KA24 overheated and now running lean?

[Promise Land]

My upper radiator hose attachment to the radiator broke and the car pegged the needle before I could get it close enough to home to tow. It car ran hot enough that it started to sputter and I finally shut it off.

So I have replaced the radiator, bled all the air out, and run the car down my road. It idles fines, but at any throttle it has a slight stumble. While driving it runs fine at partial throttle, but if you step on the gas hard it will start to stumble and backfire like it is running lean. The oil is still clean, so it "appears" the headgasket has made it through the heat.

Any idea what it could be?
- I haven't checked the plugs yet. Possibly older plugs that didn't like the heat.

[Mishkin_707]

After over heating replacing the 2 pin coolant temp sensor is important because that gets screwed up with the intense heat, That gives the signal to the ecu controlling fuel and idle (for the warm up process on cold starts) once they go bad, you run too rich because the ecu thinks it's still cold (at normal operating temp) or it will run lean on cold starts because the ecu thinks the car is warm (at cold starts)

[Promise Land]

I will try that also. The plug wires melted down in the head and cracked to pieces. They will be replaced this weekend along with the plugs. I am just not thrilled to take the valve cover off to do it all.

[Mishkin_707]

Wow, well that could be the cause lol, good luck bro

[Promise Land]

So I got all the cooling buttoned up and was able to swap plugs and plug wires. I had to take off the valve cover and got it all swapped. The heat burned up the wire boots and they cracked, thus leaking spark. After I swapped everything out the car runs like normal. I took it for a drive and on the way home it threw a CEL. Not sure what it is yet, but the car shows no signs of changing after it threw the code. I reset the ECU (disconnected the battery), but that didn't change the CEL.

On to the next problem...

[Mishkin_707]

that could be a simple 02 sensor, just pop your passenger side kick panel and look up the CEl code(s) (via blinking lights)

[Promise Land]

I looked up the codes. It showed a 34 (knock sensor) and 77 (rear heated O2 sensor). I erased the codes, drove it for about 5 miles, and only 77 came back. The car ran rough with the old spark plugs, so the 34 wasn't a surprise. My car is an OBD-I '95 model, so I picked up an O2 sensor tonight. I ran it in "monitor mode" and it showed to be running lean.

I am going to use a friend's Innovate Motorsports A/F setup to see what it is actually running (I'm guessing a touch rich), then swap the sensor. It'll be interesting to see what the sensor being bad actually is doing to the car.

[Tomsd03]

if its still running lean after fixing everything, there is a possibility that you could have done some damage to the top end. Your issue could be a burnt valve. Doing a compression test wouldn't hurt anyone.

[Promise Land]

I swapped the O2 sensor and erased the codes. It drove fine to work this mornng, but it's getting a little hot. I still have some air in the system that I need to get out. I'm going to look at the thermostat drill trick I have heard about to get more air out of the system.