misswildcat

Hello. Newbie here. I've done some reading on this board and others concerning the P0172/P0175 codes. I know there is more yet to do as far as reading up this code/issue. But I wanted to post to get some ideas of what/where to check things first on the car. I'll start by giving the car history and what hubby and I have/had done to this point.
We are second owners, 2000 Z28, with 107,000 miles currently on the car, automatic. The first owner, was an older gentleman that had his son do some mods on the car when it had about 88,000 miles on it. This will probably be a novel by the time I'm finished--
Mods done:
Comp cams 222/224 .566 .568 112 LSA camshaft
comp cams valve springs, 918 new design
LS6 Intake manifold
Ported stock throttle body
SLP air lid with smooth bellows and K&N airfilter
Long tube headers 1-3/4"
Magnaflow stainless catback system
Racetronix 255lph fuel pump with upgraded wiring kit
GM Iridium 100K spark plugs
Tuned with HP Tuners on 91 octane.

So, we bought the car in April. Drove fine when we brought it home and a few times when the weather was nice (we live in MN). Then we started having some idling/missing/stalling issues, with it sometimes dying. Eventually, the SES light came on for an O2 sensor (B2S2). So we replaced that one with a BOSCH. Seemed to sound better, but not quite smooth, didn't test drive it, but just from starting after replacing that part, another SES light came on for another O2 sensor-- I don't remember which one, but we ended up replacing the other 3, replaced with NGK. After replacing those, sounded much better, idle seemed better, once in a while, when putting car in Reverse, we'd get some rough idling, RPM dips, and sometimes the car would die. However, this was only tested a few times when moving the car in and out of the garage. During this time, the power stirring pump went out and the rack and pinion was leaking. So, we scheduled an appointment with the nearest performance shop to fix those issues and look into the idling issue.

About 2 weeks ago, when driving the car to the performance shop, we had the SES light to come on. I brought my code reader with, just in case, and my reader gave codes P0172/P0175. So, that was added to the list of things for the shop to check into. I don't think they looked into that a great deal as the mechanic said based on those codes, he thought they were O2 sensor related codes (they never read the codes with their reader is what it sounds like to me). The power stirring, rack n pinion, tranny and oil change was done, and they cleared the SES light.

On the day I went to pick up the car, I had issues with getting the car started, let alone run. When it did run, it was rough idling, when the idle would improve a bit, I couldn't get the car out of R to put into D without it dying in R. I got that mechanic out to look at it, and we did get it into drive, and took it for a run, filled up the tank, still having running/stalling/idling issues in the various stages of gears. We got back to the shop, pulled up to the garage, popped the hood, he grab his code reader, another mechanic came out to check that the air filter was place on right. Eventually, the mechanic unplugged the MAF sensor. As soon as he did that, I noticed an improvement of idling sound, and he was shifting from the gears without it stuttering/dying. He took it for a run and I waited at the shop.

We needed/wanted to get it tuned, and this shop does not do computer tuning. The mechanic, tracked down a computer tuner to have the cats deleted, and O2 sensors deleted, that was suggested from the mechanic, and probably have the MAF deleted. His thoughts were that the problem was with the MAF. I drove the car home, about 40 mils from there to home. Made one stop where the car probably sat, engine off, for 15 mins tops. I had no problems with the car idling, or with shifting to D, other than that hard jerk going into D with the MAF unplugged. The SES light had come on after the engine shut off and the code that was given was for the MAF, which would make sense anyways.

I saw the computer tuner on Monday. Car was tuned (HP Tuners) with the following:
Deleted Evap
Deleted Cats
Deleted Rear O2s
Turned on abuse mode
Deleted MAF
Then I left and had a couple of stops to make in town. At pretty much ever stop I made, where the car had to be shut off, upon returning to start up and go, putting into R, or sometimes in to D, I'd have some stuttering/RPM drops/ couple of times of it dying on me. I went back to the tuner and he made another adjustment for me to try: "Recalibrated the MAF, since it was reading 2.5g/s unplugged, and 11-12 plugged in. He took out about 2.5 out of the frequency, turned the MAF back on." This still hasn't resolved the stalling/stuttering/dying/rough idle in some of the gears. This seems to be much more of an issue after the car has warmed up and done some driving. Haven't had any issues when waiting at lights or stop signs yet, just when the engine is actually turned off and you return to leave.

I did another code scan, and I have pending codes of P0172/P0175 again, which might be related to some of the tune changes??? I also have done a data analysis with the reader. That is something that I can later add to this discussion if there is anything there. I'm still reading up on what some of the numbers mean and relate to on that report.

I also had the reader run an Evap System test, that came back failed, but that could be due to the delete of the Evap??

I was thinking of changing out the BOSCH O2 sensor and replace with NGK sensor, so all O2s are the same. But with the rear O2s being deleted, that shouldn't be an issue at all?? If I have the tuner turn the O2s back on, and turn the MAF sensor off, what problems, if any, could there be???

I did clean the MAF sensor, and from what I can tell, I think it's factory part and has never been replaced. It really wasn't all that dirty looking, and the metal mesh screen was pretty clean with the exception of a mosquito.

I have some video that I can also add of the idling/stuttering issues to.
Thanks for any suggestions on this!!

Chris97b

iTrader: (1)

PO172 and PO175 are rich codes for banks 1 and 2 respectively. These codes will be set when the upstream O2's (B1S1, B2S1) indicate the vehicle is running excessively rich. This would not be related to the downstream O2's which were deleted, nor to the cats. EGR delete is also unrelated. The most common causes would be if less air that the computer expects is actually flowing in (defective MAF, or MAP) or an injector sticking open resulting is excessive fuel delivery. With you having codes for both banks, an injector issue seems less likely, but not impossible. This can also be caused by faulty upstream O2's, but with those having been replaced twice this seems less likely.

You mentioned the tuner has messed around with the MAF numbers, that could directly cause this if the MAF is reading low. You did mention that they deleted the MAF in the tune, I'm assuming they went with an SD tune? In that case, I would be looking squarely at the MAP, as that would be a critical input for both a MAF or SD tune, and you haven't mentioned looking at it yet.

If you have data logging, it would be interesting to see the upstream O2's (B1S1,B2S1) ST and LT fuel trims and MAF/MAP readings from when the issue is occurring.

misswildcat

Hello. Sorry I didn't respond sooner.
Let me make sure that I am getting my acronyms right: SD is speed density and MAP is Manifold absolute pressure?

The MAF was deleted/deactivated, but then was turned back on with the last tune. With that change, would the SD even matter with the MAF back into play?

Since my last posting, I have installed a new MAF, and the SES officially triggered with those 2 codes on Saturday, with a quick drive. I've got some data from Friday, with the original MAF, and data with the new MAF. I'll get that updated here shortly. I have also ran a few questions by with my tuner and awaiting response from him.

Thanks!!

Chris97b

iTrader: (1)

Correct, SD is Speed Density and MAP is the Manifold Absolute Pressure sensor. Basically when using the MAF, one of the primary ways the computer decides how much fuel to inject is by using the airflow readings from the MAF. There are other inputs as well (IAT, O2s, MAP, etc.). SD is basically using a combination of MAP and IAT (Intake Air Temperature) data to decide fueling based on a series of pre-computed tables in the computer, instead of measuring actual airflow. If the tuner disabled the MAF completely then the car was by definition using SD to determine fueling while the MAF was disabled. The reason I ask is disabling the MAF and having the problem not go away strongly suggests that the MAF is not the issue.

I would be looking at things common to both scenarios (MAF disabled and MAF enabled), which is why I suggested MAP or IAT could be the culprit. Maybe someone else can chime in here, but I don't remember whether upstream O2's are still used in SD or not. Really we still haven't ruled out leaking injectors either, but that would require at least 2 injectors to be faulty (one in each bank); and it seems unlikely to me that multiple injectors would fail at nearly the same time. Just to clarify, it went from no codes at all directly to both PO172 and PO175 at the same time, right? You didn't have one first, and the other show up later?

*EDIT*
I just re-read your original post, and this started shortly after replacing the upstream O2s? That strongly suggests the computer doesn't like the new O2 sensors, as the data for setting these codes comes directly from the upstreams. You mentioned that both upstreams are NGK and one of the downstreams is Bosch? Might be worth swapping those around to see if that clears the code from that bank.

misswildcat

Correct, both those codes came together and yes, sometime after replacing the remaining O2s. I've had that in the back of my mind since those triggered so soon after replacing, that maybe that's the problem. Both upstreams, and the downstream on driver side are all NTK, while the passenger, downstream is the Bosch. (NTKs not NGKs, just realized I had that wrong).

Now, I just went back to checking the NTK O2 sensors that I had purchased. I had thought that I had gotten the upstream, right-passenger ( I think that's B2S1??), but the 3- O2 NTK sensors that I picked up fits: Upstream Left; B1S1: Downstream Right; B2S2 : Downstream Left; B1S2....

Now did I just find my problem?? I've got the wrong O2 sensor sitting in Upstream Right, B2S1??
Could the wrong one in B2S1 cause the B1S1 to also read wrong, and trigger both codes?? Well, either way, I will be picking up a B2S1 sensor to replace and see what happens.

My goal this weekend is to check the injectors, swap out the O2 and maybe replace MAP (I'll have one on hand just in case). I did get the data uploaded. This is from Sat. afternoon, with a new MAF installed. I only had one stutter/die at the start, but the reader doesn't seem to have caught that. I'm not seeing any runs in the data that reflects less than 600 rpms when this typically begins before dropping below that.
Correct, both those codes came together and yes, sometime after replacing the remaining O2s. I've had that in the back of my mind since those triggered so soon after replacing. Both upstreams, and the downstream on driver are all NGK, while the passenger, downstream is the Bosch. The NGKs that were purchased are, I guess a universal to any of those locations.

Chris97b

iTrader: (1)

Hmm. I took the cheap classes in this stuff, but something definitely looks funny there. Actually a lot looks funny. It's hard to tell with point-in-time snapshots of course, but the first thing I notice straight away is that the O2s don't seem to track each other particularly well. In a car with no cats, I would expect the upstreams and downstreams to be almost identical (B1S1 should match B1S2 and B2S1 should match B2S2); as there is nothing between the sensors to change the O2 saturation. There are times though when they are wildly different, which calls the reliability of the O2s into question. They do seem to be at least trying to switch in closed loop, so there is some degree of fuel control at idle, but it looks flaky at best to me.

Particularly under load (~20% throttle and 1500 RPM) the fuel trims jump *way* lean and the O2's are still pegged full scale rich. Normally I would point to the injectors as a probable cause, but at this point I'm still not convinced I trust the O2s to be accurate. The MAP and IAT both seem to be ok from the data, but take that with a grain of salt.

I guess I'm back where I started on this one, bad O2's (all 4? is that even possible?) or leaky injectors (again, would have to be on both sides *sigh*)

If anyone who actually does this stuff for a living has anything to say I'd love to hear it.