High Temperature rated O2 sensor?

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mthorseman69

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Installed headers on my ‘88 5.8 motor. Cascading rpms immediately started. I’m thinking the headers are cooking my Oxygen sensor. Does anyone know a good fix? Thanks.
 

Motech

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Heat won't hurt O2 sensors. In fact, heat is their lifeline. They are useless until hot.

Also, buggered oxygen sensors generally don't cause poor running. If they don't work, the system just remains in open loop. If anything, it'll run a little bit richer.

Sounds to me like you've got some restricted intake air flow. The computer will compensate over time and idle pretty decent, but once memory is erased, like extended battery disconnect, so is that compensation, and it will struggle to maintain any semblance of a decent idle until relearns a new compensation strategy.

Here's how you test for that:

When truck is completely warmed up and idling with all loads turned off, disconnect the two-wire connector on your Idle Air Bypass Valve (more commonly called Idle Air Control Valve, or IAC)
Do this WHILE ENGINE IS IDLING

images-01.jpeg

Heathy minimum air rate will still idle with IAC disconnected, between 400 and 500 RPM

If yours does, then you're good. It will probably just need to relearn its idle strategy, and will improve after a few warm engine cycles.

However, if it stalls, you need to increase that minimum air rate flow.

First thing is to clean up the dirty throttle bores. He'll probably find carbon buildup around the throttle blades when you open the throttle.

images-02.jpeg

You'll want to clean that up with carburetor cleaner soaked rags. You don't want to spray it in there directly because it will reach down and damage your throttle position sensor on the bottom of the throttle body. Put a brick on your accelerator pedal to keep the throttle open and scrub around the blade edges and the blade itself until you get all that carbon off of there til it's crystal clean.

Then with your IAC plugged back in, fire it back up, clear its throat, let it settle back into a warm idle, and unplug your IAC again.

If it now stays idling between 400 and 500 RPM, you'll be good to go. But if it still stalls, you'll need to open your throttle a little bit at the throttle set *****.

images-03.jpeg

That will be hit and miss, you'll have to open it a little bit, then repeat the restart with IAC connected and disconnect it again at idle to see where it lands.

Once it finds a happy spot and idles around 500 with the IAC disconnected, shut it down and disconnect the battery for 20 minutes so it erases all those strategies again and you should be good.

Don't expect perfection. It's an old system, and it does take a few drive cycles before your changes set in nicely. Expect some idle fluctuations, especially high on cold starts, but these will diminish and go away and you should be good again.
 
OP
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mthorseman69

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Heat won't hurt O2 sensors. In fact, heat is their lifeline. They are useless until hot.

Also, buggered oxygen sensors generally don't cause poor running. If they don't work, the system just remains in open loop. If anything, it'll run a little bit richer.

Sounds to me like you've got some restricted intake air flow. The computer will compensate over time and idle pretty decent, but once memory is erased, like extended battery disconnect, so is that compensation, and it will struggle to maintain any semblance of a decent idle until relearns a new compensation strategy.

Here's how you test for that:

When truck is completely warmed up and idling with all loads turned off, disconnect the two-wire connector on your Idle Air Bypass Valve (more commonly called Idle Air Control Valve, or IAC)
Do this WHILE ENGINE IS IDLING

View attachment 30710

Heathy minimum air rate will still idle with IAC disconnected, between 400 and 500 RPM

If yours does, then you're good. It will probably just need to relearn its idle strategy, and will improve after a few warm engine cycles.

However, if it stalls, you need to increase that minimum air rate flow.

First thing is to clean up the dirty throttle bores. He'll probably find carbon buildup around the throttle blades when you open the throttle.

View attachment 30711

You'll want to clean that up with carburetor cleaner soaked rags. You don't want to spray it in there directly because it will reach down and damage your throttle position sensor on the bottom of the throttle body. Put a brick on your accelerator pedal to keep the throttle open and scrub around the blade edges and the blade itself until you get all that carbon off of there til it's crystal clean.

Then with your IAC plugged back in, fire it back up, clear its throat, let it settle back into a warm idle, and unplug your IAC again.

If it now stays idling between 400 and 500 RPM, you'll be good to go. But if it still stalls, you'll need to open your throttle a little bit at the throttle set *****.

View attachment 30712

That will be hit and miss, you'll have to open it a little bit, then repeat the restart with IAC connected and disconnect it again at idle to see where it lands.

Once it finds a happy spot and idles around 500 with the IAC disconnected, shut it down and disconnect the battery for 20 minutes so it erases all those strategies again and you should be good.

Don't expect perfection. It's an old system, and it does take a few drive cycles before your changes set in nicely. Expect some idle fluctuations, especially high on cold starts, but these will diminish and go away and you should be good again.
Thanks, I’ll try that.
 

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