911CabSteve

on my 993 !

I was driving along normally on a quiet residential road when all of a sudden I lose a lot of power, the engine sounds like loud backfiring, and the CEL comes on blinking.. I limp 1/4 mile home sounding like a 4th of July firework show.. After flatbed tow to my wrench, I am informed a spark plug "must have worked its way loose" and was blown through the head, taking the threads with it.

I can't believe it.. This has to be a freak occurance ?? What could have caused this? Any one hear of anything like this before ?

Robin 993DX

Sometimes the spark plug will only work itself out of it's thread when they are not properly torqued into the cylinder head, the crush washer was probably not torqued down properly. To blow the plug out along with the threads is very uncommon unless if the threads were cross threaded and the threads have weakened as a result of that.

droy3

When I was yonger and stupid I cross threaded an aluminum head with similar results...which is what happens when your dad dosen't teach you how to wrench

Amfab

I had this problem several times on my 3.2. Im driving along normally . . . then: Waaooooooooaugh. . .. ! It must have happend 5 times in the 18 years I had the car. When doing a tune up one time my mechanic said that plug seemed to be a little stripped so he was
worried about totally torquing it down. It would go 20-30k miles with no problems if left unattended.
I would guess too little torque on that plug of yours is what caused it to come out.
I also figure you get the added backfire sound because there is still another plug in there firing

steve g

Amazing !
I had the same experience with my brother when we were flying a single engine plane pulling a banner along the New Jersey shore. We dropped the banner in the ocean and flew the 5 miles to the airport losing altitude thinking the whole time what road we'd have to land on. We made it to the airstrip and landed ok greeted by fire engines and ambulances. That plane was at least 40 years old.

matt777

Threads were either previously damaged and/or the plug was loose enough that the threads got pounded out over time. I've never heard of this happening before The plugs in my cars have never lasted long enough to have this happen!

John H

I had that happen on a Ford Expedition when I was towing. thankfully it happened 2 miles from my house (after a trip from Ohio to Houston and back)

mrbill_fl

not an uncommon problem on 2 stroke outboard motors, especially if running hot plugs

gr8nine93

the only times it happened to me was when I was young and stupid and thought that like a jar, it was not good to tighten things up too much. And exactly what was a tork wrench? WHo was the last person to wind those plugs in and how long ago was it. There is considerable debate aboiut whether to apply anti-seize. There are those who say it promotes misfiring grounding the spark to the head if you don't put it on just right. My best one comes from an actual Daimler Benz engineer who I rented a house from, who thought I was nuts when he saw me putting wheel bearing grease of the studs when installing my snow rims and tires. I have been doing that for 45 yrs and have yet to lose a wheel. Too much book larnin' from that engineer, IMHO. What does your wrench suggest..

atan888

had the same problems with my tt it was loose and I thought I had lifter problems. Good thing my mechanic caught it when I did a recent major service.

911CabSteve

Very interesting responses guys.. Thanks for replying...

I never would have thought so many others would have had the same (or near) experience.. Yes - with a twin plug ignition, the other plug was igniting the gas and... POW! You have some seriously loud/strange exahust popping sounds !

At least I was not in an AIRPLANE when this happened ! WOW.. That would REALLY get your heart going - thinking you might have to land on an interstate or road !! I've done quite a bit of small aircraft flying (as a passenger) and can relate to what that must have been like.. Yikes...

Quadcammer

The Ford lightning and some 2003-04 Mustang Cobras shoot plugs out all the time. They only have 4 threads for the plug though, which is typically why it happens on them. Improper torque or some screwy threads will do it as well though.

As for your situation, a nicely done timesert will limit cost and down time.

ecobb993

I might as well pipe in with my embarrassing spark plug story. Years (many) ago when working for a Ferrari shop, I was doing a tune-up on a sweet 275 GTS and guess I forgot to tighten all 12 plugs.

The owner had it towed back after blowing a spark plug out on the freeway. He was particularly pissed because he had one of his "special" girlfriends out for a ride.

It was easy enough to fix because it only took a thread or two with it since that's as far as I got on that one.

Barry_B

VERY reassuring to find it's not just me, even in an old thread - but the ONLY ready & relevant info Google pulled up with "993 spark plug blew out"...

Just happened to my car - tootling home late pm after a dinner in my '85 3.6 conversion, maybe 3k of mine since engine installed (with <40k on it), "POP" then power loss and appalling sound like a blown exhaust manifold gasket on steroids... pull over... upper front right (#6) plug is gone; clearly it's the remaining lower plug that adds some zest to the racket. Connector and wire had simply fallen down, looked fine... spark plug nowhere to be seen... AAA flatbed the 8 miles home at 2am, trailered car to shop today.

So my wrench (who did the conversion and had just changed a few gaskets and the plug wires while engine was out for x-member reinforcement) asks straightaway if it was #6 upper... he said that some mechanics and owners try to change that plug from the top, but when in a 993 it is obstructed, also the power steering pump, so using angle drives, etc., x-threading is often the result, hence it is the most likely candidate for blowing out, and that the only way to properly get to it is to remove the right engine tin and go in from the bottom - which he said is also true for my 3.6 conversion, even though steering pump is gone.

So "luckily" looks like he'll be able to Time-Sert it with the engine in... still, another weekend without the p-car

Gonna go look for the plug later today (I know EXACTLY where this happened) - would like to see how many, if any, head threads are still attached to it .

TMc993

EDIT: There was a reason, but no excuse for the post I just deleted. Apologies.