Heat riser valve leak causing O2 sensor misread?

[wrcsixeight]

My '89 Mopar LA 318 TBI has a heat riser valve on the passenger side manifold. When cold it directs exhaust gases through the intake manifold to the drivers side exhaust manifold to warm up the intake and base of the throttle body. I know these frequently clog up, but mine was not 15k miles ago, and the last time I removed the EGR valve I did not see butt loads of carbon.

Mine has been inoperable for years, and since I live in a warm environment, I just tied it open and forgot about it.

Now it has started to leak exhaust gases around the Pivot pin.

My single 02 sensor is in the driver's side manifold.

I'm wondering if this leaking heat riser valve could be sucking in air from the manifold, and somehow making it across the intake manifold to the 02 sensor, making the 02 sensor send a lean reading to the ECM which then enrichens the mixture.

My engine is running slightly rich, especially when cold, when the heat riser valve is leakiest and makes the most noise.
I have resorted to tin foil and hose clamps on the pivot pin to temporarily quieten the noise. My butt dyno tells me that this makes the engine run better, but the cynic in me does not believe my butt.

I fear removal of the exhaust manifold will result in broken bolts and/or studs in the head and do not wish to open that can of worms.

I'm leaning toward removing/ dropping the Y pipe, cutting the pivot pin in half from below, complete removal of pin and butterfly, and inserting some NPT plugs into the pivot pin's holes in the cast Iron manifold.

What say you all.

 

[Chris142]

I don't think that little leak around the shaft will goof up the 02 sensor. If it was mine I'd take the truck to a muffler shop, have the heat riser removed and a new head pipe made.

 

[wrcsixeight]

Well the solution either lies in removing the heat riser and plugging the holes, or replacing the manifold with a new one with an operable Heatriser. I think A manifold without the heatriser is slightly shorter which might require a lengthening of the Y pipe, so that option is out

Where the solution does not lie for me is paying someone else to do it. Even if money were not so tight, I simply have an issue paying others do do what I can do myself.

The leak is not tiny, I know any exhaust leak before an o2 sensor can really mess with it's readings. I am just wondering if the 02 sensor is too far from the leak, and not really down stream from it to have an effect on the A/F ratio that the ECM determines.

 

[Chris142]

Originally Posted By: wrcsixeight
Well the solution either lies in removing the heat riser and plugging the holes, or replacing the manifold with a new one with an operable Heatriser. I think A manifold without the heatriser is slightly shorter which might require a lengthening of the Y pipe, so that option is out

Bummer. Might be better to remove the shaft and thread it then screw 2 short bolts into the threaded holes.

 

[wrcsixeight]

I don't know that I could thread the Pivot pin holes in it's current location. I absolutely do not want to remove the Manifold. I thought a soft brass 1/8" NPT plug might effectively seal the holes left behind by the pivot pin, but I'm probably over simplifying it in my mind.