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Q: Car will not start every time

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It will crank each time I turn the key, but it will often take several times (2-15) to get the car running. It happens from a cold start. I usually have to pump the gas a few times to get it to run. If the cat is warm, it will start with no problems at all. I have replaced the fuel filter and fuel pump. It was throwing a code several months ago for a faulty coolant temp sensor, but the code went away and I didn't replace it. There are no codes now. I have not experienced any overheating, but I was told that it could possibly be that sensor since the issue comes with a cold start. But the arm moves up correctly when driving. The car will drive just fine after it is started. Just a very mild rough idle. No issues with acceleration. I bought a new battery and that did not help either. It has clean oil, always has enough gas. I tried starting it in neutral and that didn't help.

My car has 135000 miles.
My car has an automatic transmission.

A: I think you're on the right track with ...

I think you're on the right track with the fuel pump and the coolant temperature sensor (CTS), but there are a few things about them that haven't been addressed yet.

First, pumping the pedal on a fuel injected car when it isn't running doesn't do anything. The Powertrain Control Module (PCM) is preset to add the amount of fuel necessary on a cold start up. The primary sensor the PCM uses for this is the coolant temp sensor. The thing with sensors like this is they can go bad in certain resistance ranges, which could be the case here. Once the car is running, and beginning to warm up, the resistance of the sensor will change, possibly putting it into a resistance range the PCM expects to see.

The best way to check a coolant temperature sensor is with a scan tool. Connect the scan tool when the car is cold and hasn't been driven yet for the day. Look at the CTS information and see what it says. If it says something like -40 degrees Fahrenheit when it is 70 degrees out, there's a problem with the sensor. This is how I would check it. Some will just replace the sensor.

When it comes to sensor such as this, remember that they give the PCM a resistance value which the PCM then converts to a temperature reading we humans can understand. If a wire connected to the CTS has a higher resistance, it will affect what the PCM sees for resistance. Keep in mind the sensor may be good, but a wire may have a bad connection in the CTS circuit. If you suspect such a problem, the best way to check it is with a multimeter. You will need to find the resistance specifications for the CTS and a wiring diagram, but this is how we pinpoint where exactly the resistance failure is in a CTS circuit.

The next possible problem is with fuel pressure. You will need a fuel pressure test kit. Most auto parts stores will rent them. Once you have a fuel pressure gauge connected to the fuel rail, turn the key on and see how much pressure builds up. Cycle the key a few times to build pressure. What I am looking for here is NOT maximum pressure. I suspect it will be fine since you replaced the pump. What could be happening is the fuel pressure could be bleeding off overnight. With the key off, watch the pressure gauge and see if the pressure drops quickly. The typical spec is five pounds in about five minutes. If it bleeds off quickly, then you have an internal leak somewhere in the fuel system.

If this is the case, cycle the key again to build up the pressure. You may have to do this several times depending on how quickly the pressure bleeds off. You need to locate fuel lines that are soft rubber than you can pinch without damaging them. Grab some long needle nose pliers, or an appropriate hose crimp tool, and pinch off the rubber fuel lines that run from the fuel tank to the motor. What you are doing here is isolating what end of the car is bleeding off fuel pressure. This will help determine if the leak in the tank or at the fuel rail. If it's in the tank, then you will need to remove it and inspect the fuel pump system inside. Sometimes you will find a hose with a hole in it, if not, the fuel pump maybe allowing fuel to go backwards through it.

If the pressure loss is in the fuel rail, it will likely be a fuel injector leaking into the cylinders. To determine which injector is faulty, you will need to remove the fuel rail, keep it connected to the rest of the fuel system, and cycle the key on and off. The leaky injector should show itself fairly quickly. You're looking for fuel coming out of one of the injector nozzles. This should only happen when the PCM, while cranking or running, sends an injector pulse to the injector and opening it electrically.

Personally, I would look at the CTS first. Good Luck. I hope this will help you find the problem. If you try these steps and still need help, a certified mobile mechanic from YourMechanic can visit your home or office to inspect your vehicle's starting issues.

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