Ok, guys, I have been trying to figure this one out for some time now. I have a 91 350 tpi and it runs great when the engine is cold. Meaning , the first ten minutes or so of me starting it up and driving it. After that it just doesn't feel like it pulls as hard. I am assuming that it is switching from open loop to closed loop and therefore it starts running different. I heard that there is a value in the ecm that I can raise to 300 and the car will stay in "open loop". What is going on here? Is my timing raised and car running richer when the engine is first started and driven? The car just feels stronger if you let it sit for about a half hour OR, if it is first thing in the morning and it hasn't been driven all night. I just don't think that me manually raising my timing and bumping up my fuel pressure up a couple of pounds is gonna make it run as good as it does when it is first started up in the morning.LOL. If the car's o2 sensor's are not functioning in open loop , then what needs to be changed in the ecm to make it run like it is cold all the time?

 

Someone with a more extensive knowledge probably can help more.

I am pretty sure there is a way to tune the ecm via prom chips (correct me anyone if i'm way off) to make it run in closed loop. I believe it always runs rich when in closed loop.

It sounds more like a temperature related problem, the engine warms up and it causes it not to run as well. It could be caused by many reasons I believe. But it sounds more like a problem related to the engine not running as well after being warmed.

Sorry for the ambiguity.

 

once warm, newer vehicles go into "closed loop" meanig the curcuit is closed and your vehicle is responding to information from all of the sensors. So, with that explanation, it sounds like it's time to put your car on a scope and find out what's wrong