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[Burt4x4]

How does a motor backfire out the tail pipes? I'm not talking about a mild pop I mean BOOM loud as *&$#)!@#!!!!
To get that loud of an explosion out the back can I assume its ALL the cylinders that cause the backfire?
I'm still troubleshooting this issue and getting no were................

72K5

Led Zeppelin

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[**DONOTDELETE**]

More than likely it is a timing issue. Your engine is firing when your exhaust valves are at least partially open, causing the aforementioned explosion. Either your distributor has moved, or your timing chain has slipped, more than likely. There are a few other causes, but timing is the most obvious culprit.

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[Burt4x4]

I thinking something along thoes lines too but when I slap on my timming light I get about 8 on the tab. But then again the backfire seams to happen when accelerating. The motor idels and runs fine besides the acasional skip bang! I drove it to work this morning, about an hours drive, and while cruzin down the hwy at 65 it ran fine. If I take it real easy off the line the chances it it skipping are less than if I put my foot into it while shifting and such......
Carborator?
Ignition?
Both?
@#(*)(@*$#(*!#(*$_!#)(_!@)#*@(@*#(@!*$_#$(@#)!*$

72K5

Led Zeppelin

Rock ON!

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[Gold Rush]

Another major cause of backfires is a vacuum leak or vacuum operated solenoid leaking. check and double check all vacuum hoses.


David

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[delta9blazer]

if your compression charge isn't being burned completely, the exhaust will have enough fuel in it to detonate. and once you're on the freeway (even at the altamont crawl speed) your exhaust is getting kinda sucked outta yer tailpipes, leaning out the mixture.
i know that if you leave your truck in gear, rolling down the road, and turn the ignition off, the fuel charge will not be lit by the spark plug, and the headers/exhaust will fill with fuel. then, when you turn the key back on, the spark plugs lights, and BANG.
so you're doing close to the same thing, with unburned fuel, leaky exhaust valves, and driving it when it's freakin 32 degrees out.

anyway, that's my lame-assed guess.
you goin to long barn next wknd?


<font color=purple>delta9blazer</font color=purple>

 

[txbartman]

Just stabbing here, but could it also be a result of faulty valve springs? If a spring was causing an exhaust valve not to close all the way, the same impact would occur. Isn't that what they mean by "valve float"? Just from the physics of it, that seems to me to also be a possibility. And, it might explain why it doesn't do it at idle.

Brian
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[**DONOTDELETE**]

I concur w/ Goldrush. A vacuum leak could very well be the cause from the way it sounds.

Alcoholism isn't a problem, it's a GOAL!!!!!!!

 

[chevyracing]

I had this problem on my 72 before I put my electronic ignition in it. It drive nukkin futs!! I never could figure out what was causing it so I put electronic ignition in it and waaalllllaaahhh!! I checked out my old distributor real good and found out the advance weights were worn into oblivion. I have heard that can cause it. Bad plug wires can cause it too. If you are not firing the cylinder when it should fire that fuel is going into the exhaust and spontanously going ka-boom like a previous poster said. A bad condensor could be another cause. It will do the same as above. A loose connection on the condensor to points connection will also cause it. If it is electronic ignition a bad pick up coil could cause it too.

John

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[BurbinOR]

Vacuum leak...........check the header gaskets/collector gaskets first, then work up to the motor.

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[k5king]

i have to agree with delta and chevy,, i had the same problem on another vehicle,,to much unburnt fuel going into the exhaust,,when it get 's to that point where the exhaust is at it's hottest along the exhaust pipe,,it ignites,,causing the backfire you hear.
also,,on my old camaro i had,,the ignition module went bad in the distributor,,it didn't just quit working,,it did that same thing,,made it back fire under acceleration because it didn't have enough juice to ignite the fuel in the chamber,,after 2 or 3 day's of this,,it finally ended up blowing my mufflers right off the car when i put my foot into one evening.
this is another one of those mysteries that your going to have to prolly check,,and re-check and try several thing's before you find it. try swapping a dist. and cap from somehting else if you can just to prove that part wrong.

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