What Causes My Car Engine to Misfire?

causes of engine missMy car just had a transmission put in it and the guys that are working on it said it is misfiring now. What does it mean when a car misfires? Do you know what could be wrong with it?


Hi Nicky

Misfire means – the engine is missing…not running on all cylinders – running rough – hesitating etc. Usually something like the need for a tune up, spark plugs or spark plug wires  or ignition coil are the culprit of misfiring.

Of course there is always the possibility of them accidentally pulling a spark plug wire off or something like that while they were removing and installing the transmission.  If this happened immediately after the transmission repair I would bet they did something or unplugged something to cause this problem and would go back and see them for further inspection.

Most cars have lots of sensors and rubber vacuum hoses on them too, and any of them that get accidentally unplugged or wires or hoses cut…will usually turn on the check engine light as well as produce an engine missfire or running bad complaint.

In the case of a vacuum hose unplugged, with the engine running and hood up listen for a slight hissing noise caused by the hose being unplugged from its vacuum source. Typical areas are around the air cleaner box and the top of the engine around the throttle body.

So start with the easy stuff, look for anything unplugged or out of place first.

Please share this with your friends,
Austin C. Davis

Posted in: Running Problems

25 Comments on "What Causes My Car Engine to Misfire?"

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  1. curtisa says:

    my car started shuddering and looked at the plugs once had a crack in it so i replaced them…..it seemed to be ok then within a few hours it happened again need my car urgently, i was think MAF sensor but cant seem to find it on an X reg focus lol

    • Austin Davis says:

      Problem is, it can be just about anything…spark plug wire, ignition coil or ignition module, vacuum leak etc. etc. I would spend the $100 and get a mechanic to diagnose it for you then you can make the repair yourself if you can. Guessing just costs so much more and I would be guessing at this point without more information.

  2. edwin says:

    Chevy yahoo when I put my foot on the paddle it lose power

    • Austin Davis says:

      When you step on the gas pedal it looses power??? if so, I would check fuel pressure AT the engine with a manual handheld gauge you can rent from your local auto parts store. Could be a fault fuel pump. An engine miss due to bad spark plug wires can also cause this to happen on heavy loads where you mash hard on the gas pedal, and you usually can hear a popping or sputtering noise under the hood.

  3. Manny G. says:

    I had replaced my spark plugs and plug wires not to long ago and the engine started to miss the other day. I looked at everything EXCEPT those new plug wires since I new I had replaced them not long ago. One of the wires got burnt on the exhaust manifold and shorted out. I spent 2 hours checking other things first. Darn it.

    • By Austin Davis says:

      Yep, its a real good idea to start with the basic items first no matter how “new” they are. Spark plug wires do NOT like to get hot, use a heat shield or valve cover spark plug spacer to keep them away from the hot engine parts.

      Do not wrap them in aluminum foil though, sounds good but can cause interference on computer controlled cars.

  4. Danny says:

    Many cars these days do not have a distributor or a distributor cap and ignition rotor but those items are notorious for causing engine misses.

  5. aj says:

    if it’s a misfire then i suggest you check the cheapest to replace first! first thing is first get a scanner (OBD) make sure it is a misfire! then you work your way to spark plugs, coil and last one which can ruin everything is water on gas! that i’m not sure how to deal with if thats the case i suggest not running the car at all!

  6. tarra says:

    hello, i recently bought a 98 ford taurus and it wont pass smog. i bought new spark plugs, wires and coil pack. i also replaced the water pump because of a leak. i found out the person who i bought the car from had the wires in the wrong place and when they got fixed my car started running great. but still wont pass smog. they said there is a misfire still. i dont have the money to take it to the shop. i had a compression test done and some of my cylinders are low i guess. and i also did a diagnostic test and they dont know why its misfiring. what should i do???

    • Austin says:

      I would really need to check this out in person to be able to be certain what is and is not happening here. I would suspect that there is a problem in the cylinder heads and removing the cylinder heads and doing a valve job is probably what it will require. if compression is low, there is internal wear/damage to the engine that has to be repaired. Removing the top part of the engine (the cylinder heads) for inspection would be the next step. if you do not see or suspect any damage to the cylinders or pistons themselves I would send the cylinder heads to a machine shop for a complete valve job and resurface. This is going to be pricey, say $1500, so make sure you have ruled out everything else.

  7. mark says:

    water in the gas is something that needs to be eliminated before you start spending money on other things. A small rust hole in the top of the tank or in the filler tube can be the culprit or gas bought from a station with deteriorated tanks.

  8. Mirza S. Baig says:

    My Father is using Cadillac Deville of 1997 here in Riyadh, Saudi Arabia. It was not being used regularly as its display started giving problem since it was stuck in rain some time back. He changed the display once after that and re-programmed but then again when it went for a car wash after which the display went off again. I wanted to know what could be the reason or how to check for the problem as most of the things in this car is electrical so i feel it is complicated at the same time for the mechanics over here as its difficult to find professionals outside the showroom in this country.

    Now coming to the second part, as it was not being used regularly the engine was not starting to which the mechanic checked and changed the spark plugs. Alhamdulillah after that the engine started but with misfiring. As i have read the above comment I understand the things to be checked and Inshallah I will ask my mechanic to do the same. Is it because of not using the car regularly, resulted into this problem of misfiring as the engine was in perfect condition inspite of the display problem.

    Your help will be of great importance to us.

    Mirza S. Baig Tareq

    • Austin says:

      I have seen some issues with the Body Control Module on these vehicles give similar issues but have not experienced the exact problem you are having. These are complex vehicles with many sensors and computers etc. and a Cadillac dealership might be the only mechanics that are trained to diagnose and repair it in your area. Many mechanic in the U.S. would have trouble diagnosing the electronic display system on this vehicle. 🙁

  9. Dominic says:

    Hello all. Im interested in buying a 1995 red Pontiac firebird v6 automatic. Car has 121K on it the car looks great and the guy says it was well maintained. Here is what he posted.Car has new flow masters exhaust, engine knocks, only one code reads: multiple misfires. body in ok condition, complete tune up was recently done, coil packs replaced, drives like a beast, tranny in tact condition. He wants 1000 for it but will take $800 is this a good deal? Also he changed all o fthese things and yet engine still misfires is this an expensive fix???

    • Austin says:

      I have one question to ask you, how many 1995 Firebirds do you see on the road today? Not many, for a reason. If you are buying this vehicle just because of the cheap price (and/or you might like red firebirds) you should consider buying another vehicle with less known issues. I would not buy anything that has a knocking engine….unless I was prepared to replace the engine. So, as the worst case scenario, you will need to replace the engine. A USED engine will cost you about $1,500+++ so are you prepared to spend that kind of money? If you are dead set on buying this vehicle, be prepared for the worst. You can have a compression test done to see if the engine has internal problems causing the knock noise. Honestly, I would pass on this.

  10. Larry says:

    My 2002 Toyota Camry is missing fire I did a diagnostic on it and it said missing fire, I also took it to a certified shop and they confirmed that it was, I already got a full tune up now what else can I do please help

    • Austin says:

      If you already got a tune up including new spark plug wires, you might want to get a compression test to rule out internal engine damage like a valve problem. An ignition coil, clogged fuel injector or vacuum leak could also cause an engine missfire.

  11. Dan says:

    Hi Austin. He done the compression test and theres only a 10 psi difference. Its been in the shop for a month and a half and really starting to get me aggrivated.

  12. Dan says:

    i have a misfire on cylinder 4 of my 2001 buick century. The mechanic changes the plugs and wires, tested the ignition coils, mass air sensor, the injectors, the fuel pressure regulator, and compression which were all good. However, the problem is still there. What else would cause the misfire? Any information as to what i can do to fix it would be greatly appreciated

    • Austin says:

      I know you said you tested the coil, but lets really rule out the possibility of a bad coil. Swap that coil out with one of the others and see if the misfire follows it. I would also be highly suspect of a mechanic issue, like a valve problem so make sure you do a compression test on the other cylinders as well. There should not be much more than a 20PSI difference between them.

  13. eb says:

    The first answer is right. Looks like the mechanics at your shop didn’t know this was the main cause of your engine problems, and decided to charge you for a new transmission instead of fixing the real problem, which was the misfiring. I’ve been to a couple of mechanics who have told me it’s the transmission, but when in fact it’s misfiring. These two have similar effects, the car becomes too hesitant and one would think it’s the automatic transmission. Next time run the code first before changing anything.

  14. Matt S says:

    Check your cylinder compression.

  15. Tracie Garrett says:

    I typed my question up in the box provided~clicked submit an then I was rerouted to another website about insurance. Do I ask my question here?
    I have a 06 Taurus and it currently has a 1,2,&3 misfire. The spark plugs have been replaced, plug wires and the coil pack. Problem is consistent, what else is there to look for?

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