Intermittent O2 reading

[Dont fake it break it]

Pretty sure the scanner should also tell you if it's in park or drive.

The scanner kicks the idle up to ~1000RPM as well, correct? I really haven't dealt with TBI a ton, I can't remember if it does that when you have something hooked up to the ALDL or not. I know TPI does.
The scanner doesn’t indicate what gear I’m in. It’s the Actron 9500 for anyone who knows those devices. I have also read that

Some of the GM TBI setups were programmed to go open loop at idle.

The park neutral switch input to the ECM is partly to account for the torque converter load. But it also indicates to the ECM that it needs to watch the VSS, it will want to drastically cut fuel if it thinks it's out of gear and you are decelerating, which can lead to stalling.

dyeager535, Regarding the scanner, it doesn’t indicate what gear I’m in. I have also read like you say that a scanner connected to the ALDL will crank up the idle. Here’s a better picture of what’s happening. I took a 10 mile drive today with no issues. Parked the truck for 20 minutes and when I got back on the road, I had a lean error code after 30 yards. After a few miles I decided to plug in the scanner while driving. Not really sure if that’s a good idea or not and to be honest I’ve done it before with no repercussions. Here’s what I saw.
RPM 1775
EXHAUST lean
IAC 115
INTEGRATOR 128
LOOP STATUS open
O2MV 40
Weird right? IAC wide open at 55 mph with the integrator right where it should be considering being stuck in open loop. Then I came to a stop sign a few miles later and saw this.
RPM 975
EXHAUST rich
IAC 133
INTEGRATOR 133
LOOP closed
O2MV 613
Weird right? IAC still wide open while in an otherwise normally functioning closed loop. I am trying to track what you’re saying about the park neutral switch in that case would into the VSS also be the likely culprit? I’ve read that when it’s not functioning, the engine will run lean and the ECM will think the vehicle is rolling less than two mph and raise the idle to prevent stalling like u said, or something like that. This is my first experience with these components so I am definitely out of my depth but trying to catch up. One other thing though, my speedo did get all janky for a couple minutes maybe right around the time this all started happening. It went back to normal so I didn’t think much of it but it was definitely weird bouncing around and such. Much appreciated info.

 

[bp71k5]

Some of the GM TBI setups were programmed to go open loop at idle

that to has messed me up more than once trying to

Pretty sure the scanner should also tell you if it's in park or drive.

The scanner kicks the idle up to ~1000RPM as well, correct? I really haven't dealt with TBI a ton, I can't remember if it does that when you have something hooked up to the ALDL or not. I know TPI does.

It does sometimes if an option in the scanner isn’t switched off. I hate it cause it’s messed up my troubleshooting so much in the past. But if the idle goes way high when the scanner is removed, that’s a different issue.

 

[bp71k5]

dyeager535, Regarding the scanner, it doesn’t indicate what gear I’m in. I have also read like you say that a scanner connected to the ALDL will crank up the idle. Here’s a better picture of what’s happening. I took a 10 mile drive today with no issues. Parked the truck for 20 minutes and when I got back on the road, I had a lean error code after 30 yards. After a few miles I decided to plug in the scanner while driving. Not really sure if that’s a good idea or not and to be honest I’ve done it before with no repercussions. Here’s what I saw.
RPM 1775
EXHAUST lean
IAC 115
INTEGRATOR 128
LOOP STATUS open
O2MV 40
Weird right? IAC wide open at 55 mph with the integrator right where it should be considering being stuck in open loop. Then I came to a stop sign a few miles later and saw this.
RPM 975
EXHAUST rich
IAC 133
INTEGRATOR 133
LOOP closed
O2MV 613
Weird right? IAC still wide open while in an otherwise normally functioning closed loop. I am trying to track what you’re saying about the park neutral switch in that case would into the VSS also be the likely culprit? I’ve read that when it’s not functioning, the engine will run lean and the ECM will think the vehicle is rolling less than two mph and raise the idle to prevent stalling like u said, or something like that. This is my first experience with these components so I am definitely out of my depth but trying to catch up. One other thing though, my speedo did get all janky for a couple minutes maybe right around the time this all started happening. It went back to normal so I didn’t think much of it but it was definitely weird bouncing around and such. Much appreciated info.

the integrator should always read 128 in open loop. In open loop the computer ensures the preprogrammed fueling values are used by forcing the BLM be 128.

 

[dyeager535]

Does the actron tell you vehicle speed?

AFAIK the VSS could display speed, yet the ECM ignore that data if it thinks it's in park/neutral. But at least you know the data is getting to the ECM if the scanner displays vehicle speed correctly.

You really have to ignore the O2 mV reading UNLESS it essentially stays stuck one side or the other, IE rich or lean. If you accelerate, it should go rich and stay rich until you let off, as a for instance. But during closed loop, it should go rich/lean far faster than the scanner will ever display. The 7737 ECM data communication speed is very, very slow. This is why going to a wideband O2 on these old setups was/is beneficial for tuning...you can actually see what the mixture is doing outside of 14.7:1 AFR. All you can do with a narrowband O2 is make sure it goes rich/lean in closed loop, and if a repeatable event, stay rich (or lean) without bouncing back and forth.

What's a good IAC reading at idle? I also don't remember what the max IAC steps is, but 133 doesn't sound like it.

 

[Dont fake it break it]

the integrator should always read 128 in open loop. In open loop the computer ensures the preprogrammed fueling values are used by forcing the BLM be 128.

Understood about the integrator being at 1:28 in open loop. Kind of makes me wish she would just stay in open loop because it certainly runs better, either I know that’s not the most efficient way to run. I’m going to go through my scanner manual again to see if there’s a option to turn off the diagnostic mode effect but I kind of doubt it. And also This condition definitely exists without the scanner being hooked up. It’s idling at least 1000 in gear as I’m pulling into the parking lot at work. I can just picture it, IAC wide open

 

[Dont fake it break it]

Yes the scanner does tell me my vehicle speed and I don’t look at it very often but I don’t remember it ever being incorrect but I’ll definitely pay closer attention. I get what you’re saying about how the O2 sensor functions and I kicked myself after installing a new one for not waiting and getting a three wire. Just for the sake of comparison, by the time I get one I think I’ll have probably spent more and O2 sensors than I would have on a new ECM. LOL. When the truck is running good which does happen sometimes, the IAC is like 50. I have yet to learn of a reason for it to be wide open regardless of what is triggering The ECM to activate it, which I understand is constant. Last night while driving I got another check engine light no doubt for a lean condition. I stomped on it for a few seconds and it went away and that’s been the norm. I stopped and put it in park and the idol was doing its thing and went into open loop. I put it in gear and got on the accelerator at the same time, power brake style, and it pulled it out of a closed loop. My little brain tells me that’s a fuel delivery related and I wouldn’t be surprised if I have more than one thing going on at once. . Sounds like the first thing I’ll do is rebuild the pressure regulator so I know when I’ve actually resolved the issue. Then I’ll researching the park neutral switch and the VSS system and I could use any tips on going about that. Thanks a mil.

 

[bp71k5]

Have you checked fuel pressure? Both injectors are spraying nicely?

I think the IAC opens up all the way when your foot is on the gas, At least mine does. It should hover around 12-ish at idle. 50 indicates it’s trying to compensate for something.

 

[Dont fake it break it]

Have you checked fuel pressure? Both injectors are spraying nicely?

I think the IAC opens up all the way when your foot is on the gas, At least mine does. It should hover around 12-ish at idle. 50 indicates it’s trying to compensate for something.

I checked the fuel pressure after the filter because I couldn’t get the adapter to fit at the throttlebody but the fuel line is pretty straight so I’m confident the reading would be the same. The injectors are brand new AC Delco‘s. I think they are spraying like they should but it doesn’t seem like a very easy thing to eyeball. I’m going to rebuild the regulator again but I had done so two years ago. So it drove fine all day until I turned onto my street and got the lean trouble code. It went into open loop until I hammered down to bring it back into a closed loop. The next time I stopped the IAC was stuck wide-open again and idling high in gear and in the park. I drove a bit more and pulled over and it went into open loop on the side of the road. And it did fine until I pulled back onto the street and it went into a closed loop again and I could see the IAC opening up. Of course it was idling high when I pulled back up to the house. It’s gotten fairly easy to predict what will happen once it goes into a closed loop. That’s my only reason for thinking it’s not related to what gear it’s in because it can go back-and-forth from Open to Closed while never leaving Drive. Then again, I watched it idle fine and park and only have the IAC stay open when I put it into gear, and then to return to normal when it goes back in the park but that doesn’t happen every time either. I’ll be taking it in to the shop on Monday as a defeated man if it won’t get right. I don’t remember how long ago I changed Out the IAC pigtail. Could I have wired that wrong? I’m sure I did them one at a time to not lose track but maybe they were wrong to begin with, who knows.

 

[bp71k5]

I checked the fuel pressure after the filter because I couldn’t get the adapter to fit at the throttlebody but the fuel line is pretty straight so I’m confident the reading would be the same. The injectors are brand new AC Delco‘s. I think they are spraying like they should but it doesn’t seem like a very easy thing to eyeball. I’m going to rebuild the regulator again but I had done so two years ago. So it drove fine all day until I turned onto my street and got the lean trouble code. It went into open loop until I hammered down to bring it back into a closed loop. The next time I stopped the IAC was stuck wide-open again and idling high in gear and in the park. I drove a bit more and pulled over and it went into open loop on the side of the road. And it did fine until I pulled back onto the street and it went into a closed loop again and I could see the IAC opening up. Of course it was idling high when I pulled back up to the house. It’s gotten fairly easy to predict what will happen once it goes into a closed loop. That’s my only reason for thinking it’s not related to what gear it’s in because it can go back-and-forth from Open to Closed while never leaving Drive. Then again, I watched it idle fine and park and only have the IAC stay open when I put it into gear, and then to return to normal when it goes back in the park but that doesn’t happen every time either. I’ll be taking it in to the shop on Monday as a defeated man if it won’t get right. I don’t remember how long ago I changed Out the IAC pigtail. Could I have wired that wrong? I’m sure I did them one at a time to not lose track but maybe they were wrong to begin with, who knows.

strange. What about EGR valve. Working correctly? Got the right one?

 

[bigblock72]

I checked the fuel pressure after the filter because I couldn’t get the adapter to fit at the throttlebody but the fuel line is pretty straight so I’m confident the reading would be the same. The injectors are brand new AC Delco‘s. I think they are spraying like they should but it doesn’t seem like a very easy thing to eyeball. I’m going to rebuild the regulator again but I had done so two years ago. So it drove fine all day until I turned onto my street and got the lean trouble code. It went into open loop until I hammered down to bring it back into a closed loop. The next time I stopped the IAC was stuck wide-open again and idling high in gear and in the park. I drove a bit more and pulled over and it went into open loop on the side of the road. And it did fine until I pulled back onto the street and it went into a closed loop again and I could see the IAC opening up. Of course it was idling high when I pulled back up to the house. It’s gotten fairly easy to predict what will happen once it goes into a closed loop. That’s my only reason for thinking it’s not related to what gear it’s in because it can go back-and-forth from Open to Closed while never leaving Drive. Then again, I watched it idle fine and park and only have the IAC stay open when I put it into gear, and then to return to normal when it goes back in the park but that doesn’t happen every time either. I’ll be taking it in to the shop on Monday as a defeated man if it won’t get right. I don’t remember how long ago I changed Out the IAC pigtail. Could I have wired that wrong? I’m sure I did them one at a time to not lose track but maybe they were wrong to begin with, who knows.

What is the fuel pressure??

What's the part number on the injectors??

Does it have the original computer and PROM??

When the INT reaches it's limit (around 180) the computer will go into open loop, drop the INT back to 128, run for a period of time, re-enter closed loop run the INT up to it's limit so on and so on. The idle will roll and surge as it goes through this cycle.

This thing is LEAN so we need to figure out why. You have ruled out vacuum leaks and sensor issues, so that leaves wrong injectors, low fuel pressure, computer/PROM issue.

 

[Dont fake it break it]

strange. What about EGR valve. Working correctly? Got the right one?

Yeah the EGR valve is a couple months new so low miles on it. At idle I press the plunger in and it starts to sputter and goes back to normal when I release it so I have no reason to suspect it. I vacuum tested the solenoid recently and it seemed to be what it should although I can’t remember what those parameters were now but it was legit at the time. It’s also newer with a newer pigtail. Don’t really remember what brand, could be whatever was at AutoZone or could be AC Delco from Amazon.

 

[Dont fake it break it]

View attachment 339677 View attachment 339677

What is the fuel pressure??

What's the part number on the injectors??

Does it have the original computer and PROM??

When the INT reaches it's limit (around 180) the computer will go into open loop, drop the INT back to 128, run for a period of time, re-enter closed loop run the INT up to it's limit so on and so on. The idle will roll and surge as it goes through this cycle.

This thing is LEAN so we need to figure out why. You have ruled out vacuum leaks and sensor issues, so that leaves wrong injectors, low fuel pressure, computer/PROM issue.

Edit: please ignore the first image. It loaded there by mistake and I cannot remove it.
The fuel pressure was 14psi with a two-year-old filter. I actually threw an AC Delco on there afterwards but never checked it again. Probably should to dot the i’s. The fuel pump was new in December FYI. Incidentally I did that cutting in access point in the bed and it worked out great. Just needed to tell someone. LOL. The injectors are Napa brand 2-18202. I don’t know anything about the ECM or it’s prom. I’ve never removed it let alone touched it. I hear what you’re saying about the INT but I haven’t exactly seen that. The highest I think it’s bad is around 150 but I’ve watched it come down from there on it’s own a dozen times without going into an open loop. I thought that was normalish. After I put in the new pressure regulator diaphragm and spring, I fired it up and it idles nice. Here is the image right before I put it into gear.

The second I put it into gear the IAC starts to climb in so does the idle, but the INT does not. Here’s the image right BEFORE I took it out of gear after about 30 seconds.

Here’s the image of what it did in neutral.

Then I gave it a little gas to see what would change and it went into an open loop. The only codes stored are lean condition 44.

 

[dyeager535]

Is it me, or does that last image where you say you are in neutral, show that it's still in drive? ("P/N SWITCH")

 

[Dont fake it break it]

Is it me, or does that last image where you say you are in neutral, show that it's still in drive? ("P/N SWITCH")

You’re absolutely right on two counts. Not only did I find the setting on the scanner that shows the park neutral switch but on that occasion , it did not register being in neutral. The next 10 or so times did recognize it but on that occasion as I shifted into neutral both the INT and IAC dropped to 37 For just a second.

 

[bigblock72]

View attachment 339679 View attachment 339677 View attachment 339677
Edit: please ignore the first image. It loaded there by mistake and I cannot remove it.
The fuel pressure was 14psi with a two-year-old filter. I actually threw an AC Delco on there afterwards but never checked it again. Probably should to dot the i’s. The fuel pump was new in December FYI. Incidentally I did that cutting in access point in the bed and it worked out great. Just needed to tell someone. LOL. The injectors are Napa brand 2-18202. I don’t know anything about the ECM or it’s prom. I’ve never removed it let alone touched it. I hear what you’re saying about the INT but I haven’t exactly seen that. The highest I think it’s bad is around 150 but I’ve watched it come down from there on it’s own a dozen times without going into an open loop. I thought that was normalish. After I put in the new pressure regulator diaphragm and spring, I fired it up and it idles nice. Here is the image right before I put it into gear.
View attachment 339679
The second I put it into gear the IAC starts to climb in so does the idle, but the INT does not. Here’s the image right BEFORE I took it out of gear after about 30 seconds.
View attachment 339680
Here’s the image of what it did in neutral.
View attachment 339681
Then I gave it a little gas to see what would change and it went into an open loop. The only codes stored are lean condition 44.

The injectors are for a 350 so that is good. The BLM looks ok in one frame, a lot high in the other @ 185.... hmmmmm.....what is the base timing set at? Make sure it's 0-4 with the tan wire unplugged. Low timing might explain the high IAC and the BLM issues.

The IAC appears to be working so don't mess with the connector. Usually when the iac is wired wrong it will work backwards or stick wide open.

The fuel pressure is good if it's at 14, no need to touch the regulator.

The P/N switch is working sometimes. The last picture shows Drive when it is in Neutral, the computer will raise the IAC when it thinks the truck is in gear and is slow to drop the IAC back down until it sees P/N again. Adjust the neutral safety to read properly.

Some of these will semi randomly go in and out of closed loop so that doesn't necessarily indicate a problem.

 

[Dont fake it break it]

The injectors are for a 350 so that is good. The BLM looks ok in one frame, a lot high in the other @ 185.... hmmmmm.....what is the base timing set at? Make sure it's 0-4 with the tan wire unplugged. Low timing might explain the high IAC and the BLM issues.

The IAC appears to be working so don't mess with the connector. Usually when the iac is wired wrong it will work backwards or stick wide open.

The fuel pressure is good if it's at 14, no need to touch the regulator.

The P/N switch is working sometimes. The last picture shows Drive when it is in Neutral, the computer will raise the IAC when it thinks the truck is in gear and is slow to drop the IAC back down until it sees P/N again. Adjust the neutral safety to read properly.

Some of these will semi randomly go in and out of closed loop so that doesn't necessarily indicate a problem.

Yeah when it’s idling good the BLM will stay pretty close to 130. Honestly I think I’ve seen it higher than 182. In a previous post I think it hovered around 195 or so for sometime. When you say about setting the base idle, I know to unplug the ESC connector and I typically follow the Chilton and set it at zero, shut it down, plug it back in, fire it up and let the computer do its thing. If you think I should retard it more, say the word. But here’s the thing that got me, when you said if the IAC is wired wrong it will usually stick open. That’s exactly what it’s doing. I’ve looked at it when it’s revving over 1500 and cannot even see the head of the pintle and a scanner backs that up by pegging it out around 145. I actually questioned that either earlier today or yesterday that I may have wired it wrong when I put a new pigtail on it. If I shut it down and start it back up it usually goes back to normal right until the next time this vicious cycle happens. I know just about enough now to be dangerous, LOL, but the two most relevant factors in my mind right now or what you said about the IAC wiring and the fact that everything changed the instant I went from idle into gear. The easiest thing might be to Check my wiring for the IAC and maybe I uncover a goof there. Any thoughts on how to go about that would be fantastic. Not sure I’ll be able to google search that one with any luck.

 

[bigblock72]

Yeah when it’s idling good the BLM will stay pretty close to 130. Honestly I think I’ve seen it higher than 182. In a previous post I think it hovered around 195 or so for sometime. When you say about setting the base idle, I know to unplug the ESC connector and I typically follow the Chilton and set it at zero, shut it down, plug it back in, fire it up and let the computer do its thing. If you think I should retard it more, say the word. But here’s the thing that got me, when you said if the IAC is wired wrong it will usually stick open. That’s exactly what it’s doing. I’ve looked at it when it’s revving over 1500 and cannot even see the head of the pintle and a scanner backs that up by pegging it out around 145. I actually questioned that either earlier today or yesterday that I may have wired it wrong when I put a new pigtail on it. If I shut it down and start it back up it usually goes back to normal right until the next time this vicious cycle happens. I know just about enough now to be dangerous, LOL, but the two most relevant factors in my mind right now or what you said about the IAC wiring and the fact that everything changed the instant I went from idle into gear. The easiest thing might be to Check my wiring for the IAC and maybe I uncover a goof there. Any thoughts on how to go about that would be fantastic. Not sure I’ll be able to google search that one with any luck.

Don't retard the timing, possibly advance it to no more than 4 BTDC.

If the idle is high and the IAC reads high (145 in this case) then it's wired correctly. When they are wired wrong the idle will stay high and the reading will be 0 or close to zero.

Can you adjust the neutral safety switch to get the P/N reading correct? you could even unplug it.

 

[Dont fake it break it]

Don't retard the timing, possibly advance it to no more than 4 BTDC.

If the idle is high and the IAC reads high (145 in this case) then it's wired correctly. When they are wired wrong the idle will stay high and the reading will be 0 or close to zero.

Can you adjust the neutral safety switch to get the P/N reading correct? you could even unplug it.

You bet I can adjust to the neutral safety switch as soon as you tell me how. LOL. I can probably reach up there and unplug it. It is that little green box under the dash right? By the way I compared my IAC wiring with my old connector, thankfully I never throw anything away. I worded the same but did find that it didn’t match Something I found online saying that
A and D -.5v And C and D - battery voltage. Mine was the opposite.

 

[Dont fake it break it]

Update. I found the source of the idle issue. It was the result of a partially disconnected IAC. All four of those wires have crimped push in style connectors that were heat shrinked. At some point, I suspect at the shop that did my valve adjustment since I could not get it right, one or two had broken connection but we’re still inside the heat shrink tube. Didn’t I test it?The easiest way to test it with a multimeter was to just give a little pierce to the heat shrink and now I see the error of that method where I am contacting the wire connected to power and not the Disconnected wire to the sensor that has no power. Makes me wanna shoot myself in the face. Here’s the kicker though, it was said earlier in this thread that the scanner may be causing the computer to behave this way while running in diagnostic mode. Turns out that was also true. I tested that theory half a dozen times by letting it idle, putting it into gear which had been opening the IAC and raising the idle. It ONLY did it when the scanner was connected. Thats the Actron 9500 for those of you scoring at home. Now I still have the lean condition and never been so happy about it. LOL. As bigblock72 stated, that leaves the injectors which have been verified, fuel pressure which I recorded at 14 psi, or computer/prom. So is there a way to test the computer or do I just pick one up and fingers crossed?

 

[bp71k5]

What are the IAC counts at idle now? Can you disable the idle bump up when the scanner is connected? The idle IAC count doesn’t matter if the idle is bumped up. I forget if that’s a prom programming or not but I can do it in tunerpro.