just got done switching coils,plugs,wires,1to3 and 6to8 does samething. when you start car and the idle finally settles does it starts lightly missing and you can feel it, and the miss fire counter states about 10-20 counts per cycle then when reved to 2300rpm the miss fire counter goes right with the cycles and sets p0300 on #1 cyl. and #6 misses alot too but not as much and you can not feel the miss in or out of gear when step on throttle?
and you are 100% sure you have no vacuum leaks at all from the intake manifold? do you know how to flow the fuel injectors with a fuel guage hooked up to the fuel line test port and fire each injector and see if they all evenly drop the same PSI? but remember to only fire the injectors after you key it to get the fuel PSI at the same starting point to get accurate injector drop readings.and try this bulletin too and see if this will fix it.
Subject:Information on Engine Misfire MIL/SES Light Illuminated or Flashing DTC P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0420 or P0430
Models:1999-2007 Cadillac, Chevrolet, GMC Full-Size Pickup and/or Utility Trucks
with 4.8L, 5.3L, 5.7L, 6.0L or 6.2L VORTEC GEN III, GEN IV, V-8 Engine (VINs V, C, T, Z, B, 3, M, 0, J, R, U, N, Y, K, 8 - RPOs LR4, LY2, LM7, L59, L33, LC9, LH6, LMG, LY5, L31, LQ4, LQ9, L76, LY6, L92)
with Active Fuel Management(TM) and E85 Flex Fuel
If you encounter vehicles that exhibit the above conditions, refer to SI for the appropriate DTC(s) set. If no trouble is found, the cause may be due to an ECM ground terminal that has corroded with rust over time. Inspect the main engine wiring harness ground terminal (G103) for this condition.
Attachments are only available to registered users.
The wire terminal (G103) attaches either to the front or to the rear of the right side cylinder head, depending on the model year of the Full Size Pickup and/or Utility Trucks. If the ECM ground terminal has been found to be corroded, then follow the service procedure outlined in this bulletin to correct the corrosion issue.
Remove either the nut or bolt securing the main engine wiring harness ground terminal (G103) to the right cylinder head. Refer to the above illustration to determine where the ground is located on the vehicle (1).
Remove all rust from the ground terminal, the cylinder head and the retaining nut or bolt.
Position the main engine wiring harness ground terminal and install the nut or bolt.
Tighten the retaining nut or bolt to 16 N.m (12 lb ft).
Apply some type of electrical moisture sealant to protect the harness terminal from further corrosion.
Yes we did a fuel drop injector flow test and all passed, has no intake leak,we had already cleaned a bunch of grounds but went crazy with them again,and even added some,and that did help.now we hardly get any missfire counts except #1 it acts as follows. at idle in nuetral maybe gets 10 to 20 missfires per cycle,accelarate to almost 1750 with no missfire and from 2000to 3000rpm counter goes with cycles and sets code p0300 after 3000rpm no missfires, in gear under load or driving no missfires no code set?
here is that bulletin
Subject:LM7, L59 or L33 Engines with Cold Start Rough or Incorrect Idle, Misfire, Malfunction Indicator Lamp (MIL) or Flashing Requiring 02 Sensor Replacement (Reprogram PCM)
Models:2004-2005 Cadillac Escalade2004-2005 Chevrolet Avalanche, Silverado 1500, Suburban, Tahoe2005 Chevrolet Silverado Hybrid (HP2)2004-2005 GMC Sierra 1500, Yukon, Yukon XL2005 GMC Sierra Hybrid (PH2)
with Vortec 5300 5.3L V-8 Engine (VINs T, Z, B - RPOs LM7, L59, L33)
Some customers may comment on a Malfunction Indicator Lamp (MIL) On or that the MIL is flashing. An actual engine misfire may or may not be felt along with an incorrect idle speed. Typically this occurs during cold winter months, on cold engine starts. Some vehicles may have been previously serviced for the same condition. Technicians may also find the following DTCs stored with the Tech 2(R) P0131, P0133, P0134, P0137, P0138, P0140, P0151, P0153, P0154, P0157, P1133, which may be in conjunction with P0171, P0174, P0300 and P1138.
Water shock occurs when water droplets are present in the exhaust. The water in the exhaust contacts the sensor element inside the H02 sensor, causing the H02 sensor element to crack.
Upon diagnostic investigation, the technician may find that the H02 sensor requires replacement. In addition to replacing the affected H02 sensor, these vehicles should also be reflashed with the latest PCM calibration. An updated PCM calibration will be available to dealerships as part of TIS 2000 incremental satellite update 11.0 (NAO version 25.010) or greater. Always, make sure your Tech 2 is updated with the latest software version.
Important: If a DTC P0420 or P0430 is stored along with DTC(s) P0300, the catalytic converter diagnostics in Service Information (SI) must be followed to determine if the catalytic converters are operating properly.
Your not going to believe this,just had a 2002 suburban with 6.0 in doing the samething.
at 2300 rpm check engine light flashes and sets p0300 code you can watch the missfire counter missing on # XXXXX and 6 cylinders but no drivabilty issues?have not figured out either one.