Another 6.5 hesitating thread.
 

After doing a lot of searching I think I have it narrowed down to the OPS. When I start the rig and only warm it up for a minute or so it runs pretty good with only maybe a little sputtering on take off. The longer I let it warm up before taking off the worse it does once I get going - serious sputtering and hesitating up to and including stalling out. As I understand the 94 uses the key start to activate the LP until the OPS gets up to pressure and takes over keeping the LP running. This leads me to believe that there is enough fuel left in the Fuel Manager from the LP on the short warm up but as it sits and warms up longer the IP is sucking the fuel from the tank because the OPS is not running the LP causing the FM to NOT have any 'spare' fuel for acceleration. Having to go up a slight incline from my driveway probably compounds the IP not being able to suck the fuel out of the tank to make up for the LP not working

It also doesn't seem to have the 'git up and go' like it should when I floor it going down the road. It will sputter the most in the 50-55mph range and them smooths out. This leads me to believe the LP isn't working as it should once I get under way.

I may try bypassing the OPS and making the LP run constantly to make sure that is the problem so I don't going throwing away a lot of money needlessly. Of course I plan to put it back to the original configuration with a new OPS and maybe the OPS relay mod if that is indeed what it is.

Any input is much appreciated.

When running open the water in fuel drain and note the result-if it keeps running the LP is operating,if it stalls the LP is not running and further diagnosis is needed.

That is the little t-handle valve on the top of the IP near the thermostat on the front of the engine correct?

Correct.

I got my son to help me start it this morning. I opened the valve and watched the hose while he cranked it over. It had a good flow of fuel coming out of the hose while it was cranking over to start. Once it turned over and he let off of the key the flow stopped.

Another thing I did last night was to NOT tighten the fuel cap completely after I filled it up with fuel. When I was taking it off to fill up there seemed to be quite a bit off air rushing in when I unscrewed the cap. It is a diesel cap because it says "Diesel Only' on it. Could it be the valve has stiffened up over time? That seemed to do away with a lot of the stumbling and made it seem to have a little more pep when accelerating.

With your truck the LP runs by a relay when cranking,not the OPS.
I need to know if the LP runs when the engine is running-that why I asked you to open the valve when it is running.

Yes the fuel filler caps are vented and if the vent gets plugged it can restrict fuel flow-sounds like you need a new diesel fuel cap.

No there is no fuel coming out of the hose connected to the t-valve so it looks like the LP does not pump when the engine is running.

Sorry if my post was confusing. I should have posted 'when it started and he let off the key the fuel stopped flowing'. I also let it start back up with the valve closed and then opened the valve and no fuel flowed then either. I did these checks twice just to make sure they were consistent.

Ok,the oil pressure switch is a dual contact switch-one set powers the LP while the engine runs and the other set operates the oil gauge.
Burning out the LP circuit is common because they were under engineered to begin with.
replace the OPS with AC Delco only and then buya OPS relay mod kit from Kennedy Diesel or build your own "OPS relay mod"-google it for instructions.

I did google it but the other diesel sites that have the instructions I need to register to see images and all. Which site has the best write up and instructions? A link would be helpful.

Thanks for all your help.