SickSilverado

I have an iron 5.3 bored to 5.7 size. Its in a 2004 Silverado. I keep getting the flashing CEL. When I scan it for codes I get the P0300 and also mass airflow low voltage. The truck shakes a lot at idle and won't rev cleanly. It struggles to hit 30mph. At times I can hear the engine backfire both from the exhaust and the intake (I think). After checking plugs I found that cylinders 3,5,7, and 8 were fouled. I replaced the plugs, coils, and wires. Still runs the same. I sea foamed the motor, still runs the same. I used fuel injector cleaner in the tank, still runs the same. I sprayed around to check for vacuum leaks. At this point I'm running with the MAF unplugged. It still runs like crap but it hasn't stalled out on me and it doesn't show random misfires anymore.

Cleaned MAF
Cleaned throttle body
Seafoamed engine
Sealed PCV fitting
Changed coils
Changed to MSD wires
Changed plugs
Tightened intake manifold bolts
Checked fuel pressure (good and stead)
Checked rockers, springs, and pushrods(visually)

Fuel trims are:
Bank 1 Short term = 0.78
Bank 2 Short term = 0.78
Bank 1 Long term = 19.53
Bank 2 Long term =10.16
Bank 1 sensor 1 = 3.12
Bank 2 sensor 1 = -1.56

O2 sensor voltage:
Bank 1 sensor 1 = 0.76
Bank 1 sensor 2 = 0.16
Bank 2 sensor 1 = 0.58
Bank 2 sensor 2 = 0.83

I'm not sure what any of those numbers mean. It's just what my scanner showed. Not sure where to look next. I'd appreciate any help or advice.

LS6427

iTrader: (2)

How long has the engine been in there......?

Did it run fine for awhile....and this started out of nowhere.....?

Or has it ran like this since the first start-up...?

Engine Grounds
02 sensor(s)
PCM grounds

My first guesses.

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SickSilverado

It's been this way since I bought the truck. Previous owner can't tell me anything about it. It ran like crap before I bought it and is seeming to get worse. Message center says "reduced engine power" when I floor it.

Engine grounds seem to be intact. O2 sensors could be toast, but I wouldn't know how to check other than the voltage I posted above. PCM grounds...I'll go check that now.

LS6427

iTrader: (2)

When its all bogging down at slow speeds.....does it wake up all of a sudden when you hit the pedal......? And it feels powerful for a few seconds....

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LS6427

iTrader: (2)

What spark plugs....?
What gap...?

Are any of the spark plug WIRES touching any of the metal exhaust manifold pipes...?

I would get a scan while the engine is running to see how the 02 sensors are switching...?

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SickSilverado

Kinda...at low speeds too much gas pedal makes it bog down or do nothing at all. At highway speeds it'll kickdown and run OK at best. The 1-2 shift is probably the worst, the truck just falls on its face and slowly gains rpm/speed. My buddy has a stock/worn out/beat to **** 2003 V6 truck that will blow my truck away. Something has to be wrong with my truck.

SickSilverado

The original plugs were all NGK TR5's. But 4 were worn out and the only plugs I could get my hands on were TR55's and all were gapped a .045 or a little less. No wires are touching. What range should the O2 voltages be? What should I look for there?

The truck wobbles when I rev and it's a very lazy rev. I have tried 3 other trucks with DBW and they all rev as you would expect.

LS6427

iTrader: (2)

You need to find a guy that can read the 02 sensors switching with an OBDII scanner while its running at operating temp,,,,,,and knows what hes looking for.....I am not sure what ranges the sensors should be switching at. But you can ask that in the PCM/Diagnostics section......

I think you have bad 02 sensors......but scan it first before buying them. You have the classic symptoms.......

.045 is fine....TR55's are the plugs you want. TR5's are fine too....same plugs. TR5's just come pregapped and need to be gapped before install to what you want.

You checked all the gaps on each plug before installing....right...?

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SickSilverado

Yes, checked gaps on all plugs.

Can I just unplug the rear O2 sensors? Will that tell me anything?

Another thing I just noticed was that the purge solenoid on the intake has a plastic line the runs back to the tank...this line looks to have been broken and taped shut. Will that cause any problems? It probably explains why my truck smells like raw gas all the time.

SickSilverado

PROBLEM SOLVED!
It was clogged injectors. I did some reading about fuel trims and what they mean and came to the conclusion that I had either a vacuum leak or a clogged fuel system. The 04 Silverado only has an in-tank filter, so that only left the screens in the injectors. Sure enough they were clogged with a white crud. I used some speaker wire to dig out the crap and sprayed them out with TB cleaner. I also cleaned the rails with simple green and let the injectors sit full of TB cleaner for a while. The truck runs so smooth now. I even did a burnout. I hit highway speeds at a good rate now. Fuel trims are almost normal. Just need to clean the passenger side injectors(got too dark to see outside). Thanks for all the help everybody.

LS6427

iTrader: (2)

Sweet.....put a in line fuel filter in so this doesnt happen again.

I also run a FULL can of SeaFoam in 1/8 tank of gas......every 3-4 months. Run that 1/8 tank as close to empty as possible. Keeps the injectors nice and clean...and keeps the fuel pump and all lines clean....for $6.00 every 3-4 months. My injectors are 12 years old and been on 3 different fully built engines.

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