vacuum and clogged cat?

[B.E. Coyote]

2004 4Runner with a 4.7. 155k if it matters....

Using a OBD BT app I am seeing -22 for vacuum at idle in gear. Under hard acceleration it goes all the way to +12. It will return to -22 once the engine is at speed and no longer working hard.

Possible clogged cat or is that big of a swing normal?

No CEL, no codes, but from time to time I am seeing a huge loss in power like it goes into a limp mode. After it cools and i restart it, it will be fine for days.

 

[importman]

Maybe I'm slow but I don't understand those numbers. But I've never used an app, just a vacuum gauge attached to an intake vacuum port. Vacuum is measured in inches of mercury. It should have a range of 0 to about 28 or 29. If the cat's clogged the vacuum will drop really low at wide open throttle.

 

[B.E. Coyote]

Maybe I'm slow but I don't understand those numbers. But I've never used an app, just a vacuum gauge attached to an intake vacuum port. Vacuum is measured in inches of mercury. It should have a range of 0 to about 28 or 29. If the cat's clogged the vacuum will drop really low at wide open throttle.

No, I'm sure I am the slow one. This is what I am seeing Going from 0 counter clockwise is vacuum. Going from 0 to clockwise is Boost or what I was calling +

The yellow and red marks on the gauge show the max that each range went. In this run it went to 16inches of push instead of pull.

Is it normal to see that much "boost" on acceleration?

 

[B.E. Coyote]

Torque Pro is the app

 

[importman]

I wish I could be more help. But I'm having trouble understanding where the positive pressure is coming from. I would suggest getting a manual gauge and connecting it to a vacuum port somewhere on the intake, or at least behind the throttle plate. See what kind of readings you get at idle and wide open throttle under acceleration. I just don't understand the logic used in that app. All the gauges I've used don't have anything less than zero vacuum. One last thing. If it runs good at times and loses power other times, I wouldn't suspect a clogged cat. If it's clogged, it's clogged. Should run poorly all the times, especially during hard acceleration. Hope this helps a little.

 

[B.E. Coyote]

Thanks,
I do appreciate the reply. The only real reason I was suspecting the cat is that I read a lot of other threads where people had similar symptoms and many people suggested a partially clogged exhaust.

I'm confused about no fault codes. The two pre-cats have the 02 sensors. The larger rear cat has no sensors so I thought it could be partially clogged and if it had issues and no sensors it would make sense that it wouldn't throw a code.

Do you know if the 4th gen 4.7 has a limp mode? Running poorly doesn't quite describe what happens.

 

[rdruss]

A naturally aspirated engine shouldn't show positive intake pressure unless it has a very efficient ram air intake system and even then?? I would monitor fuel pressure if possible and see what happens when you experience your loss of power. Maybe a problem with in tank filter that doesn't restrict under all conditions. Just a thought.