will someone please help me!! i've failed smog twice, and this last time it was so close, everything passed but nitrogen oxide..... the first time i brought the car in it failed miserably but it passed NOx. ive changed my 02 sensor, my cat, spark plugs, wires, cap & rotor, oil & filter, pcv valve. i even used that "guaranteed to pass" stuff in my fuel and did what it said. all my wiring is correct and my timing is good, anyone have any suggestions?? thanks-

1987 z28 305 4 barrel

 

That is produced by excesively high combustion temps.

You have the higher compression version of the LG4. A good collection of carbon in the cylinders would make it even higher. You might want to try the water-in-the-intake trick to clean some of it out.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Your EGR system is probably plugged with carbon. The purpose of the EGR is to let exhaust gas into the intake and reduce combustion temperature. You will most likely need a new EGR valve, and take the intake manifold off and dig the carbon out of the EGR passages in the intake manifold and the cylinder heads.

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89 Transam GTA, 350TPI, auto, 3.27 rear, dual cats, gray.
Magnaflow cat-back,
K&N open element,
Best E.T. 14.63@95mph

 

how much work would it be to install a new egr valve then take the intake manifold off to dig the carbon out? would i need any special tools to do something like that?

 

Z,

The special tools you'll need are a 1/2" or 13mm wrench to get the valve off, a screwdriver to break up and dislodge the carbon buildup, and a small shop vacuum to suck it out of the passages. A bent coat hanger makes a good probe to dig around in the passages as well.

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Later,
Vader
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"Let the bodies hit the floor!"
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