The PCV valve on the toyota 4A-FE petrol engine is located on the centre of the rocker cover connected directly by a rubber hose to the intake manifold. When we clamped this hose, the idle speed dropped slightly. This is because the crankcase gases are not venting back into the intake manifold. When we pulled the PCV valve out of the rocker cover, and put my thumb over the end, the PCV clicked shut due to the vacuum inside the manifold. This click means it is working properly. There is also a 'fresh air hose' that goes from the throttle body to the rocker cover. If the PCV valve gets blocked up, oil and gasses get into throttle body and air cleaner through this air hose.
Sunday, July 31, 2011
PCV valve
The PCV valve on the toyota 4A-FE petrol engine is located on the centre of the rocker cover connected directly by a rubber hose to the intake manifold. When we clamped this hose, the idle speed dropped slightly. This is because the crankcase gases are not venting back into the intake manifold. When we pulled the PCV valve out of the rocker cover, and put my thumb over the end, the PCV clicked shut due to the vacuum inside the manifold. This click means it is working properly. There is also a 'fresh air hose' that goes from the throttle body to the rocker cover. If the PCV valve gets blocked up, oil and gasses get into throttle body and air cleaner through this air hose.
Self Test and Diagnosis
To start the process of diagnosing, we need to first bridge the terminals 'TE1' and 'E1' in the diagnosis box. This engine uses the flashing engine check light method to view the faults. The first flashes are 10's and the second flashes are 1's.
When the terminals are bridged, we then turn the ignition on and we found, after a number of flashes of the check light, our fault locations were the water temp circuit, the intake air temp circuit, and the vacuum sensor circuit. To check the water temp sensor, we should test the wiring for available voltage or open circuit. If that is good, we would then remove the water temp sensor and test the resistance as we gradually heat it up. If the values are within spec, it is ok. To check the air temp sensor, we would first check the wiring for available voltage/open circuit. If that is ok, we would then remove the air temp sensor and test the resistance as we heat it up. If these values are in spec, the component is ok.
To test the MAP sensor, we would check wires for available voltage etc, and then we would apply a vacuum with a vacuum pump, and record the voltage drops. If this is within spec, the sensor is ok.
The vehicle EFI system is ok.
When the terminals are bridged, we then turn the ignition on and we found, after a number of flashes of the check light, our fault locations were the water temp circuit, the intake air temp circuit, and the vacuum sensor circuit. To check the water temp sensor, we should test the wiring for available voltage or open circuit. If that is good, we would then remove the water temp sensor and test the resistance as we gradually heat it up. If the values are within spec, it is ok. To check the air temp sensor, we would first check the wiring for available voltage/open circuit. If that is ok, we would then remove the air temp sensor and test the resistance as we heat it up. If these values are in spec, the component is ok.
To test the MAP sensor, we would check wires for available voltage etc, and then we would apply a vacuum with a vacuum pump, and record the voltage drops. If this is within spec, the sensor is ok.
The vehicle EFI system is ok.
Fuel Pump/Lines
Fuel Lines;
The rubber fuel hose from the tank to the pump is in good condition, not perished or cracked. The rubber and copper pipes from the pump to the filter are all in good condition and fitted tightly. The rubber hose from the filter to the rail is in good condition. The fuel rail is also in good condition and fitted tightly. The vacuum hose for the regulator and the fuel return line are also in good condition and do not appear perished or cracked.
Fuel pump;
To start testing for fuel pressures, we must first plumb a pressure gauge into the section between the fuel filter and the fuel rail.
To check fuel pressure at wide open throttle, we can simply remove the vacuum hose from the regulator and this will simulate atmospheric pressure.
Residual pressure can be checked after the engine has been turned off. Pressure at idle can be read when engine is idling, and clamping the fuel return hose we can see the max pressure of the system.
If you are to remove any fuel hoses, relieve pressure in the system by un-doing electrical connections at the fuel pump, so no power is there, and then crank engine over to relieve pressure.
The manufacturers specifications for the toyota engines were as follows;
Wide open throttle - 38-44 PSI
Idle - 31-37 PSI
Residual- 21 PSI
MAX (twice idle pressure) 61-74 PSI
Our test results were all above specified. This could be due to a faulty regulator or a blockage in the return line.
Idle: 40PSI
WOT: 48PSI
Residual: 37PSI
MAX: >87PSI
The fuel pump exceeds specifications
Manufacturers specs for fuel flow after regulator: 1 - 1.5 litres per minute.
Our test resulted in 3 litres per minute. This is quite large as a more powerful fuel pump has been fitted to this engine.
We then checked injectors on the engine.
To do this, we simply unplug each connection off each injector one at a time. On each injector, as we unplugged each one, we found that the RPMs of the engine dropped by 50 each time. Doing this test we were able to see that each injector was working correctly.
Other engine problems that could give this result could be spark plugs fowling, piston rings worn or bent valves causing loss of compression in a cylinder.
We also checked the resistance of the windings in each injector and got 13.9 ohms for each. This is within the specs of 11 - 17 ohms.
The rubber fuel hose from the tank to the pump is in good condition, not perished or cracked. The rubber and copper pipes from the pump to the filter are all in good condition and fitted tightly. The rubber hose from the filter to the rail is in good condition. The fuel rail is also in good condition and fitted tightly. The vacuum hose for the regulator and the fuel return line are also in good condition and do not appear perished or cracked.
Fuel pump;
 |
| fuel pump |
To check fuel pressure at wide open throttle, we can simply remove the vacuum hose from the regulator and this will simulate atmospheric pressure.
Residual pressure can be checked after the engine has been turned off. Pressure at idle can be read when engine is idling, and clamping the fuel return hose we can see the max pressure of the system.
If you are to remove any fuel hoses, relieve pressure in the system by un-doing electrical connections at the fuel pump, so no power is there, and then crank engine over to relieve pressure.
The manufacturers specifications for the toyota engines were as follows;
Wide open throttle - 38-44 PSI
Idle - 31-37 PSI
Residual- 21 PSI
MAX (twice idle pressure) 61-74 PSI
Our test results were all above specified. This could be due to a faulty regulator or a blockage in the return line.
Idle: 40PSI
 |
| fuel pressure regulator |
Residual: 37PSI
MAX: >87PSI
The fuel pump exceeds specifications
Manufacturers specs for fuel flow after regulator: 1 - 1.5 litres per minute.
Our test resulted in 3 litres per minute. This is quite large as a more powerful fuel pump has been fitted to this engine.
We then checked injectors on the engine.
To do this, we simply unplug each connection off each injector one at a time. On each injector, as we unplugged each one, we found that the RPMs of the engine dropped by 50 each time. Doing this test we were able to see that each injector was working correctly.
Other engine problems that could give this result could be spark plugs fowling, piston rings worn or bent valves causing loss of compression in a cylinder.
We also checked the resistance of the windings in each injector and got 13.9 ohms for each. This is within the specs of 11 - 17 ohms.
Idle Speed Control Valve
The type of idle speed control device we used was a rotary type and base idle is adjusted using the ECU, and the cold/fast idle speed is activated by the engine temperature, which uses a bi-metallic strip wound up. When it is cold (by engine coolant), the strip opens the valve up. As the engine warms up, the two metals expand at different rates, causing the strip to wind up more and close off the valve. At this point, the ECU takes over to control the base idle.
To test the device, we use a multimeter, setting it to Duty cycle or frequency and test the RSO (open) and RSC (closed) with the negative probe on the earth point. We can also check the resistance between the RSO and RSC windings. The resistance between the RSO and RSC windings were 20.1 and 19.9 ohms. The duty cylce percentage is how often the valve is open or closed. Testing the RSO we got 63.3%, which means the valve is open 63.3% of the time when the engine is at idle. We then tested RSC, and by maths we should have got 36.7%, and we got 38.7% which means the IAC is closed 38.7% of the time.We also tested the frequency of the IAC. The frequency is how often the valve opens or shuts per second, and is measured in Hertz (hz). For the RSO, we got 244HZ which means the IAC opens 244 times per second. Also, for RSC, we got a reading of 244 HZ, which means the IAC closes 244 times per second. Because there is no variance in frequency between RSO and RSC, it means that the idle speed is being adjusted by the duty cycle percent.
Tuesday, July 12, 2011
Air and Water Temperature Sensors
After conducting the tests on both air and water temperature sensors, we found that both sensors are the negative temperature co-efficient type (NTC). This means that as temperature goes up, resistance goes down, which means more current can flow and a stronger signal generated. The battery was going flat in the infra-red thermometer and readings started to go all over the place, but we got enough accurate readings to get suitable results. As resistance in thermistors decreases, the signal going to the ECU gets stronger, so the ECU can tell when the engine warms up. If the sensor is faulty, it will not give the correct reading and will tend to make the engine run rich, which will make it run rough.
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