97 Lumina EGR Valve and O2 sensor Question?

[gixxeracer87]

I have a 97 Lumina that is throwing 4 codes. I took it to AutoZone and they gave me this...

P0140 - The PCM has determined that there is insufficient activity from oxygen sensor 2 in bank 1.
P0141 - The PCM has determined that a malfunction exists in the heater circuit for oxygen sensor 2 in bank 1.
P0300 - The PCM has determined that multiple random misfires have occurred.
P0401 - The PCM has determined that there is insufficient flow in the exhaust gas recirculation system.

The employee quoted me a price for two O2 sensors, and said that that could be what was causing the random misfires. Reading the receipts it looks to me that only one of my O2 sensors is out. It seems to run fine except when I accelerate hard. Any thoughts / help is welcome. I'm wondering where O2 sensor 2 in bank 1 is, and if the EGR problem could be causing the problem with the O2 sensor? I'm pressed for money right now, and was wondering if I could get away with not replacing the EGR valve? Give me your thoughts please asap. Thank you!

[jeffcoslacker]

Sensor 2 Bank 1 is the post-catalytic sensor, it looks at how the cat is working by comparing the reading to Sensor 1 (upstream, ahead of the cat)...there is only Bank 1 on this vehicle...bank 2 would be for ones that have two seperate sensor circuits on both sides of a V engine...

According to what Sensor 1 sees, it can command EGR to open when it requires oxygen to do it's thing if the o2 stage of the cat is depleted...

It sounds to me like the EGR is not working right, and the post-cat sensor is not seeing proper activity from the cat due to it...hopefully someone else can confirm...

If you are misfiring at heavy throttle, this is when the EGR opens the most, it could be causing the random miss...

I'd remove the EGR and see if the ports are clogged before doing anything...

[jeffcoslacker]

Whoops.

[gixxeracer87]

Thanks Jeff!!! Sounds to me like the guy at AutoZone didn't know what he was talking about. I'll try and take the EGR valve off tomorrow and inspect it.

Any other thoughts or comments?

[jeffcoslacker]

It could just need a post-cat sensor, but once fully warmed up the heater circuit shouldn't cause a problem, and it would run normal...the heater grid is there to make the sensor begin to work sooner when the car is started cold...o2 sensors don't give meaningful data until fully heated...

The EGR code could be unrelated...I'd still take a look at the EGR ports...then take the post cat o2 sensor out and see if it's all hogged up or eroded...

[gixxeracer87]

I took off the EGR valve today, it was full of yellow crap. I don't have any thing here to work with. I'll have to do it at work tomorrow. I'll take it off again and try to get it all cleaned up.

It misfires under hard acceleration, all the time. doesn't matter if the motor is cold or if I've been driving it for a while. I'll try to take off the O2 sensor tomorrow too. But I don't know what I'm doing really. I don't really know how to tell if they're bad. The EGR valve is $165, and the O2 sensor is $75. I'm broke, and I'd like to make sure I need something before I buy it. I guess I'll see what happens tomorrow...

[jeffcoslacker]

The o2 sensor will have an outer shell on the tip with small "vents" that allow exhaust into the sensing elements without directly exposing them...if the vents are all hogged up with crud and closed off, or the outer shell is burned away, there's no doubt it's bad...

Were the passages coming and going from the EGR to the motor caked up and closed or really reduced in diameter at all?

I know those EGRs are really pricey...don't want to be wrong on that call...

So this is actually a misfire, with rough running or bucking, as opposed to just flattening out and refusing to accelerate?

[jeffcoslacker]

Here is a heated GM o2 sensor...see the slits at the tip (well you can only see one in this pic)? Check to see that they are clear and the shell is intact....this one looks pretty good...

Yellow seems like an unusual color to find in EGR deposits...usually sooty black-brown. Have you been using some injector cleaner or something? That'll discolor plugs and EGR, etc...doesn't hurt anything, just looks weird...

[gixxeracer87]

Thanks for all your help. Yeah it's misfiring. most of the time you can feel it lag back from accelerating, but some times it really runs rough. The passages in the EGR didn't seem to be "caked" up per say. I expected it to be dry, but it was wet. The Yellow stuff was puddled in the port to the motor, and was all in the EGR and in the port from the exhaust. I don't know if it was an oil mixture or what. I'm baffled. I hope there's not something seriously wrong with my car. I'll see if I can find my camera and take some pictures of it tomorrow...

[gixxeracer87]

Here are photos of the EGR ports. The creamy yellow stuff is oily. I cleaned out as much as I could. Does that mean I have a blown intake manifold gasket? Will that just ruin a new EGR? Is there a way of testing if the EGR works? or do I just have to go buy a new one? Do you still think the O2 sensor is ok? Any thoughts or comments wlecome...

[jeffcoslacker]

Well...the EGR hasn't been operating at all, or it would look the same on both passages...that being said, that stuff is obviously not normal....I don't know if it's coolant residue or just the result of condensation, intake vapors (fuel and oil) and rust...but the consistancy and color are sure similar to what you get when you have oil and coolant mixing...

This is really puzzling, but it's a good thing you had a look before doing anything else...

Does your car have the red extended life coolant in it, or the conventional green antifreeze?

The green stuff will poison o2 sensors if it makes it into the exhaust, is why I ask...the red will not, as far as I know...but I'd think it would ruin the pre-cat first...

I'll keep thinking...

[jeffcoslacker]

If you haven't been loosing coolant or seen evidence of mixing in the coolant or oil, I think it may just be residue from not operating...being a blind passage if not working, any vapors and moisture would collect there...you'll see the same kind of stuff in a clogged PCV system...

Have you priced an EGR from a salvage yard? Can the pintle in the valve be pushed open at all? I'd try to free that one up before giving up on it...I just can't remember if the electric ones can be manually opened...

[gixxeracer87]

Yeah, while I was cleaning it I pushed the valve down. It moves freely. I cleaned as much of the pool of yellow stuff out, put it back together, and jumped on the highway and it accelerated just fine. Went a couple miles and then slowed down and accelerated again, but it choked that time. I wondered if it was the fluid that was clogging things up. I don't know how quickly condensation and vapors can build that puddle back up. The fluid is in the exhaust tube too, So I guess the EGR isn't completely broken. It's got the green antifreeze. I checked the oil dipstick and it was normal, no chocolate mixture in it. I'll look and see if I can find a used EGR somewhere.

[jeffcoslacker]

It would take months to build up that kind of mess...

This gets stranger...keep waiting for someone to chime in and say they've seen it before and set us straight...

Hot exhaust through the EGR circuit should blow/burn out any contamination like that if the valve functions...I wonder if the exhaust tube is blocked somewhere farther down?

because normally, exhaust is coming all the way up to the valve, so the exhaust side should be dry if it flows all the way to the source...

you try starting it for a moment with the valve off, see if it bellows exhaust out of the pipe side (i've done this, believe me you'll hear it if it flows...)? If it will run like this, you could also pop the throttle hard a couple of times and see if the valve reacts (leave it plugged in so it operates)...it should open wide when the throttle is stabbed suddenly...be careful...if it's blocked it may forcefully eject a wad of crap suddenly...make sure nothing in the path of the flow gets burned if you let it run like that for any length of time...

[jeffcoslacker]

What I'm wondering is if the pipe got carboned up enough to reduce flow to the point where the condensation and crud could build in there...then when you cleaned it you might have gotten a partial flow, that pushed more crap up from the exhaust side into the ports...and now it's blocked again...

I dunno...this is weird...but I do think we're on the right track...