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Hello All,

My VG30E is missing / stumbling at all ranges (smooths out a little at higher revs). I've done:

new cap, rotor, plugs, wires, fuel filter

coil resistance good

get spark at every wire boot

checked EGR, PCV valves

only trouble code is a 34- knock sensor

My neighbor held a dollar bill to the exhaust pipe at idle, and it intermittently sucked the bill against the pipe. He said that indicated a sucking valve. I put Marvel Mystery Oil in crankcase and B12 Chemtool in the gas, and drove it for a week with no results.

I've since checked compression on cylinders, which averaged 135psi. The plugs all looked similar after 120 miles except for #4, which had clean metal, with only some scorching on the ceramic insulator.

1.) Could a misfiring cylinder create enough vacuum in the exhaust to suck a dollar bill up against the pipe?

2.) Would I get good compression if a valve was burnt/stuck open?

3.) Could I have a clogged/defective fuel injector?

4.) Is there an easy yet definitive way to test a fuel injector? (#4 is buried under the intake plenum)

Thanks for any help or answers,
Dee
 

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Hello All,

My VG30E is missing / stumbling at all ranges (smooths out a little at higher revs). I've done:

new cap, rotor, plugs, wires, fuel filter

coil resistance good

get spark at every wire boot

checked EGR, PCV valves

only trouble code is a 34- knock sensor

My neighbor held a dollar bill to the exhaust pipe at idle, and it intermittently sucked the bill against the pipe. He said that indicated a sucking valve. I put Marvel Mystery Oil in crankcase and B12 Chemtool in the gas, and drove it for a week with no results.

I've since checked compression on cylinders, which averaged 135psi. The plugs all looked similar after 120 miles except for #4, which had clean metal, with only some scorching on the ceramic insulator.

1.) Could a misfiring cylinder create enough vacuum in the exhaust to suck a dollar bill up against the pipe?

2.) Would I get good compression if a valve was burnt/stuck open?

3.) Could I have a clogged/defective fuel injector?

4.) Is there an easy yet definitive way to test a fuel injector? (#4 is buried under the intake plenum)

Thanks for any help or answers,
Dee
135 psi on all cylinders is rather low which indicates possible wear on the rings. When performing a compression test, make sure the throttle valve is held wide open.

If there's a burnt/stuck open valve, the compression on that cylinder will be low in comparison to the other cylinders.

Number 4 fuel injector could most certainly have a problem since the spark plug seems to show less combustion. It's possible that the injector just has dirt in it. Run some good injection cleaner, like Techron or Redline SL-1, through the system; give the cleaner about a week or two to do it's job. Then go back and check the injector again. If still questionable, replace it.

There is also a product called BG products 44K. It is however a very strong cleaner so use it sparingly.

The knock sensor should definitely be replaced if found to be defective otherwise the motor could be exposed to excessive detonation which is harmful.
 
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