Ok first off this is not my vehicle. My younger brother owned this 2000 blazer with the 4.3 4wd automatic for the last two years. No major problems until about 3 months ago. He just finally asked me about it. I think he has more than 1 problem.Problem 1. He was late to work the other day because he couldn't get the truck to start. It was 5 degrees out that morning, the truck cranked fine, then starter went dead after multiple attempts to start(can not duplicate as of yet). It wouldn't crank anymore. The Head lights were on, dome light was lite up just as bright as always. So he didn't kill the battery. Turning the key the lights did not dim at all, no click, no nothing. ok first thought bad solenoid.At this point he gave up. Later that day the girl feind(no typo)calls She went outto thetruck and itstarted right ran fine, she drove it around all afternoon.Next day he Drives it to work and tells me that He was slowing down for the entrance ramp (coasting along) then once he makes the turn he stepped on it a little (to him a little is not exactly to the floor) and the engine stumble afew times at lower rpm and then it next 100' itsmoothed out andit ran fine the rest of the day. Thenext day after that he wasfutzin around looking for the cause of the no start, and he could'n getit to start unless he had the throttle wide open. So now i am thinking bad CTS, TPS, EGR, or CPS.So this started in with him telling me he has been having intermittent MIL. It would come on, Go off, but ran good over all except a drop in gas milage has dropped to pot in the last 3 weeks. I brought my Laptop in and hooked it up and retreived a P0300 <- random cylinder misfire, and P0303 <- Clynder three miss fire. While i was plugged into the obdII cylinder 3 maxed out the knock count. The coolant temp sensor checked out against a thermometer on the radiator hose with in 3 degrees so i feel that isnot a problem. I have not done a fuel pressure leak down test yet, i am going to do this tomorrow when i get to work. The MAF is reading with in spec. The only sensor i can find out of wack is the bank 1 o2 sensor was reading +5.5vdcat idle and did not change at all with rpm and according to the computer the motor was operating in a closed loop.I am not strong on this motor in the least bit, but to me that seems way out of normal for any motor. All the time we had the motor running at varing rpms and it seemed smooth with out any feel of a miss. Also sticking my nose in the tail pipe it has a slight rich aroma, bust most vehicles seem to idle on the rich side to me. I am hoping the fuel preesure test shows i am not leaking past the FPR or one of the injectors. Gut feeling teels me injector 3 is toast but after reading tsb it can be or not. Does anyone think 1 injector leaking a little gas would cause the o2 sensor to read that high of a voltage. I can see this killing the O2 sensor if the vehicle ran long enough this way, but also the o2 sensor is orginal and should be replaced i am thinking of starting here. I hate just swwapping parts with out knowing theWHY behindthe part failing. Also going back to the no start i just found out that this vehicle has a aftermarket remote start, so i assume that the passlock system has been by-passed, and it also remote start no longerworks since the original no start occured. I am thinking the drop in fuel milage is because it has been cold and he has been warming up the motor for 10 minutes before he leaves to and from work.

i have been over this sight, and found similar pproblems but I am looking for some advice from some one that has more experince than me and might be able to point out a quirk in the electrical or mechanicals i don't know about. If you took the time to read this post I THANK YOU for any widom you might be able pass along

 

How were you reading the O2 sensor voltage? +5.5Vdc is no where near the realm of correct for any O2 sensor. It should be in the range of 100mV to 900mV and cycle between those two during closed loop operation. Disconnect the O2 sensor and see if things smooth out. Also see if that changes the reading on the O2. If it does not, then you have some wiring damage that is feeding voltage to the sensor return wire.

Having a remote start unit installed complicates the no-start situation and makes it a royal pain for anyone not there with the vehicle to diagnose.

About your post above, please break things up a bit. That was painful to read. Paragraphs would have been wonderful!

 

Thanks for your reply. And yes I can see your discomfort in my post. 9pm server time is 1am my time.

I am reading the 5.5vdc not .55vdc through the PCM. I have an autoeginuity enhanced system analyzer. This system gives (with my expeirence) avery accurate feed back based on what the pcm is seeing from various sensors. I know the normal range of an 02 sensor. It was late and I typed Fast. The bank 1 o2 sensor is feeding back to the PCM a +5.5 volt signal. Bank 2 o2 sensor is ranging .35vdc or 350mv to a max of .65vdc or 650mv. Bank 2 looks fine and normal, hence the statement the +5.5vdc lookedWAY out of the normal to me. I have read your previous posts to others and you sound like you know what you are talking about.

Any way. The bank 1 o2 sensor through the odbII port is giving the PCM a feed back of +5.5VDC. Disconnecting the o2 sensor on bank 1, The PCM feeds back a volatage of .45vdc when jumping out the terminals to the sensor, which does cause another engine code.I believe this is because the PCM reads this as a bad voltage, Because this should be the base voltage the computer sent to the O2 sensor and the pcm should look for a drop or increase in voltage to adjust the pwm of the injector to correct for to much/little fuel enterinng the cylinder. Please correct me if I am wrong, but this suggest to me the wiring to theconnectionpoint is good.Thank you because after testing the bank 1O2 sensor with a meter; itis showing continuity to ground. I have not found a good o2 sensor to do this.

I have checked the fuel pressure and it is 55psi when the key is turned on( after the 2 sec prime)and does not drop below 45 psi after sitting over night. So i feel i can eliminate the fuel system. I am replacing the o2 sensor tomorrow.

I think the aftermarket remote start has alot more to do with the no start than a bad o2 sensor.


I hope this post was a little easier on the eyeballs than the last

 

It is possible that there is a short between the heater circuit (+12V) and the sensor return inside the sensor itself.

You could swap the B2S1 and B1S1 sensors side to side and see if you get the same readings on the B2S1 trace.

And I love my AutoEnginuity scanner as well. I have the GM enhanced data as 95% of my friends and family have GM vehicles.