84 intermitent running problem question
Thread Starter
Drifting
Joined: Mar 2008
Posts: 1,806
Likes: 433
From: Denver CO
84 intermitent running problem question
Still chasing a gremlin in my 84.I've posted about this before but I found out something new and maybe this might shed some light on what exactly is going on.While using my OTC Monitor 2000 scan tool to check all the modes ,everything is in spec when its running good. Well while I was doing this the gremlin popped up and it started running rough.The scanner then showed it went into open loop.Would this mean the ecm is bad.It was up to temp in closed loop right before. Ive replaced EVERY sensor including coolant temp senor on front of engine.NO CEL or codes. Feedback? Thanks
Last edited by gjohnson; Feb 14, 2016 at 10:42 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Assuming you continue scanning the future, watch for O2 sensor readings and especially O2 sensor cross counts. The cross counts increment every time the O2 sensor switches from rich to lean or lean to rich. They go up to 255 and then roll over to zero and start incrementing again. You should get a cross count roughly every second or two.
My guess from your symptoms is that the O2 sensor is bad. Also could be a bad connection to the O2 sensor or problem in the wiring.
Another possibility is that the TPS is doing something weird and making the ECM think you're going to WOT, which would put it in open loop mode.
My guess from your symptoms is that the O2 sensor is bad. Also could be a bad connection to the O2 sensor or problem in the wiring.
Another possibility is that the TPS is doing something weird and making the ECM think you're going to WOT, which would put it in open loop mode.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Assuming you continue scanning the future, watch for O2 sensor readings and especially O2 sensor cross counts. The cross counts increment every time the O2 sensor switches from rich to lean or lean to rich. They go up to 255 and then roll over to zero and start incrementing again. You should get a cross count roughly every second or two.
My guess from your symptoms is that the O2 sensor is bad. Also could be a bad connection to the O2 sensor or problem in the wiring.
My guess from your symptoms is that the O2 sensor is bad. Also could be a bad connection to the O2 sensor or problem in the wiring.
Thread Starter
Drifting
Joined: Mar 2008
Posts: 1,806
Likes: 433
From: Denver CO
Thanks for the replys.TPS /new style coolant sensor / o2 sensor replaced.Going to recheck connections. Would a warmed up motor going to open loop really run that bad? It runs great when its cold and in open loop.
