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Motoring Q&A: Buick shows classic symptoms of vapor lock

March 10, 2014 


QUESTION: Here is a problem that I have fought for almost two years. My 2001 Buick Regal will not start after a shutdown and heat soak. The car has 128,000 miles, never shuts down while driving, and starts and runs perfectly in the morning. When it wonít restart, you can crank it until the battery runs down but the car wonít start. After shutting the engine off, it will start immediately ó if you donít wait too long!

Engine operating temperature is normal; it never overheats and has a new thermostat and ECT sensor. There are no intake manifold leaks, either vacuum or coolant. Fuel pressure is normal but a new regulator was installed along with a new MAF sensor. In a no-start condition the spark will jump a gap of at least one inch at the coil.

In the summer I carry a jug of water in the trunk (in winter I use snow) and in a no-start condition I pour about a quart of water on the intake plenum. The car will start right away and will run perfectly until the next no-start condition.

ANSWER: I canít recall a better description of vapor lock. The proper term is fuel percolation, which describes residual engine heat boiling the ready fuel supply in the fuel rails near the plenum/intake manifold. When this occurs, fuel pressure fades due to the aerated fuel disrupting fuel delivery from the injectors. Even though fuel pressure may be "normal" when tested with the engine running, I suspect fuel pressure drops quickly after shutdown due to percolation.

Using water to cool the intake stops the percolation. The first few injector pulses bleed air from the rail and, as fuel pressure returns, the engine starts.

But how to eliminate the problem? Start with three simple steps. Idle the engine for 30 seconds before shutdown to allow coolant to carry residual combustion heat from the cylinder heads into the radiator. Pop the hood open to the safety catch position to allow hot air to escape from under the hood. And try different brands of fuel, looking for a fuel with a vapor pressure less prone to this issue.

In addition, make sure airflow through the A/C condenser and radiator is clear and unobstructed. If the cooling system hasnít been serviced recently, a power flush might lower coolant and underhood temperatures measurably.

And to cover all the bases, turn the ignition to the "on" position and listen for the fuel pump to run for two seconds and then stop, confirming that the fuel pump relay and fuel pump are operating properly. Iíd also test for injector pulse widths from the PCM to confirm that the fuel injectors are being commanded to open/close on a hot restart.

Q: I have a well-maintained 2003 Acura 3.2L TL-S model with 114,000 miles. My Goodyear dealer has continued to propose replacement of the timing belt and water pump. He said the belt should have been replaced at the seven-year mark or 100,000 miles. I canít seem to find any definitive recommendations from Acura or on the Internet about this repair. I want to maintain the car and continue to drive it for a number of years and would value your opinion on this repair.

A: Acuraís service recommendation for this vehicle and engine, as outlined in my Alldata automotive database, calls for timing belt replacement at 105,000 miles/84 months under normal operating conditions. Under severe service conditions ó operation at ambient temperatures under minus-20 degrees or above 110 ó replacement is recommended every 60,000 miles.

With this engine, a timing belt failure could allow contact between pistons and valves, resulting in catastrophic engine failure, so a new timing belt makes perfect sense. Include pre-emptive replacement of the water pump.

 

 

   

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