Fast86z

iTrader: (1)

I figured this was a good place to ask. This is my tow vehicle I recently purchased to haul a travel trailer. A bone stock (except muffler) 2000 Silverado 2500 with 6.0/4l80e with 200k.

This problem is persistent pinging and at the point where the vehicle is practically unusable for towing as it pings repetitively at about all part throttle load conditions and even sometimes when not under much load at all just normal driving. I just got done doing a trial run towing about 30 miles pulling 7k lbs. once the engine gets between 2k and 2500 rpm it starts pinging/rattling heavily to the point where I have to back way off the throttle and even then still pings. This happens in all gears even first when above 2k-2.5k rpm. This also happens with 87,89, and 93 however it is reduced as octane increases. 93 makes a significant difference but going up a grade at 2500rpm it sings like marbles in a jar.

I've noticed one thing that has remained constant. With the MAF unplugged, there is ZERO pinging that I can hear. I hooked up the scanner and viewed the live data while under load during the part throttle pinging condition.

-- MAF PLUGGED IN PINGING PART-THROTTLE LOAD
IGN ADVANCE = around 25-30 degrees
LONG TERM FUEL TRIM = around +5 both banks
SHORT TERM FUEL TRIM = constantly switching + and - a few

-- MAF UN-PLUGGED NOT PINGING PART-THROTTLE LOAD
IGN ADVANCE = 15-20 degrees
LONG TERM FUEL TRIM = around -7 both banks
SHORT TERM FUEL TRIM = around -10 to -12

From what I gather the with MAF unplugged the vehicle is still in closed loop but in some sort of conservative safety mode as the trans shifts violently hard and the scanner shows retarded ignition from normal table and a fuel table that is adding much more fuel as the computer is commanding negative LTFT and STFT.

So far I have tried:
All the snake oil cans of fuel additive.. (3 cans seafoam, 2 cans berryman b12, 2 bottles techron...About $50 worth over multiple tanks and even seafoam through vac hose) I don't think it's carbon buildup
Replaced the fuel filter
Filled up with name brand gas with all 3 grades
Cleaned the maf resistors with alcohol
Replaced MAF with parts store reman (returned it)
Replaced the knock sensors and harness
Replaced the intake manifold gaskets
Replace the pcv valve
Relaced the Egr valve with a different used one and checked for plugged ports
Fresh spark plugs, fresh wires
Checked cat converters with IR thermometer. Over 100 degrees difference on outlet vs inlet (checkd good?)
Fuel pressure at idle 54psi (within spec)

My ideas of what to try next are dwindling
Maybe replace the 200k mile upstream o2 sensors
.. Spend $500 on hptuners and tune it out
Gamble on a couple cat converters?

Suggestions? I am at wits end with this issue.

GMCtrk

iTrader: (27)

Fuel pressure needs to be checked under load.

Also, high probability that your rear knock sensor is corroded and could be causing the problem.

Fast86z

iTrader: (1)

I replaced the knock sensors already.

If it was loosing fuel pressure under load, say 50% throttle, wouldn't the o2 detect this and show a correction on the scanner by richening the fuel trims?

Btw I replaced the o2 sensors today with no luck

Fast86z

iTrader: (1)

Here is a video of the ping and one of the scanner

Fast86z

iTrader: (1)

I checked the fuel pressure under load. It stays steady at 58 psi.

I replaced the o2 sensors.

I am running out of things to change.

Should I buy hp tuners and tune the ping out? I have a lot of experience with megasquirt.