# Vibration



## Penny (Mar 2, 2017)

Check engine light was on. Vibrates bad. Had it checked and it said coil pac or plugs. Had all coils and plugs changed plus sensor under gas pedal. Still vibrates but engine light is now off. Vibration stops when you let off of gas. Any ideas. Fed up having this sucker repaired. It's a 2004 maxima


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## rogoman (Dec 16, 2004)

A severe engine vibration could be caused by one or more of the following:

- Dirty or Improper spark plug(s)
- Insufficient compression
- Incorrect fuel pressure
- Dirty fuel injectors
- Intake system vacuum leak
- Incorrect PCV hose connection
- Incorrect cam timing 

The condition you're describing can also be caused by a marginal crankshaft position sensor or a camshaft position sensor. If you're buying one or both of them, buy only OEM units from a new car dealer. Don't buy aftermarket types; they've been known to fail in a short time; some are even DOA.

To properly diagnose dirty/leaking fuel injectors, they need to be remove and tested on a flow bench tester. You can also do a quick leak test by teeing-in a fuel pressure gauge to the fuel rail input, then turn the ignition switch to the "RUN" position *without starting the engine*. The reading should be approximately 51 psi. If the pressure drops off rapidly, one or more injectors are leaking.

To check for a vacuum leak, use a vacuum gauge for good accuracy; most auto parts stores sell vacuum gauges. Attach a vacuum gauge to a full vacuum source, usually somewhere on the intake manifold. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle body and at the MAF for cracks or loose clamps.


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