Bad ECM killing O2's?

Bahlzeron · 10-07-2017, 11:55 AM

Been having issues all summer long and can't seem to figure it out. I replaced upstream o2 sensor twice, first one lasted maybe five miles, the second one lasted thirty. What could be killing the O2 sensors so quickly? Dang thing will not idle, runs great off idle though. I've replaced the MAP, throttle position, crank position, cam position, and IAC as well. And here's the kicker... the computer isn't giving any codes.

Any suggestions?

[ion] C2 · 10-08-2017, 01:55 AM

What makes you say the oxygen sensor is dead? Because after replacing it the car seemed to run OK and then acted up again almost immediately? They don't fail that fast no matter how abusive you are to them. Disconnect it so it doesn't do anything and watch as the car likely has these issues regardless...

Could be a bad connection to the sensor. If the car drives great without the sensor connected at all (for longer than your 5 or 30 minute drives so you are absolutely sure it's running fine) then maybe it's a wiring issue at the sensor. This kind of diagnosing is super easy to check with HPTuners if you know anyone nearby with it, though.

Bahlzeron · 10-08-2017, 03:31 PM

Thanks for the reply ion,

Checking and cleaning all connections was the first thing I did, months ago, and have repeated thrice, to no avail... in fact everything has been tried multiple times (by me and a garage) all with the same results. With the oxygen sensor unplugged it runs fine.. a little rich, but otherwise fine. When I plug it back in, random misfires, stumbling, and stalls... if I keep the throttle cracked to keep it running, when I let out the clutch it falls flat on it's face, as if the mixture is crazy lean. Unfortunately I don't know anybody that has HP Tuners... in fact I don't know anybody that's into cars.. or motorcycles really. Both communities around here are pretty stuck up, if you weren't born into it, you don't belong.

And as far as the length of drives I went on to test.. they were much longer than just a few miles, the mileage I listed was how far they got before failure. The garage I brought it to confirmed bad oxygen sensors. I need to find what is killing them.

And yes today I put 90 miles on it with O2 unplugged, ran fine...mostly, slightly rich (expected with sensor unplugged). engine light came on finally after I got back and car was sitting idling for about twenty minutes (why didn't it come on before with any of my other extended test drives?). When I plugged the sensor back in it went right back to being a (insert vulgar expletive here)

A thought I thunked...would the downstream O2 sensor cause this? I've been told no.. but, maybe?
Another thought I thunked.... combination of bad downstream and bad catalytic, or just bad cat?

[ion] C2 · 10-09-2017, 02:13 AM

Neither a bad O2 or a clogged catalytic converter should be able to cause this at all. The downstream O2 doesn't affect engine operation at all, it's just an emissions monitor to trip a code.

A shop with access to a scanner with a graphing function (not necessarily HPTuners, but there are other basic scantools that most shops should have) can show how the O2 is fluctuating, and you can see how it's acting when it's plugged in. See if it's hanging out way too much on the lean or rich side, or the graph is going crazy.

Bad cat will make it feel like the car has no power, but it's not likely to generate misfires like you're describing. And if it were a bad cat, it wouldn't run better with the O2 disconnected.

Seems to me like a vacuum leak. Check the hoses (especially that MAP one, if you haven't replaced ever, well, every 2.4L I've seen has had that hose super cracked this far into its life) and you can spray brake cleaner when you first turn the engine on around the intake manifold gasket area (so it's relatively cold still) and you should be able to tell if there's a leak by the way the engine reacts. (do it with the O2 disconnected)

zzyzzx · 10-12-2017, 11:52 AM

What brand of replacement O2 sensor have you been using?
Try putting a volt meter on the upstream O2 sensor wires with it unplugged and the engine running and report back.

Bahlzeron · 03-24-2018, 04:10 PM

Ok.. sorry I haven't posted back in a while, the Alero had to take the back seat for a bit while I shifted focus to keep the Bravada on the road...another never ending project, LIM started leaking coolant a few weeks ago, have the parts just need to do it.

@zzyzzx, first one was a Bosch, second was (is) an ACDelco. On car side of connector, I get a readings between 0.18v and 0.02v... sensor side reads 0.

Bahlzeron · 04-04-2018, 02:36 PM

Little bit of headway, maybe even found the cause of the whole problem... I hope. After looking for vacuum leak ad nauseam, a few days ago (Sunday) I decided to replace the intake manifold gasket, it's $30 and easy to replace. While taking off the intake manifold, I found a pool of gas in it. After exercising a little bit of google-fu, I found the most likely suspect would be the fuel pressure regulator. Go outside, turn on key, hear the fuel pump turn on and start to build pressure.... and yup, fuel coming out of the regulator's vacuum line. New Delphi regulator got here today, gonna have to motor-vate myself to do it after work tomorrow mornin. I'm hopin this get's the Alero back on the road, I want my 5 spd back! Don't get me wrong I love the Bravada.. but it's kind of a lumbering beast compared to the Alero.

So, yeah, vacuum leak of sorts