hi i'm having trouble tuning idle on my 383 with lt1 intake. i'm running edelbrock 60cc heads, 52mm tb , long tubes and a mild cam this is in a 91 chevy pickup with 730 ecm/painless harness and 24lb injectors
i have a heated 02 sensor in open loop it has 500-550 mv but slowly and steadily it climbs to 1087-1091 mv and no matter what it wont come down (open loop or closed loop) i have tried changing idle fuel and idle spark there is no way to make it leave that mv range
i'm thinking about trying another 02 sensor
i have a heated 02 sensor in open loop it has 500-550 mv but slowly and steadily it climbs to 1087-1091 mv and no matter what it wont come down (open loop or closed loop) i have tried changing idle fuel and idle spark there is no way to make it leave that mv range
i'm thinking about trying another 02 sensor
RednGold86Z
Supreme Member
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May 30, 2026
Seems pretty rich... How much change did you try? Did you lean it out until it would stall, and then did it stay so high (if so, yeah, your o2 is poisoned)? Is your MAP sensor working?? Coolant temp??
map looks good coolant temp is good i leaned it out untill it would barely run still same thing i'm gonna try a diff o2 and see if that helps
changed o2 sensor and all is well went from 1000mv to 100mv with the new sensor (open loop) it actually switches during closed loop
Moderator
Good to hear you have it squared away. The O2 reporting high like it was is a sign of silicon poisoning. I've had them so bad the engine would stop running while cruising down the highway. That gets interesting.
Anyway, try to keep an eye on the O2 readings. If they start heading upwards again then silicon is getting into the engine from somewhere. Usually sealants, fuel, oil, plug wires, dielectric/silicon grease, and outside sources such as household caulk can do it. It was the houshold caulk for me. I was thowing away the empty cartridges in the garage trash can.
RBob.
Anyway, try to keep an eye on the O2 readings. If they start heading upwards again then silicon is getting into the engine from somewhere. Usually sealants, fuel, oil, plug wires, dielectric/silicon grease, and outside sources such as household caulk can do it. It was the houshold caulk for me. I was thowing away the empty cartridges in the garage trash can.
RBob.
RBob,
"It was the houshold caulk for me. I was thowing away the empty cartridges in the garage trash can."
Can you explain this to me? I don't have a clue as to the connection here. Thanks.
Gary Anderson
"It was the houshold caulk for me. I was thowing away the empty cartridges in the garage trash can."
Can you explain this to me? I don't have a clue as to the connection here. Thanks.
Gary Anderson
Moderator
The nozzles of the tubes still had caulk in them. As it cured there was out-gassing into the closed garage. It actually stunk when I opened the door, but not thinking. . . The engine ingested the silicon and tossed it at the O2 sensor. Which absorbed it.
If there is a white fluffly looking substance on an O2 sensor, it is typically from silicon.
RBob.
If there is a white fluffly looking substance on an O2 sensor, it is typically from silicon.
RBob.
Thanks. Wow, I had no idea these things were that sensitive. Kind of makes you wonder about a trip to the body shop then, huh?
i wonder if antifreeze can ruin them?i just did the intake swap and i wiped up 99.9 percent of it but its possible that a tiny bit got threw