P1399 - random/multiple cylinder misfire detected
P0301 - cylinder 1 misfire detected
P0302 - cylinder 2 misfire detected
P0303 - cylinder 3 misfire detected
P0304 - cylinder 4 misfire detected
What the hell should you do now? Well, you aren't alone. Many owners are starting to get these misfire codes as the cars get older. Here are some possible causes and some solutions you can try. NOTE: after each of these clear the CEL code by following the instructions HERE to see if the CEL will come back or if you have found your solution. (MY00-05 ONLY...there is a different CEL clearing process for MY06+, using the earlier car reset procedure can ruin an MY06+ ECU)
1) Bad gasoline has gotten more common recently. This can cause the misfire codes. It can also make the car drive like crap. You can buy some HEET or Seafoam to put in your gas tank. That can help dry out water contamination. If it is some other contamination, like diesel fuel, then you will need to drain the fuel and put in fresh. This can be done by disconnecting the fuel line in the engine bay and running the fuel pump to empty the tank into a container for appropriate disposal (don't harm the environment guys).
Clear the code with the next tank of fuel. If it returns, move on to step 2.
Another type of bad gasoline can come from the car sitting for an extended period of time (more than 6mo) without fuel stabilizer. If the gasoline degrades, the resins can clog the fuel filter or fuel pump. If you car has the misfire and has sat without stabilizer you may need to check the fuel pressure. If it is low, then pull the fuel pump and check the fuel filter (it is more like a sock than a filter, but it does the job).
2) There has been one owner who reported that replacing his throttle position sensor (TPS) fixed the misfire codes. Checking the voltage is pretty easy and may spot your problem right off. The voltage reading should be in the vicinity of .30 volts at idle and in the vicinity of 4.5 volts at WOT. It should also smoothly increase from .3 to 4.5 as you slowly open the throttle...if it jumps to near zero or hops wildly, it may have a bad spot. If the TPS is bad, there are a couple choices since Honda does not sell the TPS individually. You can replace the entire throttle body or modify a generic TPS to work for the S2k. There are instructions HERE on how to do that.
Another has said his MAP caused the misfire codes. That may be the case, but I've seen several bad MAPs and I've never seen the misfire codes happen strictly because of the map. But it may be possible. You can always try the MAP whack (see the DIY sticky) or replace it with the newer zip tie style.
3) One owner has reported that a bad knock sensor caused the misfire code. So in reality there was no misfire.
The knock sensor is basically a microphone listening for sounds of detonation or pinging. If the knock sensor is loose it can rattle and cause a false misfire code. If you've recently done a clutch job an you suddenly get a misfire, there is a good chance the knock sensor is loose. Some may remove the knock sensor to get it out of the way of the tools needed to remove one of the bolts for the transmission. Then it's possible to forget to tighten it on reassembly.
A bad knock sensor generally throws it's own code (P0324-P0334), so if you aren't getting the knock sensor code then it's a gamble to replace it. The knock sensor is about $113 for MY00-05 cars and $55 for MY06+ cars from Majestic Honda.
Personally, if you're not getting the knock sensor code...I would check to see if it is loose and move on down this list. Come back to the knock sensor again if all the other components check out. The other items on this check list are more likely to be causing the misfire than the knock sensor.
4) Check that the alternator is putting out the proper amps, especially at idle. If the amps are too low, the coils will not fire properly and that can cause a misfire. With a load on the alternator where the voltage is between 12-13.5V, the amperage should be 87.5A or above.
If the misfire started after installing a ton of stereo equipment and you see the amperage is low, you may have overloaded the alternator's capacity. Pull the plug on some of your amps and try the test again.
Otherwise, you may need to replace the alternator.
5) Old spark plugs can give the misfire code. I recommend you use OEM NGK Laser Platinum PFR7G-11S. They are available at the dealer or at NAPA (PN 7772).
While the plugs are out also do step 4.
6) Do a compression test. The misfire code can be caused by a bent valve(s), cracked retainers or even valves needing adjustment. And possibly from a bad head gasket.
If you find an issue with compression, try adjusting the valve lash and retest. Adjusting the valves may also show you right off that you have a cracked retainer letting the valve begin to drop.
If you still have low compression, have a leak down test done to identify exactly what is causing the compression loss (rings or valves).
A valve can be bent by a mild over rev. Even an over rev that happened a long time ago can lead to a valve bending much later as the cracked retainer allows the valve to drop lower into the combustion chamber.
If the head gasket is the issue, you may only notice the misfire when the engine is cold. Once warm, the gasket/head/block expand sealing the gap.
Unfortunately, fixing any serious compression loss is going to be a bit expensive.
If the compression is ok, reset the CEL and see if it returns before moving to step 4.
7) Coil Packs. Hopefully, not all of the cylinders are showing a misfire. If you have one or more good cylinders, swap the coil pack from the good cyl and put in on a misfire cyl. Clear the CEL and see if it comes back. If it is the coil pack that is bad, then the misfire code should have moved to the cyl that was not having a misfire before and vis versa. Buy the new coil packs you need. Note that if one coil pack has already gone, the others will go soon. If you are on a budget, buy what you need and start saving for the rest.
If you have a misfire on all 4 cylinders you have your choice of replacing them all and hoping that is the problem OR finding a local s2k owner willing to swap coil packs for a day to see if the misfire clears up. If you can't find someone to trade coil packs with, then you have an expensive gamble...either the coil packs or the injectors are bad and there really isn't a good way to tell unless you replace one or the other.
Ignition Coil packs run about $90 each from Majestic Honda.
8) Injectors. If you've done everything else and you still have the CEL coming back after clearing, then the only thing left is injectors. You can try to have them cleaned (normal charge is about $20 per injector) to see if that clears up the misfire. However, those who I know that have tried this have found that cleaning is only a temporary fix. Replacing the injectors is the best solution.
Injectors run about $100 each from Majestic Honda (the part shows on the "intake manifold")
Installing injectors is not hard if you are at least an average mechanic, but there are a couple of tricks. I'll try to make some instructions and link them to this post.
If after all this and you still have a misfire, post up in this thread. You may have to take the car to a dealer to have them figure out the cause. But when you do find out, post up the solution and I'll add it to help other owners in the future.
I hope this helps...I know we have had at least 3 owners this week alone post up that they were getting the dreaded misfire. BTW...I've had the misfire too...twice. Once for injectors (at the time that was thought to be the primary culprit) and then again for coil packs. So yes...there can be multiple reasons for the misfire.
(last updated: 9/4/09)
This post has been edited by negcamber: 04 September 2009 - 09:25 PM