|01-06-2013, 12:52 AM||#1 (permalink)|
Why won’t my car start? - Comprehensive No-Start Troubleshooting Guide
No-Start Troubleshooting Guide
Please note this is currently a work in progress. Please PM me if you have any corrections or suggestions for improvement.
Dealing with a no-start can be very frustrating especially if you are stranded without any tools or test equipment. There are a multitude of reasons why an engine won’t start, but this guide will cover general troubleshooting steps for most types of no-start situations. Members are advised to read the entire guide and perform any necessary basic tests before posting a new question. If you need more information about something mentioned here, please use the forum search function or a search engine first. If you have any suggestions for improving this guide, please contact us via PM (private message).
Here’s a basic primer: An engine needs three things to run—fuel, compression (which also encompasses air), and spark. If it does not have ALL of those (at the right time), the engine will not start. The boy scouts among you will recognize this as being very similar to the proverbial “fire triangle” used to teach fire safety. An engine is basically designed around creating a fire triangle in each cylinder, so the lesson applies here as well. The fuel in our case is gasoline, and the correct amount needs to be injected into each cylinder before each combustion cycle. Compression is created when the engine sucks in fresh air (containing oxygen) and the piston compresses it inside the cylinder. Finally, at the correct moment we have the spark (which must be of sufficient energy or heat) which ignites the mixture and starts combustion. Bam, the engine starts. If you have the wrong amount of any of these things (fuel, air, spark) or they occur at the wrong time, you don’t get combustion and you have to read the rest of this guide!
The first step in the troubleshooting process is to determine if you have a no-crank no-start or just a no-start. The difference is whether the engine is turning or not (“turning over”) when you attempt to start the car. Note that many people incorrectly associate “turn over” with “start”—they are not synonymous so please use these terms correctly. If the car is cranking (you hear the normal starting noise) but the engine will not fire then you have a no-start. If you turn the key and hear nothing or just a click then you have a no-crank no-start. Please read the appropriate section for your situation. If you post a question, please be sure you make it clear which situation you are experiencing.
No-start (engine does crank/turns-over)
This is the most common type of starting problem people experience. If this happens, you need to check two things first:
If the theft light isn’t blinking and the fuel pump is running, the next most common problem is a weak battery. This can be confusing to some because the engine is still cranking. So remember this: Just because the engine cranks doesn’t mean the battery is good! Before you dismiss this as completely wrong, let me explain. Modern fuel-injected engines are highly reliant on electronics. These electronics need a certain threshold voltage to even have a chance at functioning (usually 8-9 volts). Cranking an engine puts a large load on the battery, which causes the voltage to drop across the entire electrical system. Automotive relays (which control the starter) also need about 8 volts to close, but they will stay closed until the voltage drops to as little as 1 volt. Let’s put it all together: So you can have enough initial voltage to power up the computer and start cranking, but with a weak battery the voltage can quickly drop below the minimum required for the computer to function but the starter will keep cranking away. When the computer isn’t being fed enough voltage you will lose spark and fuel injection pulses so the engine won’t start. If you test for these make sure they are regular & consistent since voltage can fluctuate during cranking (ex. look for ten evenly spaced sparks in a row without a dropout). If you get a couple sparks here and there, you’re not getting proper ignition.
One way to see if the battery is weak is to watch lights as you crank (headlights, interior lights, dash indicator lights). If they dim significantly or go out you probably have a weak battery. Another real simple test for a bad battery is to jump-start it (from another running vehicle, not from a standalone battery or battery booster). If the car starts with a jump, then it almost has to be the battery.
If you suspect a bad battery, you should have it load tested. This can be done at most auto parts stores for free, but be careful since not all techs have been properly trained. A proper load test will involve the use of a carbon pile, resistive load tester, or an automated tester on a cart (these all have big cables and alligator clips in common). If the tester looks wimpy or has small cables, then it’s probably not a load tester. A simple voltage check is NOT sufficient! Electronic battery analyzers (shows available CCA) are acceptable, but a full load test is better. If you get a print out or a reading from the tester, please keep it so you can post the results with your question.
Well, obviously you need to have fuel. In the tank that is. Make (quite) sure you have enough in there to save yourself the embarrassment of finding the simple truth not too far into the future. Yes, it HAS happened before. Gauges can break or lie. Moving on…
Fuel pump failure is a very common problem on the Taurus. Often it will manifest itself as an intermittent no-start that may be sensitive to changes in temperature or certain patterns of use (ex. car won’t start after being parked for xx minutes). If the fuel pump will not run, first make sure the inertia fuel shutoff ( ) switch is not tripped and the fuel pump fuse is not blown (see your owner’s manual). Also try swapping or replacing the fuel pump relay if you have one. If those are good, you may try whacking the bottom of the fuel tank with your hand or some other blunt object to try unsticking the pump. Don’t get carried away. Remember the fuel pump should run every time you do the (Key ON Engine OFF) self-test. If it does not run every time, you do have a problem. You may try several key cycles to “build up” pressure before a starting attempt if the fuel pump is not cooperating.
If the pump is working intermittently, you most likely need to replace the fuel pump (dropping the tank is required). In rare cases you may have a bad fuel pump driver module ( ) if you are equipped with a returnless fuel system (some 2000 and later vehicles). If the is bad, you will usually have a such as P1233.
If the fuel pump runs during several subsequent key cycles, you can generally be assured that you have some kind of fuel pressure during a starting attempt. However, it is a good idea to check the fuel pressure with a gauge if you suspect a fuel delivery problem such as a clogged fuel filter, bad fuel pressure regulator, or a stuck open injector. There is a Schrader valve on the fuel rail for this purpose on 2003 and older vehicles (newer vehicles require a scan tool to read the fuel pressure ). Fuel pressures vary by year and engine, but in all cases you should have ≥30 before and during cranking. If you do not have the required pressure, start by changing the fuel filter (it was time to change it anyway, right?). If the fuel pressure is still too low, you might still have to replace the pump (internal leak back into the tank) among other causes.
If you feel the engine is flooded, you can try pressing the gas pedal while cranking. Pressing the pedal all the way to the floor will disable fuel injection on some designs (clear-flood mode), so the engine won’t start unless it was already flooded. Be sure you also try starting with the pedal partway (so you still get injection). If the engine fires, immediately take your foot off the gas (high RPMs with a cold engine is not advisable).
Caution: Use of starting fluid (ether) on fuel-injected engines is generally not recommended. If the engine backfires, you can easily cause a fire or explosion. There have been several cases where the plastic composite intake manifolds exploded into shrapnel from people using starting fluid. If you feel you must use starting fluid (at your own risk), use only a tiny amount and stand well clear while cranking. Remember with fuel injection starting fluid will not make your engine start if it won’t on its own.
Ignition problems are generally not the cause of a no-start on the more modern (1996 and later) distributorless ignition systems ( ). If you have a bad coil or spark plug the car will almost always start on the remaining cylinders (see the misfire guide). If it doesn't, you might have the spark plug wires from the coil routed incorrectly, which may be relevant after a plug or coil replacement. If the car is backfiring while cranking check the wires first. To completely rule out the ignition coil, you should test for power going to the ignition coil at the connector, and make sure the is grounding out the remaining wires when you crank the engine.
On gen 1+2 cars (1995 and earlier) with distributors, a no-start may be caused by a bad (Profile Ignition Pickup) sensor inside the distributor or a bad (ignition control module/TFI-IV). Failure of the PIP/ICM is typically seen when operating in hot conditions or when restarting after a hot soak. To diagnose this you can pull off a plug wire and check for spark to the engine block while cranking.
Cars with distributors will also not start if the ignition timing (distributor rotation) is quite far off. First make sure the plug wires are not shifted on the cap (#1 wire is on #1 tower, etc) and the firing order is correct (1-4-2-5-3-6). If you’re recently removed the distributor, you may have put it back in the wrong gear tooth or set the timing incorrectly. Remove the connector and set the correct base timing with a timing light. If you’re in a pinch, you can try loosening the distributor bolt and rotating the distributor back and forth while cranking the engine in the hope of passing through the correct timing to get the engine to start.
Under this category we mainly have the crankshaft position ( ) and camshaft position ( ) sensors. Before you go and buy a new sensor, know that sensor failures are relatively rare occurrences (this is especially true of the crank sensors). Do not replace the sensors before checking everything else above.
The main failure in this category would be the puck sensor on top of the camshaft synchronizer shaft (which replaces a distributor) with 1996 and later Vulcan engines. Usually the syncro shaft bearings fail and the rotary vane or magnet hits the sensor and destroys it. If this happens, both parts (syncro shaft and sensor) need to be replaced together. The no-start may occur after you have replaced these parts, which almost always indicates that you did not align the syncro shaft correctly. Double check your work and consider buying the alignment tool if you haven’t already. A damaged or poorly aligned may set P0340 or P1336 DTCs.
A bad sensor has already been discussed under the ignition section.
As I mentioned before, a bad crank sensor is extremely rare. Normally you would not replace this sensor unless you saw a missing or erratic signal on a scan tool during cranking. Oil contamination from a leaking oil pan or timing cover gasket is usually responsible.
Again, we’ll start with the obvious here. Make sure the air intake or filter is not being completely blocked by anything. If the idle air control ( ) valve is sticking shut and the throttle plate is all carboned up around the edges, you might not be getting hardly any air into the engine during cranking. If you had a vacuum gauge on the manifold you would see very high vacuum during cranking. This is very rare and obviously the engine would start as soon as you pressed on the gas pedal a bit.
If you move on to checking compression, you might find that it is low in one or more cylinders. Just like ignition problems, if you only have one or two bad cylinders the engine will probably still start (and run poorly). If you’re looking at low compression in all cylinders, it could indicate an intake restriction (see above), a valvetrain timing problem (extremely rare on Taurus engines) or some other sealing problem such as a head gasket (more common). Head gasket failures usually result from the engine overheating. Head gasket leakage will cause a lack of compression, but usually you also have coolant in the cylinders (which will actually increase compression as it displaces air), so widely varying compression values are indicative of head gasket failure. Generally, there will be many other signs that you have a head gasket failure before you get to the no-start point.
If you have a no-crank no-start, it usually means you have a problem with the battery, the starter, or the connections between the two. Start at the battery. If you have a voltmeter, measure the voltage of the battery. It should be 12.0 volts or more. If you don’t have a voltmeter, you can turn on your headlights. If they don’t come on or are dim (or fading fast), you probably have a bad battery. The next things to check are the connections for the battery and the starter. If any connection is loose or dirty, the current that can flow will be reduced and the starter may not receive enough energy to crank the engine. The battery terminals should be clean and tight, as well as the connection at the starter. Don’t forget to check the body grounds as well. If the connections are all good, it’s possible you blew the mega fuse (if your car has one) or the wires themselves are bad. Note that corrosion can hide under the wire insulation, so make sure the copper strands going into the wire look a normal copper color (not blackened). You may have to cut back the insulation to properly inspect the wires. After checking the connections and the battery, try watching the headlights while cranking. If they dim severely or go out you most likely still have a problem with the battery or the connections.
Poor connections will generate heat, so a good tip is to feel the battery terminals and the wires after several cranking attempts to see if anything feels especially warm.
If you do not hear the starter solenoid click (after checking everything else above), you may have a problem with the Neutral Safety Switch ( ) or Transmission Range Sensor ( ). Check the obvious and make sure the transmission is in either Park or Neutral (or the clutch is all the way to the floor if you have a manual). If the car won’t start in Park, try it in Neutral and vice versa. Also try wiggling the shifter while cranking or try starting it other gears (parking brake on!). Note that a bad will usually come with other symptoms like muted radio or the transmission shifting abnormally.
If it’s not a NSS/TRS problem, you might have a bad ignition switch or a problem with the wring going to it. Make sure you are getting battery voltage to the ignition switch on the feed wires at all times (check with key in ON and START positions to load the circuit). If you drop voltage, then you likely have a fault in the feed wire, typically the light green/violet wire where it runs through the driver's fender. If you have good feed voltage but no output voltage on the starter terminal, then you likely have a bad ignition switch.
The other area of wiring trouble is the wire to the starter solenoid from the starter relay. Have someone turn the key to start and make sure you are getting at least 10V or a lit test light at the solenoid terminal. If not, first confirm the starter relay working (you feel it click or confirm you are getting power on terminals 30 and 86 and a ground on 85 in the start position). You may try running a wire from battery + to the starter solenoid to rule out a starter/solenoid problem.
There are numerous other electrical reasons the car might not start. If this is the case, please make a new topic and tell us everything you’ve done for further assistance.
If you hear a click when you turn the key and you suspect a stuck starter motor, you can try giving it a gentle tap with a solid object before or during cranking to loosen it up. If it still doesn’t crank after a few taps–stop! You don’t want to pound dents into the starter because it might be another problem (and you will have pulverized a perfectly good starter). At this point you would want to turn the engine by hand (wrench on crankshaft pulley) with a wrench to make sure the engine hasn’t seized.
There are numerous other causes that can cause a no start, but they are quite rare compared to what’s already been mentioned. If you’re down to this category, you should probably make a new question if you haven’t already.
If you’re recently driven through water, your engine may be hydrolocked, which will require disassembly. A completely seized or severely damaged engine due to oil starvation or severe overheating/head gasket failure is another instance. In this case you would not be able to turn the engine by hand. Another would be any extent of damaged wires (due to abrasion or rodent chewing), blown fuses, or loose connections.
Failed (powertrain control module) also falls under this category, but again this is VERY RARE. The is blamed way too often (almost by default) when people can’t find the actual cause of the no-start. Before even considering replacing the , you would want to check everything else here, and then go the extra step of checking all the power and ground feeds. You would also want some other highly direct evidence like a lack of communication with a scan tool or a complete lack of response from the injectors or coils (after you’ve confirmed power to everything of course).
Bad fuel, such as diesel in the tank (whoops!) or 10-year-old gas (shame!) is another. You can also have water in the gas from filling up at a station that has contaminated gasoline. Recently a tanker mistakenly delivered jet fuel to several gas stations in New Jersey and a few cars filled up before it was discovered (no, it doesn’t make your car go faster!).