There are so many ppl here having problems with the MAF and O2 sensors, makes me glad that I don't have either on my swap.

 

 

Houston, we have a problem...




I'd take a deeper look at your O2 sensors. It may just be the setting on your scan tool. Pre-cat O2 sensors should report a waveform, like this:

 

My downstream sensors are removed completely but you're saying my Bank 1 Sensor 1 and Bank 2 Sensor 1 are not operating correctly? I noticed it appears as if they were not as active as other peoples logs I have seen. They are brand new Denso sensors.

 

Would the temp of the vehicle at the time have any effect on this? Coolant temp was right at 153-156 F. Also fuel system reported Closed.

 

No.


I'm not saying they are definitely operating correctly, but the wafeform you are showing from your tool is not correct. I'd suggest pulling up the tool's instructions. For my scan tool, there is a special screen/mode that is required to view these waveforms. (They switch pretty fast.)

The graphs you are showing are similar to what a post-cat sensor would read, normally:




So, my theories would be:
- Something is not set right on your scan tool
- The wiring for your O2 sensors are off
- Your O2 sensors are not working properly
- Your O2 wiring is off
- Maybe a combination of the above

^ I'd lean towards an issue with your scan tool because if these readings were real - I'd expect your PCM to be throwing codes like crazy. Your O2 sensors aren't even reading in each others' ball park. One is 1V (Way rich.) all the time and the other is almost 0V all the time. (Way lean.) I'm not an expert in this, but I would expect that these values (if true) would be way out of bounds for a code.

 

Well the truck does run SUPER rich with them O2 sensors hooked up, So much that it almost appears its dumping fuel into the exhaust. I honestly am not sure how to determine if it is O2 sensor wiring. I also do not see any way to change the view of the sensors, I'm using a u-scan bluetooth scanner its pretty basic. I am getting the dongle so I can use the torque app this week though.

 

Are your readings at idle?

My 5.7 factory service manual states that the MAF should read a max of 1lb per Minute at idle (5-9 g/s). If you are getting a bad reading from the MAF, telling the car that more air is going in than is actual, then that would cause a rich condition.

Your O2 readings still aren't right and don't jive with each other - so I'd tackle that first by reading the scan tool instructions on scanning O2 sensors.

 

Yeah, all readings were at idle in Drive. My manual for my Actron U-scan is literally just a brochure and nothing else. Also, I really don't want to confuse you or myself anymore but when I disconnect the O2 sensors and it runs off the MAF it idles fine and not extremely rich anymore so I wasn't suspecting the MAF was a problem at all. I have a small short filter on it and not much for tubing so I'm not sure if that throws off the MAF readings much.

 

Go back to post #8. When you disconnect the O2 sensors, the engine falls back to open loop. When in that mode, it will ignore your MAF for the fuel calculations. (good or bad)

One more thing to check... Let's suppose your MAF isn't lying and you are getting ton of air in to the engine but the throttle is at 0%. That would be a problem. Is your throttle body leaking? Is the throttle plate shut properly when the engine is idling?

If so, I would do another scan and compare your MAF readings with your TPS sensor readings just to make sure they make sense.

If all of the above is good - what happens if you hook up the O2 sensors but disconnect the MAF? I expect that will kick it back in to open loop again and all will be well. Maybe you do that and see if you get better readings on your scanner for the O2 sensors? Perhaps a problem with the MAF was causing the bad O2 waveforms you posted earlier?

 

Throttle body doesn't appear to be leaking at all and it does close back completely. My TPS reading was like 0.04% at idle but would fluctuate to 0.00 sometimes which i assume is pretty accurate.

I tried to disconnect the MAF and keep the O2 sensors hooked up before, it seemed fine, idled great and was at operating temp fine but I drove it like that once and about 2 miles later is sputtered and I had no throttle response so I disconnected them and re connected MAF only and it ran fine (which is unexplained since it should have been in open loop like you said). I will definitely try again though and check my readings on the O2 sensors like you suggested.

 

For ***** and giggles, also do the scan with everything hooked up but your scan tool just reading:
O2
MAF
TPS

Checking the MAF vs. TPS response would be a good thing to do. As that throttle body opens, the MAF should read a corresponding larger volume of air moving through the sensor.

I just came across an article that also indicated that my point regarding your MAF reading being too high is correct. It also mentioned that if you have a dead bug or other foreign matter lodged in the sensor - that can lead to it overestimating air.

 

Ok, I will do that. I will first disconnect the O2 sensors and check the TPS vs MAF readings. I am wondering if cleaning the MAF could fix my issue or not but I will post the results here first. Unfortunately since the app doesn't have much customization I will have to view all sensors at the same time but it should still give me an idea.

The MAF is not brand new and I snatched it from a silverado the same year as my engine from the junkyard. The screen looked pretty clean so I just slapped it in.

Here is a picture of the pieced together intake just to put into perspective what I am working with.

 

Also, I have the filter basically connected right to the MAF, I wouldn't assume that would be that much of a problem though right?

 

Let's see what your next readings come up as. If you have a friend that you can do a temporary MAF swap with, that might also be a good thing to do.

Typically MAF cleaning will help you resolve issues where the MAF is reading too little air, not too much. Too much would be caused by objects that cause it to run hot or electrical short circuits.

 

Ok, I will try to get some readings and post them up tonight, I really appreciate your help thus far sir!

 

Here are some updates logs, this is mostly at idle, sometimes i did rev it to make sure the MAF reading was moving. Everything seems fine except the LT FTRM 1 appears to be dumping a lot of fuel in open loop now. I am assuming this is because it is just reverting back to what it knows from last night? It smells strongly rich, also the way the timing ADV changes when I rev it high it kind of weird.

 

That .7 lb/min MAF reading with 0% throttle is OK. The 1.78 lb/min MAF reading at 1600 RPM might be OK but was the throttle really at 6%??? THAT doesn't look right.

I'd look more at that MAF, and TPS and make sure the TPS is behaving. You could have a bad TPS sensor, etc.

 

Well when it read that it was a quick blip and its possible the scanner reads a little slow but I'm not sure. I was going to disconnect the battery for a little while to try to reset the fuel trim since its stuck where it was last night when it ran bad on closed loop mode (at least that is my guess). Is there anything else you would recommend me trying?

 

Ok, so the clear things up.

The TPS response is slightly slow on the app for some reason, but when I hold it at a steady RPM it catches up and shows pretty accurate in my opinion.

I had another ECU laying around which is the ECU that originally came with the engine which is the one I was using before doing testing (it was still acting bad on that ecu so the guy that built my harness sent me another one just in case). I installed the ECU again since the other one was just dumping way too much fuel for whatever reason even after disconnecting the battery? Not sure why... Here are the results from that ECU







This is still with the O2 sensors disconnected. So I am still at a loss, it doesn't APPEAR to be TPS or MAF related right now right? I don't mind throwing parts at it but the O2 sensors are like new (probably a little nasty now from running it so rich)