Clunking/Knock sound... pulled O2 sensor and it's gone. Bad Cat? bad sensor? neither?

[ngrover]

Here is an interesting development in my recently aquired 4.0 ohv reno process. Since I got it I've done a bit of work and got the engine running very well... but I could hear what I first thought was a clunking/knocking sound, kinda like a mellow rod knock sound. After driving a few days with it I concluded it wasn't an internal engine sound as it was worse under load and changed pitch slightly when the engine warmed up. So I kinda left it at that knowing that the motor was fine but not knowing the source of the clunking/knock. Well, today I decided to look underneath while it was running. After contorting myself to several different locations I narrowed it down to what I thought was the catalytic converter. I thought I must be on crack as it didn't seem possible for a CAT to make a knocking noise. I hammered it with a rubber mallet to see if anything rattled.. nothing. After staring at it for 10 minutes I decided to pull the oxygen sensor out (ahead of the CAT) and take it for a spin. Soon as I fired it up.... NO knocking sound! Just a bit of exhaust noise blowing from the oxygen sensor hole. Then I took it for a spin and it felt fairly normal until i FLOORED it.... woa definately more power up high.. climbed much better up the rpm's (butt dyno).

I've had someone on an Aerostar forum point out that the increased power might be due to the 02 sensor reading outside air. The second time I drove it without the sensor in, I got a P1103 code. In any case, the clunk/knock sound is gone with it out.. what's going on? Thanks for any help.

P1103: "Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1"

 

[MadExplorer93]

Here is an interesting development in my recently aquired 4.0 ohv reno process. Since I got it I've done a bit of work and got the engine running very well... but I could hear what I first thought was a clunking/knocking sound, kinda like a mellow rod knock sound. After driving a few days with it I concluded it wasn't an internal engine sound as it was worse under load and changed pitch slightly when the engine warmed up. So I kinda left it at that knowing that the motor was fine but not knowing the source of the clunking/knock. Well, today I decided to look underneath while it was running. After contorting myself to several different locations I narrowed it down to what I thought was the catalytic converter. I thought I must be on crack as it didn't seem possible for a CAT to make a knocking noise. I hammered it with a rubber mallet to see if anything rattled.. nothing. After staring at it for 10 minutes I decided to pull the oxygen sensor out (ahead of the CAT) and take it for a spin. Soon as I fired it up.... NO knocking sound! Just a bit of exhaust noise blowing from the oxygen sensor hole. Then I took it for a spin and it felt fairly normal until i FLOORED it.... woa definately more power up high.. climbed much better up the rpm's (butt dyno).

I've had someone on an Aerostar forum point out that the increased power might be due to the 02 sensor reading outside air. The second time I drove it without the sensor in, I got a P1103 code. In any case, the clunk/knock sound is gone with it out.. what's going on? Thanks for any help.

P1103: "Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1"

Ok so when the O2 sensor is out the other O2 sensors will read more Oxygen in the back-pressure and will lean out the engine on that bank.

The clunk/knock sound go very well be a miss not backfire, but a AIR-Fuel mixture not right causing a missing sensation that you can hear within the exhaust like a thunk/thunk sound and maybe intermitent or not.

Now what is causing the lean if any when the O2 is in or a Rich mixture is a guessing game i am playing with right now on my 1993 explorer and without codes that pinpoint the son of a gun problem cause a lean O2 signal does not 100% always mean the O2 sensor is the issue.

Do you have any other symtoms?

Rough Idle
Stalling at cold starts
Hesitation or Bogging down