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Guest Message by DevFuse

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cracked spark plug

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10 replies to this topic

#1 teasdam


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Posted 01 June 2004 - 11:01 AM

my car started running horrible out of the blue and I couldn't get over 55mph on the highway, also died at red lights. Pulled the plugs to find that one was cracked...er, let's see if I can explain it...around the ceramic tip, where the spark jumps.

I was wondering if this problem was a simple matter of a bad plug (using Bosch platinum) or if there is possibly something wrong with the engine that would cause this? All the plugs look whitish, like they are getting too hot, but I just set the timing, and all other things seem to be working fine. If there is a root cause here I'd like to fix it before I go through several more plugs. Of course, this bad plug was the #2 cylinder which is the hardest to reach without removing the alternator, etc.

Ideas? Am I missing something here?

(Replaced the plug and, as always, just dumped some 44K in the tank too...seems to be an automotive panacea.)

#2 Guest_taprackready_*

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Posted 01 June 2004 - 11:25 AM

Could just be a bad plug. I've never had a insulator tip break off before. Try an experiment and use the correct NGK plugs and read them for lean/rich after you run them.


#3 MorganM


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Posted 01 June 2004 - 11:32 AM

I've had insulators crack when trying to remove them. Putting it in you might have gave it a very small crack and its just now getting worse with use (lots of vibration there) Could also just be a less then perfectly formed insulator which is now giving out on you. They are pretty cheap for a reason; they are cheaply made.

I'd replace it before you have a stuck plug on your hands :)

#4 Bill90Loyale


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Posted 01 June 2004 - 02:27 PM

"Of course, this bad plug was the #2 cylinder which is the hardest to reach without removing the alternator, etc."

What works for me on removing/installing the #2 plug is one of those little universal joint adaptors for the ratchet and an extension of six or eight inches.

Congrats on the new oil pressure sending unit. When I replaced mine, my guage shot up to 70-75 psi (when cold) and about 5 psi increase at running temp. Replaced your oil pump yet? That can also have some very positive effects.

#5 teasdam


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Posted 02 June 2004 - 01:00 PM

yeah, watched my father-in-law remove the plug using a u-joint adapter thing and thought, hmmm, maybe I should get one of those ;)

resealed the pump and cleaned it up during the rebuild. It seems to be fine for now and holds right in the middle @ 45psi. The cost of this rebuild added up so quickly (like they tend to do) that I nixed my plans to buy a new pump. And yeah, I'll probably regret it someday.

Anyway, if I have any more plug problems I'll just junk them all and replace with NGK. Didn't know about NGK's during the rebuild...you live, you learn!

#6 oddcomp


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Posted 02 June 2004 - 01:27 PM

check timing..
bad detonation can chew up spark plugs also
might be a bit overadvanced for the gas your using.. just a thought

#7 blainer68


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Posted 18 June 2004 - 04:14 PM

Hey Hey,

I just had the same problem with a Bosch platinum on the #4 cylinder, blew out the electrode. I've run that brand for the last 100k, not the same ones of course, but have been very happy with them. The engine was running horrible with the check engine on and sometimes flashing. Had it flatbedded to the dealership who said the plug was bad (could of been a stealership and really nailed us). The service writer told us not to run platinum plugs in the car. 97 Impreza with 2.2 - the plug was just the regular platinum, not the ones with the extra electrodes - Hats off to Don Miller Subaru in Madison, WI on this one! tow bill $116, dealer code check and new plugs $85 - Doh!!!

#8 thealleyboy


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Posted 18 June 2004 - 05:40 PM

The cracked plug was probably due to mishandling during installation. I wouldn't sweat it unless it happens a second time (not likely). Severe overheating may be a possibility, but if it overheated bad enough to crack that plug, the plug would be the least of your worries!!

There is no better plug for this car than those manufactured by NGK. They may be available under several brands including "genuine" OEM Subaru, as well as OEM's in the same size for other makes.

Change out those Bosch Plats with a new set of NGK's. You might want to consider a new (or good used set) of OEM NGK wires as well. Also, the best set of wires for this particular car.

Don't let anyone tell you different...

good luck, John

#9 MilesFox


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Posted 19 June 2004 - 11:03 AM

i put trashwagon's motor in the rx, didnt idle good, ran choppy. i pulled some wires and there was no change at the #3 cyl. took the plug out and tried it on the wagon, no problem.

i was running bosch platinums, the same ones that took TW% out west and back, and for a lap baja'n. tried an NGK. both seemed good. found out my problem: the wire itself was up against the egr tube off the head, and burned thru, amking intermittent ground. black tape and a re-route and shes all good!

almost suspected the bosch, but i like them anyway

#10 Nug


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Posted 19 June 2004 - 12:10 PM

Plug insulators will crack from detonation, or if a small amount of coolant is leaking into the cylinder.

#11 WJM



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Posted 19 June 2004 - 02:54 PM

I know that I ran bosch plats for a good while...the engine didnt seem to run as well as with the OEM specified NGK's. Ive tried some colder and hotter NGKs.....but the best NGK's ive used are the latest ones i found....some racing specified NGKs. But at $9 a peice ($18 retail tho, as I got employee sicount) its not a plug to just buy and try....the NGK V Power (NAPA # 6261) were by far the best for any EAxx application, and affordable at around $2 a peice for a walk in customer.

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