Yeah, I had about the same results. Just passed by one. It's said that leaky
injectors and the O2S are the leading causes of HC failure.
Excess carbon buildup in the chambers can cause this reading. Someone
sugested B-12 Total Combustion Chamber Cleaner. Also suggested was changing
the oil so the new oil can absorb more HC. Remember that you do have that
silly, prone to fail EGR on that engine. Also, new PCV valve? Biff
----- Original Message -----
From: "rws" <rwsam2002@yahoo.com>
To: "DakotaTruck DML" <dakota-truck@dakota-truck.net>
Sent: Thursday, September 27, 2007 11:21 AM
Subject: DML: 94 Dak 5.2L Cat Converter Air Pump or Air Switch Valve?
>
> Hi,
>
> I took the '94 Dak 4x4AT 5.2L @ 162k mi. in for the CA Smog Test and it
> failed the 25mph test HC Passing is 50 and the Dak got 51, so it failed by
> one.
>
> Cat converter (Magnaflow P/N 94006) was replaced Aug 2004.
>
> O2 sensor, ECT coolant sensor recent replaced, Ign. Coil, TPS replaced 2
> years ago.
>
> Magnaflow tech said to test Cat by Temp differential front and back of the
> Cat and it should be 50-100oF difference. Temp will be around 400-600oF,
> so I need to find a temp gage for that range and need to find.
>
> But in the meantime I am suspecting the Air Pump or the Air Switch Valve.
>
> How do I test Air Pump and Air Switch Valve components to make sure air
> injection system is operating correctly? What is vacuum measurement at
> the Air Switch Valve?
>
> Also I am wondering if it is not getting proper air injection will that
> alter the temperature difference test on the CAT?
>
> ref:
> 15 mph test HC 85 MAX 18AVG 85MEAS NOx 491MAX 149AVG 432MEAS %O2 0.1
> 25 mph test HC 50 MAX 12AVG 51MEAS NOx 744MAX 144AVG 296MEAS %O2 0.2
>
> Please need help soon.
>
> Ron
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