P0305 - Cylinder 5 misfire.

[Mudderoy]

The check engine light came on a few months back. I checked the problem and it was a P0305, cylinder 5 misfire. I cleared it (or it cleared itself) and had not come back until recently.

The check engine light came on about a week ago when I was getting on the throttle hard, and making a turn. It stayed on about a day and went off by itself.

A day went by and it came on again, this time I checked it before it cleared.

It was the P0305 code. I cleared it and about a day later it came back.

On the way home (again during lots of skinney petal) not only was the "check engine" light on, it was flashing! I inavertaly found out that this means the misfire is really bad. It flashed about 5 times and stopped, remaining solid.

Yesterday nothing new, just your plain everyday "check engine" light.

The thing I find very strange is I have not noticed any ill effects of this misfire. No hard starts, no miss fires, no hesitation, she just blows and goes like normal.

I've read the various things that can cause this problem, but the more I think about it the more it seems to be an erroneous error. How does the computer even know when a misfire has occurred?

I was thinking about checking fuel pressure, cylinder compression, etc... but I thought I'd post here before I started buying test equipment.

Originally Posted by Mudderoy

The check engine light came on a few months back. I checked the problem and it was a P0305, cylinder 5 misfire. I cleared it (or it cleared itself) and had not come back until recently.

The check engine light came on about a week ago when I was getting on the throttle hard, and making a turn. It stayed on about a day and went off by itself.

A day went by and it came on again, this time I checked it before it cleared.

It was the P0305 code. I cleared it and about a day later it came back.

On the way home (again during lots of skinney petal) not only was the "check engine" light on, it was flashing! I inavertaly found out that this means the misfire is really bad. It flashed about 5 times and stopped, remaining solid.

Yesterday nothing new, just your plain everyday "check engine" light.

The thing I find very strange is I have not noticed any ill effects of this misfire. No hard starts, no miss fires, no hesitation, she just blows and goes like normal.

I've read the various things that can cause this problem, but the more I think about it the more it seems to be an erroneous error. How does the computer even know when a misfire has occurred?

I was thinking about checking fuel pressure, cylinder compression, etc... but I thought I'd post here before I started buying test equipment.

Maybe a bad plug wire?

[Mudderoy]

I'll check. I'd still like to know how the computer knows there was a mis-fire. Also I need to see how the number is done on the 4.0L. I'm assuming #5 is the next to the last cylinder counting from front to back.

Anyone have any recommendations on plug wires?

[xj4life2]

Originally Posted by Mudderoy

I'll check. I'd still like to know how the computer knows there was a mis-fire. Also I need to see how the number is done on the 4.0L. I'm assuming #5 is the next to the last cylinder counting from front to back.

Anyone have any recommendations on plug wires?

You are correct in your counting #1 is the one closest to the radiator and six would be closest to the firewall. Seeing how the light comes on and off its concidered a soft fault. Although its good to replace you wires on a regular basis as they do build up resistance over time, spark plugs , cap , rotor/ wires can all cause what you have and thier are some others to. I would not really worry about it unless it comes on and stays on. I would just keep an eye on it. If it needs a tune up though now would be the time to do it.Almost forgot the misfire is regestered by the crank sensor. A misfire causes the crank to change speeds the sensor see's that and tells the ECM and the light comes on.

[Mudderoy]

Originally Posted by Payless 4x

You are correct in your counting #1 is the one closest to the radiator and six would be closest to the firewall. Seeing how the light comes on and off its concidered a soft fault. Although its good to replace you wires on a regular basis as they do build up resistance over time, spark plugs , cap , rotor/ wires can all cause what you have and thier are some others to. I would not really worry about it unless it comes on and stays on. I would just keep an eye on it. If it needs a tune up though now would be the time to do it.Almost forgot the misfire is regestered by the crank sensor. A misfire causes the crank to change speeds the sensor see's that and tells the ECM and the light comes on.

The norm is for the "check engine" light to stay on. The unusual was to see it blink. It is on solid. Thanks, CPS that makes sense. I guess it would be highly unlikely for the CPS to cause this error. I mean I would assume that a faulty CPS would create mis-fire readings from cylinder 1 to 6.

I ask because the CPS was changed about 6 months ago.

Originally Posted by Payless 4x

You are correct in your counting #1 is the one closest to the radiator and six would be closest to the firewall. Seeing how the light comes on and off its concidered a soft fault. Although its good to replace you wires on a regular basis as they do build up resistance over time, spark plugs , cap , rotor/ wires can all cause what you have and thier are some others to. I would not really worry about it unless it comes on and stays on. I would just keep an eye on it. If it needs a tune up though now would be the time to do it.Almost forgot the misfire is regestered by the crank sensor. A misfire causes the crank to change speeds the sensor see's that and tells the ECM and the light comes on.

Yea there are a thousand diffrent wires out there. I have been something diffrent, and i think it works. Any where that my wires are touching each other or touching anything around them I put some of that plastic sleeve over that area of plug wire and I use the little black plastic ties one on each end to hold it in place...

[BlueXJ]

Try Taylor wires. Mine came from a local speed shop but are available in plenty of places. I picked them because they have a moulded in 90* grip and I needed that since my lift and my personal height made it difficult to reach the 5 & 6 plug wires to remove them when putting in new Champions.

[Mudderoy]

Left the office and got into the Jeep. Cranked it up, "check engine" light is off.

[MrJCRod]

since you have a single cylinder misfire it shouldn't be too hard to figure out... again, I hate guessing and replacing parts without knowing for sure what it is. In your case, you can do a full tune up and it may solve it but if the light comes back on you may have wasted money replacing good parts.

So if it were mine and the light came on regularly I would start by swapping 2 spark plug wires (cylinder 5 and any other cylinder) and see if the misfire jumps to a different cylinder. If it doesn't, then I would swap an injector and check it again. I would swap whatever I can from cylinder 5 one at a time to see if the misfire moves and if it doesn't it can possibly be in the distributor cap or possibly a problem with the actual cylinder itself (although highly unlikely). Low compression can cause your misfire but hopefully it's either fuel (fuel injector) or ignition (plug, wire or distributor cap). Good luck with it and keep us posted...

[Mudderoy]

Originally Posted by MrJCRod

since you have a single cylinder misfire it shouldn't be too hard to figure out... again, I hate guessing and replacing parts without knowing for sure what it is. In your case, you can do a full tune up and it may solve it but if the light comes back on you may have wasted money replacing good parts.

So if it were mine and the light came on regularly I would start by swapping 2 spark plug wires (cylinder 5 and any other cylinder) and see if the misfire jumps to a different cylinder. If it doesn't, then I would swap an injector and check it again. I would swap whatever I can from cylinder 5 one at a time to see if the misfire moves and if it doesn't it can possibly be in the distributor cap or possibly a problem with the actual cylinder itself (although highly unlikely). Low compression can cause your misfire but hopefully it's either fuel (fuel injector) or ignition (plug, wire or distributor cap). Good luck with it and keep us posted...

Duh! Same basic testing I do with computers. I should have thought of that. Thanks, excellent advice.

[YellowSub2000]

Coincidently my Civic had the same problem this morning. Started a while back when I noticed my engine would spuder when I took my foot off the gas to slow down. Didn't know what it was then. Yesterday it starting running like crap, accelerating, idling, whatever. I checked the plugs and wires, and notice the resistance on a wire was higher than the others. Knowing the wires were still under warranty (Thank you Advanced!), I drove the car over. That's when it kicked the code, luckly I had my reader in the car. Misfire Cylinder 3 + 4.

Replaced the wires, now all is fine. No longer spuders when I let my foot off the gas pedal either.

[Mudderoy]

Originally Posted by YellowSub2000

Coincidently my Civic had the same problem this morning. Started a while back when I noticed my engine would spuder when I took my foot off the gas to slow down. Didn't know what it was then. Yesterday it starting running like crap, accelerating, idling, whatever. I checked the plugs and wires, and notice the resistance on a wire was higher than the others. Knowing the wires were still under warranty (Thank you Advanced!), I drove the car over. That's when it kicked the code, luckly I had my reader in the car. Misfire Cylinder 3 + 4.

Replaced the wires, now all is fine. No longer spuders when I let my foot off the gas pedal either.

I went about 85k miles before the engine started running ruff, no codes mind you. I replaced the original factory spark plugs and everything ran fine again. If I remember correctly, it was during high rpms that I noticed the problem.

Anyway to try and help the mpg issue much later. I replaced plugs, plug wires, cap, rotor. I bought a new coil but I never put it on. Since then I've replaced the plugs, cap and rotor, maybe a year ago. So a new set of plug wires couldn't hurt.