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Spark Plugs and Start-Up Issues: Diagnosing and Fixing Your Car's Ignition Problems

Carbon fouled spark plug

Modern cars are more advanced than any other time in human history but are prone to hiccups and minor issues that cause them to "misbehave."

Your spark plugs not playing nicely with the rest of the components in your ignition system can cause your vehicle not to start! All it takes to freeze you out (and keep your car parked in the driveway) are spark plugs that have degraded or failed - even just a little bit!

Armed with the inside-information below, you won't have to worry about your spark plugs causing you to miss work or run late for an important date.

Table Of Contents [show]

    Four spark plugs in good condition
    Four spark plugs in good condition

    What Are the Symptoms of Bad Spark Plugs?

    What happens when spark plugs go bad is:

    1. Your engine starts to misfire, with a severe reduction in overall power.
    2. You start to hear a knocking sound inside your engine because the spark plugs aren't igniting all your fuel the way they should.
    3. Your vehicle begins to suffer from a rough idle, shimmying and shaking even when parked and idling.
    4. … And, of course, your vehicle might begin to fight you when you turn the key, either hard starting or flat out refusing to start!

    A misfiring engine happens when your spark plugs delay the overall combustion process. This leads to cylinders misfiring, power reduction, and significant fuel economy issues.

    Worse, misfires can lead to significant long-term damage to your engine. That's bad news, especially since spark plugs causing this problem are so cheap and easy to fix or replace.

    Engine Knocking

    Engine knocking (usually something that pops up when you accelerate) will sound like someone is rapping on your engine with their knuckles. This is a surefire sign that your spark plugs aren't igniting all the fuel they are being "fed" by the vehicle's fuel system.

    This is a pretty straightforward fix, too - and it's not as disastrous long-term to your engine as misfiring can be.

    (It's still something you want to square away ASAP, though).

    Carbon on spark plug
    Carbon on spark plug

    Rough Idling

    Rough idling is linked to spark plugs that aren't producing a spark when they are supposed to. The delayed spark often happens in the morning (especially on cold, wet mornings) when there is extra condensation under the hood.

    You'll see a dramatic improvement as soon as you swap those bad plugs out.

    Other problems like bad gas can also indirectly cause a rough idle by fouling the spark plugs.

    Can Bad Spark Plugs Cause Car Cranking But Not Starting?

    Bad spark plugs can cause your vehicle to "crank" but not start - though you could be dealing with a couple of different issues that contribute to this problem.

    You'll know that the spark plugs are the culprit if you've begun to notice your vehicle misfiring, having difficulty accelerating, or struggling through a rough idle before the cranking problem manifests.

    After pulling your spark plugs out, a quick inspection should also give you a good idea if they need to be swapped out.

    Fouled spark plugs
    Fouled spark plugs

    A fouled plug will be:

    • covered with oil
    • covered with fuel
    • covered with carbon
    • blistered from running too hot

    Also, if you see anything wrong with the ignition coils themselves, it's time for a change.

    Other contributing factors could be (but aren't limited to):

    • Trouble with the flow of fuel in your vehicle
    • Crankshaft issues (that's a bit more of an expensive fix)
    • Compression ratio problems
    • Problems with your battery and electrical system
    Mechanic checks and cleans spark plug
    Mechanic checks and cleans spark plug

    Can Wet Spark Plugs Cause Car Not To Start?

    Your spark plugs becoming fouled (or getting wet) can cause your vehicle to be hesitant to start as well.

    If you have gone to start your vehicle and it just turns over and over (and over and over) without even trying to fire, the chances are halfway decent you are dealing with a "flooded engine" and your spark plugs are wet.

    A flooded engine means that your spark plugs have been soaked in a fuel-rich environment, and there's not quite enough oxygen at this particular point in time to get the combustion needed to start the engine.

    You'll have to wait at least a couple of minutes (maybe 30 minutes, perhaps a little longer) for some of the excess fuel to evaporate. After the fuel evaporates and more oxygen enters the combustion chamber, you should be able to turn vehicle on.

    If that doesn't work, though, you might have to swap out your plugs for a fresh set (a dry set). When that's the case, make sure that you give the spark plug chamber plenty of time to dry out before you stuff your new plugs in.

    Can Bad Spark Plug Wires Cause a Car Not to Start?

    You had better believe that faulty spark plug wiring can lead to your vehicle not wanting to start at all.

    Any problems with the electrical wiring responsible for your ignition system can lead to your vehicle flat out not starting at all. This is because the electrical current that travels across these wires to your spark plugs (from your distributor or your ignition coil) is what sparks the spark plugs to begin with!

    Spark plug wires in good condition
    Spark plug wires in good condition

    If you're not getting any electricity at all, your spark plugs aren't going to work. If you're getting just a bit of electricity, you might be dealing with spark plugs that misfire or otherwise misbehave, which will cause the same kind of problems.

    You end up with a rough idling vehicle, a misfiring vehicle, or a vehicle that isn't going to turn on.

    Will Oil on Spark Plugs Cause a Car Not to Start?

    Any oil that gets into your spark plugs can cause them to "foul."

    Oil on spark plug
    Oil on spark plug

    No, your spark plugs aren't going to foul upon a small amount of contact with motor oil. But they will stop working the way they should - even if every other aspect of the part is in good working order.

    Secondly however, your spark plugs won't fire when they are coated in large amounts of oil and you're not going to get your vehicle to start.

    Finally, if you are getting oil on your spark plugs, you need to be sure that you address the underlying issue.

    You likely have a leaking valve cover gasket that needs to be replaced or piston ring bypass. You might even be dealing with a head gasket leak, in which case you could be in line for some pretty expensive repairs - labor-intensive repairs, nonetheless.

    First, clean no spark plugs up and get them back to just as good as new condition. After that, though, address that leaking oil problem. Things will only get worse (and more expensive) to fix later.

    Can You Start a Car Without a Spark Plug?

    No, you aren't generally going to be able to start a vehicle without a spark plug in place - simply because there's nothing to spark the fuel that needs to be ignited to cause the pistons to power your engine.

    There are stories of people driving around in vehicles with spark plugs that have failed after they have fired up their car and taken it for a trip on the road.

    In those situations, though, you're going to end up with a lot of uncombusted fuel in the engine.

    Your car isn't going to fire up without a spark plug. It might run for a while with a bad plug, but the danger level is redlined in those situations.

    Jump starting a battery
    Jump starting a battery

    Can You Jumpstart a Car a with Bad Spark Plug?

    You may be able to jumpstart your vehicle with a bad spark plug, but it is the definition of a "Band-Aid" fix.

    The underlying issue - the faulty plugs themselves - will cause so many other problems in the short and long-term that you would be much better off letting your car sit with bad plugs until you can replace them.

    Spark plugs are the most expensive things in the world. Or the most challenging thing to replace all on your own.

    Jump on YouTube, watch a couple of videos about tackling this project on your own, and then knock it out as soon as your vehicle starts misbehaving (and refusing to start) because of bad plugs.

    You'll be much better off (and so will your vehicle).

    Can Bad Spark Plugs Cause Your Car to Not Accelerate?

    If you have noticed your vehicle being much less responsive to your gas pedal, failing to accelerate - or accelerating at a much slower pace than it used to in the past - you could be dealing with spark plugs on the fritz.

    For one thing, spark plugs that aren't working the way they are designed to increase your fuel consumption dramatically. So if you notice that your fuel economy has taken a nosedive recently (with no other reason), it can be because your plugs need to be swapped out with new ones.

    Secondly, though, your bad plugs could be causing combustion issues in the cylinders, leading to a significant decline in performance.

    If fuel isn't being combusted at the rate the vehicle has been designed to with good plugs, you end up with a vehicle that is sluggish, less responsive, and sort of a "pig" - especially when you are trying to climb hills or pass someone on the highway.

    Uneven idling, engine knocking, and rough starts are all signs that dovetail with bad acceleration that let you know it's time for a plug swap.

    Old car battery
    Old car battery

    Can Bad Spark Plugs Cause Slow Crank?

    A slow cranking engine is (usually) a sign of a battery issue more than that your spark plugs aren't working the way they should be.

    That said, it's never a bad idea to poke around under the hood and look at your spark plugs.

    Sometimes you'll notice a little bit of engine oil in the plug chamber, and it doesn't take a whole lot from a valve gasket leak to inhibit the combustion process and cause a slow crank kind of situation.

    Either way, pop the plugs out of your vehicle and give them a good cleaning. If they don't show any other obvious signs of damage or degradation, put them back and jump your battery - or even better, put it on a trickle charger and see if that fixes the problem.

    You might even need to spring for a new battery (a relatively inexpensive and quick fix) to get your vehicle cranking again.

    Can Bad Spark Plugs Cause Transmission Problems?

    It's tough to imagine a situation where your spark plugs will lead to transmission problems in most circumstances.

    There's not a lot of overlap here.

    Sometimes misbehaving spark plugs can lead to misfiring issues in your engine. That will mean lower torque to your transmission, causing your transmission to have a tougher time shifting gears, and then you see serious performance and acceleration issues.

    You can fix all this just by swapping out the plugs, though!


    Bad spark plugs definitely can cause your car not to start.

    Thankfully, though, replacing your spark plugs with brand-new ones (shouldn't) break your bank account. Even better news, making this repair is something almost anyone can do with nothing but a couple of YouTube videos, some household tools, and a little bit of patience.

    It's not bad to get in the habit of visually inspecting your spark plugs every time your vehicle goes in for service, either.

    If you're dealing with trouble starting your car because of your spark plugs, you've been driving around with faulty plugs for quite a while. It's just that they've now gotten so bad that they're causing your vehicle to lockup.

    Get them fixed, and these problems disappear entirely!