Scan Master low O2 readings

[84BuickGNYorkPA]

Hi Guys,

I have a problem, I just replaced the O2 sensor and the O2 readings are great(790-810 at idle, after engine is up to tempature), untill I go WOT more then a couple of seconds. What happens is the O2 readings drop off to nothing, on the last WOT I watched the SM read a 015 with .7 kr, in about 4 seconds.
Before I replaced the O2 sensor the readings would never go over 500 range(at idle after up to tempature). I went to Auto Zone, Advance Auto, and Pep Boys they all carried Bosch, I ended up getting mine from Pep Boys it's a Bosch 12014, any ideas, what might be going on?
TIA,

Chuck

 

[TurboBuRick]

Hi Guys,

I have a problem, I just replaced the O2 sensor and the O2 readings are great(790-810 at idle, after engine is up to tempature), untill I go WOT more then a couple of seconds. What happens is the O2 readings drop off to nothing, on the last WOT I watched the SM read a 015 with .7 kr, in about 4 seconds.
Before I replaced the O2 sensor the readings would never go over 500 range(at idle after up to tempature). I went to Auto Zone, Advance Auto, and Pep Boys they all carried Bosch, I ended up getting mine from Pep Boys it's a Bosch 12014, any ideas, what might be going on?
TIA,

Chuck

Sounds like mabye your fuel pump is craping out. Did you not see knock with the old o2? Most chips don't use o2 reading for wot.

 

[84BuickGNYorkPA]

I guess that I need to get a fuel pressure gage..... where I can see it, unlike the one now on the fuel rail. The fuel pump is about 2 yrs old....only knock that I get is false knock when doing a burn out, I haven't really stayed in the gas to much with these low O2 readings, by the way the car runs great around town, for two seconds, then I let up. When I saw the 015 reading, you would think that the KR would be through the roof....
Thanks for the reply.

Chuck

 

[phillyturbosix]

hey Chuck! I'm playing with this same battle. My idle 02's are up in the 800's but when I go wot or anywhere near it I'm barely hitting 700. There is never any knock and plenty of fuel pressure as I have the gauge under my wiper. I too put one of those Bosch 02's from a parts house in the car recently. I was told they are junk and don't last. The GNX 02 is the one to go with. With this time of year and everything going on I have'nt had a chance to check into it more plus I only put maybe 1000 mioles on the GN a year. I have the scanmaster, Caspers knock gauge and the audible one so not hearing or seeing any knock ever I have'nt worried about it none to much but I've been on the war path to figure it out as well. I almost thought it was something going on with the alky but when you never use the car it's hard to figure something like this out!

 

[TurboBuRick]

hey Chuck! I'm playing with this same battle. My idle 02's are up in the 800's but when I go wot or anywhere near it I'm barely hitting 700. There is never any knock and plenty of fuel pressure as I have the gauge under my wiper. I too put one of those Bosch 02's from a parts house in the car recently. I was told they are junk and don't last. The GNX 02 is the one to go with. With this time of year and everything going on I have'nt had a chance to check into it more plus I only put maybe 1000 mioles on the GN a year. I have the scanmaster, Caspers knock gauge and the audible one so not hearing or seeing any knock ever I have'nt worried about it none to much but I've been on the war path to figure it out as well. I almost thought it was something going on with the alky but when you never use the car it's hard to figure something like this out!

Merry Christmas guys.
How are your o2 crosscounts? If o2 seems to be working otherwise I would not brush it off. The colder temps need more fuel. Sound to me like you need to add some fuel to your wot. The colder weather and alky are probley supressing knock.

 

[84BuickGNYorkPA]

What is the O2 cross count? Is that cc reading? And it should cycle from 1 to 250 or something?
Hi Jim, Should I go anywhere and ask for the O2 sensor for a GNX?

 

[phillyturbosix]

I have a 2.0 Scanmaster in my GN and a 2.1 in the TTA. I need to swap them and have Eric make me a new chip to check the CC's so I'm not sure. Chuck I have'nt had the time to search that GNX 02. I think you can still get them from GM. I have to call my buddy at the dealership and see if he can get them and how much. I'll let you know. My car was doing the same thing all summer so not sure if the cold weather has much to do with mine. Like I said I get 0 knock but those 02's are just low on WOT all the time.

 

[Jerryl]

Having searched the board for 2 years straight to combat audible KR, I came up to this conclusion.
I know you already know this and without any intend of insulting your intelligence, here is my take;
The variables for correct O2 readings are many but you have most of them covered.
Keep in mind, I am no expert and merely documenting what I learned from this board and had to verify to work on my KR issues. (I know you have no KR but these points below will have an effect on O2)

MAF reading is off
At boost level up to around 12 PSI, your MAF “may” read lower than 255 gr/sec and not limit out (depending on the combo). This will give the ECM some level of control over the fuel. If you run higher boost levels (>255gr/sec, TPS, LV, etc), the code will dump XX amount of fuel. This is a calculated fuel delivery, hence the locked 128BLM.

Exhaust leak
Do you have any exhaust leaks? This may show at higher RPM's. What about a plugged cat?

Speedo
The LV is calculated using a few variables, one of which is MPH. This has an effect on fuel as well. Is your MPH pretty accurate?

Chip code
Since you are running a TT, You have that covered.
Did you try increasing WOT fuel in the chip to see what happens?

O2
You could possibly have a bad O2
Many of the experts have stated to only run Delco O2 sensors on these cars.
I run the “GNX” style unit.
I have also come to the realization that you can not really “count” on the O2 voltage.
There is just too much fluctuation and inaccuracies between 750 and 820 mV.

Weak Fuel pump
If your FP is stable and rises 1:1, that is most likely not the issue.
Maybe a fuel filter change is warranted?

Voltage
What is your voltage at WOT? Is the pump seeing enough of it?
What about your grounds at the pump?

Does your TPS go over the 4.4V mark @WOT?
What about EGR?

Again, probably something simple, and I am no expert, but merely documenting what I learned from this board and had to verify to work on my KR issues.

 

[phillyturbosix]

Thanks for the post Jerryl that's what makes these boards great people willing to share and help with the information you post! There is a few things I can try from your findings that might help on my end..

MAF: I had a stock rebuilt one that I thought was going bad. So I replaced it with a new Translator and LT1 Maf all brand new did'nt change the wot 02's

Exhaust leak. I did see my cross pipe leaking just a tiny bit and I'm going to take it off over the winter and make sure it seals good but from the size of the leak I'm not sure that could be it.

Speedo: Is good.

Chip: I didn't try messing with the WOT FP on the chip but that will be on the list.

02: put a new Bosch one in like Chuck. No change maybe even worse idle 02's so the GNX one is next on the list.

Fuel pump: 3 years old Walbor 340 but hey anything is possible with that. Was thinking about dropping the tank and checking it out over the winter.

Volts: I have a brand new 120amp alt. with the hotwire kit but I'll need to look into how the wot volts are as well.

TPS: pretty sure it's good but I'll double check. I tossed all the EGR stuff and blocked it off with a plate.

thanks again for your post and I'll dig around some more!

 

[84BuickGNYorkPA]

Thanks Jerryl,
I have to check some things on your list, starting at the fuel filter. I'm printing your reply out so I can check them off.
Jim,
I'll try to keep in touch at the MAGNA meetings with my adventure... I mean progress...
Chuck

 

[NM Tom]

I chased a very similar problem for about 6 months. At WOT my o2's would only be about 450 to 550 but the car ran great and I had no knock. Knowing my fueling had to be OK since I had no knock I started looking into electrical things. My problem wound up being the grounds that attach to the back of the passenger head were loose. One of the wires in that group happens to be the ground reference for the o2 sensor. After I cleaned and reattached the gounds tight my os'2 acted as expected and were up in the 780 area. Good luck!

 

[phillyturbosix]

I chased a very similar problem for about 6 months. At WOT my o2's would only be about 450 to 550 but the car ran great and I had no knock. Knowing my fueling had to be OK since I had no knock I started looking into electrical things. My problem wound up being the grounds that attach to the back of the passenger head were loose. One of the wires in that group happens to be the ground reference for the o2 sensor. After I cleaned and reattached the gounds tight my os'2 acted as expected and were up in the 780 area. Good luck!

hmmmm that is something I have to look into for sure! I just had all them off not that long ago. I was pretty sure I got them on there good and installed the Caspers ground kit but anything is possible on these cars! I'll have to ground the 02 to the battery with a wire and see if it changes!

 

[NM Tom]

hmmmm that is something I have to look into for sure! I just had all them off not that long ago. I was pretty sure I got them on there good and installed the Caspers ground kit but anything is possible on these cars! I'll have to ground the 02 to the battery with a wire and see if it changes!

The ground reference at the grounding strap is a ground signal that goes to the ECM. It meets up with the one wire output of the o2 sensor in the ECM to register the voltage. I don't think running a ground to the sensor itself will do anything.

 

[turbobose13]

check the ground's on the back of the passenger head, and go to Bennett auto for the delco o2 sensor get the GNX o2 part # end's in 22.

 

[84BuickGNYorkPA]

Got the Delco O2 sensor in, new fuel filter, no change. New fuel pump is on the work bench, did not get that in yet. Ground wires are good
One other thing that I want to add, I also have a issue with the charcoal canister leaking gas... and noticed that when I open up the gas cap there is a vacuum sound. Could the charcoal filter go bad? And the system is not venting?? I never had this before untill I installed the walbro fuel pump last fall.

Chuck

 

[Eric Stage I]

Chuck,
Is it possible the vent line and return line got crossed at the tank when you installed the pump?

Eric

 

[84BuickGNYorkPA]

Eric,

With me anything is possible, would it run like that? If I remember all three lines at the tank are different diameters, I need to get a idiot guide and go check it out.. Thanks,

Chuck

 

[phillyturbosix]

I went with the GNX 02 sensor over the weekend. Some improvement while I had it out but it's still low. I talked with Eric and the WOT fuel on the chip should be good as is. I'm going to pop the valve cover off and check the grounds. I'm also wondering I had my headers cermatic coated and I don't think they chased the threads when done. Maybe I'm not getting a good 02 to header ground. This is the 3rd time running an 02 sensor in there so it should have cleaned them up a little but I'm wondering how much that might have to do with the 02 not getting a good ground but working correctly. Don't worry Chuck we'll get it worked out yet!

 

[Jerryl]

I went with the GNX 02 sensor over the weekend. Some improvement while I had it out but it's still low. I talked with Eric and the WOT fuel on the chip should be good as is. I'm going to pop the valve cover off and check the grounds. I'm also wondering I had my headers cermatic coated and I don't think they chased the threads when done. Maybe I'm not getting a good 02 to header ground. This is the 3rd time running an 02 sensor in there so it should have cleaned them up a little but I'm wondering how much that might have to do with the 02 not getting a good ground but working correctly. Don't worry Chuck we'll get it worked out yet!

Jim,
I had a new fuel pump that went bad a LOT earlier than expected. I replaced it "Again" and to make sure, performed a volume test @50 psi. Guess what I am saying is that new parts can go bad, and, you could have a weak pump or lazy MAF. So with these cars, you learn to question everyting!

 

[phillyturbosix]

Yea I know what you mean! I did the walbro 340 and hotwire kit about 4 years ago.. I've been sticking my ear back there just to see if it's sounding funny but I might drop the tank and have a look if the ground thing comes up with nothing. I have a fuel presure gauge under the wiper and I see it fly up but it's hard to watch that and the boost and not get killed on the road at the same time!