I have a misfire in Cyl. 3 (P0303) and it won't go away. I have replaced the plugs, wires, coil, and the intake pressure switch. And I still have a bad miss that throws the car into limp mode. I can rev the car up and it doesn't seem to miss as bad. But at idle it's and below 3000 rpm really rough. Now it won't start as crisp as it used to. It kind of hesitates now as if the battery is low but it's not. Can anyone point me in another direction. A cheap direction would be great!

 

Try a concentrated fuel injector cleaner like Techron 1 bottle in 1/4 tank of gas. Look at the new spark plugs and see any signs of rich / lean / carbon buil-up.
Can you also check hoses for any vacuum leak. My BMW was acting like that when one of the hose going to intake cracked.

 

Not to get ya into worry mode....but I have seen a very minor cracked/broken head gasket do this too. Piece broken can stay hot enough to re-ignite unburnt gasses causing a misfire.

 

Well I've ruled out a plug, wire, and coil. When I first put these new plugs in the car it blackened 1,2,4 really bad and 3 was wet with fuel. And with the car running I had pull # 3 spark wire off and it sparks but doesn't change the way the car is running (or missing I should say) And all the others being pulled one at a time makes the car miss even worse. So with this being done it really seems like my problem is with cyl 3. It's weird because when I first start it it's before limp mode kicks in and it revs quick and above 3000 rpm it doesn't seem to miss. But under 3000 rpm it misses or when limp mode kicks in it misses. I checked hoses today but none seemed broken or cracked. And I ran injector cleaner in it and nothing changed. Will a misfire make it not start as good as it used to? It's dragging now with a full charged battery. As far as a head gasket what do I need to look for. Will that cause any other issues or signs?

 

If you had a vac leak it would probably effect all cylinders.

Wet plug in cylinder #3 may be a hint towards a solution. A bad injector ( maybe stuck open) would be dumping too much fuel in at low idle but as air pressure/flow increases would even out. Does your misfire go away and RPM's smooth out at WOT ?

To test maybe replace #3 injector with a used good one or try swapping them around and see if the misfire follows that suspect injector.

* also. If this ends up being the solution, replace ALL the o-rings for your injectors....it's about 35 bucks but well worth it since you are already there.

 

Overrev it?!
I would take the head off, check the headgasket, but i suspect the issue might be in the valvetrain...
A compression check before you do much would help...a bent/burnt valve, broken piston ring, etc would all show up...

 

"Dragging" when cranking i think indicates a possible valve issue...

 

Can these car's swim? lol Can someone point me in the right direction of removing the intercooler and replacing the injectors. Also do I have 360's in it now being stock and what do I need to move up to. With a 15% pulley, 2% crank, header, exhaust, MSD wires, MSD coil, Cold air intake, K&N filter, JCW chip, black racing stripes. (Those stripes alone add 0.003 HP to the wheels) And for someone that has minor mechanic skills would I be able to do an injector change out job? ZippyNH might be right and with my luck he probably is but I want to try something cheaper first. So someone point me in the right direction on the right size injectors and if ebay is a good source and a intercooler removal and a change out of the injectors. Thanks so much everyone...

 

Have you done a compression check?
Burned valves on #3 could definitely cause a misfire.

I’m voting for a bad injector, much easer/cheaper.

ab

 

check the compression first in my opinion it would give u some piece of mind knowing that it isnt an internal issue....you can get a compression tester at autozone for cheap too

 

Fix the problem, rather than just trying to mask it....
You could try moving the #3 injectotor to a different spot...and seeing if the misfire follows...very smart troubleshooting.
E-bay injectors are almost always redrilled, even when they claim they are lazer drilled blank, etc....tue oem uses a dual cone spray pattern...redrilling or non factory drilling results in a single cone. There are some good injectors around for less than the cost of jcw for less money, but not needed for less than 200hp in most cases..also a custom tune is needed when running injectors beyond the jcw 380's....heck YOU WILL LOOSE HP WITH THE 380'S NO TUNE WITH A 15%....JUST TOO RICH....ok with a 17% though...
Adding a pulley to a car with a misfire..might convert the misfire to full nlown detonation...BANG!! new motor. Detonation is the spontaneous explosion of the fuel in the entire chamber, as opposed to ping or pre-ignation, which is when combustion begins in one location....ping is not good, robs power, but short term is ok...detonation...well, a few monents, and it DESTROYS a motor.

 

Having the 15+2 you have the eqivilent of a 17.
The stock 340's should be fine at most rpms...
Taking off the stock ic is easy...two torix bolts....and slip the rubber coupler off...they tend to get stiff with age and leak...new ones cost about $50-75 stock...injectors are behind there...remove the fuel psi...a valve is on the end of the fuel rail...kinda like a tire...relieve the psi, catch the fuel, then get to work...get new orings...you will tear them pulling out the current ones, even just to swap a pair.....many folks sell the used one when upgrading cheap...they are tan as opposed to having a bit of blue when you see the pics(jce 380's were introduced in 2005, so if someone says tan 340's came off a jcw car, pre 2005, they are not liying).

 

ZippyNH, Thanks for the post. I'm gonna check the compression as soon as I get my deep extension rod in. I borrowed a compression kit but he didn't have the deep well part so I ordered one. I hope all is good in this area. What ever the turn out is I'm gonna fix it right and look for a stock MCS and trade. I love my car now but it seems to break something every time I get in the throttle. I've put alot of money into this car and I just need to stop with the obsession of making it faster. It's way to small to live in it. If it had a valve down would it miss at any RPM? I can rev this car to 3000 RPM and the miss goes away and it runs smooth as silk. But misses at a idle and low RPM. I can clear the CE light and start it and never touch the peddle and it will miss and then the check engine light will come on and blink. P0303 And the car will then be in limp mode. Yesterday I pulled the plugs after running it and #3 was dry and clean and the other 3 were blackened. But at the tip of the screw in part appeared to have gotten hot and discolored some. Anyway I will repost after the compression check. Thanks to everyone for your help.

 

im working on a very similar issue, I took the head off and sent it to RMW I am waiting to here the news. My plug on the number 3 was a little wet and I found Irontite on the map sensor I am guessing that the head is cracked somewhere for that to happen
one thing at a time for sure!

 

Something to check also would be your crank damper, weird things started happening with my Mini when it started to go.

 

Jcw , what kind of symptoms?

 

Limp mode, overheating, codes

 

misfire codes? lol I have 2 out of 3 that you mention. how did you find it was the tensioner.

 

Cant remember the code I was getting but it was the Harmonic damper(crank pulley) that was going and went shortly after. The ATI damper is a great replacement and Summit racing has the best price I have seen.