Hey there,

This morning I wanted to check the timing on my 12 valve, and found no timing mark on the pump's flange...

There's a line on the gear housing, right where it should be, but no mark on the pump itself...
does this mean that I have a rebuilt pump?

The truck has 141,000 miles on it, seems a bit young for an already rebuilt pump???

 

I think it means you have a replacement pump or one that has had that portion of the pump replaced at one time.

 

It's a known fact that the majority of '91-1/2 and '92 trucks were subject to an injection pump recall.
Yours most likely has already been done, which likely explains the missing timing mark.
Some were replaced with an unpainted pump (natural aluminum in color) and bear a "Mopar" tag attached to the bottom of the pump.

A word of wisdom, if your pump is indeed a warranty replacement, expect to have to at least re-seal it in the near future, as the seals in it are not compatible with the current 15ppm (ULSD) fuel and will eventually start causing seepage.

Mark.

 

Would fuel conditioner (like Lucas Upper Cyl. Lubricant) help at all with the seals?