Exhaust leak

I have an exhaust leak that I can hear when accelerating. I can't hear it when at idle or normal cruise power. This leak has been present since I bought the van about 9 nine months ago.

A few months ago, I had to replace the head gaskets and had the exhaust manifolds and crossover disconnected. I reassembled the exhaust just like they came off and I do not believe that there are gaskets between the crossover pipe and the manifolds.

Exhaust leak on acceleration was the same after reassembly, but it was not severe by any means. Several months later, the Service Engine light comes on with a code of P1133 and the transmission coincidentally starts to intermittently shift hard. I replace O2 sensor and clean the MAF sensor to no avail. I have also read that an exhaust leak will cause the P1133 code.

Now, I am wondering whether the crossover pipe should have gaskets on them, or whether the leak is at the rear manifold to exhaust pipe connection, which I did not have to disconnect when I replaced the heads. It is impossible to hear where the leak is coming from when I rev the engine.

Has anyone else had this problem? Thanks for any advice.

I'm going to suggest the 'donut gasket' where the exhaust manifold and the exhaust pipe meet is leaking.

Thanks for the input, I will give it a try. To your knowledge, can an exhaust leak downstream of the forward O2 sensor cause a P1133 code?

It all may be moot for the time being. I had the guys from Autozone reset the SES light and I put about 350 miles on it today. All seems well for now. Somewhere, I got the impression that the SES light would go out by itself when the condition was corrected. Mine had to be reset with the scantool.

Thanks for the input, I will give it a try. To your knowledge, can an exhaust leak downstream of the forward O2 sensor cause a P1133 code?

It all may be moot for the time being. I had the guys from Autozone reset the SES light and I put about 350 miles on it today. All seems well for now. Somewhere, I got the impression that the SES light would go out by itself when the condition was corrected. Mine had to be reset with the scantool.

To my knowledge, the pre-cat O2 sensor (upstream) detects problems ahead of the cat converter and if there IS a problem (Like running too rich for eg.) signals the PO1133 code.

Not all vehicles reset messages (or warning lights) uniformly. Some won't reset until after multiple starts.