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ahh... backfire?????


bigfoo

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Was driving along... 30mph or so, decided to smash the pedal.. and it .. backfired.. i'm not sure if it was out the exhaust or the intake.. it wasn't really loud but it's never done that before.. it didn't chug or anything .... tried same thing 50 times again and it didn't backfire, then drove around a while normally and hit it again and it did it again.. only codes I had was a history U1255 .. what in the world would cause such a finely tuned engine such as this to backfire... slightly humorous, unless it turns out to be a huge problem :P

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leaky injector/injectors

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check for crossfire between spark plug wires too, those are my guesses...

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Hrm.. anyone else? I'll check the wires by misting or something at night. I hate backfires......... You know it might not even be a backfire but it sure sounds like one. It's not really loud and you can't feel it very much (maybe slightly). Maybe ill pull a few plugs and look.. it's got almost 80k miles on it and i haven't changed plugs/wires or anything and it's always driven hard :) In fact i haven't changed the PCV valve yet, i just got a new one at the store the other day .. thought that might cause a little issue since it's been forever since it's been changed....

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Also check for a leaky FPR. That would be dumping raw fuel in the intake.

PCV's almost never need to be replaced. If they rattle, they are good. If you want to clean it, just put your thumb on one end and fill it with carb cleaner. Then place your forefinger on the other end and shake it to agitate the cleaner. Good as new.

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Just locate the FPR on the fuel rail and pull the vacuum hose off with the fuel system pressurized. Look for fuel leaking out of the nipple. There sould be none.

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Ahhhhh so u mean leaking into the vacuum system.. I was trying to think of how a leaky fpr could possibly ....... Just didn't click :) Now it did.. Thanks I'll check that.

Anyone else ever have a problem like this? It never does it at idle just when i mash the pedal and then again rarely..

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Recently my '67 Camaro started to make a similar type

of pop or backfire while mashing on the four barrels. Still

trying to figure out what exactly is going on internally

to make that pop. Wouldn't bad timing have something

to do with it? :(

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You MUST know where the noise came from to determine the cause. General "Old Guy" stuff, if it came from the intake, the mixture was too lean, if it came from the exhaust, it was too rich. This does rule out the existance of cross firing plugs.

Never underestimate the amount of a persons greed.

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Hmm well it's hard to tell because i'm going 30mph or so :)

With the windows up I probaly wouldn't even hear it but with them down I do..

I'll try some revs in neutral and see if it does it and have someone listen

I'll also check the wires, maybe pull a plug, and check the FPR......

Is there any way to see the fuel mixture readouts from the computer? maybe the o2 sensors and stuff? I would assume if it got 'too rich' or 'too lean' something would complain and get a code but i don't have any.

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I used to use 92/93 octane but have switched to 87. Due to the knock sensors the Northstar will run quite well on 87. I have had absolutely no problems with it. If your gonna race it use 92, otherwise save your money.

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Any more ideas on why it might backfire when i slam the pedal?

It never used to do it..... I'm making a list of things to check and them im just going to do them all at once :)

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I wonder if the FPR could fail by getting laggy? If its not ignition, and you have no codes, I would check the fuel filter. It seems fuel related to me. In the old days, with carburators you would get a bog if the accelerator pump seal was damaged, as you would not get the required shot of fuel. Is it a backfire or a stumble. What I mean by stumble is, is it like a flame out, where you bog momentarily? Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Nothing new to add, just that if it were fpr, it would start with difficulty when hot.

At least in my experience.

Well, my 95 etc sometimes backfires into the intack if I let off the starter key just too soon. Something like that, its hard to recreate, but I will pay a bit more attention to the detail of that, next time it happens. So, it will backfire in some situations, but always related to starting.

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After rereading your original post my feeling is that if it only happens once every 50 times or greater then I wouldn't sweat it. So many possible variables and no trouble code popping up. You could drive yourself mad over something so "minor" or end up really needing to fix if you start messing around with it. Turn the music up I always say. Keep using the 91-93 octane. You can use a lower octane (short periods) but you'll get premature firing (lower octane burns at a lower compression and visa versa) so are you really saving $... that's a personal choice. Maybe you haven't been talking nice to her... girls...um cars are like that.

:rolleyes:

-kg

206,000 miles

"Burns" rubber

" I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. "

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Heh... you guys are funny :)

I don't think it bogs at all .. it just makes a pop right as it starts to rev up from me hitting the gas and just keeps revving like nothing happened. I also seem to be losing high end power .. or maybe that's just because it's hot outside.. i'm not sure.. but it seemed to be faster before in the 4000-6000 rpm range than it is now.. low end seems no different

I have corsa exhaust and a high flow cat on it so i would assume a backfire would be super loud if it came out the exhaust...but i'm not sure.. this is the first fuel injected car that i've ever worked on/modified.. i've had other FI cars but never bothered to work on them because they weren't worth working on.. the rest were all carbuerated. Even on carbuerated cars, backfires and stumbles were very hard to diagnose mainly because you have no sensors or anything like that to tell you what's wrong..... but it's also 10 times cheaper to just replace 5 or 10 things and then it fixes the problem and you never really know what caused it :)

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Well I checked the FPR and it's not leaking.. Also replaced the PCV and the intake pressure sensor seems a bit loose to me.. pops in an out real easily but i guess that's not a huge issue.. Tried to pull a plug out but I didn't have a socket that would fit in such a small area.. gotta get one of those.. also the wires look pretty nasty inside the area where they connect to the plug .. some brown stuff, looks like rust but it's not..

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Any more ideas? The only thing i notice is possibly loss of power in high rpms....... going to pull some plugs after I get a socket and look at them..

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Heh... you guys are funny :)

Maybe no one answered because we are funny! :lol: Plus I think Kger2 summerized it when he said 1 out of 50 times?... :D I had it happen to me a few months ago pulling away from a light, that it did not happen again, problem solved... It does not sound too serious to me, like you said, hot weather brings less dense air and performance will feel lesser, how is it at 2 AM in the cool air, mines flys...

I would make sure your ignition wires are OK however, maybe you are getting some cross firing. How old is your fuel filter maybe you are starving the engine. Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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