I am curious about this. I thought that backfiring occurred in vehicles that had some sort of a fuel management/choke issue. IIRC a backfire is usually produced when unburned gasoline gets into the exhaust system (muffler?), igniting in there instead of inside the engine.
But my car only has 20,000 miles on it and is in perfect working condition. This only happens right after startup (the engine is cold) and only if I wind 1st gear out to about 3,000 or more RPM’s and I let off the gas without shifting into second. Once the engine warms up it doesn’t do it anymore.
I’m not sure if this is a true backfire as its not crazy loud like I have heard other cars produce. It actually sounds sorta cool, but I am wondering what causes this.
It has very rich settings when cold. This is common in many cars, but even more-so in very high-performance cars with aggressive cams and is magnified it apparent intensity by wider exhaust pipes/outlets.
What year is your car? It isn’t technically a backfire inasmuch as a by-product of the interesting combustion as it runs rich with its aggressive cam and fairly wide exhaust pipes and how the backpressure plays off all this when lifting throttle.
Engine design (single cam) can really influence this because of valve overlap.
Its a 2008 GT Premium. I figured it had something to do with fuel. Like I said, I don’t think its a true backfire as its not ridiculously loud, but its certainly audible. I’ll go along in 1st gear, get the RPM’s up a little bit then back off the throttle without shifting and its like “burble burble POP POP POP burble”.
ETA: and I’m pretty certain my car is a single cam engine…its the latter run for the 3V 4.6 modular motor before Ford came out with the new 5.0 litre “Coyote” engine (the bastards).
Single overhead cam engine w/ rich cold settings and valve overlap = lots of resonance, especially when cold.
Your engine will actually have a ‘sucking back’ action during the initial intake stroke because the exhaust valve is still open.
This, combined with the rich fuel setting, can create a reversion/reverb (loud-arse BURBLE) when the throttle is suddenly lifted. It can ‘pop’ a bit since it’s some sound waves colliding. They should be going out, but the valve overlap creates a little reversion/reverb. That heavy, cold, rich exhaust creates some interesting sounds as it bounces around (and back into other waves).
in addition, the catalysts are cold so that rich fuel mixture isn’t being burned effectively in the converters. it’s normal, but you are hearing it because the Mustang has a relatively loud exhaust compared to the average cars.
The 3V 4.6 is a SOHC design, in this case it actually has two cams because it’s a V8. It has one cam on top of each cylinder head. It’s not considered a DOHC engine because on a V8, that would mean 4 cams. Two per head.
I believe the sound you are hearing is due to the fact that all American V8’s are a crossplane design. this design requires an “uneven” firing pattern on both banks. This causes the “burbling” sound American v8’s are known for.
The “backfiring” you are refering to is part of the wonderful sound American V8’s make.
One more data point. When cold the engine management system retards the ignition timing to help warm the engine quickly and bring the cats online faster.
So you have a rich, hot, still burning mixture going into the cold exhaust system. Yup you can get a pop or two that way.
I question if it could be valve overlap. Overlap was pretty much eliminated due to emission standards for new vehicles. I’d think more along the lines of an ignition related problem, or what Rick mentioned above. My daughter has had an 06 GT since new, and it has never backfired. I know, I heard it start every morning for several years.
This. You’ll know if it backfires. there will be pieces of exhaust shooting out the back if fuel loads into and ignites in the exhaust system. I’ve had ignition systems cut out in a carb’d car so fuel is still sucked through the power stroke. You can easily drop a set of pipes on the ground when this happens.
(here’s a hint: the Caliber was a total abortion and I’m intentionally denying any knowledge of its existence. and yes this means mine is a Neon SRT-4.)
and with DOHC/dual VVT you can even “fake” that lopey idle:
Thank God. I’m like “this guy seems to know so much about cars and he doesn’t know what a Caliber is?” And I agree…horribly ugly car, almost Pontiac Aztec-ian in its clunky appearance. Though I admit the SRT-4 variant looks a little better, but not much.
