Engine/Transmission (1994 - 1998) MPG drop-Time for injectors?

Hello Folks, Happy New Year

Awhile back I posted a question about injectors. At the time, based on responses, I held off replacing them.
But now, I'm thinking its time.
96 12v with 460k miles.

The truck was off the road for many months last summer while I restored the body and did various mechanical repairs. I routinely started and ran truck during this process.
While I had the timing cover off for a gasket leak I did the killer dowel pin thing.

I knew I was due for a valve adjustment, so I did that as well.
Fast forward, I started driving the truck again full time in the fall and notice my MPG has dropped dramically.
Im now getting 10-11mpg from the 18 or so I was getting prior.

This winter, I notice harder starting and a noticeable miss in a cylinder or two for a short time (20-30 seconds) and then its fine. Runs fine/idles fine.
It not smoking, but I due see a lot more black soot at exhaust outlet that prior.

Did I screw up the valve adjustment, or more likely a coincidence of one or more injectors finally below the threshold in performance? Any suggestions appreciated. Im not a diesel mechanic

One last note, I did have the turbo removed to better gain access to the darn trans cooler heat exchanger thing...should I have replaced the thin metal gasket? Could it be a slight turbo leak? I don't notice a leak anywhere. but???

I do not have any aftermarket gauges, fuel or turbo, in order to monitor performance.
Thanks

 

Thats too big of a mileage drop for coincidence. I would guess the valve adjustment is off since that was about the only overnight change. With 460k miles, I would think about changing out the injectors.

 

Something else I just thought of, because at my age, Im second guessing most everything i do .... I did need to pull the vac pump/power steering assembly for a new power steering pump. I put new seals on the vac pump same time.
Could I have got the gear timing off a tooth when re-installing the assembly, or doesn't that gear make any difference on tooth position? No other gears were disturbed if I remember correctly.

 

No timing on the vacuum/power steering pumps.

 

First things first, run a tank with a good injector cleaner like Power Service and see the results.

 

thanks regarding the timing...i didn't think so but don't remember.......yep, done that cleaner a tank and a half ago, yes, power service brand is what i used. slightly better morning startup, but temps have been warmer to so...who knows

 

I replace my injectors in the 350k-400k range. I had the originals pop checked at 400k. They passed but the holes in the tips had enlarged from the erosion of having thousands of gallons of fuel run through them. I had a bit of smoke and a slight drop in mileage, nothing like the 7 mpg you are seeing.