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Discussion Starter #1 (Edited)
Okay so still having misfiring issues with out check engine light. 2 1/2 years of this. Ive been reading up on stuff and something that caught my attention was reading about the throttle body snapping shut. Let me explain.

When im at higher speeds and I let of the gas the truck instantly starts to slow down and back fire like if it were a manual and down shifted. It just doesn't seem like it wants to coast anymore and I have noticed mpg drop due to this.

I have supermods ptb and tune, cai, second cat and straight pipe.
Anyone else running similar mods have misfire issues?
Valves burning up from straight pipe? Throttle body problems? Etc..?

I have to much time and frustration into this problem that wont go away. And I cant afford to pay anymore waiting while the dealer tries to "replicate" the problem while they have my truck for a week.

Any help would be awesome and I will send virtual highfives and hugs to whom ever chimes in with helpful info.

Thank you,
Manny
 

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252,000+ Miles
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1,316 Posts
This happened to me a couple times right before I took my truck in for the warranty head replacement (~79k miles for me). it jerked, stumbled, kicked, almost stalled & backfired.

As soon as it happened I pulled the resonator off, pulled the coils and went to replace the plugs...and found 2 plugs covered in oil (from the top, not the bottom) and all the plugs were pretty well shot.

Took it into the shop as the CEL came on and didn't go out this time (P0300), described what happened and a week later I had a rebuilt engine (Head, timing chain, cam, valve springs, etc) at no cost to me.

Have a compression and leakdown test done. Mine had 1 cyl around 85%, 2 in the 35% range, one in the 50% range and one around 90%.

My advice to try and fix it if it's not the head would be:
Replace Fuel Filter
Replace Fuel Pressure Regulator
Replace MAP Sensor
Clean MAF Sensor
Clean TB & Seafoam Head
New Spark Plugs & Supersparkz
New Camshaft Position Actuator Solenoid & Crank Position Sensor
Check & Clean All Grounds under the hood
Check & Clean all QD Connections to MAP Sensor, MAF Sensor, TB, Ignition Coil Harness (Back of block) & Each Coil Connection.

That about covers the "moving parts" that could cause what you are looking at without throwing a code that isn't bad valve seats.
 
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