I was installing a new fuel pin for a buddy on a box stock truck. When I got his old pin out, I noticed a whitish/ yellow nylon washer below the diaphragm (and the big metal washer that retains the diaphram. This nylon washer is thin (maybe 1/16" thick) and is just slightly larger than the diameter of the fuel pin so that it seemed to ride on the fuel pin very loosely. There is seemingly nothing that holds it in place. I have never seen one of these washers on a 1st gen fuel pin (including mine) and I'm wondering what it's for. I'm also wondering if it's bad that mine doesn't have one.

Sent from my DROIDX using Tapatalk

 

It's there to limit downward travel of the fuel pin. Lots of people have removed them without any problem. Including me. Mine resides somewhere in my tool box now.

 

Get rid of it. Don't need it. You'll get more travel/ top end without it.

 

I lost mine on my garage floor about 8 months ago. Havnt had a problem with it out.

 

On my first gens I measured the bore depth of the hole in the pump and shaved the washer. Without it on my 93, the pin would actually get hung up on the top of the pin slope causing it to defuel slightly. So with that I was also concerned that the fuel pin pressure could cause damage to the little pin that sticks out for the fuel control by forcing it down or sideways in its bore.

IIRC, I shaved about 0.090 off the washer for optimum travel and stop.. FWIW.

 

I also recommend shaving the washer when using a stock pin. The aftermarket pins are designed to not need the washer.

 

Mine had two. If I'm lyin' I'm dyin'.

 

If you look at the "Skid-Mark" (from the fuel-needle?) on the old fuel-pin, you can see where the washer limits the travel, . . . . in relation to the fuel-pin's ramp.

 

I know it is a super old thread, but lots of posts in a day from some dudes that know Cummins... I have been researching info. on getting maximum fuel pin travel and therefore better / more AFC control.
I though there might be some people on here that might find this old thread worth reading.

I saw limited travel marks on my THD fuel pin install on my '91.0 after running it for a few days. With the limited travel range I was getting on the THD pin, I was gaining very little over the ramp of the rotated stock pin. That got me thinking...
I want to pull that nylon washer and see if I can actually travel down more than just the first half of the fuel pin.

 

In my pump, the THD pin and the stock nylon washer worked together perfectly so that when the THD pin was all the way down against the nylon washer, the guide pin was flush with the casting inside the injection pump top cover . . .

Did you take out the AFC spring and get some witness marks moving the pin by hand?

I know for other parts of that assembly not all injection pumps have identical parts from the factory/remanufacturer, so it is totally possible that you need a thinner stop washer to get optimum travel . . . But I would still double check that the washer is actually what is stopping the pin travel.

 

Ah, the good ol days before aftermarket parts. I remember them well.

 

Would just removing the AFC spring, putting a smear of clean grease on the pins ramp and testing it up and down with and without the spacer answer the question?

I was just surprised by the small amount of travel mark on the pin last time I pulled it. I am guessing the mark was about 3/8s of and inch, and only used the first half of the fuel pins ramp.

 

Yes, though you have to pull the accelerator lever to the stop to make sure the "guide pin" pops out and rides on the AFC pin.

You are absolutely correct that the mark should cover the whole ramp (at least as a starting point for tuning). So, it's worth digging into.