My car has been a nightmare lately. I have replaced EVERY sensor I can, (maf,map,iac,o2's,tps,icm,air temp, coolant temp, etc). Once the car goes into closed loop, it goes to ****. I picked up a scanner from Murrays, and now I have a bunch of numbers, As soon as I plugged it in and looked at the readings the right o2 was going crazy, 600-850 or so, you could hardly read it. I did 3 readings, the first right when I started it, the second after it went into closed loop, and the third after shuting it off for ten seconds and starting it. The numbers with ranges changed so fast you could hardly read them at all. Here is the list of numbers:

Baro ("HG):29.43, 29.43, 29.43
Baro (V):4.75, 4.75, 4.75
LT FUEL TR CL:16, 16, 16
LT FUEL TRM L:128, 108, 128
LT FUEL TRM R:157, 156, 156
EVAP DUTY %:0, 0, 0
Coolant (F):72, 158, 172
EGR DUTY %:0, 0, 0 (egr removed)
EGR VALVE POS:1, 1, 1
Engine RPM:1000-950, 850-900, 800-900
KS Counter:2972, 2972, 1986
FC1 Relayff, off, off
FC2 Relayff, off, off
IAC Position:77, 80, 32
Idle Req RPM:950, 850, 850
Inj L PW (MV):4, 0, 0
Inj R PW (MV):4, 4, 0
Knock Ret:0, 0, 0
Loop Statuspen, closed, open
MAF (GR/SEC):11-12, 10, 8
MAP (V):2.16, 2.51-2.65, 2.08
MAP ("HG):14.5-15.5, 17.1-17.8, 14-15
IAT:69, 76, 86
O2S Left (MV):1097, 1097, 1097
O2S Right (MV):600-850, 90-690, 0-600
Spark Advance:21, 20-23, 20
Throttle (%):0, 0, 0
TPS Sensor (V):.76, .76, .75

*Could bad plug wires cause this? I replaced them last year, then a couple months ago I noticed the two back ones melted to the headers, so I replaced those two, (with two from the set before). I thought they were okay, they may be next on my list, but I would rather get some input before I shell out another $90. I have gone through about 4 sets of MSD's in the last 4 years.

 

Left O2 looks suspicious. If it's steady, time to change it. The O2 sensors are supposed to flucuate at a rapid rate, not hold steady.

 

That's one thing that has confused me since I posted this thread. I went back out to the car and put the scanner on it to see what the o2's read when only the ignition was on. The left one read 1097, which is the only reading I have gotten from it . I replaced both o2 sensors, in fact I even replaced the wire for the left one, I soldered a new one in. Could I have soldered it wrong??? Or worse yet put the wrong wires together?? Before doing it I read up on the wire splicing, and I made sure (or at least I think I did) the right wires were together. Does anyone have a diagram I can match it to? Is there a special metal you have to use to solder it?

 

I was thinking the same thing, the MAP readings look odd as well

 

swap the O2s right to left. See what reading you get. if it stays the same, then I would say it is the wiring. If it changes, then I would say replace the o2 senser.

 

I disconnected the left o2 and looked at the scanner, it read around 450. So I figured I would plug the sensor into the passenger side wiring harness. If it read 1097 I would know the sensor was bad, but if it read 450 or so I would know it was a wiring issue. Well it was around 450, so I know it's the wiring, but I don't know how to diagnose that. How do I confirm the wiring? And is it easy to solder the wires or could I have messed that up?

I drove it around town tonight for a while with both o2's disconnected, and it ran fine, (open loop of course).

Also what should the map sensor be reading? I just replaced that, and the wiring is still original, so I couldn't have messed that up.

 

The O2s will always read 450mV when they are cold. If they read 0mV or 1000mV then youd have a bad sensor. The numbers are supposed to fluctuate around in closed loop.. they are basically adjusting fueling constantly so you go rich/lean/rich/lean/rich/lean several times each second.

The problem I see with your car is you are running excessively lean on 1 bank and excessively rich on the other. Normally this is caused by a cam and/or exhaust leaks. You need to read Freds(Injuneer) scanmaster tutorial and then you will understand. Find that and it probably takes about 30 min or so to read and then come back. Pay close attention to the BLM(Lterms) and INT(Sterms) as well as O2 sensor outputs.

 

I'd say the left O2 sensor circuit is getting voltage from another source... most likely you have the O2 heater circuit wire spliced into the sensor, or there is leakage of voltage through the heater circuit wires to the sensor wires.

A faulty left O2 sensor explains the 108 BLM, its cutting fuel because it thinks its pig rich.

Then you have to address the right side. You have just about max'd out the right side BLM. Possibley that sensor is giving false low voltage readings. If not, you've got the worst case of split BLM's that I've ever seen.

Fix the wiring on the left side first, then see what you need to do to get the right side under control as well.

The MAP if shaky in closed loop because the "false" rich mixture on the left side O2 indication is causing it to run lean on that side, and its misfiring like crazy (I would bet?).

Have you checked the valve adjustment? Split BLM's might be related to reversion, made worse by valves that aren't closing.

Most of the other stuff looks OK... the spark advance moves around like that with the idle speed., so that's not a problem.

 

So how do I know if the o2 heater circuit is spliced into the sensor?

Also are you saying the right o2 is giving off an incorrect reading because of the problem with the left one? Or is it a separate issue? This electrical stuff is so confusing.

Thanks Injuneer

 

I got the car dyno tuned about a 10 mos ago, could I have gotten a bad tune, and now the left o2 isn't reading? They were having problems getting the LT1 edit to work, it took like 3 days.

 

No.... I'm not saying the the left O2 problem (reading) is causing the right O2 to be a problem. But something is causing the right side of the engine to have to add 20% extra fuel to the standard calculation, as evidenced by the 156BLM. (156 / 128 = 1.22, or 22% extra fuel.)

What I am saying is straighten out the left O2 problem first, since if its causing excessive misfiring, there may be some "collateral damage" worsening the problem on the right side.

I doubt its a "bad tune".... the tune covers both sides of the engine. Split BLM's can result from instability related to incorrect programming of the idle/low rpm for the cam. But a "tune" isn't going to cause the left O2 sensor to constantly read 1.097 volts. When the engine is cold, and not running, it should read 450mV. If it isn't reading that, either the sensor is shorted or the wires are messed up, and your switching of the sensors from left to right seems to confirm its a wiring problem.

There are 4 wires in the body harness, going to the O2 sensors. The brown wire is providing 12V for the sensor heater circuit. The black wire is providing a ground. The sensor signal travels in the tan and purple/white wires. Somehow, voltage appears to be entering the purple/white wire. Turn the key on, don't start if, and unplug the left O2 harness connector. Using a volt meter, measure from the pin for the brown wire to ground.... should read about 12V. Do the same with the black wire... should read 0V. Check that same black wire to ground with an ohm meter, and it should read close to 0 ohms.

Then it gets risky, because backprobing the PCM signal wiring with a voltmeter is not necessarily a good idea. You must have an extremely high impedance digital volt meter. Not sure of the best way to proceed from here. Maybe its just a matter of inspecting the wires, looking closely at any splices you made, and making sure that you have the correct wires spliced together. The brown harness wire connects to the pink wire in the sensor wiring, the black wire to the black wire, the tan wire to the tan wire and the purple/white wire to the purple wire in the O2 sensor. Make sure you wrap all the individual splices very carefully, so there is no possibility of the splices touching each other. Make sure the tape is wrapped very tight so no water can get in. Also look at the idnvidual wires anyplace the O2 harness is near the exhaust system. Its possible the wires could suffer from melted insulation.

Finally, make sure you do not have the harness wires routed in parallel with any high voltage plug wires.

 

Injuneer, thank you so much for all of the advice, this would be impossible without you.

When I get home I am going to check the wires to see if they are melted or touching anywhere.

*I think the o2 wires are zip tied right to the last plug wire
But it seems like it would still read 450 with just the ignition on, because there would be no current through the plug wire.

*The wiring harness I bought from AC Delco has all white wires
So I have no idea which is which now, because once I finished the install, I threw the old one out.

 

The o2 wire was not zip tied to the last wire.

I checked the Lt Fuel Trm readings with both o2's disconnected to see if that changed the difference a little bit, but it didn't, still 128, 158.

I don't even know how to start fixing that.
What are some things to check? Injectors?

 

I'm having some of the wildest readings on my Scanmaster lately. I've always had split BLMs, but now the gap has widened to ~50 or so (156/108, for example). At idle, it's 160/120. On the short-term, when warmed up, RIN can go as high as 193 at idle while the LIN reads 110-112. I've also got two DTC codes 33 and 44 displayed. I thought I had a bad O2, so I swapped out the left one with my son's and it's still the same....and I thought the highest it could read was 156.

 

Swapped O2's from right to left and now left is hitting 193...bad O2 it is.