Backfires

[DanielFinzel]

Hello all, i have a 99 grandam, put a flowmaster 80 series in it, i have pics if u want to see em jus do a search on my name, ull see em.(Reason i put that on there about the 80 series is just FYI just incase someone else knows something bout em) Neways, if i floor the car it will accelerate and backfire horrendously! Now i checked one spark plug and replaced it, it looked dirty so i just figured why not. But, i didn't check the other ones. I have platinum spark plugs so they can't be gapped, i may just end up getting new ones if i think that may be the problem. But neways i was told that my cat could be clogged and cause it to be backfiring by not burning the gasses inside properly...well, im considering ordering a new cat. So i need to know, should i do the plugs or the cat first? Either way i pay between 40-100 bucks plus or minus a few. Any other recomendations? you know, stuff it could be rather then spark plugs? o by the way i replaced ignition coils and the spark plug wires. IM really at a loss and just need some help. I plan on gettin my cat checked tomorrow, if i can, and if i do i will post about it but, if yall can lemme kno what you think i should replace. Thanks! Daniel

[doobiess]

ok well when you say backfiring... do mean its acutally going BANG!!! or just making a gargling popping sound as the engine is reved up... if its going BANG! well replacing a cat wont fix the prob.. backfiring is generally caused by an engine running rich.. But how you describe.. its no backfiring because no engine can backfire horendesly.. it takes a bit before the next backfire can go .. because all a backfire is a collection of fuel in the exaust sytem.. that builds up.. and then rev it to ignite that fuel. causing it to explode.. if you think your cat is clogged try this..

Ok go drive your car is more recomended .. or just get your car to normal operating temp. Once it is.. you can verify by feeling how hot the exaust is...

Ok now shut off the exaust... now for me touching something hot dont burn me( im a baker im used to that sort of thing) but what you need to do is touch the exaust pipe behind the cat.. meaning the pipe that runs to the muffler.. and feel how hot the pipe is.. then next touch the cat. converter.. now if the temps are pretty close your fine.. but if you touch the pipe and its cold but the cat is waaay hotter.. well your cat. is clogged or partially.

But by how you describe.. i dont know if your describing the sound of a backfire.. because it sounds like a gun. from what it sounds like ... your hearing the sound of your exaust that has its new muffler that has lessened the backpressure on the exaust system.. making it have a gargle farting kinda sound.. well thats how its gonna sound.. unless you make your exaust more free flowing.. but i would need know for sure if its a backfire or just the other sound

Also a backfire on our cars would be caused by either a faulty ECM or a sensor that has gone bad... and you have gotten a code if that was the case

[HeyDace]

This happened after you put the flow master on? If so, did they weld it on? Occasionally, not often though, welding on a car can fry the PCM if the Neg cable wasn't disconnected. In most cases the car would not run. I don't think its a cat problem, is it misfiring?

[rixGAphx]

Well, there are actually two types of backfire.

1. The ORIGINAL was from the first 75 years of gasoline engines:
Fuel-Air mixture (FAM) from the carb went thru the intake manifold to the cylinder.
If spark plug timing was way off (from the distributor or the magneto), then the spark might ignite the mixture while the intake valve was still open.
WHOOSH-BANG fire raced back up thru the carb into the air cleaner.
Often happened after semi-competent DIYers replaced timing gears or ditributors, and got everything 180* (actually 360*) bassackwards.

Backfires thru the exhaust system weren't very common, and they weren't known as backfires.

2. Fast forward to the mid-seventies, when cats came along. In particular, Mazda rotaries.
The FAM (still carb'd) was set way rich (to reduce NOx emissions), and the cat cleaned the excess HC's and CO.
The early cats often took a long time to heat, so they couldn't do their job upon startup. Lots of unburned HC's were present in the exhaust stream.
The roataries were even worse at this, I dunno why.
So, a second, smaller exhaust pipe was installed in the cat as a pre-warmer to help get the cat to operating temp.
This thing often ignited unburned HC's, especially when you were driving hard and slowed quickly for a tight turn: backing off the throttle created a jet of rich exhaust and POW-POW-POW out the exhaust pipe.
More than one cop drew his weapon when a Mazda raced by on the street.

GA 3.1/3.4's will do a true backfire, in the INTAKE system, under a particular condition:
Each coil fires 2 plugs at the same time.
One plug is firing at ~TDC of the compression stroke, igniting the FAM and producing power.
The 'paired' plug is firing in the middle of the exhaust stroke of the other cylinder; this is called a 'waste' spark, and only uses about 25% of coil's power.

Now, IF one of the injectors is stuck open, or is otherwise putting excess fuel into its cylinder, then the exhaust is gonna be real rich. At the completion of the exhaust stroke the intake valve opens ('cam overlap').
So, with the very rich exhaust and the waste spark, there can be a true backfire into the intake plenum.
It's like a POOF, muffled and about as loud as a person clapping hands.

-Rick

[DanielFinzel]

hhhmmm well, itll do it like once then again and again and then sometimes 2 at a time it seems (they could just be really close together and sound combined ya kno?) But like if i floor it i hear it directly under me i don't think its as loud at the end of the tips as it is under my car by where i am, not necesarily right under me but close....Now, if i just push on it it goes just fine and everything but also when i get to around 80 and try to go a lil bit faster it really does it bad and it feels like its about to just stop and die, could that be that i have that new muffler and the pipe diameter doesn't cause the right amount of backpressure? If so what would yal recomend doing about that? Im considering gettin a larger pipe of 2 and a quarter just have to wait til the money is right and everything, same with the cat. i really appreciate yals help and time! Thanks
-Daniel

[doobiess]

well a 2.25" pipe is a common upgrade but me personally if your spending all that money i personally would go with a 2.5 pipe.. but if your going bigger u need a different muffler. and if that is the case I'd say leave it.. if you want a slight increase in power.. a common upgrade is a highflow cat. but its up to you.. but as how you describe it.. its quite possible its not sealed under there and there is an exaust leak.. only way is to get under and take a look...

[DanielFinzel]

hey doobiess can u email me sometime i need to talk to you that away its not on these message boards, in ur email can u include an instant message name so i can im u thanks alot Daniel
pontiaclover05@hotmail.com

[RocketFast321]

does it soound like this
http://www.exhaustsoundclips.com/sound/oldsmobile_achievasc_1997_31v6_40seriesdf_quadtips .mp3

[HeyDace]

Ok, lets get back to basics. Forget the Flowmaster, cat and 2.25 pipe.
What you have is a mis-fire. Plain and simple. As you stated you replaced the coils and plug wires. Check your firing order!

[DanielFinzel]

lol heydace ok, my firing order, that could be it to but i changed them one at a time, so i dunno if that could really be it, does neone have a graph of what goes where to show me if maybe i did mess up somewhere along the lines? I checked back with the guy about shorting out my pcm and he said no, not with his type of welder that he uses and that most people use now adays. I really wanna solve this problem, i hate it lol but i mean, man, im saving on gas cuz i gotta be careful about my acceleration. lol. But once again i really appreciate the replies and all yals help. :) Has neone else had this problem? Ill check the firing order and get back with yal. Oh and by the way, the guy that did my exhaust fixed the little leak i had that connects the pipe to the muffler, it was about the width of my key( the silver part) and about that thick to, no difference at all other than no condensation nemore.

[rixGAphx]

Are you showing any codes? That might indicate which, if any, plug is misfiring.

It's fairly easy to install the wires and not fully seat one onto the plug.
If so, the firing loses energy jumping that gap, and has less spark within the cylinder.

God luck.
-Rick

[HeyDace]

I've done wires 1 at a time also, and still screwed em up LOL.

[rixGAphx]

Originally posted by HeyDace
I've done wires 1 at a time also, and still screwed em up LOL.

I didn't want to be the first to say that. :D

-Rick

[DanielFinzel]

well ill give em a check tonight to see if i did it wrong by chance....ill post again tomorrow after i check to let yal know what i find

[HeyDace]

Originally posted by rixGAphx
I didn't want to be the first to say that. :D

-Rick

It was a little tough to admit, but it's part of my 12 step program, Admit your faults" :lol:

[DanielFinzel]

:lol: admit your faults lol....we all have em it just sux huh? lol...i checked em tonight, they seemed fine really, i checked from connection to spark plug and to coil paks....nothing seemed wrong, could it have been the dieelectric grease i put on em? I highly doubt it but does that seem reasonable? This is a pain in the yeah lol....;)

[DanielFinzel]

Yeah so somethign crazy, my accessory belt ripped on the freeway the other night, got that fixed for 108.17, yeah nice lil chunk outta my wallet but not to bad, anyways, no more backfiring.....uuummm.....i don't get it...a belt? i mean seriously how? Unless they saw something and said hey ill do this labor for free which outta pep gurls is not likely...so anyone got a reason or explanation?

[DanielFinzel]

hey just to let neone and everyone know i got the popping fixed! lol what it was was my TPS (throttle position sensor) i guess it was bad now if i could figure out why my rpms are so damn high i might save some money on gas!!! has neone else had a problem with their rpms being at like 1-2000 in idle? its a pain and when i go to brake i can feel it pullin me forward...ne replys would help greatly