This blog was made to show people how to test and diagnose any fuel system faults they may be experiencing;
warning, be careful around raw fuel. It can catch fire! Use appropriate safety precautions. Keep sparks, flame, your body and your clothing away from raw fuel! Know where your fire extinguishers are and use them if necessary.
1. Locate the two closest fire extinguishers.
There is one fire extinguisher in the room that we are working in (the workshop up by the paid for parking).
2. If you can, look up fuel Pressure specifications for the vehicle you are testing.
The specifications read, 265 - 304kPa this is the fuel pressure specification for when the ignition is turned on but the engine is off. 265 - 304kPa, This specification is what the fuel pressure should be when the engine is on but the vacuum hose has been removed from the fuel pressure regulator. 206 - 255kPa, This specification is what the fuel pressure should be at normal, idling conditions (no vacuum leaks, regulator faults and sufficient fuel in the tank)
It is good to also relieve fuel pressure through-out the system if any fuel hoses or components are being worked on, this just allows you to do the job with-out making mess with fuel. Relieving the pressure is quite simple, start the engine, remove the fuel pump relay or fuse, keep the engine running untill the engine (turns off by itself/stalls) Double check that the fuel pressure has gone by cranking the engine to see if it starts, if it doesnt you have successfully relieved the fuel pressure, now remove a fuel line and have a rag handy to catch any left over fuel (their will still be fuel in the lines, just no fuel pressure this is because with-out the fuel pump running the fuel cant be pumped to create pressure) Remember to replace the fuel pump fuse/relay.
4. Attach a fuel pressure gauge (if you haven't already got one) and notice which scale on the gauge you will be using. Briefly crank the engine over, just enough to gain fuel pressure, check for any leaks and take note; (for this experiment we did no have to do this as the engine had a pressure gauge installed already, and our gauges displayed kpa & psi which is good because the specs were in kpa)
No leaks were found, we checked all the connections and stuff to make sure their was none, just because we didn't have to install the gauge so we doubled checked to make sure.
5. Measure the fuel pressure with the key on, engine off;
Our pressure under these circumstances displayed 270 kPa
6. Measure the fuel pressure with the engine idling, watch the pressure for a few mins;
As the engine was started our fuel pressure was 270 kPa, but as time went on the pressure dropped to 250 kPa.
7. Measure the maximum fuel pressure by using the fuel line clamp tool provided by your tutor. (do not do this for an extended amount of time);
When we used the tool to clamp the fuel line, we noticed a high jump in fuel pressure, our maximum fuel pressure jumped up to 600 kPa, this is the reason why it says not to hold it at this fuel pressure for a long period of time because it can damage components and maybe even burst fuel components.
8. WOT; with the engine idling disconnect and plug the vacuum line goning to the fuel pressure regulator.
The pressure recorded was 300 kPa, this test shows what the fuel pressure would be at full throttle, because when the engine is at high capacity the vacuum will not be as high allowing the regulator to regulate the fuel to a higher pressure due to the vacuum not being strong enough to open the diaphram inside the regulator, with the vacuum line off the regulator is reading atmospheric pressure, which basically means that it is going to operate to its full capacity meaning that the diaphram within the regulator wont open much.
9. Residual Turn the engine off and watch the fuel pressure for five minutes;
As time went on the fuel pressure increased from 250 kPa (idle pressure) to 270 kPa (residual pressure)
10. Fuel flow Hook up equipment to read fuel volume;
This test was not applicable to us as we did not have the gear to perform this test.
11. Replace any vacuum lines removed, remove the fuel pressure gauge, turn ignition on & off, check for leaks, Any leaks found?
There was no leaks found after performing these procedures.
Make sure the engine is running fine before leaving it.
12. Explain why it is important to know a vehicles fuel pressure/flow;
It is important to know this information as it can very useful knowledge to have if you encounter any fuel system faults, because it gives you a basic understanding of how the fuel system works. With a basic understanding of how this system works you can start to diagnose and rule out any faults that could be causing a vehicle to run incorrectly. For example, say we had a little bit of a misfire at idle, we could easily connect a pressure gauge, look up the manufactors specs and compare them to the readings that the gauge is reading. This then shows you if theres any variances, which can help you to rule out mis-functioning parts.
13. Describe the symptoms a vehicle would give with each of these cases;
Low fuel pressure;
With low fuel pressure the car may idle fine, but as throttle is applied the vehicle may hesitate to accelerate and also not produce the power needed for the situation the vehicle is in. The engine will run very rough under acceleration untill correct fuel pressure is achieved.
Low fuel flow;
If the fuel system has low fuel flow, the fuel rail will not be supplied the right amount of fuel, this means that the injectors will have a insufficient fuel amount to allow for a full injection spray aswell as the fuel pressure at the injectors wont be sufficient. Basically the engine will misfire and not produce power as load is applied to the engine.
High fuel pressure;
High fuel pressure will cause the air/fuel ratio to be quite rich at idle, meaning the economy and emission levels will be bad. As the engine load increases, the fuel pressure will be used correctly because at high engine load the fuel pressure is high anyway so for the amount of work the engine is doing, the engine economy and emissions will be correct.
Faulty fuel pressure regulator;
Depending on the fault, the fuel pressure regulator could give two different conditions; One fault being that the diaphragm inside the fuel regulator could be sticking open, this would cause low fuel pressure (explained above) Another fault the regulator could encounter would be that the diaphragm is stuck close or the vacuum line to the regulator is leaking, this could cause over pressurizing of the fuel (also explained above).
This concludes my post, all the tests conducted came out fine, they were within the manufactors specifications.
Image reference;http://www.google.co.nz/imgres?q=fuel+pressure+gauge&um=1&hl=en&rlz=1C1CHKB_en-GBNZ450NZ450&biw=1366&bih=667&tbm=isch&tbnid=HBg7ZHa-ExhD2M:&imgrefurl=http://www.justanswer.com/car/12ajq-1997-jeep-cherokee-4-0l-seem-problems.html&docid=gD52wsNriHO85M&imgurl=https://w05.dealerconnect.chrysler.com/service/mds2002/serviceInfo/en_US/80468d30.gif&w=640&h=639&ei=J-fVTsWfC6zMiQLZydXCDA&zoom=1&iact=hc&vpx=812&vpy=424&dur=6708&hovh=161&hovw=161&tx=108&ty=140&sig=109698256239734078907&page=2&tbnh=134&tbnw=134&start=18&ndsp=20&ved=1t:429,r:4,s:18
Practice Back-Probing connectors on the bench;
This isnt a very hard experiment but I believe that knowing how to back-probe is one of the most important things in the subject, if you dont know how to back probe correctly the components you are testing may-be damaged (meaning you will owe people $$$)
First of all we will start with a simple lesson on how to use a multi-meter;
1.0; Meter reading Ohms with wires not connected;
1.1; Turn on the multi-meter, set it to measure resistance (ohms), make sure the leads are not touching anything. What is your reading? and descibe what this readout means;
Our reading shows O.L. This is because this is basically an open circuit. Resistance will be infinite if there is no link between the two terminals.
2.0; Meter reading Resistance with wires connected;
2.1; Turn the meter on, set the test to Ohms(resistance) and touch the leads together;
Our reading shows 000.5 Ohms.
2.2; Describe what the read out above means when doing electrical testing;
This reading basically just displays small resistances with-in the multimeter circuitry, for example the test leads will almost always have a tiny amount of resistance in them.
3.0; Practice back probing connectors
3.1; Find a hard shell connector, with the attached terminals and wires that you can test
3.2; Back probe a wire on one side, probe gently from the fron on the other side, and measure the resistance, Record the reading;
The reading shows 0.51 Ohms
3.3; How can you tell if you've made a connection between the wires?
I can tell because the reading shows a slight resistance, this basically indicates that a connection has been made between the wire and also that there is a slight internal resistance with-in the wire.
Image reference;http://www.google.co.nz/imgres?q=probing+a+electrical+connector&um=1&hl=en&sa=N&rlz=1C1CHKB_en-GBNZ450NZ450&biw=1366&bih=667&tbm=isch&tbnid=oaQqoS9JuyIebM:&imgrefurl=http://www.agcoauto.com/content/Glossary&docid=ZxdhQUBNFkBRWM&imgurl=http://www.agcoauto.com/content/images/electrical/back_probing_circuit.jpg&w=278&h=216&ei=k-bVTq_1CcWdiAK_ooGHDA&zoom=1&iact=hc&vpx=975&vpy=70&dur=1445&hovh=172&hovw=222&tx=72&ty=125&sig=109698256239734078907&page=1&tbnh=154&tbnw=196&start=0&ndsp=19&ved=1t:429,r:5,s:0
WS5; Scan Tool Diagnostics
Vehicle being used; Mazda Familia 323, 1998.
This test exercise is a basic scan-tool exercise used to teach basic scan-tool skills to students.
1; Scan Tool Data;
1.1; Obtain a vehicle that is suitable for this test.
We have chosen to us the mazda familia in the workshop as it has ob2 two (on board diagnostics two) because it was produced after 1996. This is a system in which the ECU provides fault information to the scan-tools we are using. Cars produced before 1996 generally used obd1. The difference between these two diagnostic features is that obd1 focuses more on just giving engine fault codes which can be used to find what the fault is by looking at the fault code menu in the vehicles user manual. obd2 has alot more detail as to what the faults can be, this is useful if you dont have access to a particular vehicles manual. There is also another difference between the two diagnostic devices; The port in which the scan-tool connects through with the ECU can be located anywhere on different obd1 vehicles. A regulation was brought in when obd2 was being produced, Every obd plug must be with in 1 meter of the vehicles steering wheel. This makes it alot easier to find the obd plug.
1.2; Connect the scanner, power it on, follow the instructions and input the correct vehicle information it asks for so you can view the data.
Most scan tools will ask you the; Make of the vehicle, The model, The engine capacity, Chasis code, Jap import/Euro import/NZ new and Year of the vehicle. Some may ask for different details but in my experience these are the only details they generally ask for.
This is just so that the scan tool can calibrate properly to your specific make/model because some vehicle models have slight variances which can cause differences in the data you recieve from the scan tool.
1.3; Find the data for the information listed. Turn on the engine and record the live data in the graph below;
7. Repair fault;
7.1. Plug connector back in, or repair the problem as required, describe what you did;
10. Recheck for codes and record them below;
We did another fault code check after we had erased the codes in the last step, the check came back clean, we didnt have any more fault codes given to us by the ECU, so all the faults had been successfully repaired.
11. Discuss the importance of live data when fault finding;
Live data provides us with live information as to what signals the sensors are reading at different vehicle speed, load, conditions etc. This can make it alot easier to diagnose faults because by observing the live data and comparing with appropriate manufactor specifications we can understand what the parameters of each signal should be under different conditions. This gives us alot more direction as to what potential faults may-be.
12. Explain the need for parameters when checking live data;
Parameters give us a range of what acceptable signal variances should be for specified components. Basically parameters allow us to decide weather components being tested meet the specifications that require the components to function correctly. For example, Say if we were to test the resistance of a high impedance injector just by disconnecting the injectors plug and probing the injector terminal and ground, Lets just say the specification is 10-13.5 ohm, but our test comes back showing around 20 ohm, this obviously does not meet the specification set by the manufactor, this is why parameters are needed, with-out them it would be so much harder to diagnose faults.
13. Discuss how a scan tool can aid you with fault finding;
A scan tool is a very usefull device for fault finding. Scan tools can find faults that may be hard to diagnose with a multi-meter or oscilloscope. This is because the scan tool can read problems straight from the ECU, modern day cars have self diagnosis features, if anything through-out the car is wrong the ECU will show a trouble code. A scan tool is a much easier way of reading fault codes as it doesnt involve having to read flash codes.
This test exercise is a basic scan-tool exercise used to teach basic scan-tool skills to students.
1; Scan Tool Data;
1.1; Obtain a vehicle that is suitable for this test.
We have chosen to us the mazda familia in the workshop as it has ob2 two (on board diagnostics two) because it was produced after 1996. This is a system in which the ECU provides fault information to the scan-tools we are using. Cars produced before 1996 generally used obd1. The difference between these two diagnostic features is that obd1 focuses more on just giving engine fault codes which can be used to find what the fault is by looking at the fault code menu in the vehicles user manual. obd2 has alot more detail as to what the faults can be, this is useful if you dont have access to a particular vehicles manual. There is also another difference between the two diagnostic devices; The port in which the scan-tool connects through with the ECU can be located anywhere on different obd1 vehicles. A regulation was brought in when obd2 was being produced, Every obd plug must be with in 1 meter of the vehicles steering wheel. This makes it alot easier to find the obd plug.
1.2; Connect the scanner, power it on, follow the instructions and input the correct vehicle information it asks for so you can view the data.
Most scan tools will ask you the; Make of the vehicle, The model, The engine capacity, Chasis code, Jap import/Euro import/NZ new and Year of the vehicle. Some may ask for different details but in my experience these are the only details they generally ask for.
This is just so that the scan tool can calibrate properly to your specific make/model because some vehicle models have slight variances which can cause differences in the data you recieve from the scan tool.
1.3; Find the data for the information listed. Turn on the engine and record the live data in the graph below;
This graph shows the live data that the scan tool had at the time I recorded it. As you can see some of the boxes were left blank, that is because the mazda's obd system did not have communication with some of the components in the graph.
2; Trouble Codes or fault codes
2.1; Find where the codes are listed;
The codes were actually listed with-in the scan tool itself, all the details that we needed were listed quite clearly displayed in the trouble code list.
2.2; Record any codes, and what system and condition they descibe in the chart below;
We figured out that these fault codes were faults that had been corrected from the last students, but they had not remembered to clear the codes, so these readings were actually old readings from tests before our tests.
3. Lecture put in fault;
3.1. Find your lecturer and have him create a fault under the hood (no peaking)
3.1. Find your lecturer and have him create a fault under the hood (no peaking)
We had one of our tutors put a fault in the engine somewhere so that we could have a go at scan-tool diagnosis.
4. Record new codes;
4.1. Look up codes in the scan tool, and record them to the chart below;
5. Find what data has changed;
5.1. Have a look through the scan tool data to see what PIDs (Parameter indentification of system voltages) have changed. Do any readings not make sense? Also record the data changes in the chart below;
The reading variances that stood out the most to me was the ECT reading and INJ pulse rate, as they had changed so much that there was no signal from them to be displayed. Also the code given by the scan tool was an ECT trouble code, so this gave us a slight hint as to what the issue was.
6. Visual inspection to find fault;
6.1. Do a visual inspection under the hood to try and locate where you think the problem is. Use the information displayed from the scan tool to give you a guideline as to where to look.
We had a quick look under the hood of the vehicle and we found that the main ECT plug was unplugged, that's why we weren't receiving any signal from that sensor, also the vehicle wasnt starting thats why our injection pulse rate was reading 0, Some vehicles wont start with the ECT plug unplugged, our mazda is one of them. So if the vehicles not started obviously there cant be an injector pulse rate, well a constant injector pulse rate that is.
7. Repair fault;
7.1. Plug connector back in, or repair the problem as required, describe what you did;
First of all we started by inspecting the wires going into the ECT connector to see if they were visually fine, free of corrosion, still insulated etc, then we reinstalled the connector back onto the ECT sensor, then we double checked that all the wires in the connector were sitting inside the connector properly so that there is a good connection between the connector and sensor.
8. Recheck Data PIDs;
8. Recheck Data PIDs;
8.1; Recheck data with scan tool, then record the changes in data in the chart below;
First of all we started the engine to make sure that we had correctly installed the ECT connector, the car started fine so we recorded the data and put it into the chart below;
As you can see by the data recordings in the chart, all the signals are back to normal, this proves that we diagnosed the fault correctly and repaired it accordingly.
9. Clear codes, Describe what you did to clear the codes;
The scan tool we are using has a function in it that can contact the ECU and ask it to clear the codes, we used this function to erase the fault codes that came up after we had fixed the problem.
The scan tool we are using has a function in it that can contact the ECU and ask it to clear the codes, we used this function to erase the fault codes that came up after we had fixed the problem.
10. Recheck for codes and record them below;
We did another fault code check after we had erased the codes in the last step, the check came back clean, we didnt have any more fault codes given to us by the ECU, so all the faults had been successfully repaired.
11. Discuss the importance of live data when fault finding;
Live data provides us with live information as to what signals the sensors are reading at different vehicle speed, load, conditions etc. This can make it alot easier to diagnose faults because by observing the live data and comparing with appropriate manufactor specifications we can understand what the parameters of each signal should be under different conditions. This gives us alot more direction as to what potential faults may-be.
12. Explain the need for parameters when checking live data;
Parameters give us a range of what acceptable signal variances should be for specified components. Basically parameters allow us to decide weather components being tested meet the specifications that require the components to function correctly. For example, Say if we were to test the resistance of a high impedance injector just by disconnecting the injectors plug and probing the injector terminal and ground, Lets just say the specification is 10-13.5 ohm, but our test comes back showing around 20 ohm, this obviously does not meet the specification set by the manufactor, this is why parameters are needed, with-out them it would be so much harder to diagnose faults.
13. Discuss how a scan tool can aid you with fault finding;
A scan tool is a very usefull device for fault finding. Scan tools can find faults that may be hard to diagnose with a multi-meter or oscilloscope. This is because the scan tool can read problems straight from the ECU, modern day cars have self diagnosis features, if anything through-out the car is wrong the ECU will show a trouble code. A scan tool is a much easier way of reading fault codes as it doesnt involve having to read flash codes.
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