morg68stang

Hello all! Hope you had a Merry Christmas.

I've got a question regarding spark plugs. I just installed a new set of Autolite Platinums with new Petronix plug wires and now my car is running so rough it's not even funny...can hardly get over 40 mph. I pulled a couple of the plugs out and, even though I've only put about 5 miles on them, they are covered in as much carbon as the ones I took out. I didn't set the gap on them or anything...just took them out of the box and put them in. When I compared two of them that I pulled out, one looked to be closed a little more than the other...noticeable to the naked eye. As I remember, it was one of the ones with the most carbon. Can the plug gap cause that much of a miss and some backfire?

Also, I pulled one out further back on the engine and it was as clean as when I put it in? It that one probably not firing at all?

BTW...finally got my brakes fixed...bout time...I was ready to pull my hair out.

morg68stang

SuperHoss

All of the plugs need to have the same gap...they usuallyneed35-40 thousandths gap depending on how cold it is(I use a filler gauge). The closer the gap the hotter the spark.

morg68stang

Interesting...I knew about gap, but never imagined it would make that much difference. It evidently does, though. It feels like my engine is trying to jump out of the hood.

rmodel65

get rid of the platniums 1st get some old plain autolites set the gap did u do a cap/rotor button? makes sure all the wires are pushed down all the way. u didnt cross any of the wires up I alway change them one by one!

morg68stang

I'm pretty sure I didn't cross any of the wires up. I did the same thing...changed the wires one at at time as I took the old one off. I'm going to pick up a gauge tomorrow and check the gap on all of them and replace them. If I hadn't been in such a hurry when I did this the other day, I would have done it then and wouldn't have to do this again. [sm=bangbang.gif] What a pain it is to get them out...not much room to work.

No, I didn't mess with anything other than the plugs/wires. The car was basically running OK before I messed with it although a little rough...just figured it a good idea to replace the plugs/wires to try to smooth it out.

morg68stang

68SCode4speed

Might have a bad wire or two?? After you gap all the plugs the samethen what about swapping the old wires back onto the motor one at a time??.. might discover it is a bad wire in the new assembly...

I'd bet two of the wires got inadvertently crossed...

morg68stang

I thought that might be possible because I do tend to do those kinds of things without knowing it and then catching it later on. But, I pulled out the old trusty Chilton manual and rechecked the wiring. Everything is wired up to the correct firing order. Unfortunately, I threw the old wires away, so I guess I'll just gap the plugs and if that doesn't do it, I'll have to pick up another set of wires and try it again...more carefully this time.

morg68stang

longlive289s

i worked at schucks auto parts for quite awhile, autolite plats are pre gapped...u messed up the wires. trust me, ive done it a thousand times and denyed doing it till i gave up trying to figure out what the problem was and re did the wiring. if u need a wiring diagram check the net, bunch of em or if ya got a book that helps too but ill bet you $50 thats the problem. that will cause backfiring and it running like ****

morg68stang

I'd be the first to admit it if that were the case, but nope. Wires are connected correctly. They are pre-gapped, I'm sure, but I did notice that after I pulled a couple of them out that they were gapped differently. It was enough to see with the naked eye, and I'm guessing that since we're talking thousandths, then one or the other is waaayyy off. I don't really know if that will cause the problem I'm experiencing, so that's why I was asking the question. Guess the best way to know is to make sure they are gapped correctly and try again.

I see on multiple places here that people are hating on platinum plugs. Why?

longlive289s

it really depends on who you are. a lot of ppl with older plugs like copper plugs but (probably since im younger) dont like them. with copper ones you have to find the heat range and figure out if u need a hotter or colder plug depending on your engines compression. i like plats just cuz it doesnt matter, they will take all heat ranges but many ppl i talk to say that their old muscle car runs crappy with plats....idk, i think its almost a placibo affect but thats me.

back to your question, ya check them all if u can tell that they are off with the naked eye. that will cause miss firing and perhaps back firing. but since it was running fine before u changed them it is HIGHLY unlikely that their is a problem with wire, rotor, cap or anything else.