BackFire

[Big Silly]

I am having trouble with my 350 backfiring while I am traveling at a constant speed in high gear. What would cause this to happen. I have never had this trouble before.
I believe it to be a small ignition problem, wires, plugs, etc... However, I recently had to have the heads machined on my '88 Blazer. Would this in any way cause this problem or I'm I only paranoid.

 

[78Suburban]

timing? are we talking exhaust or carb backfiring?
thanks,
James

 

[13lazer]

smog air pump malfunction? i had a 3" hole in my passenger side exhaust manifold that i couldnt see under the heat shield. i swapped the donut 3 times before i saw the hole. with too much oxygen, and unburned gas you can get backfires. the 85 sub with the hole also spit my mufflers wide open a few times thanks to the diverter valve and that retarded heat riser butterfly valve.

 

[Big Silly]

Exhaust Backfire

 

[78Suburban]

what kinda exhaust system do you have?
thanks,
James

 

[Big Silly]

True duals with flowmasters

 

[78Suburban]

does it only backfire when you let off the gas?

PS: are we talking about a mild popping/ gurgling, or one of those crap your pants gernades going off under your truck?

 

[Big Silly]

It is only backfiring when the motor is running in over drive at a lower RPM. This happens while maintaining a constant pressue on the acclerator. It's only a moderate back fire.

 

[dremu]

smog air pump malfunction? i had a 3" hole in my passenger side exhaust manifold that i couldnt see under the heat shield. i swapped the donut 3 times before i saw the hole. with too much oxygen, and unburned gas you can get backfires. the 85 sub with the hole also spit my mufflers wide open a few times thanks to the diverter valve and that retarded heat riser butterfly valve.

Ah yes, the quality GM exhaust manifolds and those heat shields ... grrr

I knew it was bad when the JUNKYARDS sold NEW aftermarket pieces.

-- A

 

[dremu]

does it only backfire when you let off the gas?

PS: are we talking about a mild popping/ gurgling

<hijack>

What causes this? My bigblock pops and sputters when I let off the gas ... timing, or weird back pressure?

</hijack>

-- A

 

[78Suburban]

<hijack>

What causes this? My bigblock pops and sputters when I let off the gas ... timing, or weird back pressure?

</hijack>

-- A

well, I'm am VERY VERY far from an expert, but my old green truck did it with straight headers. My straight piped burb does it some when I let off the gas. I think it is supposedly something to do with cold air getting sucked in from the exhaust pulses and detonating left over gas or something.. I've heard that cold air can acutally suck in a chip a valve. But I'm not really certain..
thanks,
James

 

[wildmouse216]

if you are running too rich or your timing is off it can pump gas out of the cylinders and the excess gas can detonate in the exhaust system and cause mild explosions.