sometimes she starts, sometimes she just cranks
 

OK, my son's truck is a 96 12v with 200k on the clock. when you go to start the truck (hot or cold engine, warm or cold ambient temps) it either cranks and cranks or it starts right up. no pattern, but it has never started after cranking for a while. if it cranks more than a couple times you know it ain't lighting off! is there a relay or solenoid or something that is involved in getting fuel flowing when cranking? we jumped the truck to my truck to make sure it had plenty of battery just in case, but it was no different....
any ideas?

Is the shut down relay working correctly? It might be getting bad and not pulling up all the way. It's on the back of the P-pump. Try turning th ekey on and pulling the lever up and then start the truck. If the boot is gone dirt can get in there a wreck the solenoid.

i would say the shut down solinoid as well

This link might help:

Diesel Hard Start Diagnosis

Their is a relay and if it is going out it'll crank and crank but it won't start because its not getting any fuel, but it could be the solinoid as well. But the relay is about $20 and is a cheap fix

It's got to be a 70 amp relay IIRC.

i agree with solinoid

It is 70 amp relay. I just did mine about a month ago. You can get them from puredieselpower.com

Get a lawn mower cable.

you absolutely sure? wiring diagrams we have, have it labeled as a 50A relay. either way; a run of the mill automotive replacement relay wont cut it being they are typically 30A. dont bother getting it from a parts store; it only comes in a set of two (fuel heater and shut down solenoid relay) and will run you 68 bucks and up n good luck finding one. wish we would have know about the individual relays available online b4 hand. its either the relay or the solenoid. others have already described how to eliminate the solenoid from being the problem. good luck :tu: