Bartman

So I recently upgraded my engine and I’ve been working out a couple of bugs since I put it all back together. One of the last things I fixed was a problem with my Knock Sensor so that my system is no longer throwing any codes. Now that I’ve gotten rid of that code my engine can go into closed loop and as soon as it does it starts stumbling.

I hooked up TTS Datamaster to take a recording of a test run. When the engine is in open loop everything looks fine, then as soon as the system goes into closed loop the fuel trim numbers vary wildly.

So is my problem the O2 sensors or maybe the wiring to them, or could it be something else? I could post the Datamaster file if someone can read it and help determine what the problem is.

Camaro_freak

iTrader: (1)

It could be an intake air leak causing unmetered air to enter the engine, an exhause leak making the O2's read false lean, or bad O2 sensors.

Bartman

Thanks, I will check to see if that's my problem.

Tony Shepherd

iTrader: (4)

It almost has to be an O2 sensor issue. Are they new sensors?

Bartman

They are genuine GM units and only have about 1,000 miles on them (i heard the aftermarket units aren't as good), but they did sit out for quite a while during the time the engine was upgraded.

Bartman

I put on new O2 sensors, but my problem never really got resolved.

I've read that with some cams you can get false lean readings ftom the O2 sensors due to the cam overlap scavenging raw air into the exhaust. If this is true then I think the best solution may be to get my car to idle in open loop. My car runs great in open loop and in closed loop once it gets going, but it doesn't run well in low RPM closed loop.

Has anyone here tried this?

94Z28Joe

Mine was doing the same thing when I install the new engine. replaced my o2's Saturday and it fixed my problem. It now actual idles