My O2 sensor tends to run on the lean side upon start up. This sometimes makes it hard to go into closed loop mode. I think this is caused by my exhaust modifications (Edelbrock TES, Flowmaster cat back, and no cat). I have 46 psi fuel pressure but my AFPR is just about maxxed out. Would an aftermarket chip make me run richer?

 

When you start the engine, the O2 sensor is too cool to react normally for closed loop, as it begins to heat up, you'll notice the output getting higher until you begin to get crosscounts, and the O2 sensor is warm enough to function properly.

This will take longer with headers, you lose heat through the thin pipes, as opposed to retaining the heat in the thick castiron exhaust manifolds.

For this reason, may chose a heated o2 sensor, do a search and you'll find a neat diagram by Vader on the proper way to wire one in via a relay and the cannister purge output of the ECM.

 

Oh, and richening up the mixture won't allow you to go into closed loop any sooner. Closed loop is a function of the O2 sensor being heated up to 600*F to function properly. Increasing the FP only affects WOT richness once in closed loop.

[This message has been edited by 8Mike9 (edited November 13, 2001).]