98 5.7 rough idle and awful smelling exhaust

[Erik the Awful]

Cats are after the O2 sensors.

 

[Schurkey]

If your cats are bad it'll throw off your O2 readings.

Cats are after the O2 sensors.

Yes. The O2 sensors that affect engine operation are ahead of the catalyst(s) (Upstream sensors.) The downstream sensors on OBD2 vehicles would be affected by bad catalysts, but their only purpose is to report on catalyst efficiency--not to aid in fuel trims.

 

[Honkytonk]

EGR valve may be fouled and stuck open?

 

[dannyk11135]

If

Looking for suggestions…

I acquired a 1998 5.7L Suburban that has a remanufactured engine with 20,000 miles on it. An issue that I need help to get around is a rough idle and awful-smelling exhaust. There is no CEL illuminated. The exhaust sticks on your clothes similar to when you use a lawn mower for extensive periods. Not like raw gas. No loss of power. The timing is dead on.

I have replaced the following:
-Plugs
-Cap
-Rotor
-Wires
-Temp sending unit
-Cleaned throttle body
-New throttle position sensor
-New idle air control
-Upgraded spider with regulator
-New throttle body and upper intake gasket

I have access to a reader so I can get live data, I just don’t know what is within the normal range on certain things.

Thank you in advance.

If it Doenst get driven hard enough to heat up, those cats can clog and you’ll get the issues you are referring to. You definitely needs cats, now the question is why they are clogging, if your O2 sensors are bad they can result in your ECM commanding a rich mixture, a misfire can cause your cats to clog (check your data display for misfire counts if possible) or, they could just be at the end of their life cycle.