LT1 Engine Issues

joelster · 07-31-2012, 07:22 AM

In your first post you said the car "runs great" then it starts skipping like the timing is completely off. When an o2 sensor goes bad, the car will fire right up and run normal but after 2-3 minutes when it is warm, it will go into closed loop, and the pcm will look at the o2 data and make changes. If the o2 or o2's are seeing false air, or if they are faulty (they ARE a maintenance item) your car will run horrible. You can diagnose this with a tech2 scanner or similar. If you suspect it to be o2's but don't have access to a scanner, let the car warm up and go into closed loop and run rough for a minute. Then jack the car up and unplug the o2's which will put it back into open loop mode. Most race cars are run in open loop anyways. They use o2 data for datalogging, but not to adjust fuel trims.

FWIW an o2 sensor should be replaced at about ~50,000 miles. Some cars need them replaced sooner. My car went through a set of them in about 15,000 miles. A rich tune will accelerate their failure.

EDIT- as mentioned in post #6 the opti's get a bad reputation, but from what I've seen and experienced, people throw the blame on the opti way more often then what it deserves. There is a great diagnostic method for checking your opti out on shbox.com

07-31-2012, 07:22 AM	#7
joelster Member Join Date: Nov 2007 Location: Tonawanda, NY Posts: 106 Likes: 0 Liked 0 Times in 0 Posts	Re: LT1 Engine Issues In your first post you said the car "runs great" then it starts skipping like the timing is completely off. When an o2 sensor goes bad, the car will fire right up and run normal but after 2-3 minutes when it is warm, it will go into closed loop, and the pcm will look at the o2 data and make changes. If the o2 or o2's are seeing false air, or if they are faulty (they ARE a maintenance item) your car will run horrible. You can diagnose this with a tech2 scanner or similar. If you suspect it to be o2's but don't have access to a scanner, let the car warm up and go into closed loop and run rough for a minute. Then jack the car up and unplug the o2's which will put it back into open loop mode. Most race cars are run in open loop anyways. They use o2 data for datalogging, but not to adjust fuel trims. FWIW an o2 sensor should be replaced at about ~50,000 miles. Some cars need them replaced sooner. My car went through a set of them in about 15,000 miles. A rich tune will accelerate their failure. EDIT- as mentioned in post #6 the opti's get a bad reputation, but from what I've seen and experienced, people throw the blame on the opti way more often then what it deserves. There is a great diagnostic method for checking your opti out on shbox.com