so this problem has been pissing me off for awhile now. when, and only when, my car has fully warmed up, i sometimes get a backfire when i shift it at around 4000-5000 rpm from first to second. anyone have an idea why this would happen? also i notice it happens more if i let off the gas a little right after switching gears. for some reason when its not fully warmed up, this never happens. does anyone have any idea?

 

It probably because it is still in the warmup stage and running a bit rich yet.

 

so you think the car is running a bit lean after its fully warmed up? the timing is stock, otherwise that would be the first thing i took into consideration (not that im still not). also its a SD car still, its not converted yet, but i havent done any serious engine mods to throw it off(its stock except for u/d pulleys right now). the exhaust im running is just an o/r hpipe and 40 series flowies. i know since its still an SD car they can get finnicky if you are putting on mods changing airflow and such, but i really see no reason (from whats done to the car) to make me think its something i did. thanks for your input, could you explain further?

 

nothing wrong with the speed density cars, imo they are less finicky than mass air (that's why i will not convert mine)....

my guess is that you are not getting the problem when it is cold because the car is in closed loop, after it warms up and starts taking what the sensors are saying into consideration i'mwilling to bet it's not liking what the o2 sensors are reading. i always hear about people having problems after they've swapped to an off road H or X pipe. my buddy actually had to grind down where the o2s went in so they would read proper (weren't far enough into exhaust flow). try putting the stock h-pipe back on (with your mods it'll prolly feel a lot torquier with the stock h-pipe cause you've lost too much back pressure with the o/r one) and see if it runs better. if not, try putting in some new o2 sensors.

 

thanks for the help. yeah i am planning on changing the o2's soon. as for the offroad pipe, i had this problem before i had the offroad pipe on it. so i am thinking that you're right about the o2's. maybe i will consider pushing them in further if i change them and dont get the result i want. im also checking my timing tonight to see if that cant fix anything. as for sd cars, i know, ive heard the same things. problem is i don't want to have to take it in and get the value's in my computer changed everytime i do a modification. i have heard they are less finicky as well, and ive also heard some people say you can get better performance from one as well. thanks again for your help, i'll try that o2 trick for sure.

 

the only time you'll have to change the puter on a SD car is if you change the injectors or cam, and i know people that have gone to 24lb injectors with out touching the puter....you don't really need to worry about it for a long time. i'm sure i'll be running 11s SD with no computer work lol

 

really? what about heads and stuff? i heard if you do any minor things it starts to throw it off. such as cold air intake (figured that would be okay tho) and heads, cam, intake. i figure cam/intake would be the ones to throw everything off.

 

This is an old school problem with an offroad pipe and flowmasters...At least it's worse with offroad pipes, but is common on flowmaster mufflered stangs.
What's probably happening is that there is unburnt fuel that is hitting the mufflers and when you let off the heat in the mufflers burns up the raw fuel. It's more of a nuissance than a problem. I wouldn't get too concerned over this.

 

How many KM's on your motor?

You running headers as well. EGR still hooked up?

would change the O2's first

 

stock headers. car has 170,xxx on it. and yeah im not too concerned about it, but it sounds hella beater when it happens . i want to fix it if at all possible. were there any solutions for the oldschool problem??