Failing Smog Test help - 96 Xtra Cab (Auto, 4 cyl)

Dec 29, 2004 3 Replies

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Slacker 21 years ago

Here are the symptoms:

- Check Engine Light on.

- Slight Hesitation when accelerating from a dead stop.

- There's a ticking sound coming from somewhere near/underneath the air cleaner. Only happens when truck is moving, and is intermittent. This sound happened all the time before the replacement of the EVAP Solenoid and Idle Valve Assy... now it rarely happens, but still does once in a while.

Emission Test Result: Everything passed good with the exception of the

NO(PPM) @15 MPH 1993 (max allowable 539) @25 MPH 1816 (max allowable 792)

I took the Emission test when my check engine light mysteriously turned itself off.

Repairs I've had done (before the smog test): Replaced cracked exhaust manifold. Replaced AAC Valve Assy, Idle Air and the EVAP Solenoid.

The repairs were done in response to the following codes found in the computer: PO304 & PO402. There was at least on other code, but I forgot what it was :-( I want to say P442, but I'm really not sure.

Any idea on what could be causing the really high NO readings and the check engine light?

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JimV 21 years ago

You need to have the current codes read for anyone to make an educated guess.

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Idlafie 21 years ago

NO is produced when temperatures in the combustion chambers exceed 2500 degrees Fahrenheit. Excessive engine temperatures could be caused by a lean fuel mixture, by retarded timing, by carbon buildup inside the combustion chamber, or by a malfunctioning engine cooling system. The function of the EGR System is to reduce NO. It does this by rerouting exhaust gases back through the intake manifold to lower engine temperatures. Check to see if the EGR valve is getting vacuum. There is usually a little vacuum hose on the side or the top of the EGR valve. Remove the vacuum hose, place your fingertip over it & rev the engine...you should feel suction on your fingertip as you rev the engine. If you're not getting any suction, then check the secondary valves on the EGR system for either faulty sensor or cracked, melted or broken vacuum line. If the EGR system is okay, then check your timing along with pouring some Seafoam into your crankcase, intake manifold & gas tank.

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will help get rid of the carbon buildup in the combustion chamber.Anyhow, hope this helps...ID

Slacker wrote:

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Slacker 21 years ago

Hmmm... interesting, maybe my friend is right about the timing belt/chain thing??

Anyway, I got an appointment to have it looked at this Friday.

Thanks for the detailed info.

-- Slacker

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