GM Truck - Air Filter Restriction Indicator

[Jim 5]

I have had a few trucks with this little cylindrical clear plastic indicator with a multi-colored piston inside. It is located between the air filter and the throttle body in the air intake tract. The piston within the clear cylinder shows green with a good filter, and with a blocked filter, the air flow restriction creates enough vacuum to pull the piston into the red zone (if that makes sense) indicating the need for a filter change.

I have never had a filter get bunged up enough to cause the indicator piston to move into the red zone, however before that happened, UOA's showed it was time for a filter change. When this happened, the filter actually looked pretty good.

Has anyone ever seen one of these go into the red, or are they just useless indicators (with the exception of extreme blockage situations)?

My guess is you're going to see driveability issues to accompany any red indication.

 

[Rhymingmechanic]

I don't think mine has ever moved, and I've just assumed it doesn't work. I'm getting ready to change a filter with 22,000 miles on it, and maybe an eighth-inch of orange is showing. The orange has not even reached the first mark on the scale. Filters have always "looked" good when changed.

Maybe somebody who drives daily on dirt roads would see the indicator move?

 

[Rlc2500HD]

Mine moves just fine, but then again I do live on a dirt road and drive a lot off road.

 

[Mike_dup1]

Its just another one of those gadgets people complain about when its not on the vehicle, so the manufacturer puts them on. I think the first one I recall seeing was on my 1996 Z71 E. Cab. I too have never seen it move but I know it works.

 

[TLAR640]

I felt the same way, that mine was possibly stuck, so I tested it with a shop vac. Worked fine. My filter had 46,000 miles at the time.

 

[glenncof]

I took my 1997 Tahoe 5.7L out to 100K on factory filter. The indicator was still green and no visible signs of dirt on filter. All street use.

I was doing 100K plug replacement and changed the filter. I thought it may be timeto do it.

 

[NYEngineer]

I'm not sure how much vacuum it takes to pop one of those things, but I had a paper filter in my truck that looked clean but it wasn't running right. I noticed the sensor was red. I swapped out the filter, reset the sensor and the engine is much happier. Cat has been putting those things on their air filters for years.

 

[Gary Allan]

Quote:

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I'm not sure how much vacuum it takes to pop one of those things

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Neither do I ..but I hope that it's in the "inches of fractional water column" realm. I think it would mean less in MAF applications ..but a normal speed density system, or so I reason (I don't know), would be effected more by its "numbness" in somewhat single dimensional barometric variances that aren't indexed for air volume like the MAF engines. I imagine that it leans the mixture to compensate for the lower air density ..resulting in less power ..more foot. Then again, I could be totally off.