Random misfire in closed loop only
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Teching In
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Joined: Dec 2009
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From: Union NJ, Downingtiwn PA
Random misfire in closed loop only I recently installed a cam and longtube headers on a friends 2001 camaro z28. Its running an off road y pipe with no down stream O2 sensors for after cat, seeing there are none. While performing those modifications I replaced the spark plug wires, spark plugs gapped to .050 and replaced fuel filter. We also deleted the air injection system. Car runs fine in open loop holds idle at about 800 rpm and as soon as vehicle gets to operating temp its bucks and misfires and srs light flashes. Now the vehicle right now is untuned. Do you think that would be the main issue or could it be something more, thanks i. Advance for the input
check the front O2 sensors. mine ran fine in open loop and then once it hit closed loop it started misfiring really bad because thats when it starts using the O2 sensors. replaced them and its fine. Also make sure your plugs arent fouled out. i did those first and it got better but came back relatively quick. with no tune its gonna be super rich(mine was) and that starts to mess with them
Closed loop swings the fuel on purpose to get "cross-counts"
and if it swings too wide you'll see bucking and misfire counts.
You might play with the proportional fueling, lower the gain
or even zero it out just to see if that's the actor. Lazy sensors
also make the loop slow and tend to bury it at one end then
the other instead of jittering tight about center. The more gas
lag you have between cylinder and sensor, and the cooler the
sensor is, the worse that gets.
Test the thermal aspect by watching the misfiring and sensor
behavior after 30 sec of 3000RPM operation; drop to idle and
see if fast switching is there and then gets slower and wider
as the exhaust plumbing cools back down. This will tell you if
heat is the problem. What to do about it.....
and if it swings too wide you'll see bucking and misfire counts.
You might play with the proportional fueling, lower the gain
or even zero it out just to see if that's the actor. Lazy sensors
also make the loop slow and tend to bury it at one end then
the other instead of jittering tight about center. The more gas
lag you have between cylinder and sensor, and the cooler the
sensor is, the worse that gets.
Test the thermal aspect by watching the misfiring and sensor
behavior after 30 sec of 3000RPM operation; drop to idle and
see if fast switching is there and then gets slower and wider
as the exhaust plumbing cools back down. This will tell you if
heat is the problem. What to do about it.....
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i'm having the same kind of issues and performed the same mods. i have a TSP tune. i'm going to try to replace the driver side o2 as now that bank is misfiring whereas before it was the pass side until i replaced that o2.
