Im new to fourm, but my 1997 6.5 will stall right after start up after sitting for 6hrs or so, I have to keep starting it and after a few minutes of that it will never shut down again. sometimes it wont do this for days. I changed fuel shutdown selinoid and fuel filter still no change.http://www.dieselplace.com/forum/smileys/Disapprove.gif

Your fuel lift pump still working? On the 6.5 the OPS (oil pressure switch) controls the lift pump while the engine is on.


Without adequate pressure in the line the IP (injector pump) can't deliver enough fuel while the engine is starting/warming and stalls. The OPS/liftpump and related circuitry is first place to look.


With the engine running open the drain "T" that comes off the fuel filter. Fuel should come out. If not, you don't have pressure from the lift pump.

http://www.dieselplace.com/forum/smileys/Geek.gifare you saying in essence to change the oil pressure switch, because when truck is running i do have fuel coming out when t handle is opened while truck is running.

Does the truck stumble while drain is open or smooth running, a non functioning pump will cause it to stumble or shutdown in some cases when drain is opened at idle, lift pump should provide 15gph, 4-6 psi @ idle, you can install a gauge on the drain fitting when open to check. To test gph delivery catch fuel from drain from 30 sec run volume x 2 gives gpm, gpm x 60 gives gph.


OPS powers the lift pump, to check if problem is there connect power direct to pump from batt with in line fuse, run truck see if still acting up, if not fault most probable is in fuel relay/OPS side,. If you still stumble high probability partial blocked fuel filt ( you said it was new how new), the pump, or dreaded FSD/PMD starting to go bad

If fuel is comming out the "T" drain the OPS is working but the liftpump draws 3 more amps than the OPS is rated for.


I wired a relay to power the liftpump switched by the ops.


Another possiblity is dirty fuel/system. Do you use much additive?

used a little additive during winter once and a while will add 1 quart of tranny fluid to fuel, but lets remember my sympton will only stall after sitting 5 hrs or more but once warm never stall again.

my '95 6.5L is acting up the same way....my question is where do I find the OPS?

The OPS is behind the fuel filter.

lilzane,

Have you looked for fuel leaks? Could your system be depressurizing while it sits?
You would want to install an inline fuel guage to see what you have at start-up and shut down.

The only way to see what the fuel pressure really is is to install a guage in-line.

If it turns out the fuel is reaching 8 psi and holding it, You should check the wastegate solenoid.

For whatever reason a stuck wg solenoid will stall a cold 6.5.

I would suspect fuel delivery first.

Other factors that impact fuel delivery are the tempature sensors.
When cold the sensors resist more and increase the fuel for start-up.

Edited by: quantum mechanic

I suspect I had two problems. I determined the glow plug relay to be faulty and then I swapped the PMD for a new one. I also installed a new wastegate selinoid, for just incase measures. All weekend truck ran normally. No stalls http://www.dieselplace.com/forum/smileys/Clap.gif ! I did find the OPS while I was into the glow plug relay but didnt change that out. Thanks for your help QM.