O2 flat lines rich at cruise

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daveinet
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O2 flat lines rich at cruise

Post by daveinet » Sat Aug 23, 2008 5:45 am

I'm running computer 16197427 $OD mask. Computer is from a '95 GMC pickup. This has been retrofitted into an older motorhome. I had someone else do the chip. Engine runs well under everyday driving, however once I hit the freeway, after cruising for around 5 minutes or so, the O2 sensor will just go straight rich, ~800 mv and just stay there. It is no longer toggling. The cross counts stop counting. I can step into the throttle or back off and it still just stays rich. The only way I can get it back to toggling, is to step on the throttle hard enough to hit the mixture enrichment momentarily, or let off the throttle completely for a long time. When this occurs, the enrichment flag is not set - as a matter of fact, I can't find any flags that are set. No error codes. Seems to happen around 25 to 35 % throttle. Any idea why.
Dave
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502 Edelbrock/Howell MPFI Thorleys and Magnaflows - in a 13Klbs motorhome!

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daveinet
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Post by daveinet » Tue Aug 26, 2008 3:23 pm

Well, I partially found an answer. I've noticed the converter over temp flag is set at the same time it goes rich, and shuts off when it returns to normal. What i don't know is which converter. Is it the torque converter or the catalytic converter. Unfortunately, the label for the flag does not specify which converter. Also not sure why that would make it choose to run rich.
Dave
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502 Edelbrock/Howell MPFI Thorleys and Magnaflows - in a 13Klbs motorhome!

"There are 10 types of people in the world, those who understand binary and those who don't"

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dex
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Post by dex » Tue Aug 26, 2008 10:04 pm

I do not know for sure but I would suspect that it is the catalytic converter that is being monitored. The extra fuel cools the exhaust gases down.

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Six_Shooter
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Post by Six_Shooter » Wed Aug 27, 2008 3:47 am

dex wrote:I do not know for sure but I would suspect that it is the catalytic converter that is being monitored. The extra fuel cools the exhaust gases down.
Would also cause the cat to over heat, hence the flag. ;)

The converter flag that you see will be the catalytic.

The O2 should be toggling at cruise.

Does the vehicle has a VSS?

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daveinet
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Post by daveinet » Wed Aug 27, 2008 4:12 am

One other clarification. The flag and the rich flat line O2 happen simultaneously. It will maintain that condition for a minute or two and then the flag goes false at the exact same time the O2 begins toggling. So I assume the rich condition is in response to the flag, as opposed to the other way around.

The vehicle does not currently have a VSS. We removed all the trans codes (or so we think). I'm using that computer because I plan to replace the TH475 with a 4L80E next year, but that is going to be a major trick.

This condition does now make sense. This last trip, it went into that mode much more often. I'm guessing that was because I was towing a car, which brings my weight up to 18K lbs. The vehicle does not have cats on it, so it looks like we'll have to try to find that routine and remove it.
Last edited by daveinet on Wed Aug 27, 2008 8:54 am, edited 1 time in total.
Dave
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502 Edelbrock/Howell MPFI Thorleys and Magnaflows - in a 13Klbs motorhome!

"There are 10 types of people in the world, those who understand binary and those who don't"

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Six_Shooter
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Post by Six_Shooter » Wed Aug 27, 2008 5:15 am

Adding a VSS will help with this issue.

What the ECM will do, if the code you are using is like any other GM code I've looked, is go into a "lean cruise" or "highway mode", where it leans out the mixture, and uses other variables to control highway driveability and economy.

I currently don't have a VSS on my car, only because it's not an easy task to do so (Datsun/Nissan tranny, and no easy direct way to integrate a VSS sensor. I'm actually go to lok at adapting a VSS to th eback of the speedo, if that doesn't pan out, I'll be making a reluctor wheel to attach to the diff.

I also drove my Jimmy for a while with out a VSS, again, I had to adapt a VSS to it, and onec I did, the truck became MUCH more driveable ancd much better on fuel.

Get a VSS on it and it will help.

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daveinet
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Post by daveinet » Wed Aug 27, 2008 8:09 am

I think we are going to try just removing the catalytic converter routine, but it does seem like it may be worth adding the sensor anyway. In that regard, do you have any idea what the pulses out of the sensor should look like? The reason I ask is because I have an after market cruise control that uses magnets on the drive shaft to calculate speed. If the pulse signal is anything close to what the ECM wants to see, I could easily create a buffer and send the signal to the ECM. I just have no idea what kind of voltage the ECM expects to see, or how many pulses per revolution, to know if I would be even remotely close to OEM design.
Dave
http://www.geocities.com/revconprince/index.html
502 Edelbrock/Howell MPFI Thorleys and Magnaflows - in a 13Klbs motorhome!

"There are 10 types of people in the world, those who understand binary and those who don't"

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