downstream o2 scan data

[m.wynn]

Hi there,

For you diagnostic experts, is it normal for the after cat o2 sensor to read 0.000 volts under acceleration? I'm new with the scan tool, not to mention basically ignorant regarding diagnostics. It reads anywhere from 0.05x to 0.8xx under other varied conditions. Any comments appreciated and the car is a 99 v6.

Thanks.

[chronoti]

yes at wot the ecu doesnt read the o2 output anymore, just runs a blind fuel map.

i have a question at wot what does it read for timing, my gets 8 degrees btdc...

[m.wynn]

Well, I'm seeing mid 20's for timing under acceleration. You talk wot and I'm not sure how wide open you're referring to. I'm observing data during normal driving conditions acceleration, meaning a typical run from 0 to say 45 or 50 mph in a ''legal'' driving manor. I'm certainly not checking at a true wot.

I'll bounce another 02 data question back to you. I'm trying to diagnose the notorious P0171. I started by replacing the MAF and spraying MAF fluid in search of vacuum leaks with no luck. So I bought a scan tool with live data capability but have little knowledge as to what I need to look for! It seems that both upstream sensors hover right around .6xx volts with little variation. Are these two supposed to bounce around a lot? They stay quite static. The downstream sensor bounces around quite a bit when the ecu is re-set and the car is running normally. When the code sets, the car runs lean (shitty) and the downstream sensor pretty much goes to 0.000 regardless of engine load. The upstream sensors continue their static .6xxx reading whether the code is set or not. Is there anything to conclude from any of this..other than my being clueless?

[73sport]

As you figured its running to lean. I'd expect the voltage to vary from idle to 1/4 throttle and yours running lean just stays put. It could be the front O2 sensor causing it, but i think you say both sensors do it (V6 yes?)

Have you dumped any other treaments into the fuel system? How did the intake track look? Was it full of oil, sludge, ect? Does the car use oil? how many miles on it?

Judging by the time of year we have treated gas which likley has more water and other particals in it. I'd run some injector cleaner through it and before you change the O2 sensor and see if that does anything for it.

What else causes it to run lean? low fuel pressure, bad fuel pump, plugged fuel filter, faulty TPS, plugged injectos, exhaust leaks, faulty EGR. . . long list.

Sorry, not much help.

[m.wynn]

Hey, any input is appreciated!

The car has 170,000k and pushes ~2 qts of oil in between changes. I think it's always had valve seal issues but never seems to sludge up like that engine is notorious for. I replaced plugs and wires with NGK shortly after the P0171 arose. That fixed a misfire at idle but didn't touch the 171.

I've run 16 ounces of seafoam through the gas tank in the past few weeks but it hasn't helped. Should I try Techron or are you talking about having the dealership do their injector clean process?

Both of the upstream sensors stay put, yes. Is it possible for the bank 2 sensor 1 to be causing the lean condition on bank 1? I'm not trying to ignore the long list of things to check, just trying to eliminate the easy fixes first. I'm starting to think the fuel system and all of it's possible issues are going to have to become the real focus...

Again, thanks for any thoughts.

[73sport]

Need more info. . .

How many miles between changes 3k? 4k? 2qts is alot!

I understand the issue was there before the seafom but sensors hate additves. I'm sure it says sensor safe but there are limits.

Oil consumtion is a concern for the injectors IMO. Not so much when driving but when the engine is off. Why? All those oil fumes are now in the intake and dry on the injectors ever so slowly chocking them.

I'd run the Techron. Good stuff and the only stuff I use. Just before winter every year I run 3 bottles through in 6 tanks. A week of rest I guess between each bottle.

Do you feel tempted to pull an injector and look at it? Though I doubt this will help. But i do think the fuel system is at fault. . .

[chronoti]

well yes because the ecu is trying to correct a clogged sensor, so if you look at the short term fuel trim data bank 1 and 2 should have very different corrections.

try the seafoam through the intake,

[m.wynn]

73sport, what you say about oil fumes in the intake makes sense. Why do you doubt pulling one will help? I'm kinda thinking it might be my next move. I've never pulled a fuel injector, is a clog visible to the naked eye? If you have a sequence with which you'd approach trouble shooting the fuel system, I'd love to follow it!

The car has pushed that much oil for half it's life. I change oil around every 4500, give or take a few. When I changed the plugs, cylinders 1 and 3 (plugs) were really loaded with sooty carbon, enough so it's amazing the thing still ran pretty much fine. Cylinder 2 was fairly gunked up and 4-5-6 didn't look too bad other than some electrode wear. Would it be logical to pull cylinder 1 injector first, since it's plug was so nasty?

chronoti, I'll look at the trim data at some point tomorrow. I'm guessing bank 1 should have the way high correction?.. How do I go about seafoaming through the intake?

Thanks again guys. I've spent hours and hours searching 0171 threads. So many of them seem to just end without a clear conclusion. I'm not expecting a miracle here, but do want to follow it through and learn as I go.

[73sport]

I say that because most of us don't have the tools to open them and clean them w/out damaging them. They are calibrated and expected to perform nearly equally. Us lay people don't have a means to test them either.

Beyond those little details go for it! You'll learn something you didn't know!

IMO you'll almost always find that the front bank runs leaner than the rear.

Cylinders that consume oil are hard on plugs and when contaminates build they cause pre-ignition which results in everyone (engine) getting the timing knocked back ( = bad mileage). Because of the "glow plug" effect, that cylinder runs lean and is the first to trigger the knock sensor, plug an injector, and possibly create the cascade effect of the errors you're seeing now over a period of time. Just to clarify; that's based upon oil consumption cylinder(s) that stand out. Example (#1 and #5) having broken rings using more oil than the others.

I think the step would be to do a compression test and tell us more about plug #2 and any better decription of the others.

I don't have time to find an online photo -shoot of plug conditions but here are some ball-park thoughts.

Normal = rounded from wear, dry, no deposits, more whitish
Lean = glazed, rounded, dry
Balls = aluminum from detonation from being lean
Oily film with build up towards chunks = oil
Rich = no oil, but lots of sooty build up. Color varies by gas. Change plugs an check them after some miles.
Red/brown haze = fuel additives from manufacture (Chevron, Texaco, ect)

Thought: a single lean cylinder could trigger the knock sensor and retard the timing. I think the A/F ratio is coded to such a point that temperature and pressure are the priamry stake holders in the ratio delivered. But my thought was that a lean cyl would make the ECU richen all cyl's to compensate? Is this possible? I don't think so but I don't know.

Is that sort of what you're eluding to chronoti?

EDIT: OK - broken rings is a bad exaple as it drops the compression, but you get the idea. . .

[chronoti]

well 1 lean cylinder will throw the ecu to richen that bank while leaving the other bank running at the correct reading, the engine only corrects per bank not cylinder, this imbalance will throw a lean code.

[m.wynn]

I've got some scan data from when the code is set:

-both LT FT's hover at ~50
-both ST FT's at ~20
-IAT drops from mid to upper 60's when no code to mid to upper 40's if that means anything.
-upstream 02's stay around 6.xxx and downstream goes to pretty much 0.xxx
-MAF doesn't change much from .3xx to 3.xxx depending on throttle, similar values to when no code.

Is the knock sensor ultimately what tells the ecu to set the code? I'm thinking if I need to get into a valve and/or ring job I may just start shopping for a different vehicle and scrap this one. If I unplug the knock sensor will that buy me a little time without having to constantly re-set the fuse every few days?

Thanks.

[chronoti]

Originally Posted by m.wynn

I've got some scan data from when the code is set:

-both LT FT's hover at ~50

that is crazy high correction

-both ST FT's at ~20

still high

-IAT drops from mid to upper 60's when no code to mid to upper 40's if that means anything.

not good? if it is really sucking in 40 degree air (guessing it that cold in ny) and the system is reading it is 60 degrese then the fuel map will be wrong, colder air is denser so more fuel, so with a warmer map and it should should be fueling less but getting more air with less fuel = lean code.

-upstream 02's stay around 6.xxx and downstream goes to pretty much 0.xxx

post-cat not a problem

Is the knock sensor ultimately what tells the ecu to set the code? I'm thinking if I need to get into a valve and/or ring job I may just start shopping for a different vehicle and scrap this one. If I unplug the knock sensor will that buy me a little time without having to constantly re-set the fuse every few days?

nope knock sensor will just retard timing and if too many knocks then it will throw a code

-MAF doesn't change much from .3xx to 3.xxx depending on throttle, similar values to when no code.

noooooooooow..... here the thing, last i checked the mz's dont have a separate iat sensor my 96 1mz didn't nor did my 02 3mz. the ecu makes that number from the maf sensor, you can try and clean the sensor but be careful, you need to find the right cleaner or i have read that you can drop it in a ziploc bag with rubbing alcohol and shake it around, but that was something i read on a bmw site so, search to find the best and safe way to clean it, i say this because that sensor expensive to just be willy nilly with.

Thanks.

welcome

[m.wynn]

Ha, more confusion for me! When the car first acted up I cleaned the MAF sensor with MAF cleaner, by spraying the two wires that are captive down in a barrel type arrangement. This didn't help so I ordered an Autozone rebuilt which didn't work either. By this point I'd read some stuff about the rebuilts not getting it done in Toyota's, so I returned the rebuilt for core and went back to the original. Is it possible the wires I sprayed send signal to the MAF but the IAT gets signal by alternate means? I suppose it's possible that the original MAF is bad and the rebuilt was no good, also...

I've wondered why the MAF mounts to the air intake by two 10mm bolts yet has two phillips head screws in within the sensor housing. Is this the IAT within the MAF, and if so can it be cleaned separately?

[m.wynn]

No, actually all 3 02 sensors are original...at 170,000 miles. I know that's a ridiculous amount of miles but the car has never thrown an 02 code. Actually, the only other code besides the current 171 was a 441 about a year ago, solved with a new VSV for the char-can.

If it comes to doing new 02's, I will do factory for sure. What are wideband?