Last night I was getting on the freeway towing an empty horse trailer (4k,lbs)
went to step on it a little to merge into traffic and felt a small pop/thud and the truck died. Still had electrical, just no engine, (and no power brakes or steering.....that was fun.). Coasted to an off ramp and got it stopped. It would crank but not start. This truck has ALWAYS started on the 2nd crank.
Had it towed... this morning the only code is P1688. Does anyone have any thoughts or reccomendations for me?
the truck is..... 1999 24v, 4x4, 5spd, 100hp chip, 188k miles

 

P1688 is telling you the electronic control module inside the VP44 has problems. I got this code and my engine stopped just as yours did. Unfortunately the fix is a new IP. Look on the bright side, if the VP44 in your truck is the original one, your new one will have dozens of upgrades and should last longer.

 

Looks like the VP44 has said "I'M done".
P1688 reads "Internal Fuel Injection Pump Controller Failure"
Best Choice I can offer is look up Pesnacola Diesel on Ebay and call them.
Last time looded they were offering VP44 at 995 or so and 113 for lift pump and set of aftermarket new injectors for 217 dollars. I have done business with them five times without hitch. Perhaps the same pump as some of the big boys offer for less fanfare and cost. JMHO

 

these people will take care of you

Industrial Injection & Turbo Service
1201 South 700 West
Salt Lake City, Utah 84104
Phone: 800-955-0476 or 801-972-0476

 

http://www.sourceautomotive.biz

Those people will take excellent care of you as well. Rip is one of the three most stand-up guys I have ever dealt with on parts for these trucks. The other two are Russell at Solid Steel, and Richard at Glacier Diesel.

Any problems that arise, in their respective fields, those are the guys to deal with.