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Revised Datalog #2, Idled for 4 minutes to let the car get into closed loop. Drove around town normally, got onto a country road and gave it a little bit, turned around and gave it a bit more, then headed back home. The trouble code you see is a P1661, my CEL bulb burned itself out like two days ago so I'll have to fix that sometime. Let me know if you need anymore info.
Downloaded, appears to be complete. Says you have 1 trouble code.... do you know what that is?
I'll format it, convert a couple of the sensor units (MAP and MAF) to something I am more comfortable with. Hopefully it will tell us the condition of the engine control system. Appears to be adding a lot of extra fuel (19%) at idle on Bank 2 (right). But that's just at a quick glance.
Downloaded, appears to be complete. Says you have 1 trouble code.... do you know what that is?
I'll format it, convert a couple of the sensor units (MAP and MAF) to something I am more comfortable with. Hopefully it will tell us the condition of the engine control system. Appears to be adding a lot of extra fuel (19%) at idle on Bank 2 (right). But that's just at a quick glance.
Yep I do know what it is, its P1661 if my memory is correct, my check engine light bulb burned out a few days ago, doesn't display at all when the key is in the run position. I noticed the 19% as well, I also thought I saw a passenger bank O2 sensor reading very strangely compared to the other oxygen sensors, I don't have cats at all for reference.
I looked through it a bit, even though my knowledge on this stuff is very limited. I take back my previous comment about an O2 sensor acting up, after looking through the over 2000 lines of data it doesn't appear to be acting out of line compared to the other ones.
At cold start the Bank 1 O2 sensor is cold, and not working, but the Bank 2 sensor is warmed up and working. Eventually the Bank 1 sensor catches up and it goes into closed loop. Was the car sitting with the ignition key in run before you started the data log, and then only a couple seconds after started the engine?
The coolant is at the ambient (same as inlet air temp) temperature 71.6-degF, so it hadn't been running in the recent past. And as slow as it warms up, it goes into closed loop in a little more than a minute, and with the engine coolant still cold. Doesn't match anything I have seen before. If it was sitting for a while with the key in "run", engine off, the Bank 2 O2 sensor could have heated up with it's heater, but the Bank 1 O2 sensor did not. OR the position in the exhaust is different enough to delay the Bank 1 from heating up. I only mention this because the two O2 sensors are behaving differently.
The 19% Bank 2 LTFT appears to be an issue only at idle. Could be a vacuum leak that only affects the right bank of the engine. At very low loads, closed or closing throttle, Bank 2 does still show signs of high LTFT but not 19%. That again seems to be pointing to something affecting the right bank only, and only at low air demand... like a vacuum leak.
When you put the engine under any load, the situation reverses and Bank 1 becomes the bigger problem. It's really strange, because the big LTFT numbers are switching side to side with high LTFT on Bank 2 at low load/closed/closing throttle. But under any sort of load, the Bank 1 numbers go up.
When you go into the equivalent of Cell 15, and it appears the engine goes into power enrichment (PE) mode, BOTH side are short on fuel, and that's when the Bank 1 LTFT soars to 22% while Bank 2 is at 15%. The O2 sensors are indicating high 0.8xx volts, so it isn't running out of fuel, but it isn't running rich either, and that's a lot of extra fuel required to keep it from running lean. In between idle and PE mode, it's very hard to correlate the engine operating conditions to the traditional "cells" that get reported in OBD-1. Not sure why GM didn't make them visible, without requiring the royalty payment for access to enhanced parameters.
Bottom line, best I can come up with:
- check for a vacuum leak that will only affect Bank 2. Or possibly an exhaust leak BEFORE the O2 sensor., or misfires on Bank 2.
- Put a fuel pressure test gauge on it, tape the gauge to the windshield, take the car out on the road at WOT above 5,000 RPM, and see if the fuel pressure starts to drop, indicting a weakness in the fuel system.
- keep an eye on the pre-cat O2 sensors. The Bank 1 sensor may have a heater problem, or the location is further from the engine. You could try swapping the two pre-cat sensors side-to-side, to see if the slow response switches with the Bank 1 sensor. I can't see any specific problem this might be causing once the engine is fully warmed up, but, why do they respond differently?
Not as much info as I would normally be able to provide, but the limits of the OBD-2 content make it difficult to be as thorough as the OBD-1 software capabilities.
At cold start the Bank 1 O2 sensor is cold, and not working, but the Bank 2 sensor is warmed up and working. Eventually the Bank 1 sensor catches up and it goes into closed loop. Was the car sitting with the ignition key in run before you started the data log, and then only a couple seconds after started the engine?
The coolant is at the ambient (same as inlet air temp) temperature 71.6-degF, so it hadn't been running in the recent past. And as slow as it warms up, it goes into closed loop in a little more than a minute, and with the engine coolant still cold. Doesn't match anything I have seen before. If it was sitting for a while with the key in "run", engine off, the Bank 2 O2 sensor could have heated up with it's heater, but the Bank 1 O2 sensor did not. OR the position in the exhaust is different enough to delay the Bank 1 from heating up. I only mention this because the two O2 sensors are behaving differently.
The 19% Bank 2 LTFT appears to be an issue only at idle. Could be a vacuum leak that only affects the right bank of the engine. At very low loads, closed or closing throttle, Bank 2 does still show signs of high LTFT but not 19%. That again seems to be pointing to something affecting the right bank only, and only at low air demand... like a vacuum leak.
When you put the engine under any load, the situation reverses and Bank 1 becomes the bigger problem. It's really strange, because the big LTFT numbers are switching side to side with high LTFT on Bank 2 at low load/closed/closing throttle. But under any sort of load, the Bank 1 numbers go up.
When you go into the equivalent of Cell 15, and it appears the engine goes into power enrichment (PE) mode, BOTH side are short on fuel, and that's when the Bank 1 LTFT soars to 22% while Bank 2 is at 15%. The O2 sensors are indicating high 0.8xx volts, so it isn't running out of fuel, but it isn't running rich either, and that's a lot of extra fuel required to keep it from running lean. In between idle and PE mode, it's very hard to correlate the engine operating conditions to the traditional "cells" that get reported in OBD-1. Not sure why GM didn't make them visible, without requiring the royalty payment for access to enhanced parameters.
Bottom line, best I can come up with:
- check for a vacuum leak that will only affect Bank 2. Or possibly an exhaust leak BEFORE the O2 sensor., or misfires on Bank 2.
- Put a fuel pressure test gauge on it, tape the gauge to the windshield, take the car out on the road at WOT above 5,000 RPM, and see if the fuel pressure starts to drop, indicting a weakness in the fuel system.
- keep an eye on the pre-cat O2 sensors. The Bank 1 sensor may have a heater problem, or the location is further from the engine. You could try swapping the two pre-cat sensors side-to-side, to see if the slow response switches with the Bank 1 sensor. I can't see any specific problem this might be causing once the engine is fully warmed up, but, why do they respond differently?
Not as much info as I would normally be able to provide, but the limits of the OBD-2 content make it difficult to be as thorough as the OBD-1 software capabilities.
Thank you for taking the time to go over it, it really helps out since I believe this is an issue I've been facing for going on a year. I do believe that I had the key in the ignition for a bit while I started the laptop and connected to the car, not sure on how long however. I replaced the pre-cat O2 sensor on the driver side somewhat recently after one had died, I am unsure on the brand. I've got a screenshot from another post of your data logging guidelines, I'll do another one tomorrow morning and will not let the key sit in the ignition. I can connect the laptop then start it almost immediately. Then if the issue warming up persists I can swap the two pre-cat O2's and we can go from there. Only a few weeks ago I filled the exhaust with propane and used an electronic sniffer to try and find leaks believing this may be an issue, I found zero leaks, both by nose and with the sensor. I don't own a smoke machine to check for vaccum leaks, but I may just purchase one or could possibly use the propane method as well. The bank one O2 sensor is actually a bit closer to the engine than the bank 2, so this may make the bank 1 pre-cat sensor suspect. Somedays I wish the car had OBD-1 as well lol. One other thing, I'lll use the GDscan file with GM Enhanced parameters for this next log, may provide some much needed info. Is it possible that any kind of modifications were made to the PCM that would cause the car to go into closed loop so early?
Don’t redo it for the O2 sensor. That is not a big issue. I only mentioned it because there is a difference between Bank1 and Bank 2. But once it goes into closed loop, it doesn’t appear to affect how the engine runs. Just something to keep in the back of your mind for future reference.
I don’t know enough about programming the stock PCM to know if changing closed loop requirements is possible. It looks for the O2 sensors to be active, which means they are warmed up and working. There is a timer the usually waits 206 seconds even if the O2 sensors are ready, and the coolant is hot enough. In cases where the coolant is slow to warm up and becomes the controlling factor, the transition usually happens at 120-140°F.
Don’t redo it for the O2 sensor. That is not a big issue. I only mentioned it because there is a difference between Bank1 and Bank 2. But once it goes into closed loop, it doesn’t appear to affect how the engine runs. Just something to keep in the back of your mind for future reference.
I don’t know enough about programming the stock PCM to know if changing closed loop requirements is possible. It looks for the O2 sensors to be active, which means they are warmed up and working. There is a timer the usually waits 206 seconds even if the O2 sensors are ready, and the coolant is hot enough. In cases where the coolant is slow to warm up and becomes the controlling factor, the transition usually happens at 120-140°F.
Ok gotcha I won't, my train of thought was to fix any possible O2 sensor issues so I've got the most accurate data possible, but if they're not a big issue that's fine. So at this point check for vaccum leaks and a loss of fuel pressure? That's just fine if you don't know, I had just remembered the same closed loop requirements and thought that it was odd how fast it went into closed loop.
I tried to find vacuum leaks last night with compressed air and soap/water solution. Thought that I had found a possible source and fixed, went outside with laptop and let car run for a bit. Passenger side long term fuel corrections stayed at 19% throughout the four minutes of idling and going into closed loop. So no luck there. I'll do a fuel pressure test today before possibly breaking down to have a shop check for vacuum leaks with an actual smoke machine.
Have you tried locating the vacuum leak by spraying brake cleaner, carb cleaner, or (unlit) propane around the outside surfaces of the engine, with the engine running? When you hit the leak, the engine will start running faster. Don't forget areas like the injector ports on the intake manifold, which are sealed with rubber O-rings, the brake booster, intake manifold to head gaskets, the throttle body, etc.
Since this involves flammable materials, do it outside, cool engine, have a fire extinguisher with the correct rating handy.
When you start the engine cold, and until it goes into closed loop, the PCM is using the stored LTFT's, the STFT's are locked at 128 (0%), and learning is disabled. It can't change the LTFT's until it goes into closed loop, and then it can take a while, because the PCM has to recognize that the average value of the STFT's is not 0% for a period of time, before it moves the LTFT's up or down.
Have you tried locating the vacuum leak by spraying brake cleaner, carb cleaner, or (unlit) propane around the outside surfaces of the engine, with the engine running? When you hit the leak, the engine will start running faster. Don't forget areas like the injector ports on the intake manifold, which are sealed with rubber O-rings, the brake booster, intake manifold to head gaskets, the throttle body, etc.
Since this involves flammable materials, do it outside, cool engine, have a fire extinguisher with the correct rating handy.
When you start the engine cold, and until it goes into closed loop, the PCM is using the stored LTFT's, the STFT's are locked at 128 (0%), and learning is disabled. It can't change the LTFT's until it goes into closed loop, and then it can take a while, because the PCM has to recognize that the average value of the STFT's is not 0% for a period of time, before it moves the LTFT's up or down.
No I have not tried that method but I definitely will either tonight or tomorrow. Super windy today which is kind of annoying. Ok thank you for the info on how the PCM would react and change with LTFT's and STFT's. I find it really interesting.
I tried finding any leaks with brake cleaner and couldn't find even a slight one. Did all of the portions you listed, vacuum hoses and lines, injectors, brake booster, intake manifold etc.., I took a couple photos of some possibilitys to what may cause one in the future. I plugged the end of the second photo with a vacuum cap, the first photo is just the IAT sensor rubber cracking. I'm going to check my long term fuel corrections after driving for a bit since I may have already fixed my issue, testing fuel pressure in just a bit.
Just got done testing fuel pressure, followed your guidelines from another post. Fuel pressure primed up to 42psi with the vacuum line attached. Started car and disconnected FPR vacuum line (plugged with golf tee), jumped about 6-7psi (Larger cam than stock), took it down the street and revved it up to 5,500rpm and didn't budge one bit from 43psi. Had a passenger watch for me and did afterward with the car sitting in neutral with parking brake tight just in case. So pump tests out good according to the given guidelines, however I have not put in the 30ib fuel injectors from FIC which will strain it just a bit more. Also watched to make sure the pressure wasn't dropping too quickly, pressure took about 1min and change to drop from 28psi to 22psi slowly.
Something wrong in the fuel pressure test, or at least the way it’s described, or the way I’m reading it.
You got 42 PSI prime with the vacuum line attached. You removed the vacuum line and the pressure JUMPED 6-7 PSI. That would make the “no vacuum” pressure 48-49 PSI, which is outside the GM spec (41-47 PSI). Or, did the pressure DROP to 36-37 PSI when you started the engine, and return to 42 PSI when you removed the vacuum line?
I'll have to ask Gary if it’s possible the system is logging the wrong data. Because it definitely shows it’s adding a lot of extra fuel when the engine is under load.
If you are revving it to high RPM under no load - DON'T. It doesn’t represent a real world driving experience, the data is meaningless, and fuel consumption is nowhere near the fuel required under heavy load.
Something wrong in the fuel pressure test, or at least the way it’s described, or the way I’m reading it.
You got 42 PSI prime with the vacuum line attached. You removed the vacuum line and the pressure JUMPED 6-7 PSI. That would make the “no vacuum” pressure 48-49 PSI, which is outside the GM spec (41-47 PSI). Or, did the pressure DROP to 36-37 PSI when you started the engine, and return to 42 PSI when you removed the vacuum line?
I'll have to ask Gary if it’s possible the system is logging the wrong data. Because it definitely shows it’s adding a lot of extra fuel when the engine is under load.
If you are revving it to high RPM under no load - DON'T. It doesn’t represent a real world driving experience, the data is meaningless, and fuel consumption is nowhere near the fuel required under heavy load.
My bad, it's the way I described it. Priming the fuel pump with engine off made it go to 42 then drop down to 35-37ish range with the vacuum line attached. Then once the vacuum line was removed fuel pressure was 41-42psi. "Or, did the pressure DROP to 36-37 PSI when you started the engine, and return to 42 PSI when you removed the vacuum line?"= Correct. Yes it really is adding quite a bit of fuel, maybe tag him to the post here, I'm not sure how to...
I know it won't represent real driving load, was just making sure the friend was paying attention because if it fell under no load then he was obviously wrong when he said that it never moved at all.
08-02-2020, 09:37 AM
