that 1100mv was with a bad 02s... with no sensor installed, bias voltage was correct..although I don't recall the exact number.

as soon as it goes closed loop, ST drops to about 80, and then pulls the LT down to about 109....

I'm going to get an 02s wave form next..

 

I am not understanding. I was reacting to this comment "unplugged the o2s, tech one showed 1096mv.". It is essential to check the bias voltage on the harness from the ECM with no O2 sensor attached with the ignition on or the truck running (whichever powers up the harness). It should read around 450mv. Then you have to confirm a good signal ground if 4 wire. Then you have to confirm a good power and ground for the heater (if 4 wire). A waveform is best.


George

 

here are the same 2 wave forms.. the blue one is complete from startup.. the black one is just as it goes closed loop. voltages here, were sampled at every 0.5 seconds. . I have another with the data sampled at 0.25 seconds but I can't figure out why I can't read the file.. DOH!

x axis is just number of samples.. so divide the x by 2 and you've got number of seconds.

voltages were read directly from the back of the PCM.. Red Connector, A10 for signal, A12 for ground.

 

ok, I got the data for the 3rd run with it set at 0.25 seconds sample rate. (data got corrupted, but I recovered it from the source)

 

For what its worth, i made a short video of the tech 1 showing how fast the fuel trims drop... Good stuff is about 1:40. You can just hear the exhaust get rougher as it pulls the fuel.

 

Also... Spider wont hold fuel pressure... It drops fast enough to ser. It dropping

 

If I understand your O2 graphs correctly it looks like the switching is about 1 hz and the upper and lower values are about right so it looks like the sensor is functioning properly.Are you reading this data with a scope on the signal wire or is it output from the ECM?

What are you ST and LT fuel trims if you stop resetting the values and run the engine long enough to let them stabilize?

What is your key on fuel pressure and what is it after the 10 min leakdown time? Assuming that its less than 55 PSI you have a leak somewhere and I am betting its injector(s) leaking into the cylinders. I bet if you pulled some plugs one or more would be fouled. In open loop the injectors are getting theoretical fuel delivery based on the ECT, TPS, MAF/MAP, IAT, etc and a couple of cylinders are probably running rich. When the O2 sensors get involved they see all this unburned fuel and try to bring the exhaust gases back to balance but this leans out the remaining cylinders in a vain attempt to fix the problem. If I am wrong then you may have an ignition problem.

The fuel pressure needs to be corrected.


George

 

Directly from the signal wire at the ecm..Red connector A10 and A12

They drop to their maximum lean values and stay there.
61psi. koeo. i haven't put a stop watch on it..but the pressure bleeds off quick enough i can watch the needle drop...

I believe you are right. I've suspected this reman spider right from the beginning... just trying to confirm it.

 

Since you are reading the O2 sensor signal on the input wire to the ECM we know that the O2 sensor is working correctly but we don't know if the ECM is reading it and using it correctly. That said, If 10 min after key on your fuel pressure is below 55 psi, the leak needs to be fixed literally regardless of any other piece of information.

The system has a single prime directive: 14:1 air fuel and minimum emissions. The secondary mission is don't kill the cat because then you violate the primary directive. Once the O2 sensors come online they are trying to do their job and the ECM is removing fuel because emissions are sky high. It doesn't think your running rich, you are running rich. You like the way it runs in open loop better but you would fail an emissions test and This needs to be fixed more sooner than later or the cat is next along with cylinder scoring, bearing wear, .... The fuel management system, along with the trims are doing exactly what they were programmed to do. The lean fuel trims are not the root cause, they are a clue, along with failing fuel pressure on your way to root cause.

BTW, nice work on the O2 graphs, I don't think I have seen anybody do that with an ODBI vehicle.

George

 

Thanks!! I used an antique data logger to read the analog voltage on the 5000mv scale (options are 50,500, and 5000) set it up to do that every 0.25 seconds.. and just dump the data to the serial port.

Then I tell the connected laptop to record the data to text file.. that generates something like this:
01+0104. 02+26.47 03+1058. 04+11.37
01+0104. 02+23.75 03+1058. 04+11.37
01+0104. 02+14.93 03+1058. 04+11.37
01+0104. 02+0853. 03+1058. 04+11.37
01+0104. 02+0899. 03+1058. 04+11.37
01+0104. 02+0922. 03+1058. 04+11.37
01+0104. 02+0926. 03+1058. 04+11.38

the only column that matters is 02+ that's the sensor voltage in mV

I import the entire file, 1076 records in this case.. into Excel.. use a couple functions to turn the strings "02+0926." into a number that can be graphed.. then let Excel graph it.. sounds more complicated to explain that it actually is.

I have a GM VSI.. but with no software and no instructions.. it's not a lot of use...