Stalling and Cold Start Diagnostics
What can be more frustrating than turning the key on a cold, winter morning and the car doesn’t start? Well, for your customers, probably nothing. When the car doesn’t start, you can’t go anywhere. And this type of problem tends to manifest itself much more as the temperature drops. So, this topic is timely for most parts of the country.
When a vehicle won’t start, you have to determine which system is causing the problem. This is pretty easy to do. If the engine does not crank, check the electric system (battery, starter, etc). If engine does crank, you can assume that the starter and battery are good, so you’ll have to check the fuel system. You might also want to verify that there is spark.
STARTING SYSTEM
Quite often, the starting system is the culprit during the winter when your customer’s car, minivan or truck will not start. And, within the starting system, usually something simple and basic is the problem (corroded battery terminal, cracked battery cable, undercharged battery). Before we start performing tests, let’s do a visual inspection. We don’t want to overlook the obvious.
Let’s begin our inspection with the most accessible component, the battery. Visually inspect the battery for physical damage (cracks in the case, electrolyte leaks). Also, check the cable connections. Are the connections loose and/or corroded?
The next component to check is the ignition switch. Look for any signs of physical damage. Check the wire harness connections for loose or corroded terminals. Corrosion is a major cause of poor terminal connections that can lead to starting problems. The condition of the connections should also be checked on the starter relay, starter solenoid and starter. Be sure that all connections are tight on these components and that none of the connections are damaged.
While we’re discussing electrical connections, the wiring harnesses and cables in the starting system should also be inspected. Look for physical damage in the form of cracked or split insulation. Pay close attention to the areas in which the wiring can rub against another component or the structure of the vehicle. Check for loose and/or corroded connections at the main engine ground and the remote jump post.
Finally, check the transmission range sensor or, park/neutral switch. Inspect the sensor, looking for any signs of physical damage. Be sure all the wiring harness connections are clean and tight.
If everything checks out okay with the visual inspection, test the battery. The battery test is performed using the Micro 420 Battery Tester (Figure 1). When the battery test is being performed with the battery in the vehicle, be sure that all vehicle accessory loads are off, including the ignition. Connect the tester to the battery, with the red clamp to the positive (+) terminal and the black clamp on the negative (-) terminal.
Using the ARROW key, select in or out of vehicle testing, then press ENTER to make a selection. If it is not selected, choose the Cold Cranking Amp (CCA) battery rating. You can also select the appropriate battery rating for your area as shown on the menu. The tester will run its self-programmed test and display the results. Refer to the Battery Test Results Table shown in Figure 2.
Note: If Replace Battery is the result of the test, this might mean that a poor connection between the battery and battery cables exist. After disconnecting the battery cables from the battery, retest the battery using the out-of-vehicle test to verify that the battery requires replacement.
If the battery is good, perform a voltage drop test to determine if the battery cables and terminal clamps are good. There are four versions of this test that are performed using a voltmeter that is accurate to 0.1 volt. These tests involve connecting the positive (+) and negative (-) leads of the voltmeter in the following manner:
1. + lead to - battery post / - lead to - terminal clamp (Figure 3)
2. + lead to + battery post / - lead to + terminal clamp
3. + lead to + battery post / - lead to starter solenoid B(+) terminal stud
4. + lead to - battery post / - lead to ground on engine block
For each of these tests, rotate and hold the ignition switch to the Start position and observe the voltmeter (the battery must be fully charged and the Auto Shutdown Relay (ASD) must be removed to prevent the engine from starting).
For tests 1 and 2, if voltage is detected, that indicates a poor connection between the terminal clamp and battery post. Clean the connection.
If the voltage reading for tests 3 and 4 is greater than 0.2 volt, clean the connection on the starter solenoid B(+) terminal stud or ground terminal on the engine block (whichever is applicable). If the voltage reading is still greater than 0.2 volt, the battery cable is bad. Replace it.
FUEL SYSTEM
We’ve determined that the basics of the starting system are working properly. Now, let’s turn our attention to the fuel system to see if we can find out why the vehicle won’t start. The fuel system consists of the fuel pump module, fuel filter, tubes/hoses/lines and the fuel injectors. If the engine cranks, let’s make sure that fuel is being delivered.
Let’s start with the fuel pump. Turn the ignition on. Using a scan tool, actuate the fuel pump control to On (100%). Listen for fuel pump operation at the fuel tank. It should operate smoothly without excessive noise. If necessary, compare the sound to that of a known good vehicle of similar year, make, model. If the fuel pump is not operating, check for a ground circuit open or high resistance.
If the pump is good, check the fuel pressure. In order to perform this test, the fuel system pressure must be released. Install a fuel pressure gauge on the fuel rail. A typical fuel rail test port (for the 3.3L/3.8L V-6) is shown in Figure 4. Using a scan tool, actuate the fuel pump relay control. Observe the fuel pressure.
If the fuel pressure is within specs, the basic fuel system is good. The starting problem is being caused by another condition. If the fuel pressure is above specs, replace the fuel filter/pressure regulator. If the fuel pressure is below specs, there is a restriction in the fuel supply line.
In order to find this restriction, turn the ignition off, release the fuel system pressure, raise the vehicle on a hoist and disconnect the fuel pressure line at the fuel pump module. Install the special 5/16 fuel line adapter tool #6539 between the disconnected fuel line and the fuel pump module. Attach a fuel pressure gauge to the T fitting on the tool. Turn the ignition on. Using a scan tool, actuate the fuel pump relay control. Observe the fuel pressure.
If the fuel pressure is within specs, repair or replace the fuel supply line. If the fuel pressure is out-of-spec, there might be a problem with fuel tank siphon hose, the fuel line or the inlet strainer. First, determine the style of the fuel tank. If it is a saddle type, check the siphon hose. If not, check the inlet strainer. Now let’s check the siphon hose and fuel line.
Gain access to the fuel pump module and fuel tank module. Inspect the fuel line and siphon hose between pump module and tank module, looking for disconnected or damaged hoses and lines. Inspect the fuel pressure regulator or a condition that might cause a fuel flow problem. Correct any problems found. If none are found, check the fuel pump inlet strainer.
Remove the fuel pump module and inspect the inlet strainer for damage or a condition that might cause a fuel flow problem. If a problem is found, replace the fuel pump inlet strainer. If no problems are found, replace the fuel pump module.
