Buick Enclave Can Not Start by EVAP Trouble & Rich Mixture

One of my regular customers called me to tow his car away from petrol station,because his Buick Enclave can not start.Finally,I his Buick Enclave can not start was caused by rich mixture.And this article share the experience I solved this problem.


Vehicle info:

Buick Enclave LLT 3.6

Made 2010

With about 90,000 miles


Trouble symptom:

Can not start the car after refueling the car.


Trouble Diagnosis:

1. Try to start the car to verify the symptom the owner described:turn on the ignition,the starter was running powerfully,and the engine signs of starting occasionally.

2. Use GM Tech 2 to scan the trouble code,but there was not any DTCs.

3. Read the data stream,the engine starting speed was 400 r/min,it mean that the ECU can receive the engine speed signal.It suggested that ECU work correctly,control to ignition and inject.

4. Detect the relevant wire harness,all of them work correctly.

5. Connect the spark plug tester,then start the engine,the tester show the bright and intense spark.Remove the spark plug of Cylinder 1,observe the spark plug appearance:a lot of oil on the surface of spark plug electrode(show as below picture).It most likely that the engine flooding.Remove the spark plug of cylinder 2,the spark plug was same as cylinder 1.So I believed that the engine can not start was caused by the oil inject excessive of fuel oil system.

Buick Enclave Can Not Start by EVAP Trouble & Rich Mixture -1

Suspected high fuel pressure result in fuel-injection quantity excessive.Start the engine,read out the data stream of fuel oil pump control module:

The low-pressure fuel pressure is 380 kPa (normal value :300 kPa-400 kPa)


Read out the ECU data stream:

The high-pressure fuel pressure is 4M kPa(normal value:1.9 MPa-5.0 MPa)


Both of data suggest that the engine flooding was not caused by fuel oil system pressure trouble.Clean the cylinder inner fuel and make them dry,replace 6 new spark plug,then try to start the engine.The engine starting difficulty and vibrating with black smoke.


Read out the data stream of engine:

Air flow sensor:4.97 g/s (regular)

Cylinder 1 short-term fuel correction is -20%

Cylinder 2 short-term fuel correction is -21%

Both of them mean the rich mixture.


Consult the repair manual,the main reasons result in rich mixture show below:

1. High fuel oil pressure

2. High signal voltage of air flow sensor

3. Leaking of high pressure oil pump

4. Excessive fuel adsorpt by Evaporative carbon canister

5. Evaporative emission purge solenoid valve normally open

6. Poor fuel quality

Trouble Shooting:

Use external fuel cleaning equipment to test car,then read out the fuel correction value change by diagnostic tool.But the fuel correction value still unchanged,ruled out the possibility of poor fuel quality.


Then try to disconnect and block the evaporative emission purge the solenoid valve pipeline.read out the fuel correction value changing,found the fuel correction value changed,it indicated that evaporative emission system related to the car trouble.Turn the ignition off,then turn the ignition on again,perform action test on evaporative emission purge solenoid valve,found the solenoid valve work incorrectly.So focus on the solenoid valve relevant wire harness.

Remove the evaporative emission canister purge solenoid valve,compressed gas test on solenoid valve to test air impermeability.The results showed that evaporative emission purge solenoid stuck in the always on position.


Replace the evaporative emission canister purge solenoid valve,turn the ignition,the engine starting successfully and fuel correction value return to normal.

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