Very hard to start when car is warmed up

SANWLEE

MEMBER
2010 SCION XB
2.4L
4 CYL
2WD
AUTOMATIC
161,000 MILES

The starts fine in the morning and after the car cools down after driving. When I drive the car a few miles and turn it off for 15 to 30 minutes it is extremely hard to start. Sometimes it can take 10 to 15 minutes of on and off trying. The car will crank but not start. I have replaced engine coolant sensor, Oil valve control, 4 new coil packs, new plugs, new O2 sensor upstream, new mass air sensor and have thoroughly clean out the throttle body. It seems to be either a leaking injector or failing fuel pump. When the car starts it drives perfectly fine. I have test the throttle response and there is no lag even at higher speeds. Please help. Thank you for your time.

2 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Often times, a bad crankshaft position sensor will fail when it gets warm. Take a look through these links. The second one describes symptoms. See if they seem to mirror what you experience. What you described it typical when these sensors begin to fail.

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

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Since this happens when it's hot, here is what I suggest. When it doesn't start, check to see if there is spark to the plugs or if you have a live data scanner, see if you have an RPM signal. If there is no signal or you find no spark, replace the sensor. Let me know if that is the case and I can give you specific directions for your vehicle.

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If spark is good, then you need to check fuel pressure. Here are a couple links that explain how to check both spark and fuel pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Let me know what you find.

Take care,

Joe