Truck Trend Garage: 2002 Dodge Dakota Sport Running Rough
Question: I have a 2002 Dodge Dakota Sport with the 3.9-liter V-6. It runs fine at first start of the day, and after shutting it off and sitting for 30 to 60 minutes, it will start normally. But when I first start to accelerate slightly it will choke down and run very rough. When I gun it, it will backfire several times and smooth out. I've had it diagnosed at two Dodge dealers and three independent shops. They haven't been able to find or fix the problem. The attempted fixes: fuel system flush; new fuel pump/filter; spark plugs, wires, distributor cap and rotor; fuel-pressure check; intake manifold gasket; injectors and fuel rail checked and cleaned; throttle body removed and cleaned.
Answer: Your situation is similar to another reader's recent question, but it's definitely worth another look. The problem occurring 30 to 60 minutes after shutdown is a little off (15 to 20 minutes is more typical), but otherwise the symptoms do match that of a hot soak condition. This happens when you turn off a hot engine and let it sit. The heat saturates the fuel in the fuel rail and causes it to boil. Then, at startup, you'll experience multiple misfires. The engine is burning fuel with boiling bubbles, instead of the straight liquid version, which causes an extremely lean condition. Nowadays, this problem is becoming more common due to the increasingly higher alcohol (ethanol) content being added to the gasoline mixture. There are kits (your local dealership might have one) that can test the alcohol content of the gas in your tank. Alcohol has a lower boiling point than gasoline. So the more alcohol, the more apt an engine is to suffer from a hot soak condition. A quick check is to run your tank down close to "E" and refill with super unleaded. Typically, the alcohol content in premium blends is significantly lower than in regular gas. If this solves it and fuel pressure is truly correct, you've diagnosed the problem. There's currently no Dodge service bulletin providing a hot soak fix. But you can either stick with the premium fuel, or try lower-octane samples from different filling stations. These types of problems are more pronounced in the winter months (especially in hot-climate winters) because the ethanol level in fuel production increases. This is just a simple check. If it does not cure the condition, it will at least eliminate another possible cause. No luck? I'd suggest giving a Dodge service department another shot at the repair after giving them the full list of the work and testing previously performed.
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