Engine sputtering, check engine light flashing, codes P1072, P0300, P0340, P0442, P0128

2003 GMC ENVOY
150,000 MILES • 4.2L • 6 CYL • 4WD • AUTOMATIC
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EGUNS80
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Yesterday my truck started running rough, the engine is sputtering, has lack of power, and my check engine started flashing. I hooked up the OBD2 we have at work and got these codes P1072, P0300, P0340, P0442, P0128. I was hoping it was only a coil pack, but the scanner didn't give me a specific cylinder.any chance you guys might know what the problem could be?
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Jul 30, 2019 at 11:05 PM
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ASEMASTER6371
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Good morning,

The 300 is multiple misfires on all cylinders. I would start by checking the fuel pressure. Low fuel pressure is the most common reason for this code.

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

128 is a thermostat. The engine is not running at the desired temperature from the thermostat staying open.

https://www.2carpros.com/articles/replace-thermostat

442 Is an evaporative code for the emission system. The purge valve is the most common failure for this.

1072. There is no code 1072. Can you verify?

340 is for cam sensor circuit.

P0340
Descriptor
Probable Causes
Cam Position Sensor (CMP)
Cam Position Sensor (CMP) Foreign Material
Cam Position Sensor (CMP) Improper Installation
Camshaft Reluctor Wheel
Powertrain Control Module (PCM)
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Jul 31, 2019 at 3:06 AM
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EGUNS80
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It is 0172. sorry my mistake.
Jul 31, 2019 at 6:57 AM
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EGUNS80
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I have no way of checking the fuel pressure. is there any chance the cam sensor would cause this problem?
Jul 31, 2019 at 7:34 AM
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EGUNS80
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What are the pictures you sent for?
Jul 31, 2019 at 10:42 AM
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ASEMASTER6371
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The pictures are for the thermostat for the 128 code.

You can rent a fuel pressure tester at a parts store.

Yes, it could be but it may not fix the issue.

Roy
Jul 31, 2019 at 1:00 PM
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EGUNS80
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The 1072 code was a typo its actually 0172.
Aug 1, 2019 at 12:21 AM
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ASEMASTER6371
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Okay, that is from the misfires. That is a rich running code. when the 300 is repaired, that code will go away.

Roy
Aug 1, 2019 at 1:40 AM
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EGUNS80
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I replaced the CMP and the spark plugs and it still ran rough. I was finally able to get a fuel pressure tester and my fuel pressure was almost 60psi. I reran the scanner and now its giving me a P0305 cylinder 5 misfire, would that mean the coil pack is bad?
Aug 11, 2019 at 4:41 PM
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ASEMASTER6371
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It could be a bad spark, coil, vacuum leak, injector or low compression. All these need to be tested for the misfire on the cylinder.

Roy
Aug 11, 2019 at 4:50 PM
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EGUNS80
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I replaced the spark plugs. how would i go about doing the other tests?
Aug 11, 2019 at 6:24 PM
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ASEMASTER6371
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You need to rent or purchase a compression tester to test the cylinder for compression.

https://www.2carpros.com/articles/how-to-test-engine-compression

the other tests require an advanced scan tool to monitor the coil operation and the long term trim readings for a vacuum leak.

Roy
Aug 12, 2019 at 2:18 AM
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EGUNS80
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Replaced cylinder 5 coil pack, with a used one, problem is fixed. Now to get some new ones and replace them all.
Aug 13, 2019 at 3:31 PM
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ASEMASTER6371
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Good job.

Roy
Aug 13, 2019 at 3:52 PM