8.1 Vortec engine backfiring at times

[SUREK1]

I have 2004 adventure with 496 cid 8.1 engine.i have changed the egr and plug wires but no help. I can't pull up any codes.if i'm on cruise control and the trans downshifts for more power i backfire like it's making pop corn. Only 26000 miles on it. Maybe someone else has had this problem.thanks chuck surek1@verizon.net

[Rocky Larson]

I would include cleaning the Mass Air Flow Sensor in your search. CRC Mass Air Flow Sensor Cleaner, 11 Wt Oz - CRC05110

It is located just aft of the air filter box and has two bands holding it in place. It is round and about the size of a tin of mixed nuts. The wire connections maybe a little tight the first time you try to disconnect it.
http://www.brazelsrv.com/PDF_Files/C...structions.pdf

If you haven't changed the air filter I would consider that while in the vicinity.

[JonBrazel]

It sounds like your engine may be pre-detonating or "pinging". Do you have scanning software that can log long & short term fuel trims? Check your fuel pressure (should be between 55-62 psi at idle) and you can try cleaning the MAF sensor however in some instances it requires replacement of the MAF sensor to fix the problem.

[garyspang]

I have the same problem that started at 75,000 miles, when the changeover to 10% Ethanol occurred. Am now over 100,000 miles and must use high-test gas. The intake manifold backfire still exists as you described it. I do 100% self maintenance, The following did not fix it: new cam position sensor, new crank position sensor, new intake manifold pressure sensor, new mass air flow sensor, new pair of oxygen sensors, new fuel filters.
Injector boost was +15% on both sides. Cleaned the injectors with positive cleaner injection into the fuel rail. no change. Increased the fuel rail pressure to 70 psi, no pressure loss in rail during acceleration. Now the long term injector boost is around +-1% for both sides. No change in engine behavior. at 75000 miles the backfire used to be very bad at even the slightest acceleration attempt. Four treatments with SeaFoam at the throttle plate as per Mfr instructions reduced the problem to only backfire at 80-100% throttle opening. Checked the throttle plate dual potentiometer tracking with a differential input oscilloscope, tracking is perfect.
Used Zmax Micro-lubricant in oil and gas. engine runs smoother after 1400 miles. Gas mileage improve by about 0.5 mpg. Backfire problem is less, but still there.
What is next? A bore-scope examination through the plug holes, a colder plug and more vigilant driving to keep the throttle opening below about 80%.
Very frustrating, and no one knows why for sure.