Is This Backfiring?
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5th Wheeling
Joined: Nov 2025
Posts: 32
Likes: 7
Is This Backfiring?
I have a 2004 6.0l truck with 47,000 miles on it. Sometimes when it starts, it lopes, then goes into a fast idle, but eventually settles into a normal idle.
But I took it out the other day and it started making a "backfire" noise under the hood upon hard acceleration. Normal acceleration it doesn't do it.
After a while, this behavior stopped and I could hard accelerate and everything is great. But then, it came back doing it again. I did notice it smoothed out temporarily when I put in a fuel additive, but that is still in the tank.
Anyone have a clue what is happening? It isn't backfiring out the exhaust. Seems to be under the hood. Thanks for any ideas!
But I took it out the other day and it started making a "backfire" noise under the hood upon hard acceleration. Normal acceleration it doesn't do it.
After a while, this behavior stopped and I could hard accelerate and everything is great. But then, it came back doing it again. I did notice it smoothed out temporarily when I put in a fuel additive, but that is still in the tank.
Anyone have a clue what is happening? It isn't backfiring out the exhaust. Seems to be under the hood. Thanks for any ideas!
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5th Wheeling
Joined: Nov 2025
Posts: 32
Likes: 7
I'm not sure how I would do audio. Not a bad idea, but the sound is somewhat muffled from within the cab. I get it - it's hard to describe a sound, but it's like a dull popping sound, as though some of the cylinders are misfiring but not all of them. And they only misfire when hard accelerating.
Hotshot
Joined: Apr 2010
Posts: 19,055
Likes: 235
From: Saratoga Springs,UT
FYI
Common for these to lope and go into high idle when cold
oil fired inject is cold blooded in winter high idle warmup in park is programmed by dealer under certain ambient temp conditions and should also be equipped with a block heater to plug into a 110ac outlet
Backfire is uncommon
does the truck actually stumble/hesitation upon the backfire event or just a popping noise in engine bay
Read codes
any gauges
Common for these to lope and go into high idle when cold
oil fired inject is cold blooded in winter high idle warmup in park is programmed by dealer under certain ambient temp conditions and should also be equipped with a block heater to plug into a 110ac outlet
Backfire is uncommon
does the truck actually stumble/hesitation upon the backfire event or just a popping noise in engine bay
Read codes
any gauges
Last edited by BLADE35; Nov 25, 2025 at 09:34 PM.
Thread Starter
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5th Wheeling
Joined: Nov 2025
Posts: 32
Likes: 7
FYI
Common for these to lope and go into high idle when cold
oil fired inject is cold blooded in winter high idle warmup in park is programmed by dealer under certain ambient temp conditions and should also be equipped with a block heater to plug into a 110ac outlet
Backfire is uncommon
does the truck actually stumble/hesitation upon the backfire event or just a popping noise in engine bay
Read codes
any gauges
Common for these to lope and go into high idle when cold
oil fired inject is cold blooded in winter high idle warmup in park is programmed by dealer under certain ambient temp conditions and should also be equipped with a block heater to plug into a 110ac outlet
Backfire is uncommon
does the truck actually stumble/hesitation upon the backfire event or just a popping noise in engine bay
Read codes
any gauges
Logistics Pro
Joined: Jan 2010
Posts: 4,085
Likes: 1,627
The more I think about this it sounds like a failed injector (stiction). You'd need to do an injector contribution test, not something every shade tree mechanic can do.
There are preventative things you can do to prevent this, such as running full synthetic engine oil and/or adding an oil friction modifier like Archoil's AR9100. However, once it reaches this point there's very little you can do besides replacing the injectors...but you'd need to know which one it is, which is where the contribution test comes in.
There are preventative things you can do to prevent this, such as running full synthetic engine oil and/or adding an oil friction modifier like Archoil's AR9100. However, once it reaches this point there's very little you can do besides replacing the injectors...but you'd need to know which one it is, which is where the contribution test comes in.
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335 Series- 5.8/351M, 6.6/400, 351 Cleveland
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