G'day All,
I don't frequent this forum but thought you guys might appreciate the info.
I've had a VZJ95R in my workshop which has been causing me absolute frustration.
Aside from actual testing, etc, I've done internet searches to see if the problems common and if there have been solutions. There are posts from the past from around the world where the fault has been identical though no body has posted a certain solution. In many cases the vehicles have been taken to workshops/dealerships and the faults have not been fixed.
I'm not saying this is the fix to all 5VZ-FE's that experience this symptom, but in this case it was, its pretty strange and could likely be the cause for the cases that I read about on the net.
This EFI system is simple and does not incorporate oxygen sensors.
FAULT:
The vehicle came in with what felt like a misfire developing at 3,000 rpm and a dead set rev limit at 3,200 rpm while the engine was warm regardless of free revving while stationary or while driving. There was no engine light on.
While the engine was cold, the engine would rev limit at 4,200 RPM
In the early stages of testing, using an oscilloscope, I found that the computer was intentionally cutting the fuel injectors to cause the symptom.
ACTION:
I started with an ECU scan to confirm there were no fault codes and that the sensor reading that the ECU was getting were all within specification.
I replaced plugs, leads and coils and then went on to check all the sensor voltages, resistances, waveforms, ECU inputs and outputs. All tested within specification and all waveforms were as specified. All tested at the sensors and at the ECU plug.
I swapped the AFM, TPS, igniter, CTS with known good units and the fault remained.
I sent the ECU, immobiliser control unit, key reader, etc away for testing to 2 different companies and no fault was found.
I swapped the ECU with a known good unit and the fault remained.
I removed and refit the timing belt to confirm valve timing and also made sure that the keyways were not flogged out.
I removed the exhaust to confirm there were no blockages suffocating the engines air flow and causing an in accuracy in AFM reading.
SOLUTION:
Out of pure frustration the last sensor I swapped with a known good unit was the crank angle sensor and the problem was solved.
MYSTERY:
WE had never suspected that the crank angle sensor was the fault for a few reasons:
The engine was running and perfectly smoothly with no power loss up until 3,200 RPM! When crank angle sensors play up, normally, 99.9999999999999% (it was 100% until this experience) of the time the engine will either not start or it will run and stall when it gets hot.
We had a good wave form coming from it through the oscilloscope showing 34 oscillations followed by a long reference oscillation.
The ECU was always displaying the correct engine speed through the scan tool and tacho.
The ignition timing was always correct which is a setting that the ECU bases off a correlation between the cam angle sensor and crank angle sensor.
The resistance of the crank angle sensor was to specification.
THE CONCLUSION:
Having oscilloscoped the replacement crank angle sensor we were able to see that it had a slightly higher amplitude in the waveform. The EFI system on the 5VZ-FE obviously needs to see an increase in amplitude of the signal along with the crank reference position when accelerating the motor to operate correctly. The lack of signal amplitude is not a fault that is registered by the ECU hence no check engine light.
ADVICE:
Although air flow meters are common faults on them and cleaning them often rectifies faults, if any body experiences a rev limit type scenario where the engine otherwise feels great, consider the crank angle sensor. Its not a normal culprit in this situation but obviously is in the 5VZ-FE EFI system due to the reliance of the amplitude side of the signal and not just the reference side of the signal.
I hope this helps people.
Cheers,
Denis.
I don't frequent this forum but thought you guys might appreciate the info.
I've had a VZJ95R in my workshop which has been causing me absolute frustration.
Aside from actual testing, etc, I've done internet searches to see if the problems common and if there have been solutions. There are posts from the past from around the world where the fault has been identical though no body has posted a certain solution. In many cases the vehicles have been taken to workshops/dealerships and the faults have not been fixed.
I'm not saying this is the fix to all 5VZ-FE's that experience this symptom, but in this case it was, its pretty strange and could likely be the cause for the cases that I read about on the net.
This EFI system is simple and does not incorporate oxygen sensors.
FAULT:
The vehicle came in with what felt like a misfire developing at 3,000 rpm and a dead set rev limit at 3,200 rpm while the engine was warm regardless of free revving while stationary or while driving. There was no engine light on.
While the engine was cold, the engine would rev limit at 4,200 RPM
In the early stages of testing, using an oscilloscope, I found that the computer was intentionally cutting the fuel injectors to cause the symptom.
ACTION:
I started with an ECU scan to confirm there were no fault codes and that the sensor reading that the ECU was getting were all within specification.
I replaced plugs, leads and coils and then went on to check all the sensor voltages, resistances, waveforms, ECU inputs and outputs. All tested within specification and all waveforms were as specified. All tested at the sensors and at the ECU plug.
I swapped the AFM, TPS, igniter, CTS with known good units and the fault remained.
I sent the ECU, immobiliser control unit, key reader, etc away for testing to 2 different companies and no fault was found.
I swapped the ECU with a known good unit and the fault remained.
I removed and refit the timing belt to confirm valve timing and also made sure that the keyways were not flogged out.
I removed the exhaust to confirm there were no blockages suffocating the engines air flow and causing an in accuracy in AFM reading.
SOLUTION:
Out of pure frustration the last sensor I swapped with a known good unit was the crank angle sensor and the problem was solved.
MYSTERY:
WE had never suspected that the crank angle sensor was the fault for a few reasons:
The engine was running and perfectly smoothly with no power loss up until 3,200 RPM! When crank angle sensors play up, normally, 99.9999999999999% (it was 100% until this experience) of the time the engine will either not start or it will run and stall when it gets hot.
We had a good wave form coming from it through the oscilloscope showing 34 oscillations followed by a long reference oscillation.
The ECU was always displaying the correct engine speed through the scan tool and tacho.
The ignition timing was always correct which is a setting that the ECU bases off a correlation between the cam angle sensor and crank angle sensor.
The resistance of the crank angle sensor was to specification.
THE CONCLUSION:
Having oscilloscoped the replacement crank angle sensor we were able to see that it had a slightly higher amplitude in the waveform. The EFI system on the 5VZ-FE obviously needs to see an increase in amplitude of the signal along with the crank reference position when accelerating the motor to operate correctly. The lack of signal amplitude is not a fault that is registered by the ECU hence no check engine light.
ADVICE:
Although air flow meters are common faults on them and cleaning them often rectifies faults, if any body experiences a rev limit type scenario where the engine otherwise feels great, consider the crank angle sensor. Its not a normal culprit in this situation but obviously is in the 5VZ-FE EFI system due to the reliance of the amplitude side of the signal and not just the reference side of the signal.
I hope this helps people.
Cheers,
Denis.
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