Tunerpro log - rough cold start 1995 7.4L

[termite]

Looks to me you have a problem with the O2 sensor.Your engine doesn't go into Closed Loop until the 24 minute mark because the O2 sensor doesn't start acting like it should until then.If you jump to the 24 minute mark and select O2 sensor,vehicle speed and engine speed you'll see it all wakes up.Anyway that's what I see.Looking at a couple of my data logs mine is much different.

I'm still running a one wire O2 sensor. I've only ever seen it go closed loop while under throttle, and thought that was normal for the TBI systems. Perhaps I've had the wrong idea on that for years.... wouldn't be the first time either.

 

[grampadirt]

Here's a snapshot of one of my logs...

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[grampadirt]

The way I understand it the engine runs on preset values until it goes into Closed Loop and then it responds to the sensors on the engine.

 

[grampadirt]

I'm still running a one wire O2 sensor. I've only ever seen it go closed loop while under throttle, and thought that was normal for the TBI systems. Perhaps I've had the wrong idea on that for years.... wouldn't be the first time either.

Mine is also a one wire O2,you could be right about going into Closed Loop when moving....never thought of it like that.

 

[termite]

Mine is also a one wire O2,you could be right about going into Closed Loop when moving....never thought of it like that.

I’m not 100% certain that I’ve got that correct though. I’m going to try to find a clear answer in the FSM sometime today. Hopefully, got three small kids under my supervision today while the better half is working 7-7.

 

[grampadirt]

I’m not 100% certain that I’ve got that correct though. I’m going to try to find a clear answer in the FSM sometime today. Hopefully, got three small kids under my supervision today while the better half is working 7-7.

Good Luck,remember watching our three kids a very long time ago....gotta be ready for anything lol

 

[PlayingWithTBI]

I'm still running a one wire O2 sensor. I've only ever seen it go closed loop while under throttle, and thought that was normal for the TBI systems. Perhaps I've had the wrong idea on that for years.... wouldn't be the first time either.

Mine is also a one wire O2,you could be right about going into Closed Loop when moving....never thought of it like that.

In some calibrations you can select OL or CL at idle. Originally GM had CL to help pass emissions. Depending on where your O2 Sensor is located, a one wire may get too cold so, it'll drop out of CL. With a heated one you'll go into and stay in CL as soon as your water temp reaches a certain point (in the .bin).

I see the @grampadirt log is spaced in ~90 second increments while the @termite one is ~10 seconds so, grampa's looks even more erratic than if it was in 10 seconds.

I went back to when I was using TunerPro RT to tune my 7747 on 02-04-19. Of course the old ECM only updates ~every second (160 baud) where the 7427 is 8192 or ~50 times faster but, you'll kinda get the idea.

In the second graph, you'll see the heated O2 crossing (Cross Counts) over and under 450 mV, which is supposed to be ~14.7 AFR .

In the bottom graph, you'll see that MAP pretty well follows TPS and then RPM does too. Please disregard the spike at between 4:00 and 4:10, that's when I caught my ICM wigging out, LOL.

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I agree with grampa - something is probably going on with your O2

 

[termite]

In some calibrations you can select OL or CL at idle. Originally GM had CL to help pass emissions. Depending on where your O2 Sensor is located, a one wire may get too cold so, it'll drop out of CL. With a heated one you'll go into and stay in CL as soon as your water temp reaches a certain point (in the .bin).

I see the @grampadirt log is spaced in ~90 second increments while the @termite one is ~10 seconds so, grampa's looks even more erratic than if it was in 10 seconds.

I went back to when I was using TunerPro RT to tune my 7747 on 02-04-19. Of course the old ECM only updates ~every second (160 baud) where the 7427 is 8192 or ~50 times faster but, you'll kinda get the idea.

In the second graph, you'll see the heated O2 crossing (Cross Counts) over and under 450 mV, which is supposed to be ~14.7 AFR .

In the bottom graph, you'll see that MAP pretty well follows TPS and then RPM does too. Please disregard the spike at between 4:00 and 4:10, that's when I caught my ICM wigging out, LOL.

You must be registered for see images attach

I agree with grampa - something is probably going on with your O2

Looking over the log again on 4x playback, seems its only hitting closed loop while driving. Also went through the FMS driveability supplement and it seems to indicate closed loop should be achieved at idle in P/N after warm-up but doesn't indicate HO2S or O2S.

I'm going to upgrade it to a heated when I change it. Another thing on my list of stuff to do that may improve its fuel economy. Last tank was 5.3mpg, including pushing snow on our half mile shared road 3 times.

Edit: I've had several spikes on my datalog as well that resemble what yours shows. Is that indicative of a faulty ICM/harness to it? Mine is 'new' with the assembled carquest distributor but only warrantied as a complete unit...

 

[Sabinoerc]

Interesting thread. Well, interesting if you’re not the one struggling with the problem.

I'm still running a one wire O2 sensor. I've only ever seen it go closed loop while under throttle, and thought that was normal for the TBI systems. Perhaps I've had the wrong idea on that for years.... wouldn't be the first time either.

I have a 93, could find the details on bins and pcm if needed. Mine definitely stays in CL on hot idle. I had problem once where it was dropping out of CL on hot idle and causing me to fail emissions. O2 looked as it was following the commanded swings in AFR - i forget the limits but something like getting below 0.4v and above 0.8v . But it wasn’t moving fast enough or always getting there and would fail qualification for CL at hot idle. Some here called it a Lazy O2.

Looking at your O2 data above it seems it’s barely getting over 0.7v? I tried to find criteria for staying in CL when I had the problem and it wasn’t clear, multiple conditions, conflicting info on sites, etc. It could be criteria different over years, models but if same as mine it would seem O2 not reaching high enough voltage. Good luck.

 

[termite]

Interesting thread. Well, interesting if you’re not the one struggling with the problem.


I have a 93, could find the details on bins and pcm if needed. Mine definitely stays in CL on hot idle. I had problem once where it was dropping out of CL on hot idle and causing me to fail emissions. O2 looked as it was following the commanded swings in AFR - i forget the limits but something like getting below 0.4v and above 0.8v . But it wasn’t moving fast enough or always getting there and would fail qualification for CL at hot idle. Some here called it a Lazy O2.

Looking at your O2 data above it seems it’s barely getting over 0.7v? I tried to find criteria for staying in CL when I had the problem and it wasn’t clear, multiple conditions, conflicting info on sites, etc. It could be criteria different over years, models but if same as mine it would seem O2 not reaching high enough voltage. Good luck.

I'm suspect of the O2 for sure, at least for not hitting CL. Dont think it is responsible for the rough cold starts that randomly occur though. Pretty sure its the one it came off the line with ~30 years ago.