PLease evaluate this plug

[widebody911]

I'm debating replacing my plugs. Here's the first one I pulled out. The set has only a couple thousand miles on them, but I had a fuel contamination issue. I replaced the injectors and the car runs better, but I'm still on the fence as to whether I should replace the plugs...

[Walter_Middie]

Thom,

What does a set of plugs cost? Come-on! That plug looks terrible - just put a new set in and be done with it.

[RichF]

I would, I used that spit fire style plug in my car and they craped out in 10 miles (biggest mistake I have mad yet was putting those in my car). What happens is the plugs can't burn the gas and they crap out. I switched back to the bosch.

[spikej40m]

THATS FOUL

[T77911S]

that plug looks bad! looks like you have been driving in a lot of city traffic were you are on the idle circuit mostly, if not, you may want to check mixture/timing or maybe even try a hotter plug. like richf said, bosch supers are the way to go. i have not heard how well the iridium plugs do.
do a search on reading spark plugs. there is a lot to learn out there.

here is some of what i have pulled off the net. some contradicts itself, such as timing. some say read the center electrode, some say the ground strap. some of this may repaet, i copied sections from different sites. i was having a detonation problem, so i started researching plugs, timing and miture. turned out my CAMS were advanced 15deg. by PO.

Try to use a too-cold spark plug and you very likely will have to jet for a lean mixture to avoid plug fouling - and as you lean an engine's air/fuel mixture down near the roughly-14.5:1 chemically-correct level it becomes extremely detonation-prone. Excessive spark advance is even worse in its ability to produce detonation, and when combined with a lean mixture it's enough to quickly destroy an engine.


a slightly lean mixture detonates at a lower temperature It's all a function of ignition timing and mixture in any given engine, and spark plug heat range plays absolutely no part in it.

It's impossible to separate the question of ignition advance from the primary evidence of spark plug overheating, which is most strongly shown on the plug's center electrode. If you inspect this electrode's tip with a magnifying glass and see that its edges are being rounded by erosion, or melting, then you know there's overheating. You should also have a close look at the tip of the ground electrode, checking for the same symptoms. Finally, inspect the condition of the insulator, which should be white but with a surface texture about like it was when new; a porous, grainy appearance is evidence of overheating. If the signs of overheating are confined mostly to the center electrode you can bet you're using too much ignition advance. Retard the spark timing in small (two or three degrees) increments and as you get close to the optimum advance you'll find two things happening: first, the whole plug will be running colder; second, the center electrode will begin to acquire a film of fuel deposits extending out from the insulator nose toward its tip.


when you have found plugs of a heat range that will keep that insulator nice and clean you can start adjusting your engine's air/fuel mixture

If you think about it you'll realize that the only color you can get from an air/fuel mixture is the color of soot. When the mixture trapped in an engine's combustion chamber has more fuel than can be burned with the available air, then combustion will be incomplete and the excess fuel will remain as soot, which is not brown or tan or magenta or any color other than black. And if your engine's mixture is too rich, the sooty evidence will be present on the spark plug's insulator, in a very particular area

best performance is achieved when the mixture contains only enough excess fuel to make just a wisp of a "mixture ring" on the plug insulator

excessive spark lead is the most frequent cause of detonation, which is a real engine killer. You can't stop advance-produced detonation with a cold spark plug, nor with anything but a wildly over-rich mixture


Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability
Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage
It is important to read spark plugs many times during the tuning process to achieve the optimum air/ fuel mixture

Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C

[widebody911]

Well, I ended up replacing the plugs. I didn't want to, not because of cost (although it's double that of a normal 911 engine), but it's a major pain in the ass - I don't fit well into a 911 engine compartment.

I went ahead and replaced them, and the car seems to run better; I'll know for sure at the track tomorrow.

I guess I should have mentioned that these are the stock plugs - this is a 3.6L 1990 Carrera 2 engine.

[WydRyd]

If your car sees a lot of track time, you should probably go for a plug one range colder, since your motor is under extreme loads for extended periods of time.

FWIW, I'd rather run a colder plug than a plug that's too hot. That can be catastrophic to your motor. At least with a colder plug, all you'll get is premature plug fouling/sooting and you may have to renew them more often. Better safe than sorry.

[MichiganMat]

Originally posted by widebody911
Well, I ended up replacing the plugs. I didn't want to, not because of cost (although it's double that of a normal 911 engine), but it's a major pain in the ass - I don't fit well into a 911 engine compartment.

I went ahead and replaced them, and the car seems to run better; I'll know for sure at the track tomorrow.

I guess I should have mentioned that these are the stock plugs - this is a 3.6L 1990 Carrera 2 engine.

Stock as in "never been touched"? Wow, ballsy. I had to change plugs in my Subaru about every 10K miles or it would have trouble starting so Im pretty paranoid about changing plugs in my Porsche these days.

[WydRyd]

IMO, you should really check the condition of your plugs at every oil service, just to ensure everything is in check. They can tell you a great deal about the way your engine is running/performing.

[T77911S]

wydryd, if you are worried about detonation, from what i have read, detonation is related to timing and fuel mixture and not the plug heat range. if you put in a cold plug, the soot left on the plug is unburned fuel which equals inefficient combustion which is why you have lean back out.

[Rot 911]

Originally posted by MichiganMat
Stock as in "never been touched"? Wow, ballsy.

I think Thom meant "stock" as in the three electrode spark plugs are the correct plugs for his 3.6 engine.

[widebody911]

Originally posted by Kurt V
I think Thom meant "stock" as in the three electrode spark plugs are the correct plugs for his 3.6 engine.

Correct. Note in my initial post that this set of plugs only had a couple thousand miles on them.

I took the car to the track yesterday, and for the most part it ran great, but it started cutting out at random - it would just stop for 1/4 to 1 second or so - and always in the higher RPM ranges, but it wouldn't do it consistenly. I did 3 back-to-back sessions without an issue, and then on the very next session the car barely made it around the track.

[Hayabusa]

Could someone please steer me to a link here on 'How to change the plugs" on my 1977 turbo!?

Can't find it. Thanks, guys!

[Walter_Middie]

Chris,

This thread had some good advice:

Spark plug replacement/door threshold rubber
Or you can PM me and we can get together for some basic maintenance tips.

[Hayabusa]

Thanks, Rex. Let me dig into the bonnet and pull of what I think are the original tools. I think I just need to get dirty on my car for the first time.

It sat since last October with a full tank (and cold start switch having been replaced due to previous non-start issues last session) and then when our weather broke went three weeks ago I broke the car out dusted it off, started it, drove it for one day and then came back to drive it the next and,,,, (full charge on battery) ,,, crank but no start.

So I stopped thinking I most likely fouled the plugs. So that is my first step to take them out and see if I am dealing with just plugs.

Hate the see the turbo sit through a sweet summer. I know this is going to be a nice one for Seattle.

You're right down the road from me, too! Let me look in there and I will give you a holler!

[T77911S]

if it has been cutting off and then back on, it may be the CD unit. mine started doing it for just a split second and gradually got wosre. usually it would come back to life with a backfire if i didnt get the clutch in fast enough. put in an MSD and all is better now. bad plugs will just make it run BAD.
the higher rpm range is going to stress the CD unit more than idle. the charging and discharging is happening much fast.

[unclebilly]

That plug looks like you've been driving like an old lady. Don't be a afraid to rev it a little...

Anyway, I just did the plugs in my 90 C4. This is how they should look...

All 12:



Right Side:



Left Side:

[WydRyd]

Originally posted by T77911S
wydryd, if you are worried about detonation, from what i have read, detonation is related to timing and fuel mixture and not the plug heat range. if you put in a cold plug, the soot left on the plug is unburned fuel which equals inefficient combustion which is why you have lean back out.

Running a plug that is too hot for your motor could potentially result in pre-ignition. The tip of the spark plug is too hot and this ignites the A/F mixture even before the plug fires a spark. Not good for a motor.

Anyway, just replace the spark plugs with whatever the factory manual states, especially if the plugs are old and the gaps have changed due to wear'n'tear.

I think the 964's ran the BOSCH FR6DTC triple electrode plugs.

[T77911S]

like i said, those are just some of the quotes i found on different web sites. do a search on "reading sparkplugs".
you will find some good sites the drag racers have on reading them. there are some that say you cant tell if it is the plug or combustion temp, after all, nobody can see in there when it happens
here are a few

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

http://www.4secondsflat.com/Spark_plug_reading.html


http://www.4secondsflat.com/Spark_plug_reading.html

http://www.strappe.com/plugs.html

[boxster03]

repeat after me

Bosch Bosch Bosch