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Try unplugging the front O2 sensor and then see if it starts with the sensor disconnected. Check the wiring for the O2 sensor circuit at the computer. Look for a possible short to power. Signal wire voltage from sensor to computer should be less than one volt.
It’s normal for the AC to cycle on off when the defroster is on. You can confirm this by setting the heater air control to floor only. Anytime the air control is set to defrost or defrost blend (and heater fan on) the AC will cycle weather or not the AC is “on”.
Sorry, that link didn’t work right, but follow that link and scroll down to number 25, No Start Diagnosis- FASTTEC method part 1
Hi, Instead of focusing on the computer to solve your problem, try Matt’s no start diagnostics here:
FASTTEC method link –
I wouldn’t expect a compression test to show anything because it’s a very small type of leak. If it was a large leak it would blow the hoses off. What you could do to confirm a head gasket leak is apply compressed air to each cylinder individually using a compression tester fitting and then watch for bubbles in the radiator. It might take a few minutes for bubbles to appear. Test with engine off, of course, and test cold engine vs warm engine. Make sure that the transmission is in neutral (if it’s a standard transmission) before you put the air pressure to it because the engine will turn over suddenly as the pressurized cylinder moves to the bottom of it’s travel.
Never ending air bubbles in the cooling system is likely from a bad head gasket. Compression gasses are pushing past the head gasket into the water jacket. I’m guessing that when they replaced the head gaskets a year ago they just replaced the gaskets and didn’t have the heads resurfaced at a machine shop.
When the fuel trims are at -10%-20% it means that the ECU is having to lean out the fuel mixture to compensate for a rich condition. The ECU uses the exhaust sensor to verify the correction.
Hi, The post cat sensors are typically used by the ECM to monitor catalyst efficiency. The front sensors, judging by the voltage reading, are wide band sensors. Sometimes referred to as air/fuel sensors. The voltage reading is a little different than from o2 sensors. O2 sensors will often oscillate between 200 millivolts and 800 millivolts. Hi voltage is richer, low is leaner. Wide band sensors will tend to be somewhat steady at say 3.3 volts, 3.2 volts if rich, 3.4 volts if lean. The actual voltage reading varies by car manufacturers, but you get the idea. If you monitor the voltage as the engine warms up from cold start you’ll see how they respond.
It could have been caused by debris in an oil passage that went unnoticed during the repair, or cam bearings that weren’t lubricated during assembly and ran dry for a minute on initial startup, or the cam bearings were questionable to begin with. I’ve personally seen the latter on cheap rebuilt heads. Improper cam bearing bolt torque can also cause problems.
