Well done. Thank you Rob/Shoebox !

You might want to run a new data log after the cat is replaced. The LTFT's are high. It's adding a lot of extra fuel. Let's see if the cat fixes that too.

 

Welded cat back in and engine started straight off no noise and idle was perfect, rev'd up with no bogging - nice and 💪strong. I didn't let it run because I wanted to drop the oil out of caution. I will run a log tomorrow and take pics again as it warms up.

 

Again thank you guys for your input priceless. I probably would have started pulling motor apart cause of my frustration. Lol

 

The expert guys here know their fecal matter for sure ;-)

 

Glad to still be able to pull out a usable idea from time to time.

Nice looking car!

 

Ok guys, I gutted the cat cause they wanted $500 just for cat. I'm posting a few pics of 20 min run time. Only seems to be o2 sensors never settle down. My son just doesn't have the $$$ to put that in right now. Car has a little miss while running at idle. (And now a squeak on front of engine, I'm sure not related I did both idler and tension pulley.
one of last pics shows fan relay on, then fan cycle off.

 

Here r pics I think last one was wot.

 

I thought I explained this above, but I'll try again. In “closed loop” the O2 sensor readings will NEVER “settle down”. It is totally normal for the O2 sensor on each bank to move rapidly back and forth between very low = lean (0.100 volts or less) and very high = rich 0.900 volts or more) readings, and everything in between.

The PCM toggles the short term fuel trims up and down between slightly rich and slightly lean to make the catalytic converter work. I have one reference that indicates the PCM calculations are run ~9 times per second. It will continue to do this even though you have deleted the cat. In OBD-1 the PCM has no way to tell if the cat exists, or if is working. This was corrected in OBD-2 by installing additional O2 sensors after each cat. 93-95 (OBD-1) have a single cat. 96-97 (OBD-2) have dual cats, one for each bank of the engine.

The cat has two precious metal coated ceramic elements. The first stage breaks down oxides of nitrogen (NOx) in the exhaust into nitrogen and oxygen. The second stage stores the oxygen from the first stage, and uses it to convert the carbon monoxide (CO) and unburned hydrocarbons (HC) into carbon dioxide (CO2). By toggling the A/F ratio back and forth between slightly rich and lean it creates the correct ratios of NOx to CO+HC in the exhaust that allow the cat to operate more efficiently.

The O2 sensor used in production vehicles is a “narrow band” device. It is only accurate at 14.7:1 A/F ratio, +/- 0.1. Hence, the readings are not linear. And beyond those limits, the accuracy of the sensor is more dependent on operating temperature than on A/F ratio. That's why you can't use a narrow band sensor to tune an engine for maximum torque/power that typically occurs at an A/F ratio in the range of 12.8-13.2:1. You need to use a wide band sensor that is linear and accurate over a range of 10:1 to 20:1, with an operating range of 0 to 5 volts.

You will see the O2 sensor movement in real time if you look at the data logs. The important things there are how quickly the sensors respond to the toggled A/F ratios commanded by the PCM. In OBD-2 GM added a proprietary diagnostic code to detect “slow” sensor switching. Over the long haul the O2 sensors should average 0.450 volts. If the average departs from that number within a “cell”, it causes the PCM to make a correction to the fueling calculation by increasing or decreasing the long term fuel trims. A “cell” is a specific mode of operation defined by a grid of RPM on one axis and engine load (as determined by MAP) on the other. There are 16 different cells for closed loop operation, plus one for idle, one for open loop “load” operation and one for open loop decel operation. The last two are derived mathematically from the 16 closed loop cells.

It’s really hard to sort out problems from screen shots. You need the dynamics of a continuous data log, run over a significant range of operating conditions. Problem is one of those logs can contain 10,000 lines of data, with over 500,000 data points. Gets time consuming. And doesn’t always find the problem.

 

Thank you again. I did forget that you explained the o2 sensor. I did watch screen the whole time engine was running I just didn't post all the pics. It did seem pretty straight forward watching items cycle thru. I waited til it got to full operating temp and fan cycled to check for leaks cause while I had it apart I flushed each line both direction with a small pump. Heater in car worked for crap and I saw post on forum to flush heater core. I'm not going to chase this miss while idling, winter is coming and it's 🥶 freezing and damp outside. Hey guys Merry Christmas 🎅 🎄 and a safe New Year. I will help out on these posts where I can. Hopefully pointing guys in right direction. Even if it's to another posting.

 

Best wishes for the Holidays! We need all the help we can get. Stay safe.