I need HELP!

[artiz77]

Does anyone know what to do when the decoder says
"PreCat oxygen sensor response time, Cyl #1-3"?
Please help...my engine has a strange slight thumping sound coming from the engine head. Any help is highly appreciated. Thanks

[parolof]

It's one of the two O2 sensors, the one for cyl 1-3. Cyl 1 is the one closest to the radiator

[artiz77]

So is it just telling me to replace the O2 sensor. Thanks

[Dave at Pelican Parts]

Thumping from the head is likely something different. Not sure what, though--timing chain tensioner, maybe? Something in the valve train? I assume it varies with engine speed and not with road speed...

--DD

[parolof]

yes, natúrally, I missed the thumping part

[artiz77]

The thumping sound is not that aweful. I guess it's more like a soft knocking sound. I thought it was a vacuum hose leak or something so I double check all my vacuum hoses and they were fine. I used the OBD II decoder and it told me the "PreCat oxygen sensor response time, Cyl #1-3" I just wasn't sure what it meant by that or what causes that. So do you think by replacing the O2 sensor will help elimate that noise?

[artiz77]

The thumping sound is not that aweful. I guess it's more like a soft knocking sound. I thought it was a vacuum hose leak or something so I double check all my vacuum hoses and they were fine. I used the OBD II decoder and it told me the "PreCat oxygen sensor response time, Cyl #1-3" I just wasn't sure what it meant by that or what causes that. So do you think by replacing the O2 sensor will help elimate that noise?

[Dave at Pelican Parts]

Nope--it is extremely unlikely that replacing the sensor will have any effect on the noise. (Other stuff you do to be able to replace the sensor might--moving things around, etc.) But I would guess that there is something bumping something else in the valve-train, or the camshaft drive, or one of the other moving bits in the cylinder head.

Have you used a mechanic's stethoscope (or piece of vacuum hose held up to your ear) to verify where it's coming from?

I don't know enough about these engines to really say what can cause a knocking sound or thumping sound in the cylinder head, sad to say...

--DD

[lozer]

i had an old odge 318 that made a slight thumping at the valve cover turned out to be a broken valve spring. if the exhaust side is whats broken that could explain the o2 sensor code. just speculating tho.