Puff Limiter Revisted

[thomastractorsvc]

I finally bought a new Puff Limiter valve and air cylinder.  Yesterday I changed the Puff limiter and thought I would see how that made things run since after messing with the old one the smoke dyed down for awhile than it came back hence the ordering of the parts.

This morning when I was headed to a job site the truck did not blow any smoke out the exhaust no matter how hard I mashed the gogo pedal so I figured that must be the problem.  About 3 miles from home I was finally getting into the taller gears and it acted liked it was stalling so I held it to the floor the RPMs started to slowly rise and the boost never got above 20lbs and the pro holding steady on 700.  I made it onto I 70 thinking well maybe I need to get used to it but when she hit high gear she dogged out like it was starving for fuel boost still at 20 and the pyro holding steady between 600 and 700.  I hit the next exit and headed back to the shop I pulled inside cranked on the heater and put the old valve back on.  Took about 10 minutes then headed out Boost was immediately back to normal, black smoke when I got hard on it and boost topped out around 32 or 33 and pyro holding steady around 400.

Obviously the air actuator valve must not be shimmed right so when the new Puff Limiter valve was working it held the rack partially closed.

I guess my question is how do measure and shim the air cylinder and once I do get it right will it still make the truck doggish?  I have learned to run the truck with out making it smoke bad by throttle control but wanted to see it fixing it would save on fuel.

[Rob]

In my experience with them they will not save fuel or boost economy. When they are adjusted and working correctly they limit off idle torque rise in the lower gear or two and reverse. This has saved many a driveline when loaded heavy and in soft ground. Also helps out a bunch with hired drivers whom don't have to pay for parts when the fail. Ensure the reversing relay is operating correctly by plumbing a pressure gauge into it and the air cylinder on the trans is not leaking internally if so equipped. You need air to the reversing relay from and air receiver, and manifold boost for the relay to cause the cylinder on the pump to operate correctly along with the shims to allow proper rack movement.

[j hancock]

There is a PLE (Puff Limiter Extension) number stamped on the pump.  You also have to measure the throw of the air cylinder.  The example in the manual shows throw of 1.125" minus PLE of 1.037" so the shim should be the difference at 0.088"

On an American pump, the PLE info is stamped in front of the No. 1 injector outlet on top of the pump.  On a Robert Bosch pump, the PLE is stamped above the throttle arm near the top of the housing.

[thomastractorsvc]

When I get a chance I will see if I can find the number and put air to the valve.  Yesterday it didn't look like there were any shims between the pump and the air cylinder.   Of course until I get it out it is hard to say and the air conditioner pump makes it hard to crook your neck in for a good look.

I guess what i will do is look for the stamp and measure the trow of the new cylinder and by the right number of shims than replace the puff limiter at the same time then everything should work like factory.

[theakerstwo]

That is the proper way to set it but for years i would shim and drive till i got only small amount of smoke when you mash on it.I like to set them in the winter with light smoke and that way next summer they dont smoke too much.When you get use to it not smoking then you will notice your oil gets more miles on it before a change.

If any one needs a Ambac pump for a 4 valve 350 HP i have one and injectors which was exchanged with mack 5 years ago with maybe 200000 miles on it for sale. It is still set to specs and then went down so i took it off and saved it.1200.00

[Dirtymilkman]

Theakerstwo is right. I used the numbers for a baseline and then shimmed it for how I like it. If there are no shims it will definitely hold your rack back and you'll get no fuel in steeper gears. 

[Swishy]

May B we were slak

or din kno any better

but with 2 trucks with the puff limiters ..... we just unscrewd m and fitted a flat washer from a nut n bolt set

and screwd her back in

wam bam thank U mam

result twaz a bit more get up n go and a little more blak soot

Cya

§wishy

[39 Baby Mack]

13 hours ago, j hancock said:

There is a PLE (Puff Limiter Extension) number stamped on the pump.  You also have to measure the throw of the air cylinder.  The example in the manual shows throw of 1.125" minus PLE of 1.037" so the shim should be the difference at 0.088"

On an American pump, the PLE info is stamped in front of the No. 1 injector outlet on top of the pump.  On a Robert Bosch pump, the PLE is stamped above the throttle arm near the top of the housing.

Spot on Jim,

I have an old rack setting gauge I used to to use along with a depth mike to measure how far the piston extended from the puff limiter cylinder.

Ron

[fjh]

Try a 9/16 flat washer it will likly cut the smoke to a resonable level!