Brody
November 28th, 2010, 09:19 AM
This is a very basic article that discusses a logical manner to diagnose a rig that won't start. Please note that is written around diagnosing a fuel injected engine, but a lot of the same principles will apply to all engines:
http://www.bc4x4.com/tech/2008/nostart/nostart.jpg (http://www.bc4x4.com/tech/2008/nostart/nostart.jpg)
There are few things more frustrating that turning the key in your truck's ignition and being greeted with the jarring silence of a non-starting, non-running engine. This usually happens when you're late for work or hundreds of miles in the woods and all you want is a quick solution. It's easy to succumb to panic but it's important to begin diagnosing the problem in a systematic and logical manner. Glen Hogenson is an ASE Master Mechanic who feels your pain. Here is his trouble shooting guide to help you fix that no-start condition.
I'm going to make a few assumptions here:
First, that you're working with a fuel injected engine.
Second, that the engine doesn't have some obvious problem, like a rod sticking out of the side of the block, or a head missing. (I've had people bring in vehicles like this, expecting us to work miracles.)
Third, that this is not one of those cases where it was running okay, and your buddy/brother-in-law/automotive consultant offered to tune it and actually detuned it into automotive infarction.
Now, please understand, this is the way that I do things. There's lots of paths to the same results. If you have another way of doing things that works for you, cool. Let's just not call each other wrong just because we disagree, okay?
Preliminary checks: Is there fuel in the tank? Are all of the fuses good? Are the plug wires secure and in the right order? Oil in the engine? Ground straps present and okay? (Make one with your jumper cables if you're not sure.) Got enough coolant in the system? Extra warning lights on that usually aren't?
Note: Some of the questions I'll go through here seem pretty ridiculous, but I've seen techs troubleshoot for a long time working with a wrong assumption about something simple.
First, let's see what the engine actually does when you try to start it. Does it turn over? If so, fast or slow?
Starting and dying quickly is different than not starting; especially on a fuel injected engine. Once the engine is started, the computer starts reading sensors and inputs that it wasn't during the start (oil pressure is an example).
If the preliminaries check out and the engine is turning over too slow to start, we need to get that resolved. Also, even if the engine is turning over just a little too slow, we still have to address this before we can go any further. A jump start from a charger/ another vehicle/ jump box/ swapped in battery is worth a try. Also, drag out that multi-meter that's buried in your tool box, set it to voltage, and check it against a known good battery.
The reason for the multi-meter is to check the voltage while the engine is cranking. ASE says 9.6V minimum is required. If your battery is a little low (remember, 12V on a modern battery is about 90% discharged), it'll drop real low during a high load (engine cranking). If the clock goes back to 12:00 every time you try to start the vehicle, that's another clue that the battery pulls too low. If the battery pulls too low, there's not enough voltage to power the engine computer. No Power=No Go.
Note: Tools such as multi-meters and test lights should be checked often for functionality. Test lights are cheap, and do go bad. Multi-meters have batteries, and as we all know, batteries go bad after awhile.
http://www.bc4x4.com/tech/2008/nostart/Multimeter_.jpg (http://www.bc4x4.com/tech/2008/nostart/Multimeter_.jpg)
Multimeter.
Okay, so we've got the cranking issue resolved. Next, we look at the three things that all internal combustion engines need, regardless of pedigree, fuel, or design:
Air
Fuel
Ignition Source
Are we getting each of these? Then, if we are, are we getting each one correctly (amount and at the right time)? I know this is obvious to most people, but I'll state it since it's not obvious to all:
If the vehicle won't crank, it won't start. Think about it; you have a perfectly good, running engine. You pull the starter out. It won't start, will it? Fix the cranking issues first.
If the engine cranks, we're probably getting air and some compression. You can pull spark plugs and use your compression gauge, but if the engine has run okay before, I'll usually forego this one for awhile.
Now, when you turn the key to run, it should build up some fuel pressure. There's a Schrader valve test port on the fuel rail (or, in the case of throttle body injection, you might find one on the throttle body).Take a small screwdriver and press the little metal pin in the valve. Careful; if everything's okay, fuel should come out real hard and fast. (A small dribble sometimes will come out; this signals no pressure, not high pressure. Don't be fooled.) If you've got a fuel pressure gauge, put that on the test valve instead, and get an accurate (and safer) reading.
http://www.bc4x4.com/tech/2008/nostart/FuelPressure_.jpg (http://www.bc4x4.com/tech/2008/nostart/FuelPressure_.jpg)
Fuel pressure gauge.
If you want a double-check that the only problem is a lack of fuel, squirt in a good spray of starter fluid or even brake cleaner (don't get any on the mass airflow sensor if you have one). You'll have to pull the air filter on carbureted vehicles, or the snorkel tube on fuel injected vehicles. Quickly, try starting the vehicle. If it stumbles, or even starts for a couple of seconds, you've confirmed that you've got a lack of fuel problem and that everything else is working.
http://www.bc4x4.com/tech/2008/nostart/DakotaMAP_.jpg (http://www.bc4x4.com/tech/2008/nostart/DakotaMAP_.jpg)
Example of a mass airflow sensor.
For those of you that aren't familiar with a Schrader valve, go look at the valve stem on one of your wheels; that's a Schrader valve. Just like the one on the wheel, the one on the engine should have a plastic cap on it.
http://www.bc4x4.com/tech/2008/nostart/ShraderValve_.jpg (http://www.bc4x4.com/tech/2008/nostart/ShraderValve_.jpg)
Schrader valve attached to the fuel rail.
Let's also check for spark. We can set this up at the same time, and check both the fuel pressure gauge and spark at the same time. There's a few different ways to do this.
Have someone crank the engine for you, or use a remote start wire if you can. Watch the spark. It should be white or yellow-white. Green is too low. For those of you can than hear and work in a quiet area, you should also hear the sharp snap every time the spark fires.
http://www.bc4x4.com/tech/2008/nostart/RemoteStart_.jpg (http://www.bc4x4.com/tech/2008/nostart/RemoteStart_.jpg)
A remote start wire is a handy tool to have when you're working on your own.
Got a spark?
Is your fuel pressure gauge reading okay?
If the answer is "no" to either of the above, fix it. Trace it back.
Fuel: Filter clogged? Pump working? Pump relay good? Fuse good? If you spray brake cleaner or starting fluid into the throttle body (not the mass airflow sensor) while cranking, does it fire or try to fire?
Spark: Spark at the coil? Spark signal going to the coil?
Old, but working spark plug stuck into a plug wire. My favorite. Pull a plug wire, stick the plug in, and pin the plug to the head with a plastic handled screwdriver. Oh, and don't touch the car with any other part of you. No Ground Path=No Accidental Grounding=No Big Ouch.
Pull a plug and use it as above. Okay, but there's a fire potential, especially if the fuel system works and blows out of the cylinder and the plug fires.
Pull a wire off of a plug, and stick the end of a screwdriver in it, then hold the shaft of the screwdriver real close to part of the engine. Okay, and my second favorite. This also works for pulling the coil wire off of the distributor to check for spark at that point.
Pull the wire off of a plug, cram in a short piece of wiper hose, and put the free end of the hose over the end of the plug. (The hose is full of carbon, and will conduct.) Hook your test light wire to a good ground, and while the engine is cranking, bring the point end of the test light real close to the hose. If the ignition works, you'll get a flash.
(Getting your buddy to put his tongue on the end of the plug wire is funny, but not recommended.) If you have access to a scan tool, use it. See what codes you get, if any. These can lead you to some possible areas to fix.
Away from work, I use a $30 Harbor Freight OBD-II code reader that lives in the car.
If we have fuel pressure, let's check the injectors. Put a screwdriver (that big one that you like to have around) against the injectors one-at-a-time. Put the handle against your skull. Feel/hear the clicks? Good. If not, are you getting signals to the injectors? (Noid lights if you have them, else, backprobe with a test light.)
TBI injection is even easier. Pull the snorkel or filter off of the throttle body, and watch the injectors as your partner cranks the engine. See a nice spray pattern?
Yes, they really are called "noid lights". They come in a set, and plug into the wiring harness in place of an injector, and light up when the injector signal is present. Handy little tools, and preferable over a test light, as they provide the proper resistance and avoid shorting out the engine control computer.
http://www.bc4x4.com/tech/2008/nostart/noid_light_kit_.jpg (http://www.bc4x4.com/tech/2008/nostart/noid_light_kit_.jpg)
Noid light kit.
If we have spark at the end of the plug wire, pull the spark plugs out of the engine. There's lots of sources on reading plugs, so I won't go into it too much here, other than to mention to make sure that there's a gap that's about right, and that it's not clogged or shorted.
Forget that "close enough" crap. Plug gauges are cheap, so there's no excuse not to have several tossing around in your stuff. Use them, and use them correctly. If the gap is to be 0.040", set it to that. 0.045" isn't close enough. This is easy stuff to do, so do it right.
If there's no spark, you need to know what kind of ignition setup you have. All of them pretty much work the same way. If you imagine a one-cylinder engine, the ignition has a switched "on" or power wire that goes to the coil. The coil also has a ground (either a wire or a case ground). Either the power wire or the ground is controlled by a switch. Coming from the coil is a plug wire, that then goes to the spark plug.
http://www.bc4x4.com/tech/2008/nostart/DakotaCoil3_.jpg (http://www.bc4x4.com/tech/2008/nostart/DakotaCoil3_.jpg)
Ignition coil.
Points are notorious for burning. This can make the gap in them too big, or cause them not to conduct when they touch. A quick pass with a very fine file or a piece of emery cloth supported by a knife blade can work to clean them.
Caps and rotors can also get burnt or corroded. Especially in the case of high-energy type ignitions, you may also find carbon tracks on the inside of the cap, which can short out the spark. These two parts, like plugs, are so cheap that when in doubt on your own rig, just replace 'em.
If you have a distributor ignition, you have one coil and a rotor and cap that direct the output of the coil to each individual plug wire at the right time. Also, inside the distributor is the switch, either old-fashioned points (obsolete), or some kind of electronics.
Since wires come out from the sensor, you can test the signal. Since most non-points switches can't handle the power of the coil directly, they'll have some kind of a module that goes in line between them and the coil. Backprobe the wires, and check what's going in and what's coming out. These modules are a go/no go type of thing, so that makes it easier to troubleshoot.
The electronics can be either a Hall effect sensor (magnetic), magnetic pulse generator, or an optical sensor. Pull the cap and rotor and take a look. Make sure the parts look clean and not damaged. Hall effect sensors and pulse generators have a magnet that can collect metal particles. Optical sensors make static that can attract dirt.
http://www.bc4x4.com/tech/2008/nostart/hall_effect_sensor_.jpg (http://www.bc4x4.com/tech/2008/nostart/hall_effect_sensor_.jpg)
Example of a Hall effect sensor mounted in a distributor.
If you have a distributorless ignition system, you'll have one or more coil assemblies (blocks or individual coils) that are switched by the engine control computer based off of position sensors on the crankshaft and the camshaft. This is where that scan tool comes in; if you get codes about bad sensors, the computer's not getting its signals and thus won't trigger the coil(s).
If your scan tool setup doesn't give you explanations of the codes (or your dog ate the book), a good site is www.obdii.com (http://www.obdii.com/) for the OBD-II standard codes (as well as some OEM-specific codes).
http://www.bc4x4.com/tech/2008/nostart/CodeReader_.jpg (http://www.bc4x4.com/tech/2008/nostart/CodeReader_.jpg)
Code scanner.
After we've fixed any turning over, voltage, spark, and fuel problems, the engine should run. If not, what did we miss? Let's go back to what happened before the engine wouldn't start. Did it run really rough before it was turned off? Now, we're getting into major stuff; bad sensors, slipped timing components, stuff like that that I can go on and on with, as we're getting real vehicle-specific.
If you're sure you've done all of the above, get someone else to look over your work.
Once it's running, how well is it running? Any misfires? Is the charging system working? Do the headlights come on nice and bright? Can you turn on everything and still have a decent battery voltage? Any tuning to do?
Now, if you're me, it's time to finish the inspection form, stamp the time card, and turn the whole works in and get the next job.
Thanks to BC 4x4.com!
http://www.bc4x4.com/tech/2008/nostart/nostart.jpg (http://www.bc4x4.com/tech/2008/nostart/nostart.jpg)
There are few things more frustrating that turning the key in your truck's ignition and being greeted with the jarring silence of a non-starting, non-running engine. This usually happens when you're late for work or hundreds of miles in the woods and all you want is a quick solution. It's easy to succumb to panic but it's important to begin diagnosing the problem in a systematic and logical manner. Glen Hogenson is an ASE Master Mechanic who feels your pain. Here is his trouble shooting guide to help you fix that no-start condition.
I'm going to make a few assumptions here:
First, that you're working with a fuel injected engine.
Second, that the engine doesn't have some obvious problem, like a rod sticking out of the side of the block, or a head missing. (I've had people bring in vehicles like this, expecting us to work miracles.)
Third, that this is not one of those cases where it was running okay, and your buddy/brother-in-law/automotive consultant offered to tune it and actually detuned it into automotive infarction.
Now, please understand, this is the way that I do things. There's lots of paths to the same results. If you have another way of doing things that works for you, cool. Let's just not call each other wrong just because we disagree, okay?
Preliminary checks: Is there fuel in the tank? Are all of the fuses good? Are the plug wires secure and in the right order? Oil in the engine? Ground straps present and okay? (Make one with your jumper cables if you're not sure.) Got enough coolant in the system? Extra warning lights on that usually aren't?
Note: Some of the questions I'll go through here seem pretty ridiculous, but I've seen techs troubleshoot for a long time working with a wrong assumption about something simple.
First, let's see what the engine actually does when you try to start it. Does it turn over? If so, fast or slow?
Starting and dying quickly is different than not starting; especially on a fuel injected engine. Once the engine is started, the computer starts reading sensors and inputs that it wasn't during the start (oil pressure is an example).
If the preliminaries check out and the engine is turning over too slow to start, we need to get that resolved. Also, even if the engine is turning over just a little too slow, we still have to address this before we can go any further. A jump start from a charger/ another vehicle/ jump box/ swapped in battery is worth a try. Also, drag out that multi-meter that's buried in your tool box, set it to voltage, and check it against a known good battery.
The reason for the multi-meter is to check the voltage while the engine is cranking. ASE says 9.6V minimum is required. If your battery is a little low (remember, 12V on a modern battery is about 90% discharged), it'll drop real low during a high load (engine cranking). If the clock goes back to 12:00 every time you try to start the vehicle, that's another clue that the battery pulls too low. If the battery pulls too low, there's not enough voltage to power the engine computer. No Power=No Go.
Note: Tools such as multi-meters and test lights should be checked often for functionality. Test lights are cheap, and do go bad. Multi-meters have batteries, and as we all know, batteries go bad after awhile.
http://www.bc4x4.com/tech/2008/nostart/Multimeter_.jpg (http://www.bc4x4.com/tech/2008/nostart/Multimeter_.jpg)
Multimeter.
Okay, so we've got the cranking issue resolved. Next, we look at the three things that all internal combustion engines need, regardless of pedigree, fuel, or design:
Air
Fuel
Ignition Source
Are we getting each of these? Then, if we are, are we getting each one correctly (amount and at the right time)? I know this is obvious to most people, but I'll state it since it's not obvious to all:
If the vehicle won't crank, it won't start. Think about it; you have a perfectly good, running engine. You pull the starter out. It won't start, will it? Fix the cranking issues first.
If the engine cranks, we're probably getting air and some compression. You can pull spark plugs and use your compression gauge, but if the engine has run okay before, I'll usually forego this one for awhile.
Now, when you turn the key to run, it should build up some fuel pressure. There's a Schrader valve test port on the fuel rail (or, in the case of throttle body injection, you might find one on the throttle body).Take a small screwdriver and press the little metal pin in the valve. Careful; if everything's okay, fuel should come out real hard and fast. (A small dribble sometimes will come out; this signals no pressure, not high pressure. Don't be fooled.) If you've got a fuel pressure gauge, put that on the test valve instead, and get an accurate (and safer) reading.
http://www.bc4x4.com/tech/2008/nostart/FuelPressure_.jpg (http://www.bc4x4.com/tech/2008/nostart/FuelPressure_.jpg)
Fuel pressure gauge.
If you want a double-check that the only problem is a lack of fuel, squirt in a good spray of starter fluid or even brake cleaner (don't get any on the mass airflow sensor if you have one). You'll have to pull the air filter on carbureted vehicles, or the snorkel tube on fuel injected vehicles. Quickly, try starting the vehicle. If it stumbles, or even starts for a couple of seconds, you've confirmed that you've got a lack of fuel problem and that everything else is working.
http://www.bc4x4.com/tech/2008/nostart/DakotaMAP_.jpg (http://www.bc4x4.com/tech/2008/nostart/DakotaMAP_.jpg)
Example of a mass airflow sensor.
For those of you that aren't familiar with a Schrader valve, go look at the valve stem on one of your wheels; that's a Schrader valve. Just like the one on the wheel, the one on the engine should have a plastic cap on it.
http://www.bc4x4.com/tech/2008/nostart/ShraderValve_.jpg (http://www.bc4x4.com/tech/2008/nostart/ShraderValve_.jpg)
Schrader valve attached to the fuel rail.
Let's also check for spark. We can set this up at the same time, and check both the fuel pressure gauge and spark at the same time. There's a few different ways to do this.
Have someone crank the engine for you, or use a remote start wire if you can. Watch the spark. It should be white or yellow-white. Green is too low. For those of you can than hear and work in a quiet area, you should also hear the sharp snap every time the spark fires.
http://www.bc4x4.com/tech/2008/nostart/RemoteStart_.jpg (http://www.bc4x4.com/tech/2008/nostart/RemoteStart_.jpg)
A remote start wire is a handy tool to have when you're working on your own.
Got a spark?
Is your fuel pressure gauge reading okay?
If the answer is "no" to either of the above, fix it. Trace it back.
Fuel: Filter clogged? Pump working? Pump relay good? Fuse good? If you spray brake cleaner or starting fluid into the throttle body (not the mass airflow sensor) while cranking, does it fire or try to fire?
Spark: Spark at the coil? Spark signal going to the coil?
Old, but working spark plug stuck into a plug wire. My favorite. Pull a plug wire, stick the plug in, and pin the plug to the head with a plastic handled screwdriver. Oh, and don't touch the car with any other part of you. No Ground Path=No Accidental Grounding=No Big Ouch.
Pull a plug and use it as above. Okay, but there's a fire potential, especially if the fuel system works and blows out of the cylinder and the plug fires.
Pull a wire off of a plug, and stick the end of a screwdriver in it, then hold the shaft of the screwdriver real close to part of the engine. Okay, and my second favorite. This also works for pulling the coil wire off of the distributor to check for spark at that point.
Pull the wire off of a plug, cram in a short piece of wiper hose, and put the free end of the hose over the end of the plug. (The hose is full of carbon, and will conduct.) Hook your test light wire to a good ground, and while the engine is cranking, bring the point end of the test light real close to the hose. If the ignition works, you'll get a flash.
(Getting your buddy to put his tongue on the end of the plug wire is funny, but not recommended.) If you have access to a scan tool, use it. See what codes you get, if any. These can lead you to some possible areas to fix.
Away from work, I use a $30 Harbor Freight OBD-II code reader that lives in the car.
If we have fuel pressure, let's check the injectors. Put a screwdriver (that big one that you like to have around) against the injectors one-at-a-time. Put the handle against your skull. Feel/hear the clicks? Good. If not, are you getting signals to the injectors? (Noid lights if you have them, else, backprobe with a test light.)
TBI injection is even easier. Pull the snorkel or filter off of the throttle body, and watch the injectors as your partner cranks the engine. See a nice spray pattern?
Yes, they really are called "noid lights". They come in a set, and plug into the wiring harness in place of an injector, and light up when the injector signal is present. Handy little tools, and preferable over a test light, as they provide the proper resistance and avoid shorting out the engine control computer.
http://www.bc4x4.com/tech/2008/nostart/noid_light_kit_.jpg (http://www.bc4x4.com/tech/2008/nostart/noid_light_kit_.jpg)
Noid light kit.
If we have spark at the end of the plug wire, pull the spark plugs out of the engine. There's lots of sources on reading plugs, so I won't go into it too much here, other than to mention to make sure that there's a gap that's about right, and that it's not clogged or shorted.
Forget that "close enough" crap. Plug gauges are cheap, so there's no excuse not to have several tossing around in your stuff. Use them, and use them correctly. If the gap is to be 0.040", set it to that. 0.045" isn't close enough. This is easy stuff to do, so do it right.
If there's no spark, you need to know what kind of ignition setup you have. All of them pretty much work the same way. If you imagine a one-cylinder engine, the ignition has a switched "on" or power wire that goes to the coil. The coil also has a ground (either a wire or a case ground). Either the power wire or the ground is controlled by a switch. Coming from the coil is a plug wire, that then goes to the spark plug.
http://www.bc4x4.com/tech/2008/nostart/DakotaCoil3_.jpg (http://www.bc4x4.com/tech/2008/nostart/DakotaCoil3_.jpg)
Ignition coil.
Points are notorious for burning. This can make the gap in them too big, or cause them not to conduct when they touch. A quick pass with a very fine file or a piece of emery cloth supported by a knife blade can work to clean them.
Caps and rotors can also get burnt or corroded. Especially in the case of high-energy type ignitions, you may also find carbon tracks on the inside of the cap, which can short out the spark. These two parts, like plugs, are so cheap that when in doubt on your own rig, just replace 'em.
If you have a distributor ignition, you have one coil and a rotor and cap that direct the output of the coil to each individual plug wire at the right time. Also, inside the distributor is the switch, either old-fashioned points (obsolete), or some kind of electronics.
Since wires come out from the sensor, you can test the signal. Since most non-points switches can't handle the power of the coil directly, they'll have some kind of a module that goes in line between them and the coil. Backprobe the wires, and check what's going in and what's coming out. These modules are a go/no go type of thing, so that makes it easier to troubleshoot.
The electronics can be either a Hall effect sensor (magnetic), magnetic pulse generator, or an optical sensor. Pull the cap and rotor and take a look. Make sure the parts look clean and not damaged. Hall effect sensors and pulse generators have a magnet that can collect metal particles. Optical sensors make static that can attract dirt.
http://www.bc4x4.com/tech/2008/nostart/hall_effect_sensor_.jpg (http://www.bc4x4.com/tech/2008/nostart/hall_effect_sensor_.jpg)
Example of a Hall effect sensor mounted in a distributor.
If you have a distributorless ignition system, you'll have one or more coil assemblies (blocks or individual coils) that are switched by the engine control computer based off of position sensors on the crankshaft and the camshaft. This is where that scan tool comes in; if you get codes about bad sensors, the computer's not getting its signals and thus won't trigger the coil(s).
If your scan tool setup doesn't give you explanations of the codes (or your dog ate the book), a good site is www.obdii.com (http://www.obdii.com/) for the OBD-II standard codes (as well as some OEM-specific codes).
http://www.bc4x4.com/tech/2008/nostart/CodeReader_.jpg (http://www.bc4x4.com/tech/2008/nostart/CodeReader_.jpg)
Code scanner.
After we've fixed any turning over, voltage, spark, and fuel problems, the engine should run. If not, what did we miss? Let's go back to what happened before the engine wouldn't start. Did it run really rough before it was turned off? Now, we're getting into major stuff; bad sensors, slipped timing components, stuff like that that I can go on and on with, as we're getting real vehicle-specific.
If you're sure you've done all of the above, get someone else to look over your work.
Once it's running, how well is it running? Any misfires? Is the charging system working? Do the headlights come on nice and bright? Can you turn on everything and still have a decent battery voltage? Any tuning to do?
Now, if you're me, it's time to finish the inspection form, stamp the time card, and turn the whole works in and get the next job.
Thanks to BC 4x4.com!