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no i have not modified the stock GM tune or computer i just use this program because it easier than a scanner
screenshot no.3 in my previous reply has me in park revved up to 2500
heres is the full throttle shift 1-2 the mass airflow reading is on the sidebar on the left
and o2 is in the graphs on the bottom right its the blue and purple 2nd from the bottom
and unfortunately i didn't get any info when it was cold this thing takes forever to cool down
and i also noticed looking at the previous pictures the PCM goes into a CL - Fault condition
im going to try to replace that o2 sensor today and see what that does i think it just went bad
and i will also put one where i was idling for a little while
and MAF is in pounds per minute
hopefully these numbers make sense to everyone because there is a lot going on in these screenshots
Your MAF is working good and your engine is breathing properly.
Your idle fuel trims are a mess but I cant compare them to 2500 rpm because the chart is cut off
We need all 3 O2 sensors graphed and you only provide one. On the 2500 rpm graph there is a definite problem because that sensor is not switching right. What we dont know is if the sensor is hosed or it cannot control fuel delivery properly. The sensors are labeled: B1S1, B2S1 and either B1S2 or B1S3. That last one should be a straight line between 0.5 and 0.7v after the truck warms up and the other two should be switching between 0.15 and 0.85v at around once per second at idle and faster at 2500rpm.
Your engine temp when warmed up is too low and we should address this. This will affect fuel delivery but probably not enough to cause fuel trims at 40 and they would probably have the opposite sign.
In open loop the fuel is delivered based on sensors other that the O2 sensors and the factory look up table for those conditions. Once the O2 sensors kick in they only care about one thing: a 14:1 air/fuel ratio and minimum emissions. The fuel trims are the difference between those theoretical values and what he O2 sensor wants.
I need to see those 2500rpm numbers to help narrow this down but the trucks computer thinks that it has to correct for a lean condition by significantly increasing fuel delivery based on the O2 sensor output. Many things can be wrong in a case like this:
Sometimes the resulting engine operation can be counter intuitive. If the O2 sensors get the exhaust gases just right then why does the engine run crappy on its way to closed loop? Well the O2 sensors can be hosed but even if they work perfectly, lets say you have a stuck injector on one cylinder. it runs lean and the rest of the cylinders run perfect. Not ideal but the truck runs pretty good, good enough. Now the O2 sensors come online and see all that extra air and start raising the fuel delivery to that entire bank. Now all the cylinders run crappy and the truck is still a mess even though the exhaust is better. Or its not fuel delivery at all and all is perfect but one of the other sensors is hosed and hence the big fuel trims. Thats why we need the cold numbers.
George
Last edited by GeorgeLG; Oct 23, 2022 at 01:44 PM.
I did change the third o2 sensor with another today and that p0147 is gone, the computer goes into a Closed loop Normal mode however but the fuel trims are still horrible.
George here is the 2500 rpm graph that was cut off for your comparison.
Also it was cooler than normal yesterday when i did this my car usually runs around 185F when fully warmed up and drops to what you see running around town, i like to keep the radiator clean.
And for those cold numbers it maybe some time before i get those to the forum, I don't have constant access to the OBD2 adapter but when i do and my car is cool i will get them here for you ASAP.
I'm always going to try the simplest option first so checking like you mentioned for unmetered air, Faulty PCM, and Faulty wiring. I can do a compression test but with some difficulty as you have to go through the side of the car under the fender to get to the plugs.
And i will keep checking for faulty sensors as well
My issue appears to be vacuum related or a vacuum leak I'm swinging for unmetered air entering the system.
These codes did exist when i got the car but really never been an issue until these past few months when it really started to act up.
Ultimately the last largest vacuum leak has to be around or on the throttle body or gasket as i have checked and verified the other common, possible vacuum leak prone areas just not that one.
As this car has sat for around 5 years before receiving it, the throttle body gasket could have potentially decayed due to years of sitting and requires replacing hence why i can't locate a vacuum leak. As they are cheap i may just buy and install a new one anyways.
And lastly George you said the O2 sensors could be hosed, does that mean worn out, contaminated? If not please explain because I'm unfamiliar with that term.
Last edited by That64Guy; Oct 23, 2022 at 09:08 PM.
If you look at your 2500 RPM fuel trims you’ll see that they got half as bad as they are at idle which says that unmetered air is a distinct possibility as the air leak becomes a less significant percent of the total air being consumed by the engine. Let me know if you need any help with that but make sure you’re looking at both intake and exhaust leaks. With regards to your engine operating temperature it should be in the 190s irrespective of ambient conditions, being maintained by the thermostat. George
sorry I didn't quite get to working on my car when I wanted to this week, been a little busy and it was raining earlier this week, anyways this is what I got for an update.
The SES light has been out for a little while again and will most likely be back
Removed the throttle body and everything looked ok seal and all, I cleaned it up before reinstalling it. But I'm pretty disappointed with the results of my work.
it seems that the engine runs smoother but the fuel trims are still terrible
I'm out of vacuum components to check. the last component I have checked was the intake hose and its in perfect condition just a little dirty on the outside.
but since cleaning the throttle body it now has a p1122 but that's probably because I foolishly turned on the car not running and forgetting to plug in the TPS and the IAC.
also I may have forgot to mention the fuel trims immediately go down about 4% to 9% when I put it in gear reverse or drive, engine loaded. And instantly jump when put in neutral or park, around 23% engine unloaded. high enough to present an issue but low enough to keep the SES Satisfied.
I cant find any vacuum leaks or exhaust issues either
I love my car but I guess my car just knows how to be sometimes confusing, annoying, and frustrating simultaneously.
reading around the forum could the Evap system be an issue since its vacuum related?
Last edited by That64Guy; Oct 27, 2022 at 12:25 PM.
I finally figured out how to look at some of these graphs which are difficult because of the small purple font against a black background. Your O2 sensors are switching pretty good especially at idle, a little less well behaved at 2500rpm but not your main problem
Whats the history on the lower intake manifold (LIM) gaskets? They are a weak point in these engines and almost everyone winds up replacing them after 100,000 miles. This can cause all manner of problems. The fact that your positive fuel trims get halfway back to normal at 2500 rpms is classic for a vacuum leak but not always. It sounds like you did some visual inspection of the vacuum system but did you spray anything around the usual air leak points to watch rpm? Did you check the PCV valve?
Why can fuel trims be so positive (40 at idle is extreme):
The sensors and engine computer evaluate the conditions related to fuel delivery (engine temp, air temp and pressure, throttle position, airflow at the intake, etc) and then go to the factory programmed look up table and determine the proper fuel delivery (injector pulses in ms) for those conditions. Once in closed loop however fuel delivery is determined entirely by the O2 sensors which have one goal - minimum emissions by getting air/fuel to as close to "stoich" as possible, which is a 14.7:1 air/fuel ratio. If the truck runs like crap, so be it. The computer then looks at the difference between the commanded fuel delivery and the theoretical fuel delivery and fuel trims are the difference. positive trims compensating for a perceived lean condition. Thats all the computer knows. It does not know whats wrong, just that something is wrong. On a new engine with no problems fuel trims are close to zero. My 2006 GMC is in good condition at 70,000 miles and trims run around 1 - 3. Any one of these sensors could be reporting an out of bounds condition perfectly or it could be reporting improperly. Thats why we need all your sensor values on a cold engine with just key on, not started.
No I have no clue of the condition of those LIM gaskets never dug that far into my engine my car has 206,900 miles and they could be bad.
And i will have to see when i can get those cold numbers. Also I thought if a sensor was behaving erratically then the PCM would throw a code maybe not in every circumstance.
and yes the PCV is operating normally the seal that it sits in was a little loose i put a small amount of high temp RTV to help hold it in.
No i didn't spray anything just been listening for any hissing, do I just use water for that?
I'll have to try that but I'm not a huge fan of taking anything flammable around a hot running engine makes me kind of nervous.
Though watching the video it seems simple enough and super straight forward, I guess i will try brake clean and see if i can find it.
