Impala Balko

I just finished changing all my spark plugs to NGK TR6 gapped to .035" and when I went to fire it up the car immediately started misfiring and back firing out the exhaust. I noticed that #2 cylinder didn't fire because the header was cold, I pulled the plug it smelled like gas but the plug looked brand new. I pulled that spark plug wire and it appears that that cylinder will spark outside the engine.
Now the one snag I ran into when changing the plugs was that #2 plug got cross-threaded and i needed to tap the hole. Is it possible that all the grease I used on the tap may be causing a ground issue with the plugs? I pulled that plug and it didn't seem like there was a build up of grease or anti seize on it however when I screw the plug in it does sound like I hear grease being smooshed around.

Could it be possible that I just have a dead plug in that cylinder because I have tried 2 different NGK plugs in there and none seemed to work? Could the fact that it is a colder plug with a tighter gap be causing this issue? The original NGK plug that I cross threaded had a defect in the threads which only allowed it to go in 2 turns so 2 dead brand new plugs wouldn't surprise me because obviously the quality control is a bit off on their end.

tbirdsps

You can ohm check them to see if there is any resistance. If not they are bad. While you are at it check those plug wires. If I remember right they are supposed to be around 6,000 ohms per foot.

You didn't mention year but since you mentioned anti-seize you probably have aluminum heads, right? It's always been my feeling that on an unmodified engine use what the MFG used, a/c plugs gapped to factory specs and you can't go wrong. The only other thing is to "clock" the plugs so the open side of the ground is towards the middle of the cylinder so the spark is not shielded but the factory never bothered with doing that.

I've never had anti-sieze compound prevent the plug from grounding properly.

Tom400CFI

No way is the grease going to insulate the plug from ground when it's torqued down.

Move the plug and the wire...see if the problem moves.

Impala Balko

So it would have to be a plug or wire or both... but didn't I rule out the wire by plugging it into a loose plug and having it spark outside the engine

Tom400CFI

Technically, no. It takes more voltage to jump a given gap, the higher the air pressure....so jumping teh gap under atmospheric pressure could be possible, when 190 PSI or whatever, cylinder pressure, may not.

The "poor man's method" for checking spark power under compression is simply to have your spark jump to ground, to the tip of a plug in a cylinder. In other words, put a plug in #1. Set your number one plug wire up, so that it jumps to ground, at the TIP, of #1 plug. An easy way to do this is to use another spark plug as your gap, grounding the body of that plug, to the tip of the plugs screwed into #1. If you see a spark jump the external gap, it pretty much HAD to jump the internal one that is under compression too, to get to ground. That would prove that you have "enough" spark to at least run that cylinder.

Impala Balko

So test the wire and it should test 6000 ohms per foot, and the number 2 plug is approximately 2 ft so it should be 12000 ohms of resistance.

Impala Balko

I am sorry i never answered this question the car is a stock 94 LT1 6 speed with a 76mm remote mounted turbo. .. is it necessary to clock the plugs, I have never done this in the past and have never run into problems by not doing it.

Tom400CFI

Not necessary to clock plugs. "Old racer's trick"....though I've never seen it documented to show a meaningful or repeatable gain.

Impala Balko

I thought I saw where they engine dynoed this on "Horse Power TV" on Spike TV (older show that was on the "Power Block" on the weekends before they changed the namea) and they gained something like 10 flywheel horse power on an engine dyno

Tom400CFI

IDK. I've never seen it documented, but that doesn't mean it doesn't work.

383vett

I bet you switched wires on #2 and #4 cylinders. A bad plug would cause a misfire, not backfire out the exhaust. If a valve was open on #2, the header would not get hot because there is no compression to allow the cylinder to fire.

C409

..... ..... It sounds like you have some wires mixed up .............

Impala Balko

The wires are definitely not crossed as I traced them back to the opti and the wires are numbered for the perspective cylinders. The exhaust smells really rich almost like raw gas and the wide band reads really high like 18-20 on idle

383vett

18-20 is lean.

Impala Balko

I know which leads me to believe a cylinder is not firing aside from the #2 cylinder being cold

383vett

If you can find another wire, swap with #2. If all you did was change plugs, it has to be the wire or plug. You can also ground the plug to an engine part using the original wire and crank the motor over. If you have spark, then something else is wack.

Impala Balko

I think i am going to throw a set of wires at it and see if that fixes her

cudamax

Thats because you haven't been around long enough and are too young and just don't know. You shouldn't give bad advise
Indexing Spark plugs Works and is go for 2% to 5% gain and some motors even more.
Indexing is especially useful if the combustion chamber has a 'squish' area where the piston almost touches the head but benefits all engines.
so 5 hp to 20 hp or so not good enough for a little labor time and requires different plug washers

Tom400CFI

Try this^

lt4obsesses

Maybe a silly question, but it can be easily overlooked. Did you double check the wire connections at the opti? Maybe in moving the wires around #2 slipped enough to cause misfire?