SureTrack Community Fix: It’s All in the Fuel

When a customer brings you their car but leaves out a critical detail, either on purpose or not, it can wreak havoc on your diagnosis. SureTrack community member DYERDAD had a Pontiac Bonneville in their shop that was running poorly and they checked everything that could have been the obvious cause. What they didn’t know from the customer could have saved a lot of time and frustration. They posed the question to the community, and with the help of fellow community member DAG1365 and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

Vehicle
2005 Pontiac Bonneville GXP 4.6L

Title
Vehicle running rich, wrong fuel.

Complaint
Customer states that vehicle isn’t running right.

Diagnostic Steps Performed/Parts Replaced
Confirmed customer’s complaint. Runs super rich at start up. 5:1 on PCM. Fouls plugs in one start and can’t clear flood to start warm. Can get to run but says it’s adding 20 percent on trims. Still rich but startup won’t happen or is hard to start. Smokes horribly when it is running. Checked EVAP system, fuel pressure, MAF, PCM, grounds and engine coolant temperature. Fuel pressure is good. Unplug 02 to reset fuel trim and still does it on cold startup. What am I missing.

Cause
Decided to drain fuel tank and found last couple of gallons to be diesel. Not enough to make it smell like diesel in the gas when running. Customer didn’t mention accidently putting diesel in tank.

Correction
Drained bad fuel and replaced with fresh. After running vehicle for a while it is back to normal.