M923A2 Air Restriction Guage in the yellow???

[dieselsmokem35a2]

Hey Guys,
I recently picked up an M923A2 with the 8.3 Cummins. She runs well but smokes a bit (black smoke). I have noticed that my air restriction guage is always in the middle part of the yellow. Have reset it several times but always goes back. Since I just got it I thought for sure the filter was dirty but upon inspection it looks brand new. I pulled off the rubber elbow over the engine and all looked clear there too. It doesnt seem to be clogged or kinked anywhere. Is this a normal reading for these motors? Also if the motor is craving more air would this cause the black smoke? I thought I read somewhere these 8.3's dont smoke at all. Again, it's not a lot of smoke but at idle even after driving a while it still smokes. Changed the fuel filter too but that did nothing. As far as the air intake problem the only other thing I can figure is that the rain cap is too restrictive or the mesh has too much paint on it. Gonna remove it and see if that makes a difference. Just wanted to see if this guage reading was normal?

 

[cranetruck]

The air restriction gauge is a calibrated instrument and tells you what kind of vacuum you have in the filter canister. Full deflection (=all red) is about 20 inches of water. With a fresh filter, there shouldn't be more than a few, 5 or 6 IIRC depending on engine load and the gauge should not have any deflection.
Yeah, black smoke is an indication of unburnt fuel, too little air most likely.

 

[Shrapnel]

Old thread, but I have similar issue!

I know this thread is older, but I'm having a similar issue. I don't have any power issues or excessive black smoke, but my vacuum gauge in the intake will climb fairly high when the turbo is fully spooled up driving down the road. If I reset the gauge at idle it will stay where it's at, but as soon as I go down the road it climbs almost 3/4 of the way up the gauge.

I also checked my air filter, brand new, no oil or visible restriction in the canister and line. My intake cap, however, has way too much CARC on it. Anyone know a good way to remove the CARC without damaging the cap? Solvent, wire brush, sanding, picking every hole out with some kind of rod, etc? Is there a less restrictive, cheap alternative I can just replace it with?

Thanks!

 

[Parker Shorten]

From your pictures it looks like it is just held in with a clamp. If it is not to hard you might be able to just take it off and clean it out with fresh water (from the inside out) and maybe some dish soap. I have done that cleaning reusable oil less air filters and never had an issue. I assume that will work but I dont have the part in hand to reference. There could be a baffle in the way but I hope that helps. Have a great day sir!

-Parker

 

[Shrapnel]

I'm planning to remove it to do anything to it (and verify it's my restriction point). My main concern is removing the CARC paint, but maybe when I pull it off and get it in my garage I'll have a bright idea moment of clarity and figure it out. I think my starting point will be a wire brush and just go from there.

 

[Parker Shorten]

For taking paint off there is a off the self stripper at Wal-Mart that I found to be effective on tool box I have been restoring over the past year or so. Cant remember the name of it but saw it there the other day. I think it went for $10. Not the cheapest but it is effective. Watch out, it will make any scratch feel like a stab wound and it will destroy most nitrate gloves! If didn't have half a can lying around I would start by doing just what you're doing. Hitting it with a brush first before buying anything.

 

[mcmullag]

I picked up a M923a2 in July 2013 from GL and it does the same thing. The yellow thing inside the glass rises up and stays at a line that states '250'
The truck does not smoke when warmed up, except under load. The filter looks new and somebody wrote on the end of it 7/2012.
An ex army truck mechanic, now a diesel mechanic said he saw the gauges read like that a lot and just did not worry about it.

 

[Shrapnel]

I pulled the cone-shaped thing in the picture off tonight and took the truck for a cruise. The cone-shaped thing is separate from the mushroom cap, so I left the mushroom cap on (it has larger holes in it, so I figured it would have less restriction).

Vacuum gauge still went up 3/4 of the way under full load. Next time I drive it I'll pull the mushroom cap as well and see if that makes any difference. If it doesn't, then it's time for me to start looking for a better flowing filter setup.

 

[Shrapnel]

So today I pulled the rest of the mushroom cap off and took it for a drive. My vacuum gauge still climbs up to 3/4 of the way.

I already checked my filter and it is brand new. I might do a really short no-filter run to see if my gauge still reads high.

 

[chadande]

It's beginning to sound like the vacuum gauge is faulty.

 

[DJones]

 

[4XDesign]

Old thread but I'm living it now any updates!?

 

[74M35A2]

Filter gauge near the red line with even a new filter is the norm for these trucks, or at least the A2's. It is a poor design. I am also wanting to try the no-filter run, as I believe the filter CFM rating is less than the engine lungs. Not sure if the smaller diameter filter helps, hurts, or is neutral to this. I plan to run a high resolution vacuum gauge to decipher this and the possible restrictions in the system. A MAP sensor is a low cost and fabulously sensitive vacuum gauge, of which I will route that signal into a data logger and just look for the peaks and compare them. Then we can all stop guessing and have some data to work with. I also don't like the kinky turbo inlet elbow. Most all other semi trucks do not run this, they will instead use a conventional rubber elbow that is not kinked down. It looks like we have room to use this type. The restriction gauge measurement point is in between the filter and this elbow, so we can't easily measure if there are easy improvements to be made here, unless you could see a difference in manifold boost level.

Black smoke is inefficient air/fuel ratio. Definitely not normal if you have not increased your injection pump flow rate.

 

[4XDesign]

I reset the Guage after cutting the fins and associated metal out of filter housing. I only left a baffle right in front of the air inlet that is bringing fresh air to the filter. The Guage has not moved since so I'm guessing this helped


.

 

[74M35A2]

Interesting find. Thanks for posting the info.

 

[4XDesign]

I reset the Guage after cutting the fins and associated metal out of filter housing. I only left a baffle right in front of the air inlet that is bringing fresh air to the filter. The Guage has not moved since so I'm guessing this helped


View attachment 588720.

I just made a 1100 mile run to Florida and back and the gauge was still pegged. My earlier test run must've been a fluke. I do apologize.

 

[infidel got me]

I replaced my filter with a k&n for a 8.3 turbo. Guage goes up under half way under load or long pull. I thing that these gauges are just a poor design.

 

[walkerhunter]

i have tried mine without a filter and it is still in yellow.

 

[74M35A2]

i have tried mine without a filter and it is still in yellow.

Useful info. The only thing in the inlet tract when doing so is the empty tube between the filter canister and the turbo compressor inlet, of which the restriction gauge port tap is located half way between. Well, that sucks (get it?).