M939 air cleaner indicator

[juanprado]

This weekend I checked my air filter to find a nice completely black unit that obviously had seen a better day. I got to thinking about it today that my air cleaner indicator was always green and even when I reset it after changing the air filter, It did not move.

Do these things really work? Has anyone had a "red" indicator?

I have the NHC250 one and I know the a2 have a multi colored one. Do they operate at different air pressure? I assume they work on air pressure?

Please school me on these indicator thingys as mine obviously did not do the job.....

 

[TwistedOaks]

Funny you should mention that. Mine is also completely green, has never had any change in position. I pulled my filter to switch to the K&N last weekend... Looked like this...


The K&N made a HUGE difference. Actually had a couple downshifts during throttle up!

 

[juanprado]

Funny you should mention that. Mine is also completely green, has never had any change in position. I pulled my filter to switch to the K&N last weekend... Looked like this...
View attachment 631846

The K&N made a HUGE difference. Actually had a couple downshifts during throttle up!

Are you using an adapter bracket or does K&N have a replacement the same size?

 

[Swamp Donkey]

The filter gauge works off vaccum (the variable), being pulled against a plunger in the gauge, which depresses a spring (the constant). The more vaccum, the higher the restriction if everything is working right. There is a hose that connects the gauge to the intake pipe. If this line leaks then the gauge doesn't see any vaccum and always shows green. Or the gauge could be bad.

 

[TwistedOaks]

Are you using an adapter bracket or does K&N have a replacement the same size?

Nah, I just squished a couple stainless c-clamps I had in my electrical drawer down to about 3/4" and drilled them into the four holders in the tank lid. It's not perfect, but I didn't read far enough into the thread that talked about the K&N to realize I needed a spacer until it showed up at my door (thank you Amazon Prime) . It does create a perfect seal, however, as the height of the K&N is an exact match, and the rubber they use on the seal side is top-notch. I'm keeping an eye on it.

 

[TwistedOaks]

The filter gauge works off vacuum (the variable), being pulled against a plunger in the gauge, which depresses a spring (the constant). The more vacuum, the higher the restriction if everything is working right. There is a hose that connects the gauge to the intake pipe. If this line leaks then the gauge doesn't see any vacuum and always shows green. Or the gauge could be bad.

I looked through three TM's and couldn't find anything that would've led me to that. I'll be looking at that come daylight.

 

[Swamp Donkey]

Basically you have a tube that goes from the intake pipe to the gauge. The plunger and spring are in the gauge. The tube on my truck appears to be clear nylon. Mine does work, although I don't know how accurately, because it sits right below 8 on the scale. If I hit the reset button on the bottom, the plunger drops back to the bottom until I start the truck again. I have a perfectly clean filter right now. The whole thing is just basically a remote vaccum gauge.

The picture below shows the elbow with the tubing going into the firewall. On the NHC250, the elbow should he on the engine side of the rubber coupling connecting the intake pipe to the intake manifold. On my truck the part of the tubing under the dash is nice and flexible, but there was alot of slack, so a kink could be possible. The other end under the hood is pretty stiff and I assume brittle. A break in this line would make the gauge inoperative.

 

[Tinstar]

My gauge is at 10

Checked filter and still looks brand new.
Nothing even blew out when I used air nozzle from the inside out


This is after 3500+ miles since new.

 

[jcollings]

My gauge was reading about 14 I checked air filter and it was very clean maybe a little dust changed it because it was a 1998. new one is still reading 14 ? Whatever do these 939 run at in terms of this indicator?

 

[simp5782]

Gauges are junk. Just clean your air filter as a part of your regular maintenance. I clean mine every oil change but i am also running mine alot more than everyone else usually. Plus i am using 2 air filters.

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