Customer Concern

On cold starts the engine runs rough for approximately 15-20 seconds.

Findings

Prior to starting the engine the cooling system reservoir was checked to see if exhaust gases were present in the cooling system. Two different tools were used to perform this test. One tool detects carbon dioxide and the other detects carbon monoxide. Both tools did detect traces of combustion gases before and after the engine was started. Combustion gases in the cooling system is indicative of an internal engine issue.

At start-up the engine had a rough idle for a little less than ten seconds. Once the rough idle went away the engine idled in a normal fashion for the rest of the inspection. When the engine was started (at the beginning of the inspection) it was the first start of the day.

Before the engine was started two different pressure transducers were placed at the left side exhaust outlet. In addition, a back probe was placed at one of the wires for the ignition coil for cylinder one so that a ” cylinder synch” (a reference) would be present. The two aforementioned transducers were then connected to an oscilloscope so that the exhaust pulses (positive and negative pulses) out of the exhaust) could be monitored when the engine was first started. If a reference cylinder is selected and the engine firing order is known the individual exhaust pulses can be identified and ultimately used to detect cylinder specific combustion anomalies.

When the engine was started the transducers detected misfires at cylinders three and five. The exhaust pulses for cylinder two had some irregularities as well. More specifically, the pulses for cylinder two (right after start-up) were lower and not as defined  as some of the others. Later in the waveform it was easy to see how the engine idle quality had improved.

Scan tool data (Mode Six) showed misfire activity at cylinders four and six before the engine was started and at cylinder six after the engine was near normal operating temperature. There were no stored, pending or active diagnostic trouble codes.

Addendum:

A second inspection was done on Tuesday, September 22nd at 3:15pm. At this time the cooling system was checked again for the presence of combustion gases. Three different tools were used to do the tests. Two of the tools are designed to detect carbon monoxide, while the other tool will alert to the presence of carbon dioxide. When placed over the coolant reservoir all three tools quickly detected the gases that they were designed to detect. The carbon monoxide levels were higher than the previous inspection.

The engine had a rough idle for less than 15 seconds. Afterwards the engine idle quality was normal as the engine transitioned from fast idle to natural idle.

Beginning Mileage: 34370

Ending Mileage: 34372

Inspection Time: June 24, 2020 10:15 am

Inspection Location: 2602 Tulip Poplar Circle Durham, NC 27704

Temperature at Time of Inspection: 79 degrees

Humidity at Time of Inspection: 61 %

Weather Conditions During Inspection: Mostly clear skies