Backfire

Does anyone else have backfire issues? I occasionally get one when I blip the throttle on a leisurely down-shift, usually after I've been driving hard, but not always. Today, after several minutes near the red line and about 30 secs of cool-down, I got one at the following parameters: clutch -- depressed, RPM about 2K, throttle blip to floor, immediate 'pop' noise I buy 93 octane gas in Alabama. Can this hurt the engine? Please advise ...

Although I'm still waiting for my Cayman , the 'backfire' was very common with my '01 Boxster S . Dealer reassured me that there was no problem. it would occur when I would rev the engine ; I described it more as a 'bark'. Don

It is no problem - I guess this will happen on a Porsche since it has a more sporty exhaust but anybody correct me if I'm wrong

Backfires come in a couple different varieties. 1) ignition related: bad plug, timing off, bad wire, etc. 2) Valve related: a stuck valve or hung valve when hot is also a possibility. While a backfire is one explosion out of millions 'gone wrong' it doesn't necessarily mean you have a problem. If it happens repeatedly, then you need to have it checked. If you had the engine 'red hot' after driving hard, you could have experienced ahung valve as it was cooling down (somewhat common). Paul

I tried and cannot make mine backfire no matter what I do. It should not backfire at any rate. I would just monitor it to see if it gets worse. Has anyone else gotten a backfire? THis is the first I have heard of it. Russ[/quote]

I get the occasional backfire when during either decel or steady state cruising and I do a quick on/off blip of the throttle (hitting the gas pedal all the way to the floor and releasing quickly). In my experience this is pretty normal with cars that I have driven that have engines that use mass air flow sensors, so I'm not worried about it. If i remember correctly, what happens is that since the MAF is located before the throttle body, there may be some instances where the MAF tells the ECU that a larger amount of air has passed through it than the engine has really taken in, thereby causing a temporary overly rich mixture in the combustion chamber. The unburnt fuel vapor then ignites in the hot exhaust port exit area or the headers, causing a small backfire. Admittedly I'm just guessing, and have not really thought about it too much or looked into the possible causes...

Yes I do. I have posted several times in other threads that I have had this occur from pretty much new. Also Devo, it does this even if the engine hasn't been driven very hard. Sure it is warm, after a 10 mile -60mph trip, but not raced. Jack

Well, backfire as I said is an 'explosion gone wrong'. None of my recent sports cars ever backfired. Today's modern electronics and close tolerances should keep this from happening on a 'regular' basis. I'm not saying it might not happen once or twice, but it is something that if it is happening on a regular basis - something is wrong. It might be poor design (as in theMFS being upstream of the injectors)or it may be a bad ignition or valve 'item' (wiring, ghosting, hung valve, etc). Regardless, it isn't something you want happening on a repeated basis.... Paul

So, sorry for my ignorance Devo (or anyone else) but is a backfire unburnt fuel ignigting in the exhaust system, rather than inside the cylinder? This was my assumption, that it was unburnt fuel expelled from the cylinder, down the outlet manifold, that was then lit by hot exhaust fumes ffrom a subsequent cycle........is that correct? Jack

Can be unspent fuel in the exhaust. It can be an open intake valve and blown back through the intake. It can be a hung exhaust valve and be from the cylinder chamber. It can come from improper ignition (ie: pre-detonation) and blown out both intake and exhaust, or from a fouled spark plug (shooting unspent fuel into the exhaust where it's ignited), etc.... There are 'several' ways to create a backfire - none of them are 'normal' operations in progress. Ideally, all explosions happen inside a closed cylinder - for the obvious reasons. Also, are you certain it is a backfire and not resonance? It could be possible that you are hearing exhaust resonance. When I idle mine and 'blip' the throttle it makes some odd exhaust resonance noises that possibly could come across as sounding like a backfire. Paul

Mine also backfires occasionally. J

In my last car (2003) Nissan I put on a Header and Stromung Cat-Back Exhaust. It is my understanding that MOST if not ALL cars backfire. It's just that normally you can't hear it backfiring through the stock exhaust system. Sporty cars that are tuned to be quick (tuned with a 'lean' air to fuel ratio) will often times have unburnt fuel in the exhaust system which will often times ignite. It is completly normal and is nothing to worry about. I'm sure that Porsche has put hundreds of thousands of hours into the engineering of their engines and a hung exahaust valve is just not likely. It could also be 'resonance' as someone stated above. During down shift, or while the RPMs are dropping, some 'backfiring' sound is normal. On the other hand, if you are hearing LOUD shotgun sounding noises coming from your engine like an old 70's car backfiring and scaring everyone on the street; then you could have a problem. Shane

as i mentioned in the uk forum, my cayman backfire on the second heal-n-toe down change is a sequence. i guess i'm in the habit of taking two down shifts when slowing down for a slow corner from high speed: i'll go from say 5th to 4th and then 4th to 2nd: the second down shift can take a fairly hefty prod on the accelerator to match revs...

To answer your question about buying 93 Octane gas in Alabama. No, it will not hurt your engine. It is considered Premium fuel. The Cayman S requires premium fuel. In Utah the highest Octane normally available is 91 Octane. The reason there is a difference is due to altitude. 93 Octane is not required at such high altitudes (such as Salt Lake City). At high altitude, your engine will be less likely to experience detonation (due to the lower density of the air). I could get into the physics or chemistry of it but I'd rather not. Bottom line up front: At high altitudes, engines don't need as high of Octane Ratings. Therefore, the gas stations in Utah only sell 91 as their highest Octane Rating and Alabama sells 93 Octane. Won't hurt your car. You're doing the right thing. keep buying 93. Shane

Has anyone brought their Cayman S in to ask the service managers about the backfires? It happens to me when blipping the throttle and I intended to bring it in, but haven't because I cannot readily reproduce it. But it certainly happens to me all the time.