running bad

[LOUVETTE]

can anyone help out here.......few weeks ago i put in new plugs...ac rapid fire gapped at 40.....seemed to run ok....no better or worse...last week i put on a free flow exhaust from cat back.....there was a y pipe there with two turbo mufflers.....now i have on side pipes real free flowing......seemed to run ok after install.....i did notice the cat had been gutted but havnt put a new one on yet.....then after a week it started missing and cutting out and in ......sometimes ran good and sometimes missed..........i did have some excessive idling time on the engine one day as i let it run for an hour or so at idle....could it be i fouled a plug by idling so long....could it be the rapid fire plug with its wider gap and my stock ignition are not a good match............or could it be that the exhaust is flowing so free now that with little back pressure that it wont run right with this exhaust............anyone able to help i apreciate it....

 

[-=Jeff=-]

Have checked or replaced:

-O2 sensor
-Cap and Rotor
-IAC housing and motor
-wires

??

 

[evolution]

Check fuel pressure! Might need a new filter or pump. Easy check and a quick fix!

Try to pull some trouble codes from it

 

[secondchance]

I know these are brand new plugs BUT remove and check for signs of arcing. I had a problem with defective AC delco plug that took me 5 months to track down. Also, start the car at night in the dark and look for arcing between the plug wires.
Cap and rotor is also a suspect.
Good luck!

 

[mvftw]

I had a problem like that after a put in Platinum Plugs. Car ran good for 5-6 months, then started to miss/run like crap. Tried everything, figuring the plugs can't be bad...I replaced the plugs again w/Platinum, it ran good again, thought I'd fixed it (a bad plug), after 5-6 months ran bad again. I was told from the powers-to-be, put in what the book calls for!!! Put in stock ACDelco's and problem gone. I believe the reason is that the fancy plugs have different heat ranges then stock.

 

[secondchance]

Plug in question was AC Delco platinum tip. Defect was cracked insulator. I suspect that its not the heat issue but these newer designs may be manufactured in such a way that makes these plug insulation to crack during torqing or due to heat. In my case I went back to original AC Delco.
Next time, I think I'll try NGK. Heard a lot of good thing about these plugs.
Also, there are two types of AC Delco Rapidfire. Older ones are non platinum tip and newer ones are platinum tipped. I am interested in knowing which Rapidfire you were using.

 

[evolution]

NGKs are good for imports but I believe the heat ranges are off for domestics. Same applies for Bosch +4's. Although the Boshcs are off by a smaller margine.

Go by the book and you cant go wrong. As long as there is spark, there will be fire.

The only things that can change the dynamics of combustion is air/fuel atomozation (and ratio), fuel octane, combustion chamber temperature, timing, cylinder head design and plug design(heat range)/placement inside the combustion chamber.

....only? That turned out to be more variables than I expected!

Well, you could always change the dynamics by putting Arco in your tank (not for the better!).

 

[evolution]

What I was really trying to get across was how much a spark does not differ much from plug to plug in optimum conditions. It either sparks or it doesnt.... right?

Whats the point in a hotter spark unless it actually burns off potentially fouling matter from the plug? I think if you are fouling plugs so often, the last thing you would need to worry about is what kind of plug you are using (providing it is in the correct heat range). I would look rather to the cause of the fouling in the first place like oil seeping past the valve stems or other contaminates entering the intake pre-carb.

Correct me if I am wrong, I hate to sound like a misinformed fool! Or worse yet, practicing what I preach!:L

 

[secondchance]

My concern is not so much over heat range. I'm beginning to suspect newer AC Delco plugs are having quality control problem.

 

[evolution]

Always a possibility