Ok, so I'm chasing an issue and ran across something that might or might not be a cause or a result.

Had a 0301 code. Pulled the cap and rotor and they looked bad IMO. Replaced those and then got a MAF code? Cleared that and now have no codes, yet the car won't hold idle. I think I caused the maf code, sorry can't remember the exact code right now. Replace the wires, don't ask why I didn't do those with the cap and that.

Anyway, pulled the plugs and found that three of the five have a crack in the insulator. All three have two cracks in the insulator from the tip to the base. They look like "newer" NGK plugs.

Any thoughts as to how or why three are "cracked"? Yes I have new plugs with me now and will install them as soon as I can - work, cold and rain are stopping me right now.

EDIT: Working on/with a 96 Volvo 850R

 

Thanks for the edit; I had forgotten that Volvo had done a 5-cylinder engine as well as VW and Audi.

As for the cracks, the only causes I've ever run across for cracked insulators has been either detonation due to poor quality fuel (or the consistent use of fuel with too low of an AKI rating) or a significant enough "carbon" buildup in the combustion chambers to either create hot spots or effectively raise the compression ratio beyond the point where the recommended fuel grade is insufficient.

 

Why do you think you caused the MAF code? Watch whether it comes back.

I'm guessing here, but bad MAF reading causing lean mixture; in turn causing too-high combustion temperatures.

 

I think I caused the maf because after replacing the cap and rotor - I didn't get the air intake and air filter box back in. I cranked it up to be sure I had the wires on correct, code came right on. I turned it off, got the tube and filter box back in, cleared the code and it has not come back. Total time of running with the maf code....maybe a minute

Car has 93 in it, I filled it up a few weeks ago.

This is Cam's car so it doesn't move/drive much. One weekend I moved it to the end of the driveway to do something, no issue. Next weekend I went to move it again and got the 0301, ran maybe two minutes with that. Shut it off, read the code. Pulled #1 plug, don't know if it was cracked then or not, I was mainly looking at the end - since the car is new to him/me, we have no idea of history. Wiped it off and put it back in. Pulled the cap and rotor....eek. So during the next week I picked up new cap, rotor and wires. Weekend before last I replaced the cap and rotor, this is where the maf code came up when the air box and intake were not all back in/together. Got that back together and cleared the code. No codes but no idle. The past weekend I put the wires on (Sat).

No codes but still won't hold idle...tries two or three times but dies out. Sunday I decided to look for any vac lines I might have messed up, any connectors I might have knocked loose, ect. That is when I decided to pull all of the plugs. 1, 2 and 3 are cracked, hard to see - lucky I caught a fingernail on one of them, that is what made me look closer at the rest.

So there it is. I'm still open to ideas. I've been e-mailing with Cam about the issue as well.

 

Perhaps a systematic error during plug installation, wrong socket size, trying to install w/o spark plug holder in socket, or other problem during installation. Hard to imagine any engine condition that would crack 3/5 plugs.

good luck

 

Agreed

 

I'd agree if the cracks were above the metal wrench-hex part of the sparkplug.

If the cracks are on the (+)electrode insulation post on the bottom (inside the combustion chamber) then I don't see how you can do that by wrenching.

 

I've never seen a cracked plug before. But my gut still tells me vacuum leak on the codes/poor idle issue.

 

The cracks are from the hex to the tip where the wire goes on.

Cam, yes. I'm going to get the plugs in and start the hunt again this Friday. I'm giving myself a 3 day weekend . I was just trying to see if/why these might be an issue or how it happened.

My stupid theory, could the cracks from the wire end to the hex cause the spark to "bleed" off? Higher RPM's and there is just "enough" to somewhat fire the plug, but at idle too much is being lost before getting to the firing tip? The new wires have not been on long enough but I might look at the old ones for any "tracks" inside the plug boots.

The back to the Easter egg hunt....that dang vac line or connector I knocked off or lose.

 

Given the relative pressures involved, any "bleed off" of the spark current would most likely happen at mid to high RPMs and wide throttle openings. The greater the pressure in the cylinder the greater the resistance to the spark jumping the gap which in turn means the higher the likelihood the energy will seek an alternate route.