liquidh8

Ok, here it goes. I have the 7747 w/EBL. I had an o2 sensor crap out a few weeks ago. I had to putin a 2 wire cause that's all I had in "stock". It was new. And a few days ago I got a new Boshc 3 wire to put back in it.

Ever since the 2 wire replacement, my o2 voltage, as displayed on the WUD, new see 700mV or higher. It'll drop down to the low mV readings, 100, 200 and so forth, but when it switches, it only goes as high as 680 mV or so.

I am running an Innovate LC-1, I know it gets to the 12.8 AFR a WOT that I have set.

If I take an VOHM meter to the sensor itself, it does go to over 700mv, when I hold the rpm's up to 2500 in park, and when I rev the p!$$ out of it in park, the o2 swings.

So, anybody have any ideas?? Is there something in the code causing the misreading? The ECU jacked up? I has been a nightmare driving and tuning cause the ECU thinks it is constantly lean, adding fuel and making super rich.

HELP

dimented24x7

iTrader: (2)

What does a wideband show while driving? If its outside of around 14-15:1 when it swings and the BLMs are showing higher then 128, there is a definate issue. I dont know exactly whats in RBobs code, but in some masks, there are limits placed on when learn is enabled. Low MAP could be causing the ECM to disable closed loop when you rev the motor in park.

liquidh8

when I am driving, the BLM's would be 140 to being pegged at 152, but the WB will show 13:1 to 13.8:1, so the ecm is thinking that is is really lean, but in reality it isn't, the NB is throwing everythin off. I check the wire from the NB o2 to the ecm, it has near zero resistance, and it isn't shorted to ground. I also checked the o2 grond from the ecm to ground, and it was fine. So I am kinda SOL. unless I have been getting a string of bad o2 sensors But as I said, if I backprob the o2, it swings in voltage, then when the BLM's go up, lean, the NB o2 actually reads rich at the backprobe, 900mv and up, even as high as 1.2mv. So I know it is getting fuel, but the ecm isn't seeing that.

dimented24x7

iTrader: (2)

In that case, it definatly sounds like there is an issue somewhere. Do the O2 voltages at your DVM match those shown through the WUD? Sort of sounds like a faulty connection, or a partially grounded signal wire.

liquidh8

No, not exactly. The lower voltages, 680ish mV and below seem to be OK, it's from there up that doesn't register. I even logged it and did a WOT run, the NB never "showed" above 700mV. Though the WB said I was @ 12.6 to 12.9 AFR, which I believe.

I also went and checked the wire for the o2, the wire from the o2 to the ecm, and the o2 ground from the ecm to ground, and they were fine. Not open or shorted to ground. And they both were under 1 ohm in resistance point to point. SO I am kinda at a stand still now.

dimented24x7

iTrader: (2)

Thats interesting. So, even though the actual O2 voltage exceedes .7V, the ECM wont register anything above that? If the O2 voltage reads properly at the ECMs connector, then my guess would be faulty hardware. As a final check, probe the voltage between the O2 signal wire and ECM ground at the ECMs connector. If theres a discrepency there, then you know the issue is with the computer itself.

RednGold86Z

iTrader: (1)

or a badly grounded exhaust system (but I kind of doubt this is your problem).

The 3 wire sensors' ground reference the sensor only through the housing of the sensor which connects to the exhaust. A 4 wire can be either case ground or isolated, but both ways have a ground wire for ECU O2 Lo reference.

liquidh8

I was kinda thinking the ECM could have an issues.

Red, I check for a good ground from the exhuast to the o2 sensor, and from the exhuast to ecm grd, batt grd, and so forth.

What sucks is I don't have immediate access to a Snap-on Vantage anymore, so I can get an accurate reading on what the o2 is doing in reference to what the WUD is displaying. Using a DVOM for o2 checks isn't the best thing to do, they are TOO slow.

Now the question is, is there a way to check the ECM itself to see if that is at fault?? It's not like I could take out the EBL and put it in another ECM. I do have a spare ECM though.

RBob

iTrader: (1)

It is interesting that the issue started with the first replacement O2 sensor. Myself and others have had problems with Bosch sensors, and good results with AC Delco/GM sensors.

However, more to the point, to test the ECM need a 1.5 volt battery (AA, C cell), a 10K pot, and a 10K resistor. Wire one leg of the pot to the battery +, the other leg to battery -, then the center tap to the 10K resistor.

Now connect the 10K resistor to the ECM O2 input pin, and the battery - to an ECM ground. Put the DVM on the 10K/O2 input pin, fire up the WUD, and start the engine (engine has to be running for the ECM to use the O2 input and not the default value).

The reason to use a 1.5 volt battery is to not fry the O2 sensor amp inside of the ECM. Doesn't even need to be a new battery, if it has more then 1 volt with the 10K across it, should be good to use.

Now the WUD voltage should track the 10K/O2 sensor input voltage.

Adjust the pot to various voltage levels and compare the WUD against the DVM.

RBob.

{edit: added a drawing showing the test rig connections}

RBob

iTrader: (1)

Hmm, even though it uploaded the attachment, it didn't stick. New post to show the drawing.

RBob.

liquidh8

RBob, you are a savior!!

That is exactly what I was looking for! Later on this evening I'll try it out. I have top go to Radio Crap to get the parts.

BTW, what Delco o2 do you recommend?? I am running a 3 wire set-up, the original was a one wire, so I added the heater. But you already know that.

RBob

iTrader: (1)

If the 1-wire was working I would stay with it. The 1-wires I use are the ACD# AFS-20. The GM part number is: 25162693

RBob.

liquidh8

RBob, sorry for the confusion. I haven't used the one wire in a long time, I've been using a 3 wire. Just that when the three wire went bad, I had a 2 wire laying around. Then bought a botch replacement 3 wire. I did a search and came up with this from another post

Sound right??

RBob

iTrader: (1)

Yes, the AFS-74 is the heated one to get.

RBob.

liquidh8

Thanks, I'll use that little circuit to test the ecm tomorrow, never got to it today. But I am still buying the Delco o2.

liquidh8

Update.

I went out today after getting home from the base, and made that little circuit. The ECU and EBL are fine apparently. I can max the displayed voltage and make it minimun, so the Botch o2 sensor must be crapped out like everyone said. BN too. I go to pepboys, autozone, etc, and all they sell is the botch o2 sensors. Even the local chevy dealer doesn't stock the delco's, they use the aftermarket crap! So, I'll have to go to GM parts direct after I getsome cah and order like 3 of them, so I have them in stock.

Thanks for all the input guys

Fast355

iTrader: (2)

Got news, the last "AC DELCO" O2 sensor that I bought for a 1993 4.3 Astro was a DARN Bosch.

liquidh8

hmmm, maybe I should try a tomco, or a standard?

dimented24x7

iTrader: (2)

Speaking of the devil...

I just replaced my old 1-wire Botch with a new one, and it does this same thing. The engine runs around 15-15.5:1 when the sensor is 'cool'. After lots of driving, it targets my stoich AFR of 14.1:1 once warm. Its definatly the sensor, becuase if I disable closed loop, the engine runs at 14.1:1 around idle.

liquidh8

I'll tell ya, it's urning out to be a pain in the rear With o2 sensors being 50 bucks a pop, you have to make small investment to get a stock of the part that you know works. I'll try a different brand in the meantime, but I am going to order a few of the Delco's online so I have them.

HaulnA$$

I just bought two AFS74's from rockauto.com and they were the real deal and significantly cheaper than anyone else. HTH