Spark plug gap gone???

[jjm525]

We have a 15k mile 03, my son's car. Bought it a few months ago and about 1500 miles back it developed a miss. Pulled the spark plugs and find #7 has been closed to zero gap. WTF?

Well, we change all the plugs, the car develops a bit of a rattle around the low-mid 2k RPM range and under load and now, tonight it is making the same miss symptoms we had last month.

Mods are minimal, a CAI, flowmaster catback and gears, Bama SCT tune. The car had 6700 miles on her when we got it, no evidence of massive beatings, seems to be gently used, original tires and such.

So, how is the plug gap getting closed? I saw no evidence of any hit on the strap, no bits of anything stuck to it and no oil/fluids present. It looked like a good plug with no gap.

Thanks for theories!

[Tyson]

I had that happen on a 04 gt I had before the Mach did a compression check it was bad and stuck a snake cam down in there and a chunk of my piston was missing

[DSG2003Mach1]

get a new tune

the rattling is likely detonation, detonation can close the gap on a plug, this needs to be taken care of sooner or later before something gets seriously hurt

[jjm525]

I'll drop the stock tune in later after I pull the plugs to check them. Our theory was detonation the first time we found a closed plug but the new Bama tune was supposed to be safe with Sunoco fuel. Hmmm

Thanks

[DSG2003Mach1]

the stock tune would likely be lean as well...the weird part is that its rattling at part throttle, its usually a WOT thing.

is there a dyno anywhere nearby where you could attempt to make a pull or two with their wideband/tail pipe sniffer?

If you have a laptop you could also could try logging your timing to see what its doing

[jjm525]

Could a bad COP cause it?

[DSG2003Mach1]

if a cop was bad it could cause a misfire but that wouldnt explain the detonation/closed gap

[jjm525]

I was thinking if it was erratic it might screw up the timing in that cylinder. I hope to have the exact details of what we are dealing with in a few hours. Thanks for the advice.

[DSG2003Mach1]

nah, the coil is only going to fire when its suppose to, if somethings wrong with it the only thing that would happen is it wouldnt fire/wouldnt fire full strength when commanded

[jjm525]

He took it apart at work and found #7 had again zero gap and this time the porcelain broke too. A bore-scope shows the piston is nicked up from that now too.

Why would only #7 knock? Why knock at low RPM, low load too? We had Bama rewrite a new tune last time and have stuck with 93 Sunono religiously.

[DSG2003Mach1]

is there anything actually in the cylinder bouncing around they could see (other than the porcelain)?

bad injector maybe? I think Id get a compression tester from the loan a tool program and check everything out. If thats fine then Id follow it up with having the injectors flow tested

[jjm525]

He works at a very tuner/mod heavy VW dealership and the tech/motorheads are looking at it with him. They say it looks rich by the plug color. I'll see if they can get a comp reading on it too. They didn't see anything floating around.

[DSG2003Mach1]

Even with an appropriate A/F mix enough timing or something causing a hot spot in the cylinder ( which Ive heard rumor certain spark plug inserts can cause) can cause detonation. I suppose another option is to move the injector and see if the issue follows

[jjm525]

A spark plug insert or the actual spark plug, like a different style/brand is better? I hate to play russian roulette with another cylinder but may not have much choice.

A one time Ford tech at his shop suggested a new COP just because they were common to go bad?

[jjm525]

New info,

both times the plug gap dissappeared the engine had been spun to near redline.

A compression test result should be available tomorrow! I'm suspecting a damaged valve spring or lifter assembly = valve floating and plug contact.

[DSG2003Mach1]

Floating valve can't hit the plug.

It needs to go on a dyno with a wide band

[jjm525]

I don't know if that is a relief or not, LOL!

I got that from my mechanic, thought they might be close enough to do that. Well, comp test tomorrow and I'll look for a dyno guy/wideband.

Thanks!

[DSG2003Mach1]

valves and pistons can hit but only a chunk of something bouncing around could hit the plug itself

the plug itself wont cause a hot spot but if a threaded insert was used in the head its possible

[jjm525]

The threads look original, and the plugs were too. The lead tech in the VW shop is thinking bad big end or wrist pin as he thinks at high RPM the piston hits it. More inspection today with comp and a stethoscope for that rattle.

Thanks for sticking with me on this, my 19 year old son has near 3 years of financing due on the car and is in a panic mode over this.

[4a7191a]

could be wrist pin. seen em fail on a stock lightning before.

[birdman941]

One way to isolate if the piston is hitting it,
use 2 or 3 of the plug gaskets (temporarily) instead of one
to get the electrode away from the piston.
If the electrode stays intact, I would suspect a wrist pin.
Does that make sense?

[TKat13]

Originally Posted by birdman941

One way to isolate if the piston is hitting it,
use 2 or 3 of the plug gaskets (temporarily) instead of one
to get the electrode away from the piston.
If the electrode stays intact, I would suspect a wrist pin.
Does that make sense?

Simple Genius... great idea...

[birdman941]

Occam's razor.
The simplest solution is usually the right one.

" the simplest or most obvious explanation of several competing ones is the one that should be preferred until it is proven wrong."

[jjm525]

Well, we have a piece missing at the edge of the piston. Don't know if it is the wrist pin or big end bearing but both are suspect if the piston can make the trip to the plug, right? So, doubting it is possible but might as well ask;

Can a new piston/rod be installed from the oil pan after dropping the K?? It seems the cylinder is OK, the piston has taken a beating and unknown on the head but it runs super smooth if kept at low RPMs, we haven't gone over 4k at this point. Rattles but strong/smooth.

Probably going to look for the cheapest solution, maybe a used engine?

I guess our defective tune from XXXX that had the engine detonating like St. Mary's bells did more damage that I thought. The kid, my son, didn't know what the detonation noise was and drove it a day or two clattering at mid RPM WOT. We got a proper tune the day after I heard it but seems it was too late.

Thoughts?

[birdman941]

Has to come out the top.