Ok, I've been running a slight tune (timing, TM) for about 6 months and last week I stared to get misifres out of the blue. So I flash the PCM back to stock and the misfires become terrible about 4000 RPM.

The funny part is that it only happens on 1-3-5-7 cylinders... isn't that just 1 side of the engine? Any thoughts?

2003 4.8L Silverado, Automatic, Bone Stock

 

Sounds like maybe your coil packs aren't pluged in well, or something along those lines.

 

check the wiring to the coil packs

 

yeh the whole bank is pretty suspicious. Done anything at all as far as upgrades? wires? plugs? check the grounds on that bank (driver's side). make sure all connections in line with those coil packs are golden (good condition & securely fastened). pull you left bank plugs, check em out just for ***** and giggles.

 

Yea, I checked the plugs and they look fine. All the wiring is solid as far as I can tell. I think its just strange that its an entire side of the engine al at once. I'm no expert on this, but I can't really thing that is common on that side expect that they are all on one fuel rail together.

No mods have been done other than a wet NOS kit that has been on the truck for 2 years and never used once (long story).

 

the "common" is the big plug that all of the coil packs tie together to which links it to the rest of the harness... I would inspect grounds for that section of the harness along with the fuel injector portion

 

Plugged Cat on that side.....If it were the coils the truck would barely idle. If it comes on at 4000 I would suspect the Cat in that bank.

 

what about an 02 sensor?

 

Nothing to do with it I was selling these blowers 5 years ago

 

There is a bulletin about the o2 sensor actually causing the misfire on one bank... I will look and see if I can find it...


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Subject: 97-05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires on One Bank - kw CEL diagnostics driveability DTC P0171 P0172 P0174 P0175 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 #PIP3056 - (07/12/2004)



Models: .




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The following diagnosis might be helpful if the vehicle exhibits the described symptoms in the PI.

Condition/Concern:
Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

Recommendation/Instructions:
If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:

Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.
Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.
Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.
Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.



Hope this helps!!!