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V6 VT won't start

Dr Info Red

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I just bought this cheap VT commodore that won't start. Security light stops flashing when the key unlock is pressed or is inserted in barrel and turned to start (normal). When key turned to start, engine will crank for about 1.5 secs and stop or engine will sometimes fire up to 1000 RPM before stopping again all within this same time frame. All that is happening now is an oil and battery warning light and high speed fan still running. Any attempt to restart and nothing happens, except the fan stops. Securtiy light is still off. Only way to get it to crank again is to lock and unlock with key and turn key to start. I also got codes 35 IAC valve, 48 Cam angle sensor, 92 low speed fan fault. Not sure if I trust this diagnois as far as I could kick that ECU. Checked all fuses relays and wiring for continuity earths etc found no faults. Fuel pump can be heard working for that brief time and battery is okay. I am thinking of replacing just the ECU module. If I do that would the car need to be taken to a dealer with specialised gear to program it? Thanks any help would be muchly appreciated.
Doc
 

fitz_vt

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sounds like replacing the ECU might be the go but i would do theses steps first, most of them have the replace ECU step in them. but you never know you might just have a base idle that isnt right.

Code 35 IAC Valve
Code 35 will set if the curb idle speed is more then 250 RPM above the specified range and a cannot be controlled by the ECU apart from the IAC Valve Circuit this code can be set by the following possible causes.
Incorrectly Adjusted Throttle Cable
Sticking Throttle Cable
Vacuum Leaks
Faulty PCV Valve
Incorrect Air - Fuel Ratio

1. Disconnect the wiring from the IAC Valve and Measure the Resistance between terminals A and B and C and D respectively. Renew the IAV Valve if the resistance is not 40-80 OHMS.
2. Check there is no continuity between terminals A and D and also B and C
3. Check the wiring between the IAC Valve and the ECU for Continuity and Shorts.
4.Remove IAC Valve and check that the pintle shaft is not seized
5. Remove throttle body and Thoroughly Clean the throttle valve and bore and the IAC Passages. Check and adjust base idle.
6. run engine to normal operating temperature (maybe not lol)
7. Ensure all Accessories are off and Disconnect wiring from IAC valve while engine is idling .
8. Connect a test lamp between the IAC Valve Harness and terminals A and b, and c and D respectively with the engine idleing the test lamp should flicker
9. if test lamp flickers check for ditry terminals at the IAC Valve if no fault is found renew the IAC Valve.

48 Cam angle sensor (most probably the problem)
1. Disconnect the Cam Angle Sensor Wiring.
2. measure the voltage between the sensor harness terminals a and Band B and C with the ignition on the voltage between a and be should be 5-7 volts and between B and C should be 8-11 volts
3. if either the voltages are incorrect, check the wiring between the sensor and the DFI module for continuity and shorts to earth.
Check continuity to earth at the sensor harness terminal B if no fault can be found renew the DFI Module.
4.If both voltages are correct connect the wiring to the Cam Angle sensor and measure the voltage at ECU pin D3 with the ignition on.
5. If Voltage is not approximately 4.8 volts, momentarily crank the engine and check the voltage again with the ignition on.
6.if 4.8 volts is not present at terminal D3 run the engine at idle speed for one minute then check the voltage at d3 and the DFI module fr continuity and short to earth. If wiring is not faulty, renew the cam angle sensor.(if you can get your engine running)
7. If 4.8 volts is present at D3, run the engine at idle speed for one minute and then check the voltage while engine is idling
8. if voltage is fluctuating above and below approximately 4.1 volts check for loose or dirty connection at D3 if no fault can be found and the Fault code remains renew the ECU.
9.if the voltage is not fluctuating as described stop the engine and disconnect the injector wiring connectors
10 switch the ignition to ON and back probe terminal A of the Crank Angle Sensor with a voltmeter.
11. rotate the crankshaft pulley manually two revolutions the voltimeter reading should drop to 0 as the magnet in the crankshaft passes the sensor.
12. if the voltage does not drop to 0 within two crankshaft revolutions check for a faulty connection at the sensor, a faulty sensor or a missing pickup magnet.


92 low speed fan fault
1.if the engine starts and the fault is intermittent. check the wiring between ECU terminal A3 and the BCM terminal 2 (black/red) for continuity and intermittent shorts to earth ensure that the terminals are clean and secure.

2. confirm the low speed cooling fan in cycling off and on with the engine at operating temperatures.

3. clear the fault codes and road test the vehicle if the code resets then take the vehicle to a automotive specialist with ECU and BCM Diagnostics tools to isolate the fault to the BCM or ECU.
 

fitz_vt

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could be a blown engine too if you bought it so cheap
wouldnt be a blown engine otherwise it wouldnt crank at all
 

Dr Info Red

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I have known the guy I brought if off for years and a bit about it's history. He has just brought a new car and was only offered $750 for a trade. I gave him a bit more and he was delighted. He did mention that at times he had to remove the key and lock / unlock before it would start. It is still does this but now it conks out as soon as it starts. I have tried all the tests by fitz_vt thankyou, and now I will look at fuel and spark. I still think the ECU is sus. Does anyone know if these units can be swapped from one VT to another for testing without causing any problems.
Doc
 

jazza15

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I only had a quick glance over this, but as you said it works for about 1.5 seconds. It may be your key reader or something to do with your BCM.
Basically, the vr - vs had a delay where you would turn the key and nothing would happen for a short delay before the engine would crank then start. this was the BCM communicating with the key. the BCM gets the code off the key before the engine is allowed to start (12 volts is allowed to be sent back).
Now how this affects the VT/VX is that in the VT they got the BCM to just start cranking the engine so as not to waste time, thus eliminating the delay, however if the incorrect code is sent back to the BCM, there lies your problem.
I am not an expert on the issue, i found it somewhere in this forum. search vt key reader for more info on the issue, there is a few threads on it.
 

Dr Info Red

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I will check those threads out but the starter relay requires the key to be in the start position to provide 12v+ to it's coil and feed this to BCM and ECU. An earth is required on the other side of the coil to complete circiut and is provided by the ECU when all conditions are met. For some reason this earth only lasts for about a 1.5 sec then starter relay drops out and cranking stops.
Doc
 

fitz_vt

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it sounds like coil packs and/or a faulty earth wire i would either rewire or have an auto elec rewire it for you. also check that the battery terminals have a firm connection and that the battery has at least 12.2 volts for cranking.
 
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