tune change.
  • If you are consistently seeing “bad gas” in your area, consider having the tune adjusted.