How Do I Fix a Misfire?

[hayleys_c0met]

A couple days ago I bought a 2002 Jeep Liberty and it's misfiring. I haven't had my license long and this is only the second car I've ever driven so I don't hear anything wrong with the engine, and nothing feels wrong. A few times though I was driving and it lurched. The only way to describe it is that it felt like a sudden drop on a rollercoaster. It scared the daylights outta me. The check engine light wasn't on right after first, but now it alternates between a steady light on and a blinking light. I took it to Autozone and they plugged a little computer thing in and it said there's a misfire in Cylinder 4. A bunch of other stuff came up too- like the torque converter, speed censor, and ABS sensor- could that be from the misfire? I know absolutely nothing about cars let alone Jeeps. My boyfriend has been training at a garage and has been doing what he can with the help of my grandfather, but I'm really worried I got in way over my head. So far we replaced the coil in the 4th cylinder and the spark plug that went with it. It looked like a rubber ring was missing off of the old coil and the spark plug was wet with water and I think they said maybe anti-freeze. I had the engine, transmission, fuel lines, and power steering all flushed out when I had the oil changed the morning after I bought the Jeep too, along with replacing the battery. The engine light is still on, but for the couple miles I drove it home from my grandfather's after changing the coil and plug it felt a little more stable if that makes sense. My hood latch is locked, but doesn't stay completely down- could this also be a factor? If what I did so far ends up not being the solution to the problem then what should my next step be? Thank you in advance for any help and guidance you can give! It's much appreciated!

 

[streetglideok]

How many warning lights are staying on when you drive? Just the engine light, or does the ABS light stay on as well? If the ABS light isn't on while you drive, then the ABS code(s) may not be current issues and may not be an issue at all. Torque converter code could indicate a problem looming in the transmission. Was the engine light on when you bought it? You said a speed sensor, vehicle speed sensor, input speed sensor, or output speed sensor? The codes would need to be erased in order to really see if they return or not. They won't clear themselves out anytime soon.

As for your actual question, fixing the misfire. There are a few things that can set a misfire. When a gasoline engine runs, it needs fuel supplied to the engine, it needs fuel sprayed in a mist like a perfume bottle into the engine, it needs to squeeze air and fuel in the cylinder at high pressure, and finally it needs spark to ignite it all and make power. A misfire means that cylinder didn't make power when it was supposed to ignite all of that stuff. So, you're either missing spark, fuel to the engine, fuel being sprayed, or pressure(compression). You have already done a spark plug and coil which are what creates a spark and ignites the fuel. So, is there enough fuel reaching the engine(fuel pressure), and does the injector on #4 work correctly? How is the compression on #4 compared to other cylinders? If there is suspicion of coolant in the cylinder, then it might be wise to perform what is called a "block test". The shop your b/f is working at should be able to guide him in how to do it.

One thing to advise you and warn you, since you're young and learning. Whenever you buy a used vehicle, always, always take it to a reputable shop and spend the $60-$120 to let them look the thing over and tell you the condition it is in. I have seen far too many people, mostly younger people like yourself, learn the hard way and fork over a lot of money on a lemon they bought. While I like making money fixing cars just as much as the next guy, I hate telling that new owner that it's going to cost $3k to fix their vehicle, and had they came to me before buying it, I could have saved them a lot of heartache.

 

[hayleys_c0met]

How many warning lights are staying on when you drive? Just the engine light, or does the ABS light stay on as well? If the ABS light isn't on while you drive, then the ABS code(s) may not be current issues and may not be an issue at all. Torque converter code could indicate a problem looming in the transmission. Was the engine light on when you bought it? You said a speed sensor, vehicle speed sensor, input speed sensor, or output speed sensor? The codes would need to be erased in order to really see if they return or not. They won't clear themselves out anytime soon.

As for your actual question, fixing the misfire. There are a few things that can set a misfire. When a gasoline engine runs, it needs fuel supplied to the engine, it needs fuel sprayed in a mist like a perfume bottle into the engine, it needs to squeeze air and fuel in the cylinder at high pressure, and finally it needs spark to ignite it all and make power. A misfire means that cylinder didn't make power when it was supposed to ignite all of that stuff. So, you're either missing spark, fuel to the engine, fuel being sprayed, or pressure(compression). You have already done a spark plug and coil which are what creates a spark and ignites the fuel. So, is there enough fuel reaching the engine(fuel pressure), and does the injector on #4 work correctly? How is the compression on #4 compared to other cylinders? If there is suspicion of coolant in the cylinder, then it might be wise to perform what is called a "block test". The shop your b/f is working at should be able to guide him in how to do it.

One thing to advise you and warn you, since you're young and learning. Whenever you buy a used vehicle, always, always take it to a reputable shop and spend the $60-$120 to let them look the thing over and tell you the condition it is in. I have seen far too many people, mostly younger people like yourself, learn the hard way and fork over a lot of money on a lemon they bought. While I like making money fixing cars just as much as the next guy, I hate telling that new owner that it's going to cost $3k to fix their vehicle, and had they came to me before buying it, I could have saved them a lot of heartache.

I just got back from driving around town a little and the ride was so much smoother. Before it felt jumpy, like a train chugging along and that's gone now. The check engine light is gone as well so I have my fingers crossed that I found the solution.
The ABS light and brake light with an exclamation in a triangle come on and off. As of just getting out of my car and coming home though it was off. I had know idea there were so many different sensors just regarding speed. I'm completely lost as to which one was popping up. I do know though, that it was for the back right and the ABS was showing the front left.
When I bought the car I was told by the mechanic that it probably needed a new computer, and I waited three weeks for him to look at it, but he "never got to it". The check engine light was off and I figured I could just have one of my car savvy relatives work on it. I thought that no light meant it was good to go. As you mentioned though that wasn't the best idea.
I know that the head gasket was recently replaced. Could the possible coolant be from that and having someone do a ****** job on that or should I still try that block test? Are there any tests like the block test that I would be able to do in order to check the fuel injector, and other stuff you mentioned?
As for the torque converter you said that's in the transmission, and as I understand it- those are hard to get into and expensive to fix so should I make sure that it gets looked at ASAP too? Or is it a lower priority that I could fix later on after I get the misfire taken care of?

 

[TheZombieNinja3]

Hi there Hayley. I see you are from the Hudson Valley, I myself am in the Hudson Valley and was wondering where you were? If you are close to where I am I know to very good mechanics right in my town. One is a family friend who has worked on my family's cars as long as I can remember, and I trust him fully. The other guy's daughter and I went to school together and my family has known him for a while. He is also a Jeep specialist. So depending where you are I can recommend reputable mechanics in the area to help. Also, Welcome to the forum!

 

[hayleys_c0met]

I live in the Wappingers area which is about an hour from Ellenville I believe. I'd rather stick closer to my neck of the woods so in case anything happens I don't get stuck having to tow it too far. I appreciate it though, and if I need any more help I'll gladly give either of the two mechanics you suggest a try.

 

[TheZombieNinja3]

Understandable, I hope everything works out!

 

[hayleys_c0met]

UPDATE! A brought my Jeep into my boyfriend's shop to get it inspected, plus make sure the misfire was fixed properly. I passed inspection- and they even fixed my hood so it closes the right way. Turns out that while the coil and spark plug needed to be replaced, those weren't the immediate cause of the misfire. Engine coolant found a way to leak from the hose (not through a hole either). We fixed the hose and now no more problems on that end. Going back tomorrow to fix the ABS sensors (I guess one is a normal and another is a speed related), and to see if the torque converter still pops up on the computer. Fingers crossed for more good news! So glad things are starting to look up. Thank you to everyone that's given me help and advice!

 

[TheZombieNinja3]

Glad to hear it wasn't a super expensive fix! Hope you get more good news