: bad 02 sensor = knocking?

02-12-09, 11:08 AM
I had my codes read a couple months ago due to a check engine light I've had on for about 6 months now. I dont have the code with me right now but it was stating I have an 02 sensor bad on one of the banks. . I've been to broke and lazy to replace the sensor, plus the car has been running fine in the meantime til recently. When I drive the car in the cold morning, the engine knocks a whole lot when the accelerator is pressed. After about a block of driving it goes away. The knock has been getting louder so I figure I better fix this thing.

My question is, will having a bad 02 sensor cause the engine to knock like this or is this maybe its own problem?

It only does it when the car is not at operating temp. and only for about a block. And only when accelerating, not at idle. The oil needs to be changed as well so perhaps that could be the prob. Its been prolly 6 months since y last oil change too. I know, shame on me.

Thanks guys

02-14-09, 08:33 PM
It doesn't seem like your knocking is the O2 sensors this time. The way I understand it, the fuel injectors work "open loop", i.e., they ingnore the O2 sensors until the O2 sensors are warmed up anyway. So a bad O2 sensor wouldn't come into play before the engine is warmed up.

In my state, you won't pass emission inspection with a bad O2 sensor.

If you were asking this question about a GM OHV V6, I'd say it's normal. My 3400 V6 on my other car, an Olds Alero, always "knocks" (actually piston slap, not pre-detonation) for the first few blocks and they all do. The colder the weather, the more it does that. Oil level makes a difference.

However, I don't get that noise on my '97 Catera 105K, so it seems you do have a problem. I'd say open the hood in the morning and see if you can tell where it is coming from. Could be the cold serpentine belt until it warms up. Make sure the oil is filled up.

I've always used premium gas, had the car since new. You could try that if you don't now.

02-15-09, 08:21 PM
I'll try the premium gas. Just got the oil changed and am still hearing it. its hard to pin point where its coming from. Sounds like its coming from all over when I walk around the front of the car. Very well could be the cheep gas i always use. might try some octane booster to see if thats the prob. I passed emissions by unhooking the battery and resetting the CEL. hat gives me a couple days before it returns. I'm gonna get a new o2 sensor to get rid of the light.

02-17-09, 12:22 PM
if it is either the B1S1 or B2S1 sensor (the front pair) then the above assumption is correct (no effect in open loop). The rear pair (B1S2 or B2S2) checks the condition of the cats and have no effect on operation. It is 'possible' that if it is a rear sensor failure there 'could' be a clogged cat. Why that would affect the startup but not the warn-run condition I do not know. Therefore I would suspect it is not the problem.

However I would highly suspect the low-octane gas. Mine runs worse on the cheap stuff.

Old oil (especially the dino / non synthetic type) may be allowing lifters to bleed down and allowing a lot of rattle. I've noted on mine if it sets for a long time (a week or longer) there is some lifter noise on the first startup. Just another possibility. Although it's pretty easy to tell the difference between lifter noise and engine knock unless it is just one lifter bleeding down.