I guess I should have started with this post instead of butting into someone elses conversation, so I'll make amends now. Getting 147 and 151 fault codes, and my engine stalls and knocks a bit at around 2k RPM's, but other than that sounds great, in idle I can rev to any RPM's without incident. It appears that it has something to do with the heating of the engine, and it must be giving a lean mixture to be cutting me off at 2k RPMs. Is this a standard thing when the engine switches to OPEN LOOP or is my engine dying a symptom of the real problem? I have replaced the sensor aft of the CAT, and still have the problem. It was physically damaged (heat induced cracks) so I imediatley replaced it. Now, I guess I will replace the other one, bank 2 sensor 1, (the most foward sensor?) and see what happens. Also, I have a small hole in my muffler, that shouldn't be a problem, should it? Only if the baffles were busted and creating back pressure would it be killing my engine, right? I banged on my CAT, no rattles. When I go to replace the other O2 sensor, I will run it with it out to check for a backed up CAT. I've also checked the volts and ohms of all source power, all within limits. Anyone else have ideas? A clogged fuel filter should chug at any RPM's, right? As you can see, I'm lost and need some help. I hope someone who had these same two codes can give me some insight, because everyone I ask tells me to do something different and I don't have a pile of cash to replace everything. Thanks for your help guys!

 

*Moving to 2nd Gen Tech*

Brett,
What is it that you are driving... I know it is a '96+, but beyond that...

As far as the fuel filter goes, it would be worse at higher fuel demands (ie. higher RPM under moderate to heavy throttle).

 

It's a 96 Blazer. I took out an o2 sensor yesterday and drove it around and still the problems, so the CAT is out of the question. I drove around with the PCM unplugged just in case that was malfunctioning, still the problem. I took the intake section off and checked everything, looked fine. I'll replace the fuel filter today. If that doesn't work, do you think it could be the injectors? Or maybe the fuel pump not getting the higher RPM signal that it needs to push more fuel?

 

Doubt you drove around with the PCM unplugged... That just wouldn't work.

The sensor after the cat has nothing to do with fuel delivery. Only the sensors before the 'Y' in the y-pipe have anything to do with fuel delivery.

P0147 - HO2S Heater Circuit Bank 1 Sensor 3
P0151 - HO2S Circuit Low Voltage Bank 2 Sensor 1

P0151 is the code that is pointing at the cause for your performance problems. I would have started by looking for an exhaust leak on the passenger side of the engine. An exhaust leak can cause a low voltage code such as this. If you had an exhaust leak, you would hear a ticking around that side of the engine. If an exhaust leak is not present, then you probably have a faulty O2 sensor at the B2S1 location (between the passenger side exhaust manifold and the 'Y' in the y-pipe).

The good news for you is that you can swap the B2S1 sensor for the new sensor you just installed in the B1S3 location (after the catalytic converter). See if that cures your performance issue. If you still have a problem with the P0147 code, then you may have to replace that sensor as well.

 

Well, I did unplug the computer's center wire harness in between the BLACK and WHITE terminal which includes the wire going to the battery, so I thought this would kill the computer- but maybe it didn't? Hmmm. I'll check the engine's right side for a leak, I haven't heard or seen anything funny yet but I'll give it another look over. I'll also change the o2 sensor over like you suggested. Another thing I see that doesn't look right is the way the intake mounts to the manifold area, were the butterfly valve is. There is just a stud on the back side of it with a plastic T shaped nut that holds the intake cover on. Is there supposed to be some sort of other locking mechanism that holds this on? Because it doesn't seem to be a great seal. My main question is, and no one seems to have the answer, how is the engine "supposed" to perform in OPEN LOOP? Is it just supposed to have poor gas economy or does it sputter out like it's doing to me?

 

Unplugging anything to the PCM isn't going to prove anything other than unplug enough and the truck just won't do anything. The PCM is the brains of the vehicle and controls everything.

As far as open loop operation... Open loop is used when the PCM is waiting for the engine temp to reach a preset value as well as other criteria (O2 sensors to get hot for one). In this mode, the PCM is using preset fuel and spark tables for the operation of the engine and using inputs from the MAF, MAP, TPS, KNOCK, ECT and IAT for lookups to these preset tables. It really isn't directly monitoring the O2 sensors for the precise control of the air/fuel system. When the PCM switches to closed loop, the PCM will take into account inputs from HO2S as well as the previously used sensors for precise control of the fuel system for optimum efficiency.

When stuck in open loop mode, the mileage will suffer, but it should not sputter. You have a problem, hence why I am trying to help... Don't know how much more "no one seems to have the answer" type comments I'll stick around for though...

 

Hey man, I'm sorry you got the wrong idea on my last post, by no means was I trying to be an *** by saying "no one seems to have the answer". That was not directed to you, that is directed to my friends and other Chevy/Blazer people. I was trying to show that I have much more faith in your input and wanted to hear a professional answer. Now that I re-read my statement I can see how it might be mistaken. Anyway, thanks for the solid answer-I have a serious problem, it's not just a simple sensor malfunction. I checked the exhaust system on the right hand side and foward of all the sensors, and no leaks are found. Played with the engine for a while, when cold it acts normal, no knocking, skiping, sputtering at idle and at any RPM's in park. Even when it heats up (I waited till my oil temp got to about 210) still acts fine in park when I rev it. When I drive it however I can't get it above 2K RPM's, and as I continue to drive it eventually won't go above 1500 or so, sputters and stalls. When this occurs, I put it back in park or neutral and rev it, and now it sputters in park at around 2k again. Hmmmm. Plugged injectors? Fuel filer? Fuel pump? Thanks for the help man, I'm not an *** I swear! I've read your help with other people and I know you are good at this, I need your input.

 

No worries man. Sometimes I just take things a bit literally. If I didn't want to answer, I wouldn't have.

I wouldn't call it a serious problem yet and it still can be a sensor malfunction. Sensors can go wonky without triggering a CEL for some time. But with the last explaination, it does seem like this is either a ICM heat issue or a plugged catalytic converter.

You can try taking the ICM (located in front of the coil pack near the passenger side valve cover) in to your local autoparts store (Advanced or Autozone) and have them test the ICM. Test it atleast 10 times to get it nice and hot to see how heat and load affect it. Don't know how this would be related to the two codes you have listed, but the symptoms are sometimes better than the codes.

Now with the catalytic converter, you need to pull an O2 sensor out that is in front of the converter. I would choose the B1S2 sensor which is the one directly ahead of the converter. Remove the sensor and disconnect it from the wiring harness. This will trigger a CEL because the sensor is missing, but won't cause any problems with the operation of the motor.

Let us know the outcome of either of those recommendations.

 

I already tried the Cat check, pulled a foward sensor and it still ran like crap. I'll give the ICM a check, thanks!

 

Replaced fuel filter and cap and rotor, same problems. Took it in for a full diagnosis and they tell me it's the fuel pump. Asked them how much for them to replace, and they said 800$. YEAH RIGHT. I'll do it myself, but even then, do you think this could be the problem??? Don't you think that if the pump was bad it would run crappy at low RPM's? I'm not that familiar with the system, but it seems that a bad pump would mean the vehicle wouldn't run.