Dan Ferrell skriver om underhåll och reparation av gör-det-själv-bilar. Han har certifieringar inom automation och styrteknik.
1. Dött batteri
2. Dålig startmotor eller system
3. Felaktig generator
4. Igensatt bränslefilter
5. Felaktig bränsletrycksregulator
6. Dålig bränslepump
7. Defekt tändspole eller modul
8. Felaktig vevaxelpositionssensor eller kamaxelpositionssensor
9. Stort vakuumläckage
10. Misslyckad kuggrem
Senare i den här artikeln hjälper vi dig att navigera genom några tester och avgöra vilket problem som är ditt så att du kan komma tillbaka på vägen.
Ditt problem passar ofta in i en av dessa fem kategorier:
När du har att göra med en motor som vägrar att starta kan du använda ljud, eller avsaknaden av dem, som ett diagnostiskt verktyg. Ljud hjälper dig att fokusera på systemet eller systemen där problemet kan finnas, vilket eliminerar andra potentiella problem.
1. Ett enda klick
Om du hör ett enda, fast klick när du försöker starta bilen, kan problemet finnas i startmotorn eller kretsen.
2. Ett skramlande ljud
Ett skramlande ljud som kommer under motorhuven när du försöker starta motorn kan peka på ett underladdat batteri, lösa eller korroderade batteripoler eller ett problem med generatorn eller laddningssystemet.
3. Inget ljud alls
Om du inte hör något när du försöker starta din bil, kontrollera efter:
4. Ljudet av motorn som välter
När du vrider på tändningsnyckeln för att tända motorn kan du höra det vanliga vrålet från motorn, men motorn startar aldrig. Om så är fallet:
Om det behövs, se Resurser avsnittet längst ner i det här inlägget för hjälp med dessa och andra frågor.
Ofta kan ett tillstånd utan start härledas tillbaka till ett fel i bränslesystemet. Om din motor välter men vägrar starta, gör detta enkla test. Detta test kan berätta om problemet är relaterat till bränsleleverans.
Om motorn startar i ett par sekunder och sedan dör, är ditt problem troligen bränslerelaterat. Kontrollera bränslefiltret, bränsletrycksregulatorn och bränslepumpen enligt anvisningarna i följande avsnitt.
Följande video visar hur du använder startvätska.
Nu när du har en uppfattning om vilket system som behöver utredas kan du börja utreda. De kommande tio avsnitten behandlar de tio vanligaste felen som du sannolikt kommer att hantera när din bil vägrar starta, och hur du går tillväga för att kontrollera varje potentiellt fel.
Detta är en av de vanligaste anledningarna till att en bil inte startar. Ett bilbatteri kan hålla i upp till sex år, beroende på underhåll och driftsförhållanden. Extrema väderförhållanden kommer till exempel att förkorta dess livslängd.
Det är dock inte ovanligt att ett batteri plötsligt tappar laddningen.
Kontrollera batteripolens anslutningar. Ta bort korrosion och se till att terminalerna är täta. Kontrollera sedan elektrolytnivån om batteriet har avtagbara lock.
När din bil vägrar att starta, se till att ditt batteri har en bra laddning. Du kan använda en digital multimeter (DMM) för att kontrollera dess laddningstillstånd.
Så här kontrollerar du batteriets laddningstillstånd:
Om du behöver ladda om batteriet, använd en långsam laddning, om möjligt. Detta hjälper till att återställa batteriets tillstånd.
Din lokala reservdelsaffär kan kontrollera om ditt batteri fortfarande är bra.
Startmotorn och dess krets är andra vanliga källor till problem. Detta system kan vara boven om du hör ett fast klick när du försöker starta motorn.
Det kan vara problem med startmagneten, reläet eller startmotorn. Vid behov, kontrollera kretsen med ett spänningsfallstest. Se Resurser avsnittet längst ned i det här inlägget för hjälp med detta test.
Dessutom kommer din lokala bildelarbutik att kontrollera startmotorn gratis, men du måste ta bort startmotorn från fordonet.
Along with a dead or bad battery, alternator issues are one of the most common reasons for a no-start condition.
Usually, the charging system will turn on a warning light on the dashboard alerting you about a fault in the system. However, there are many reasons a charging system may fail to deliver a charge to the battery or electrical power to other systems in the vehicle.
Points to check:
Keep in mind that a corroded battery terminal could be a sign of an alternator overcharging the battery.
If you don't want to do it, your local auto parts store will check the alternator for you.
Most manufacturers recommend replacing the fuel filter every one or two years. Replace your fuel filter as recommended.
Although many fuel filters include a bypass valve in case the filter clogs, not all come equipped with this valve. Besides, rust and other sediments in the fuel tank can make their way to the fuel filter and clog its filter element.
Before giving out completely, a clogging fuel filter will give you one or more signs. For example, you may notice a lack of engine power at high speeds, difficulty starting the engine, or poor acceleration.
Check your repair manual to inspect the fuel filter and system in your particular model, if necessary.
If you suspect insufficient fuel reaching the injectors, do the quick fuel system delivery check as described in the second section of this post.
A fuel pressure regulator (FPR) limits the amount of pressure buildup in the system, typically to between 35 and 45 psi. Check your vehicle repair manual for your model specifications.
But FPRs can fail. If the internal diaphragm begins to leak fuel into the intake manifold, pressure will drop, and the cylinders will be flooded with fuel, making the engine hard to start.
Also, if too much raw fuel reaches the catalytic converter, the Check Engine Light (CEL) will begin to flash on your dashboard.
If you suspect insufficient fuel reaching the injectors, do the quick fuel system delivery check as described in the "Pre-Diagnostic 2" section of this article above.
You can perform a few FPR tests at home. See the Resources section at the bottom of this article for some help.
Fuel pumps have a long service life. They can last 80,000 miles or more. If your fuel filter and fuel pressure regulator are fine, but you have a fuel issue, probably your fuel pump is bad.
When turning the ignition key to the "On" position, before trying to start the engine, you should hear a buzzing sound for a couple of seconds. This is the sound of the fuel pump motor being activated to prime the fuel delivery system.
If you don't hear this sound, it may be that:
To verify a fuel delivery issue, do the quick fuel system delivery check as described in the second diagnostic section near the top of this article.
Also, check the repair manual for your particular model to see how to test the fuel pump, if necessary.
For the most part, ignition coils or modules are pretty reliable. Unlike spark plugs, wires, and distributor caps (depending on the model), an ignition coil or module doesn't require much attention.
However, they can fail from time to time. The conditions under which they operate, like heat, vibration and other engine performance issues, can have an adverse effect on any of these components after many miles of operation.
Older vehicle models used a single ignition coil and module to deliver a spark to the spark plugs. Newer models may use a module and one coil per spark plug. A failed coil or module in one of these models will certainly prevent the engine from starting.
You can use a spark tester to verify the presence and condition of the spark. You can buy one at your local auto parts store. If possible, get an adjustable spark tester you can use in different vehicles.
The Resources section at the bottom of this post, and your vehicle repair manual, can help you check an ignition coil or test for the presence of a spark in the ignition system.
The crankshaft position (CKP) sensor monitors engine speed, and the camshaft position (CMP) sensor tracks the position of the camshaft.
The electronic control module (ECM), the car's computer, uses the signal from both sensors to control fuel injection operation, direct ignition, and, depending on vehicle model, the variable valve timing system.
If any of these sensors fails, your car may fail to start.
Sometimes, depending on the specific fault, a bad CKP or CMP will trigger the check engine light (CEL). Whether the CEL illuminates on your dashboard or not, it's a good idea to scan the computer memory for potential diagnostic trouble codes (DTCs) that can help you diagnose a no-start condition.
If you don't have a scan tool, your local auto parts store may download DTCs for you without cost.
Also, check your vehicle repair manual. And, within the Resources section at the bottom of this post, you'll find links to other posts to help you check these sensors yourself, if possible.
Major vacuum leaks are not common, but they definitely happen. A vacuum leak can make the air-fuel mixture too lean, preventing the engine from starting.
A leak may come from a vacuum line, intake manifold gasket, throttle body gasket, leaking EGR valve gasket, power brake booster or positive crankcase ventilation (PCV) valve.
Vacuum leaks can be tricky to find. You can visually inspect every vacuum hose and trace it with your hand, feeling for tears or damaged spots. Also, pay attention to hissing sounds that may indicate a leak.
A leaking gasket is harder to detect, though, unless you have a smoke machine designed for this purpose.
Vid behov, konsultera din fordonsreparationsmanual.
You won't see this type of failure often. Timing belts can last between 50,000 and 100,000 miles or more, depending on your particular model. And if you have a timing chain rather than a belt, you may never have to worry about replacing it.
Still, if you've checked the usual suspect without success, check for a failed timing belt or chain.
The engine's crankshaft and camshaft are joined by a timing belt or chain through a series of sprockets. When this belt or chain brakes or wears out, or the tensioner fails, the crankshaft won't be able to rotate the camshaft anymore, making it impossible to start the engine.
Checking for a failed timing belt or chain:
On a vehicle fitted with a distributor, you can remove the distributor cap and try to fire up the engine. If the distributor rotor doesn't move, most likely your timing belt or chain, or one of the system components, has failed.
On models with multiport fuel injection systems, sometimes it's possible to remove the timing belt or chain cover to check for camshaft movement while trying to start the engine. Or you may be able to remove the oil cap from the valve cover, or the cover itself if necessary, to check for valve movement while trying to start the engine. If there's no movement, it's time to check the belt, chain, or system components.
If the camshaft rotates, you may still want to verify ignition timing. If the belt or chain has skipped some sprocket teeth, it may be difficult or impossible to start your engine.
Consult your vehicle repair manual to check crankshaft and camshaft synchronization.
Of course, there are other model-specific components or systems that can prevent your vehicle from starting. Till exempel:
Consult the repair manual for your specific make and model for help on these and other systems or components.
To sum up, when your car won't start, begin your diagnostic with the most simple components or obvious potential problems, as in Diagnostics 1 and 2 at the beginning of the article:
Then you can start checking the alternator, starter motor, ignition, fuel system pressure, and their circuits.
Most of the time you'll be able to fix the problem yourself. Sometimes, you will need to replace a fuel pressure regulator, ignition coil, module, or fuel pump, or fix a vacuum leak.
See the Resources below for diagnostic ideas if you have narrowed your problem down to a particular system.
Det här innehållet är korrekt och sant enligt författarens bästa kunskap och är inte avsett att ersätta formella och individualiserade råd från en kvalificerad expert.
