2 weeks ago, I change the plugs in my car cause it was misfiring like mad. They were toast.

well, its doin the same thing as before, misfiring like mad. I am affraid the plugs could be shot, but what could cause them to die so fast.

Wires? Coil? O2 sensor?

please help

Spark knock sensor on the fritz, sounds as if the engine is advancing to much and overheating/ frying the plugs in the process, it'll get a lot more expensive when it melts a hole in the top of your piston. That, or crappy low octane gas, did you put the cheap shit in the tank when the price went up? Fess up.............

my impreza runs fine on 87, but if I need to, I will up it to 89
its been running 87 for 2 years now, no issues at all


how expensive/difficult is it to replace the knock sensor

The timing is off. Knock sensor?

cheaper to runa diagnostic to detemine if its retarded timing makng it hot, advanced timing making is detonate or O2 allowing it to run lean. Diagnostic is usually less then a C note and  can get you really close to the prob...

When you installed the plugs, did the misfire go away?

If so, remove the spark plugs you installed and look at the terminal end of the ceramic insulator.  The terminal end is the end where the wire connects.  

Turn the plug while looking ath the ceramic portion.  Do you see any black lines runnning down the insulator?  If so these are carbon tracks which are cause by bad plug wires.  Replacing the plugs gets rid of the tracks and the car will run fine for a while until more tracks build up.

If that is the case you need to change the plugs again and the wires.

A knock sensor would not cause a misfire.

What does the electrode end of the plugs look like?

I ran my codereader/diagnostic tool doodad, the only thing it is reading is misfire in #2

need to hook up a diagnostic machine to a three wire O2 sensor and determine the Air/fuel ratio, as well as get a real time reading on the ignition timing..

Is it super or turbocharged?

If so it could be leaning out.

Quoted: 2 weeks ago, I change the plugs in my car cause it was misfiring like mad. They were toast. well, its doin the same thing as before, misfiring like mad. I am affraid the plugs could be shot, but what could cause them to die so fast. Wires? Coil? O2 sensor? please help

Hey, if you don't find the answer you're looking for here try North American Subaru Impreza Owners Club.  They've got a ton of forums...

~Dg84

Quoted: When you installed the plugs, did the misfire go away? If so, remove the spark plugs you installed and look at the terminal end of the ceramic insulator.  The terminal end is the end where the wire connects.   Turn the plug while looking ath the ceramic portion.  Do you see any black lines runnning down the insulator?  If so these are carbon tracks which are cause by bad plug wires.  Replacing the plugs gets rid of the tracks and the car will run fine for a while until more tracks build up. If that is the case you need to change the plugs again and the wires. A knock sensor would not cause a misfire. What does the electrode end of the plugs look like?

the insulators are grey and the electrode looks kinda chewed up

What do the plug electrodes look like? Melted? Clean looking [light tan] black and greasy? That'll help a lot. [2nd batch]

the car is a 2.5L NA engine

Be absolutly CERTAIN you have the correct plugs installed - always this is the first step.

Doesn't matter what you took out, they may have been the wrong ones.

Look up in the book or better yet buy a set from the dealer or at least have the dealer look up what should be in there.

If you put in a NEW set of the CORRECT plugs and still have problems then look at gas (try premium for a test, knock sensor, have timing and O2 sensor checked, fuel injection checked etc.

Quoted: Quoted: When you installed the plugs, did the misfire go away? If so, remove the spark plugs you installed and look at the terminal end of the ceramic insulator.  The terminal end is the end where the wire connects.   Turn the plug while looking ath the ceramic portion.  Do you see any black lines runnning down the insulator?  If so these are carbon tracks which are cause by bad plug wires.  Replacing the plugs gets rid of the tracks and the car will run fine for a while until more tracks build up. If that is the case you need to change the plugs again and the wires. A knock sensor would not cause a misfire. What does the electrode end of the plugs look like? the insulators are grey and the electrode looks kinda chewed up

The ground electrode is melted maybe?  Are all the plugs like that or just one?

Quoted: Quoted: Quoted: When you installed the plugs, did the misfire go away? If so, remove the spark plugs you installed and look at the terminal end of the ceramic insulator.  The terminal end is the end where the wire connects.   Turn the plug while looking ath the ceramic portion.  Do you see any black lines runnning down the insulator?  If so these are carbon tracks which are cause by bad plug wires.  Replacing the plugs gets rid of the tracks and the car will run fine for a while until more tracks build up. If that is the case you need to change the plugs again and the wires. A knock sensor would not cause a misfire. What does the electrode end of the plugs look like? the insulators are grey and the electrode looks kinda chewed up The ground electrode is melted maybe?  Are all the plugs like that or just one?

all the plugs had some damage on the electrode.  I made sure I used the right plugs and everything.  I am gonna try new plugs and wires tomorrow, cant find the antiknock sensor, I really dont wanna take it to the dealer

anyone have any idea where the knock sensor is?

any chance of us seeing a picture of a "damaged" plug?

It is important to know what the damage is.  Is it mechanical impact damage?  Or is it thermal overload damage?

If the plug tips are melted, you have a lean condition, or an advanced timing condition (which is rare since you do not have a distributer)

A knock sensor would not cause you plugs to melt.  A knock sensor detects spark knock (pinging) and retards the timing by 3 degrees.  If it detects more, it retards the timing again by 3 degrees.  It will only retard timimg a maximun of 9 degrees in 3 steps.  If this is the case you need to find the source of the spark knock, not replace the knock sensor.

If all plugs are effected, i would look at the air flow meter, or for a huge vacuum leak, ...see what the oxygen sensor is doing.

I can only describe.


the electrode is pitted

the insulator is grey

the metal around the insulator by the threads is covered with carbon

the O2 sensor reads ok, I may need to check the MAF

I will check all vaccum lines in the morning

IM inbound.

Quoted: I ran my codereader/diagnostic tool doodad, the only thing it is reading is misfire in #2

I can help you find the cause. Luckily I know these cars very well, we have a good dozen that I take care of at the shop, all types of setups from stock to insane!

What kind of scantool are you using? just curious..

Well don't worry about the scan tool, it already did it's job and the rest is up to you right now. Just follow the diagnostic below and you should be able to pinpoint the cause....


First, if #2 cylinder is misfiring at a high rate(as seen on a scan tool under misfire counts), or not firing at all, your car will run like sh*t. It would take a VERY serious problem to completely burn up a plug -in a modern car- in such a short time. You may however see fouled plugs due to flooding, oiling etc.

second, The #2 misfire code is probably due to a bad plug wire. A bad Knock Sensor would set a DTC (trouble code) of it's own. You may need to go through some typical Subaru diagnostics on the fuel injectors and PCM. Let me know if you need help with this, but before we get into that do the following:

Because you only have a misfire in one cylinder, you need to check the following first;

Spark plug  Pull the plug and re-check the gap. Eyeball it well, lok for anything unusual. Due to the design of the boxer engine it is not uncommon for a plug to get fouled with oil (or gap bridged from contact)on the way into the head. Clean, Gap to 1.0-1.1mm(.039-.043 in) and go to next step.

Spark plug wire Check the wire for a torn boot, pushed in terminal, or other signs of damage. Ohm it out with a multimeter, oddly enough the Subaru wires all have different specs. #2 wire should be between 6,200-14,500 ohms.

You should have found your problem by now, but if not you need to check the last two items;

Since you have the plug out you should probably check compression, if you have a compression guage handy check it now, if not, just replace the plug and wire if they were good and go to the next step; nomally you won't have to go this far anyway, so no sweat if you can't check it now. Compression should be 160-180 PSI, unplug  the connector at the DIS coils on top of motor and #2 injector connector before cranking. Open throttle fully and crank with strong battery.

Fuel Injector There are a number of very complicated tests for this, but to make it simple just do the following;
Replace the plug and wire and start the motor. **Pull the electrical connector off the #2 terminal and see if the motor stays the same or starts to run a little rougher.
**This is best done with a partner(ONLY if it's an automatic trans), have your partner set the parking brake and hold the regular brake down and put vehicle in drive while you unplug the electrical terminal at the #2 injector.

If it runs rougher AFTER disconnectig the terminal, your injector is working fine, replace terminal and CHECK COMPRESSION on #2 cylinder; if it runs the same, you have to do some more tests because your injector is not firing. Unfortunately I can't go into it any further due to the time, I have to get up at 5:30am every day for work.

Good luck, and let us know what you find.

My 2000 RS had very similar problems, although it was hard to diagnose because I had some pretty aggressive cams in.  

My problem was wires - check the wires, and the posts on the coil.  I not only had bad plugs, but I also had a scored post.

Any luck with the car? Sent an IM yesterday.