'02 Silverado. CarMD says P0304.

[airtight_python]

'02 Silverado 4.3L. CarMD says P0304 - misfire on cylinder 4.

Misfire is most prominent when letting off of the accelerator at highway speeds and in low gear at higher RPM. Exhaust smells rich and fuel economy is poor. Wires and plugs were replaced at one point and the problem persists. Distributor cap and rotor also replaced. I run Seafoam in tank and through vaccuum once or twice a year.

I assume it's an injector sticking open, but where do I go from here rather than throwing money at it?

[j cAT]

Originally Posted by airtight_python

'02 Silverado 4.3L. CarMD says P0304 - misfire on cylinder 4.

Misfire is most prominent when letting off of the accelerator at highway speeds and in low gear at higher RPM. Exhaust smells rich and fuel economy is poor. Wires and plugs were replaced at one point and the problem persists. Distributor cap and rotor also replaced. I run Seafoam in tank and through vaccuum once or twice a year.

I assume it's an injector sticking open, but where do I go from here rather than throwing money at it?

how about a broken valve spring ?

[slo99sierra]

Originally Posted by j cAT

how about a broken valve spring ?

I wouldn't think this unless oil flow had stopped. The 4.3 internals and other components are spec'd out like 350 specs - strength and durability wise.

Is it a persistent code? Does the SES flash?

Since it's an 02, I'd say the poppet valve is stuck open on cyl.4. Find someone with a scan tool that can do an Injector Balance (or with the spider injector system, the poppet valve balance) test and see what that does.

[j cAT]

Originally Posted by slo99sierra

I wouldn't think this unless oil flow had stopped. The 4.3 internals and other components are spec'd out like 350 specs - strength and durability wise.

Is it a persistent code? Does the SES flash?

Since it's an 02, I'd say the poppet valve is stuck open on cyl.4. Find someone with a scan tool that can do an Injector Balance (or with the spider injector system, the poppet valve balance) test and see what that does.

since this is just #4 or it could be any ONE cylinder , reports have shown this is where its defective the springs for some reason break on these engines. this is the 4.3L ..V6..

checking compression should confirm this , as well as the valve cover removal.

no compression you will get missfire !

[airtight_python]

Originally Posted by slo99sierra

I wouldn't think this unless oil flow had stopped. The 4.3 internals and other components are spec'd out like 350 specs - strength and durability wise.

Is it a persistent code? Does the SES flash?

Since it's an 02, I'd say the poppet valve is stuck open on cyl.4. Find someone with a scan tool that can do an Injector Balance (or with the spider injector system, the poppet valve balance) test and see what that does.

SES comes on rarely. I can't clear the codes with the CarMD to see if it persists. The engine is slightly rough at idle at all times but not terrible. The missing does seem to get worse with the vehicles heater running.

[airtight_python]

Upon further observance I notice that the passenger side bank of cylinders has much more noticeable 'valve tap.' Cylinder 4 is center on this bank correct?

The valve cover gaskets are reusable if I am to pull it off for a peak?

[j cAT]

Originally Posted by airtight_python

SES comes on rarely. I can't clear the codes with the CarMD to see if it persists. The engine is slightly rough at idle at all times but not terrible. The missing does seem to get worse with the vehicles heater running.

when this totally craps out then it will be easier and no guessing or testing as well.

might have to replace the converters, as that unburned fuel will kill them.

[airtight_python]

Originally Posted by j cAT

when this totally craps out then it will be easier and no guessing or testing as well.

might have to replace the converters, as that unburned fuel will kill them.

??? Id rather fix it before it craps out.

[j cAT]

Originally Posted by airtight_python

??? Id rather fix it before it craps out.

If so check compression, check plugs and plug wires at this time . measure wire resistance in OHms should all be close in value.

if the compression is low remove the valve cover and check that the valve springs are good.. then it can get into head gaskets etc..