O2 normal voltage

[RichLo]

You have the 7.4 Vortec, right? I wouldn't worry about it not occurring in open loop, the ECU is not even using O2 data in open loop as it warms up.

See if you can record or screen shot the fuel trims, spark advance, all 4 O2 sensors, and at the same time looking at fuel pressure when it does it. What are your fuel trims anyway?

Yea 7.4 Vortec with 'mods' done by an owner 2 or 3 people behind me. The previous owner didn't know much about what was done but everything looks really professional from the outside... mandrel bent exhaust, all new body mounts, feels like a Detroit locker in the back, etc.

I'll see how much I can log, I just got that scanner yesterday and was just playing around with it and so far I think it can only log 4 data streams at a time but I'll play more tonight.

I do not know my fuel trims but I will post them up once I get home.

I'm just wondering, why should I log the downstream O2s? I thought those were just monitors for the cats and only cause a CEL to pop on?

Thanks again for all the help!

 

[PlayingWithTBI]

This problem is only noticeable to the driver in closed loop, just off idle and only after idling for approx. 10 seconds or more

You may wanna take a look at your IAC steps. If you have a vacuum leak the PCM will try to control idle by closing it down closer to zero - that could be an indication... Do you have a high idle condition?

 

[RichLo]

ok, after more diagnostics, the fuel pressure actually increases whenever I give it more throttle, from approx 55psi at idle up to 60psi.

I put propane all around all of the areas for possible vacuum leaks and no rise in RPM.

The top graphs here are the short term fuel trim and the bottom graphs are the two upstream O2's. This was a really bad surge, the drop in O2 reading then 3 spikes and another drop was all one long stumble before recovering and revving during the long rich event.

 

[RichLo]

Oops, here is the picture of the graphs, I still need to find how to upload them but this works for now, lol

You must be registered for see images attach

 

[PlayingWithTBI]

This was a really bad surge, the drop in O2 reading then 3 spikes and another drop was all one long stumble before recovering and revving during the long rich event.

Can you trap RPMs during a stumble? I saw a jump in revs while cruising at ~2200 RPM up to 4775 (which is impossible). That was due to a bad ICM and coil, it would send an intermittent pulse to the ECM which thought the engine was running faster so it changed timing and fuel which caused the stumble. It may not be your issue but may be worth looking at.

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[Erik the Awful]

I still need to find how to upload them but this works for now, lol

Ctrl + PrintScreen
Click the Windows key
Type "paint" and hit enter
Ctrl+V
Drag and crop
Save

Edit: Doh! I just spotted that it's a tablet. I'm too old to figure that out.

 

[PlayingWithTBI]

If you're running Windows, there's an app called "Snip and Sketch" or "Snipping Tool" you can play with, then copy and paste here.

 

[badco]

People still have down stream 02s? Lol jk. I know some states are still kinda strict on than still