Post Three: On Car Testing

These last two weeks we continued with out on car testing. We had a set of worksheets that needed to be completed. Each worksheet had a diagnostic task that we had to perform on our cars.

Flash Codes
When ever there is a fault in a vehicle and the ECU picks it up a code is displayed. One way you can check these codes is by the way of the 'check engine' light in your dashboard flashing. It will flash a number of times indicating a code number. The check engine light can display more than one code at a time. Now how do you know what codes the check engine light is displaying? Well this is simple. There is a pattern that the check engine light flashes in. The first flashes represent the tens in the code number. There will be a very small pause and then the second flashes occur. These represent the ones in the code number. For example say the check engine light flashes three times and then pauses. After the pause it flashes six times. The flash code number being displayed here is 36. To get the flash codes to display you have to follow the correct manufacturer's procedure.

Each manufacturer has his own way of bringing the flash codes up on the display unit. We did this on my friend Richard's car. The check engine light on his car would randomly appear when he is driving and then would stay on for a length of time. It would after some time go off. This started to happen more and more rapidly while he was driving. Flash codes are done with the key ON and engine OFF position. To bring up the codes in his 1997 Mithsubishi Legnum we had to first ground the number one terminal with an earth wire on his data link connector. The Data link connector is situiated under the dash on the drivers side. It was easy to locate. After the terminal was grounded we turned on the ignition and watched the check engine lite flash. It flashed twice first and then it flashed three times. The code number it displayed was 23. There were no additional code. We searched the code number up pn the internet and found out what it meant. The code was signaling a low voltage output from the Camshaft position sensor.

After the fault code was diagnosed we did a visual inspection under the bonnet to see what was causing this problem. When we located the camshaft position sensor we noticed that there was a lot of dirt and grime that had built up around it. When we unpluged the sensor connector plug we noticed that it was dirty and was a bit clogged up with dirt and grime. This could have been causing the problem with the sensor signal being too low. So before we moved ahead we cleaned out the connecter plug and all the dirt and grime around the sensor. After the cleaning we pluged the sensor back in and checked for the flash codes again. It was still on. We had forgotten to clear the car's memory as the fault codes are recorded. To clear the code we disconnected the cars battery for 30seconds. The reason why we do it for so long is because we need to let the capacitor discharge fully. As we know a capacitor stores charge. This charge is then used to with hold information while the baterry is disconnected. After the capacitor dicharges fully the memory is lost and therefore the code is cleared off. We then connected the battery back in and checked for the codes again. There were no codes!

The cleaning of the sensor plug made a good difference in the car's behaviour. Before the car would take a few seconds to start up as it would not fire or would fire in the wrong order. This was because of the low voltage being sent to the ECU from the camshaft position sensor. The ECU at times didnt know the engine position and therefore it wouldnt fire the spark plug at the right time causing a miss fire. This was causing rough running of the engine. It would also cause the engine to miss fire every now and then. We then took the liberty of checking all the other sensors and made sure that their connection points were clean and free of dirt and grime. 


Scan Tool Diagnostics
This was a fun and simple task to do. All we had to do was connect the scan tool to the vehicle and record the car's live data. The live data was recorded with the car turned on and on idle (engine running). The scan tool connects via a cable to the car's Data Link Connector. You then have to select the make and model of the car you are testing. The scan tool the brings up the data for the specified car and then shows you the car's live data. Live data shown by the scan tool is the actual real figures that the car is producing. We had to record this live data on the worksheet. 

After we had to find fault codes with this scan tool. Code number 23 came up. Camshaft position sensor voltage too low (This worksheet was done on the same day as the flash codes but was done before). We then had our lecturer create two faults under the hood. We had no idea of what he did but we had to use the scan tool and find out. So after the faults were created we checked for the codes again. Apart from the existing code (Code number 23) two other code numbers appeared. Code number 31, Map sensor voltage too high and Code number 22 ECT (engine coolant temperature) sensor voltage too high. We also observed the engine and how it was performing with the faults. The engine was stalling and didn't idle smoothly at all.

Also we recheched the car's live data to see what figures we were getting now. The intake manifold pressure had jumped up to 46 KPA from 27 KPA. The increase pressure reading would cause the ECU to supply the engine with more fuel. This is because the MAP sensor is telling the ECU that intake manifold pressure is high. The intake manifold pressure is directly related to engine load. This means that the engine now requires more fuel. But since the car is at idle the excess fuel injection causes the engine to choke resulting in the engine stalling. Another chance was in the ECT (engine coolant temperature) sensor output. It read the coolant to be at 0 degrees. This will tell the ECU that the engine is very cold. As we know when an engine is cold the ECU supplies it with more fuel bacause the fuel condenses inside the combustion chamber. So as a result even more fuel is suplied to the engine causing the engine to run very rich and therefore choking it. This resulted in a rough stalling like idle.

To locate the fault we did a visual inspection under the hood of the car. We discovered that the MAP (manifold absolute pressure) sensor and the ECT (engine coolant temperature) sensor were unpluged. Since they were unpluged the ECU got the wrong readings. To repair the fault we pluged the sensors back in and the engine began to idle normally again. We rechecked the affected readings from the live data and discovered that they were back to normal. Intake manifold pressure was back to 27 KPA and ECT sensor read 90 degrees. The next thing we had to do was to recheck the faults using the scan tool but before we did that we had to erase them from the memory. This meant that we had to disconnect the car's battery for 30seconds and then re-connect it. The two new faults were now earased and did not show up again in the scan tool. But the existing fault (code number 23) camshaft position sensor viltage too high was still there.

I found this scan tool to be a very handy tool. It has all the specs for the car you are testing which is good because it gives you something that you can compare your live data too. The live data from the vehicle makes it easier to check and see how the car is actually performing and what exactly is causing the problem.  


Fuel Pressure
This was a small and easy task to see how the fuel pressure works in cars. This test was done on a engine with a fuel pressure gauge all we had to do was run the engine in various conditions and see how the fuel pressure reacts. We did these tests when the engine was warmed up. This engine was from a Toyota Corolla; engine name 4A-FE.

The first thing we did was record the fuel pressure when the engine was idling. We had to watch the fuel pressure gauge for a few minutes till the pressure stabilized. The fuel pressure recorded was at 38 PSI. Next we had to get the maximun fuel pressure reading when the engine was at idle. To get this reading we had to use a special tool that our tutor gave us and clamp the fuel return line. Clamping the fuel return line can only be done for a very short period of time and therefore this reading had to be recorded quickly. The maximun pressure recorded when the engine is ildling was 80 PSI. We then had to record the fuel pressure at wide open throttle. Opening the throttle fully and waiting for the pressure to jump up would damage this engine so therefore we took out the vacuum line going to the fuel pressure regulator instead. This is similar to a wide open throttle senario. The pressure reading we got was 48 PSI. The last pressure reading we needed was the residual or the rest pressure. For this we had to turn the engine off and wait for a few minutes for the fuel pressure gauge to settle. The pressure reading we got was 42 PSI.

Why is it important to know a vehicle's fuel pressure?
Checking the fuel pressure of a vehicle is an important part of fuel injection system troubleshooting. Fuel pressure relates to the amount of fuel being injected into the cylinders at the injector on time. High fuel pressure will cause the engine to run rich. A car with high fuel pressure will idle rough and would idle low as the increased fuel pressure will inject too much fuel into the engine. This will cause the engine to choke, as a result it would struggle to stay on. The engine will also experience problems when cold staring as too much fuel will be injected. The car will also experience bad fuel economy. High fuel pressure can also put too much pressure on the fuel return line causing it to tear. Where as low fuel pressure will cause the engine to run lean. This will cause the engine to have lack of power as it is not getting enough fuel. It will also cause the engine to stall at lower rpm or at idle. Low fuel pressure can also cause the engine trouble when starting up. This is why it is important to know the fuel pressure in a car.


Fuel pressure is regulated in the fuel lines by the fuel pressure regulator. The fuel pressure regulator is mechanical and therefore can go faulty. A faulty fuel pressure regulator can either increase or decrease the fuel pressure permanently. This can cause damage to the fuel injection system (fuel lines) and can also cause rough engine running (bad idle and problem starting). I read this one case in which a turbo charged vehicle was modified but the fuel pressure regulator was still kept standard. When the car was driven around town normally it operated fine but as the car was taken onto the motorway the driver felt loss of power and a strong smell of fuel. When he checked under the hood of the car he noticed one of his fuel lines had a hole blown into it. Even when he got a high pressure line the same thing happened. At the end the problem turned out to be the fuel pressure regulator. Since the car was modified, when it hit boost on the highway the added boost fuel pressure was too much to handle for the standard fuel pressure regulator. So it jammed closed increasing the fuel pressure. This increased pressure became too much for the fuel lines and therefore he kept blowing holes into them.   

As you can see fuel pressure is very important to keep a track off and should always be under specification.




Exhaust Gas Analysis

This task was based around the emissions a car produces, and how they change under different circumstances. Before we began this task we needed to know what emissions are. What particles are used inside a engine and how the react in combustion. We also learnt about how a catalytic converter reduces these emissions. 


The air that we breathe consist of two major particles; Nitrogen (N2) which makes up about 78% of the air and Oxygen (O2) which makes up about 21% of the air. These particles get sucked into the engine when a engine is running. Hydrocarbons (HC) is the fuel particles. So in an intake stoke we are taking in a combination of HC + N2 + O2 in other words air and fuel. Under ideal conditions a good combustion should produce H2O (water), CO2 (carbon dioxide) and N2 (nitrogen). But this isn't always the case as the emissions produced by a car depends on many thing. For example is it running rich or running lean, is it under acceleration or is it on steady cruise. The catalytic converter helps to reduce the emissions. A catalytic converter is placed straight after the exhaust manifold. The reason for this is because it only works efficiently when it is hot. Placing the catalytic converter so close to the exhaust manifold helps it warm up fast. Inside a catalytic converter there are two seramic blocks. Each block is filled with thousands of micro pockets. There are so many of these pockets to maximise particle to metal touch. From an engine the gases you can get are Nitrogen Oxide, Hydrogencarbons and Carbon Monoxide. In the first block oxygen is seperated from the Nitrogen Oxide particle creating Oxygen and Nitrogen (the particles we have in our normal air). In the second pocket the oxygen particles are stored. The extreme heat inside the catalytic converter causes Hydrocarbon particles and the Carbon Monoxide particle to join up with the stored oxygen particles creating water and carbon dioxide.


The four particles that come out of an exhaust are:
HC : Hydrocarbons (unburnt fuel particles) 
CO : Carbon Monoxide (means you have a rich condition as there is not enough oxygen to produce CO2)
CO2 : Carbon Dioxide (this tells you the engine efficiency. Should be about 15%)
O2 : Oxygen (A lot of oxygen can indicate a lean mixture)


To perform this task we needed a car and a exhaust analyser. The car we used was a Ford Ka. Before you plug the exhaust analyser probe into the tail pipe you need to calibrate it. We first tested the normal air using the analyser probe. The readings we got was HC 12ppm, CO 0.0%, CO2 0.0% and O2 20.9%. This is a good result as it tells us that there is no CO2 and CO in the air that we are breathing. The small amount of HC was the left over HC in the probe from the last time that it was used. We then put the probe into the tail pipe and started up the car.


The first recordings from the engine were done when the car was turned on and was idling cold. The readings we got were CO 4.46%, HC 1839ppm, CO2 9.88% and O2 9.26%. This information tells us that the combustion taking place is not very efficient. As we know an engine is only efficient when it is warmed up and up to operating temperature. A cold engine also runs rich as fuel condenses. Since the car has just turned on the catalytic converter is also not working because it is still cold. This is why the emissions coming out of a cold engine are bad. We were then meant to record the exhaust gases at warm idle but unfortunatly I wasnt able to record it.


Next we ran the warm engine at 2500 RPM and recorded the four gas readings. CO 1.114%, HC 173ppm, CO2 12.7, O2 1.64%. What these readings tell us is that the engine is running rich but is still efficient. When you rev an engine you demand more power out of it. At higher revs the air content and the fuel content increases. The engine does run rich under acceleration. Because of the rich running of the engine the HC levels are relatively high. A rich mixture consist of more fuel than air as a result of this higher amounts of CO is produces as there is not a lot of O2 to make CO2. The oxygen content is also high because a rich mixture will not burn up all the intake mixture as a result higher levels of O2 is produced. The CO2 content is still good indicating a good working catalytic converter.


Now we made the engine run rich at idle. A rich running engine is not an efficient running engine. The four gas reading now were CO 1.859%, HC 197ppm, CO2 14.07%, O2 0.79%. Now as you can see the rich mixture has increased the HC and CO content. This is because the rich mixture has a higher ratio of HC (fuel) compared to O2 (air). More fuel in the combustion chamber causes for less efficient burning. This means that not all the mixture is burnt of as we have too many fuel particles. This is why the HC content and the CO content increases, because of the lack of O2 particles. The unefficient burning also has increased the O2 content slighly. The CO2 content is still within good marjin as the car has a good working catalytic  converter.


Next we made the engine run lean at idle. A lean condition is when the engine is being supplied with more air (O2) and not enough fuel (HC) to compensate for the air. The lean mixture readings were CO 0.179%, HC 959ppm, CO2 7.75%, O2 9.65%. Now as we can see the readings have changed a lot. The increase in air supply has caused the HC and O2 levels to jump really high. When the spark is created in the combustion chamber, the spark ignites the fuel particles. To create a burning the fire jumps from one fuel particle to another. Now because of the increased air supply into the engine the fuel particles are more spread out from each other. This makes it harder for the burning to jump from one fuel particle to another and as a result of this not all of the intake mixture is burnt. This is why the HC and the O2 levels have increased. The CO2 level has droped becuase of this inefficient burning taking place inside the combustion chamber.

We then disconnected a spark plug and caused one of the cylinders to not fire, creating a miss fire situation. The four gas readings were CO 0.58%, HC 1291ppm, CO2 12.40%, O2 7.61%. As above the HC and O2 content has increased. This is because on of the cylinders is not firing. This means that the intake mixture that enters that cylinder is not burnt at all and this unburnt mixture is then sent out through the exhaust valve like normal. Since none of the air and fuel is being burnt in one cylinder the HC (fuel) and O2 (air) content have increased.