94 1/2 ton 6.5 wont start
 

I have a 94 1/2 ton 6.5 it will not start. ran fine then one day no more start. I did some looking on here and thought i figured it out. thought it may of been the oil pressur switch unpluged it tried it started right up. jumped in it to go to part store to get new one left it idleing about 5 in whentook off it died will not start back up at all now could the injector pump be going out too. also forgot to mention before i disconted oil pressure switch the transfer pump would run all the time key on or key off. any help would be greatly appreciated

Have you cracked open either of the bleeders the one on top of you're fuel filter or the T valve by the oil cap to see if you have fuel running to the injector pump this is where i would start and you can run a wire frome the positive terminal on one of the batteries to the G terminal this will make the lift pump run unless it has failed.

Jump the lift pump relay an crack the cap on the fuel filter see if you getting fuel.
If not could be bad lp clogged sender in tank or bad fuel filter. If your getting fuel to the fuel filter crack an injector free and start the truck. If no fuel, it could be a possible PMD.
If you have another swap it and see if it starts.
Tell me how you make out.

I am having same issue thanks for posting I am goin to try jump LP as well thanks!!

LP running with key on or off is a bad OPS-stuck shut.
Replace OPS with AC Delco only.
Then do the LP tests and confirm it is capable of pumping fuel.

At the next no start crack an injector line loose and see if you have fuel to the injectors?
PMD failing is most likely cause of no fuel at injectors but be sure that the FSO clicks with key going from off to run.
Also have you checked for any codes even if the check engine light is off?

Can I test the OPS before I buy one any way and do u know price on one?

Sorry to Chuck Beck for taking over the thread but;

The OPS powers the LP when oil pressure is enough,to check it's function check the grey wire from the OPS for power when the engine is running,also that same grey wire should have no power when the engine is off and there is no oil pressure.

The OPS can however fail in a manner where it has battery voltage but can no longer carry enough amps to run the LP,the switch contacts get burned.

For long term reliability for 95 and earlier trucks google "OPS relay mod" to put an end to failed OPS problem.
The switches were under engineered by GM and severely underbuilt by aftermarket producers,hence AC Delco only for replacement.
During startup/cranking the LP relay and fuse supply power to the LP(different relay than the mod).

Rock auto has AC Delco OPS $28 part #19244500 I belive.

If your truck is 96+ the OPS relay mod is built in and OPS seldom fails.

K so if I turned key on and gettin fuel at T valve and fuel filter what next could it still be OPS?

If yours is 95 or older it has to be OPS,unless someone added a toggle switch to run the LP independant of the OPS because they fail often without the relay mod.

Note:there is still enough oil pressure to run the LP for about 3-4 seconds after the engine shuts off.

Also if the LP runs with the key off you would likely have dead batteries a lot.

Hmmmm ill get back to u my buddy is comin to help right now thanks and yes a 95 6.5 2500 is what we're talkin about lol