Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
- 2008 silverado 5.3 engine
- P0300 code, snap-on scan tool indicates misfiring on cylinders 1, 2, 4, and 7
- before current issue vehicle had slight lifter tap sound and white smoke from exhaust on every start up. Never had any check engine light. Took engine apart and did the following:
- Headgasket replaced
- Headgasket bolds replaced
- Valve gasket replaced
- Valve stem seals replaced
- Cleaned and reseated existing valves since there was no damage
- Intake mainfold gasket replaced
- Exhaust gaskets replaced
- Upgrade driverside valve cover
- Valve cover gaskets replaced
- Replaced all 8 amf lifters with new amf lifters
- Replaced all 8 non amf lifters with new non amf lifters
- All lifters were put in correct locations, there was no damage to any of the old lifters, all rollers where in great shape, only issue was a few of the amf lifters could be compress slightly by hand
- Visual inspected cam and no damage of any kind
- Cam and Crank sensors replaced
- Engine coolant temperature sensor replaced
- Waterpump replaced
- Thermostat replaced
- Spark plugs had been replaced 1,000 miles ago
- Spark plug wires had been replaced 1,000 miles ago
- Fuel injectors had been replaced 1,000 miles ago
- All o2 sensors replaced
- All rocker arms torqued down to 22lbs, turned engine for each so they where not on head on cam for installation
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- Once engine was put back together flashing check engine light present with code p0300
- Moved coil packs to see if misfires followed, no change
- Compression test on all cylinders with reading of 180psi for each
- Performed tps relearn, no change
- All rocker heads move while engine is cranked with valve covers removed
- Cylinder 1 misfire count of 53
- Cylinder 2 misfire count of 27
- Cylinder 4 misfire count of 107
- Cylinder 7 misfire count of 58
- While under load all misfires dissappear but come back at idel
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Any suggestions to resolve this issue would be greatly appreciated
Does the engine actually misfire? Did you do a crank pattern relearn?
If true misfires are present I suggest to check the engine's vacuum while cranking and at idle and to do a cylinder leak down test. Do you have the means to do in-cylinder-pressure /intake manifold pressure testing with a transducer?
Are the cylinders indicated as misfiring those that are controlled by the amf ?
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
cylinders 1, 4, and 7 are the afm lifters but the afm only becomes active while at a cruising speed on 40mph, when engine starts all cylinders are running as a v8 engine
Cheryl wrote: Betting it’s the cam that has damage. So how bad is the misfire? Does it feel rough
I imagine a bad cam would perform worst and manifest itself under high load/rpm as these are the conditions where a restriction will have greater effect.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
The misfire is rough, rides fine while actually moving, rides terrible at idel, the cam never had an issue with the old lifters so why would there be a new issue with new lifters and did not see any damage while roating the engine with no lifters in.
dgs000 wrote: Even tho all cylinders are holding air at 180psi during compression test you still think there is possibility of a air leak
ABSOLUTELY!!
A compression test with a gauge will only show the (accumulated) peak pressure achieved during the 5, 6 puffs. There is a so called Schräder valve built into which will retain the pressure in the hose where the gauge is connected.
It is not a conclusive test at all regarding possible leakage.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
