after cat mod problems
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Senior User
Joined: Mar 2003
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From: ontario
after cat mod problems
I preformed a high tech catalytic converter mod.(popped off muffler and smashed out all the guts of the cat with a tire iron)
but I find that now often when I shift I will backfire, could it be that I need to advance the spark or something? doesnt do it all the time but it didnt do it before. It dosnt really bug me but it scares the crap out of the girlfriend, and I just got her used to the no doors thing so any help or ideas would be great.
Thanks
but I find that now often when I shift I will backfire, could it be that I need to advance the spark or something? doesnt do it all the time but it didnt do it before. It dosnt really bug me but it scares the crap out of the girlfriend, and I just got her used to the no doors thing so any help or ideas would be great.
Thanks
Senior User
Joined: Jul 2003
Posts: 353
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From: Saskatchewan, Canada
after cat mod problems
I just breformed the same mod on my 89 f150 (only i used a pice of pipe 
) an am experiencing the same popping sound when i let off the throttle. What is causing this and how can i fix it? Even if it is not dangererouse for the engine and is was cool for the fisrt day or so but now it is just anoying.
Please help! JJ
) an am experiencing the same popping sound when i let off the throttle. What is causing this and how can i fix it? Even if it is not dangererouse for the engine and is was cool for the fisrt day or so but now it is just anoying.Please help! JJ
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Senior User
Joined: Mar 2003
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From: ontario
after cat mod problems
I put a cherry bomb and 12 inches of pipe with a turn down (Icut the stock exhaust pipe from very end to after the bend so it had a turn).It seems to have really deepened the rumble and it was cheap, cherry bomb cost about $32 . sounds really good. Also have to be a little quicker getting the foot off the gas as I clutch. I was thinking about advancing the timing slightly to see if that would help.If anyone has any thoughts on this please let me know.
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Joined: May 2002
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From: Broken Arrow, OK
after cat mod problems
It's caused by the unburned fuel in the exhaust exploding when they get to some oxygen. To fix it you either have to get the extra fuel out of the exhaust, or keep it from finding oxygen until it has cooled to a temp. that won't initiate combustion.
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Joined: May 2002
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From: Broken Arrow, OK
after cat mod problems
If there is air in the exhaust it's probably due to an exhaust leak. Excess fuel is probably a carb calibration issue, but some pull too much fuel when the vacuum spikes at throttle closure no matter what. You can try closing the idle mixture screws a little, but that might not be enough.
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Joined: May 2003
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after cat mod problems
My guess is that the air is being pumped in from the smog pump.
Try to plug both vac lines to the valves that are controlling the air injection system
Try to plug both vac lines to the valves that are controlling the air injection system
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Senior User
Joined: Feb 2003
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From: West Virginia
after cat mod problems
That popping sound is just your engine racking (why it's called racking, I can't remember right now and it's the hick term for it) and the only way I know to get rid of it is to get a muffler (if you don't have one) or if you have one and it still does it, get another kind of muffler. I think glasspacks, strait pipes, and most race or strait-through flow mufflers let your truck do this. Your engine "racking" won't hurt anything, unless you have your exhaust clamped together and it's not clamped real tight. And you might loose an exhaust tip or two if they aren't on real good either.
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Joined: Jul 2003
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From: Chicago, IL
after cat mod problems
It's caused by the unburned fuel in the exhaust exploding when they get to some oxygen. To fix it you either have to get the extra fuel out of the exhaust, or keep it from finding oxygen until it has cooled to a temp. that won't initiate combustion.
my '86 Thunderbird 3.8V6 experienced the same exact thing, even with a muffler! emissions-wise it ran perfect, passed emissions with flying colors. the car was equipped with the CFI setup so air/fuel was not adjustable.
what you need to do is eighter replace or remove entirely the cat. this will allow all unburned fuel to just exit the pipe or get absorbed by the cat. believe me, i've tried several types of mufflers and none ever even muffled the popping sound.
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From: Laveen
after cat mod problems
My courier used to do that also after I dumped the pellets out of the cat and put on a straight pipe, I leaned out the carb with smaller jets and made a stainless steel tip and I just clamped it down a little till it popped less. It worked real well and passed emissions it only popped when you decelerated hard and then not badly.
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