So I recently replaced my old plugs with NGK Iridiums hoping I wouldn't have to replace them in my lifetime but now I am suspecting they are the culprit in my 305 running rough.

I do have to replace my valve stem seals since the No. 2 plug was oil fouled but the compression came back as 180 psi.

My rough running came shortly after I did a major cleaning with Gumout Multi-Tune in the tank and poured into the brake booster vac line followed by an overnight soak.

I just finished replacing my factory Multecs with Bosch D3 injectors and the engine is still is missing.

I took out the No. 2 plug and it was fouled with oil looking deposits. I blasted it and resinstalled and the engine runs better but is still missing during and after warm up.

I am now thinking all of my plugs are fouled. That's about all that is left.

Maybe the Iridiums are too sensitive for this kind of application or the ignition system just likes to work with good old coppers?

It's enough of a pain the rear to do the plugs that I really would like to just get it right.

Any thoughts on copper vs fancy plugs?

 

The oil looking stuff is probably carbon turned to sludge from the GumOut. I'd pull all the plugs and clean them to start with.

 

I love NGK iridium plugs I run them in all my daily drivers. Iridium is the standard in all newer cars weather they are NGK, delco or some other brand it does not really matter. For my TA I run NGK racing plugs because that is what the head manufacture told me to run. The only real issue I have ever seen is bosche platnumn +2 and +4 in anything that is not german. Lots of missfires and generally poor performance.

 

Yeah, that's what I'm thinking but I did know that when I first changed these plugs about 1,000 miles ago, that old No. 2 plug copper was fouled far more than the others so it's valve stem seals for me. But I am wondering if these Iridiums tend to foul more easily or otherwise just don't work as well with these older engines.

 

Iridium should resist fouling more the smaller surface area of the electrodes, and the high conductivity of the metal on the electrodes means they are way more reliable especially in hi temp lean conditions. The small surface area of the electrode really does a lot to maintain a good spark and they really stand up to high energy ignitions vs copper.

 

Mmm. Maybe I'll just clean my iridiums then...

 

I run the NGK Iridium in my car to replace the Bosch Platinum I was using for years and actually they perform better for me. Engine runs really smooth and starts up quickly with the good spark.

 

Call me crazy , but , I've always found that engine condition matters a whole lot more than what sparkplug I've used . In a good running engine that's not having any leakage issues of oil into the cylinders or fuel induction problems (too rich or lean) the stock plugs have given me just as good of service as have the fancy ones , and to be honest with you the fancy ones didn't make the car feel one iota faster than the factory recommended plugs provided everything else was in proper working order .

PS , if I WAS having any kinds of oil fouling or too rich fuel soaking problems that would be ruining plugs faster than they would wear out in a healthy engine , the LAST thing I'd be doing would be putting fancy high dollar plugs into it hoping to "mask" the problem ! If the plugs are being fouled , that must be addressed first before any sparkplug is gonna last be that a big $$$ one or the cheap factory recommended ones .

 

Well I replaced the 1,000 mile old NGKs with AC Delco R45TS (stock) and no difference. This engine is starting to get to me.

Here's what they looked like. Pretty OK. Interesting though that the gap had grown from the .035 to almost .039. And I am really careful when I gap so something grew that gap. Plug two had been removed, grit blasted and resinstalled the other day since it was heavily oil fouled.

 

i love my accel shorties - 10 minute spark plug changes are mint

 

I am no mechanic by any means but those plugs look like they have a heck of alot more than 1000 miles on them. The ceramic looks good but there is an awful amount of black soot on the end of the plugs. Running a little rich maybe?

 

My old 454SS pickup truck ran the basic AC Delco copper plugs. RH bank would always foul up so I put hotter plugs in that side to help burn off the residue. Instead of removing and cleaning the plugs every 6 months, they lasted over a year before needing to be cleaned.

Finally I changed all the valve seals and the fouling of the plugs went away.

My race car uses NGK copper race plugs with a very cold heat range. Using triple valve springs, there's no room for valve seals. The plugs are all indexed in the head so that the piston doesn't make contact with the ground strap. It doesn't need platinum/Iridium plugs since it isn't a high mileage engine.

If you had the engine on a dyno with new copper plugs then tried new iridium plugs, performance power won't change and if it does, the amount is so small that you would not notice the difference. The main advantage to running platinum or iridium is for plug life. A typical copper plug is designed to last about 2 years of normal driving. The platinum or iridium plugs are designed to last at least 5 years.

The biggest thing about choosing a plug is to determine the correct heat range. jetting, timing, power adder etc all affect where the heat range should be. Depending on how dirty the plugs are, you can normally see the heat range on the ground strap. There should be a blue dividing line about half way down the strap. Something as simple as changing the timing will move that dividing line up or down the ground strap meaning you need a different heat range plug to compensate for the different ignition timing. Advancing the timing means you need a colder plug than normal.

 

AlkyIROC knows what he's talking about.