[Clifford57]

Need advice.

• New coils and plugs, 3000 miles ago.
• New Water pump,
• New alternator,
• New power steering pump.
• New purge valve (3 weeks ago) - checked and no issues
• 130,000 miles

• Engine started running rich while driving ( local 30 MPH)
• Only code is P0300
• engine coolant temperature sensor - no issues
• MAF sensor - no issues
• MAP Sensor at idle is showing 2.5volts and should only show 1 volt. The sensor was swapped out and the new one had the same issue
• above 2000 rpm the problem of running rich goes away
• O2 sensors swapped out for check - no issues
• Mechanic has checked all sensors, checked all injectors, checked all plugs, looked at wires controlling individual injectors, can not determine what is causing the engine to run excessively rich

Update

Isolated injector on #4 cylinder as a potential problem and replaced the injector with a slight improvement at idle but still random misfire. Had a guy look at it who has sold used cadillacs for 30+ years and he kept saying 'electrical problem' but wouldn't provide any real ideas. Any ideas would be helpful.

Looking for advice on what else could be causing the problem.

 

[jimmcd1974]

With a tech 2 scan tool there are things that can be inspected. Gm misfire counters are pretty sensitive and should be counted in "misfire history". Another thing is long and short fuel trims. Looking at fuel trims can show how far the pcm is trying to correct the fuel zero % is perfect. Number below zero shows the pcm is taking fuel away and positive numbers shows its adding fuel. A +5% fuel trim shows the pcm is adding 5% more fuel than normal. It takes a fuel trim of -/+15% to set a code. O2 sensors can be tested with a lab scope to see if it can report properly and have the correct reaction time.

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