I have the same issue, jerks at part throttle, starts and runs fine otherwise. Can accelerate and jerk goes away, have to drive at above 2500rpm to keep truck from bucking. new and relocated PMD, new lift pump, filter, goin nuts here. Where are the 6.5 gurus?

I have the same issue, jerks at part throttle, starts and runs fine otherwise. Can accelerate and jerk goes away, have to drive at above 2500rpm to keep truck from bucking. new and relocated PMD, new lift pump, filter, goin nuts here. Where are the 6.5 gurus?

well first off start a new thread for your issues , second do the diagnostic check list so we dont guess as to what your particular issue is.

here ya go, your own personal thread ;) try not to hijack anymore

Here's what i've got , i bought the truck with 140,000 km, started stalling at about 150k, changed the pmd and that fixed it for awhile. Now it jerks intermittently and stalls occasionally as well. It starts like a dream, idles fine, no miss, no smoke. Bit of smoke on acceleration, nothing excessive. Did a lift pump flow test, is OK, did the check for air in the diesel fuel stream at the pump inlet and return line, no air at inlet, a wee bit at the return, hard to see any without having your eyes about 2 inches from the hose. hope this and the checklist below will help out 1h. Check turbo inlet and air filter for obstructions. Cone filters have lost disk and stopped air to turbo. =All good
1i. In a no-hot start, pour a bottle of room-temp water on the injection pump. Does it start now? yes/no= Starts fine
1.1 Lift pump test (http://dieselplace.com/forum/showthread.php?t=39350)- describe results= good as per GM test-250ML after 15s cranking, flow good up to inj. pump
2. Service Engine Light while running?- on/off/intermittent=off
2a. Service Engine light does glow during start/cranking/bulb check: Yes/No=yes during bulb check
3. Model year=1998
3a. Odometer reading=166,000km (indicate if in miles or km)
3b. Miles on major engine components if been replaced (example Injection pump)40k on inj pump, 10k on lift pump
3c. Indicate the model number on the Injection pump (starts DS4 or DB2......)can't see it, have to look closer
4. Have you scanned for engine codes? (varies by pre/post 96) yes/no=no codes
5. List exact results on engine codes (http://www.dieselplace.com/forum/dtc.php):
6. Air Filter condition (visual check)=new
7. Fuel filter condition (freshly changed/condition unknown/mileage since changed)=new
8. Condition of Battery terminal connections (removed, cleaned and tightened)=all good
8a. Known condition and age of the batteries=6 months old.
8b. Are batteries of differing age or are they a matched set=matched
8c. Condition of Major Grounds (http://www.dieselplace.com/forum/showthread.php?t=157085). (same drill as batt - removed, cleaned, retightened)=all good
9. Upon cold start, does the radiator hose get hard quickly? Yes/no=no
10. Upon cold start, do you have excessive white smoke? Yes/no=no
11. Do you have excessive cranking time before the engine starts?=no
12. Have you used the block heater, and does this effect engine starting?(only try for starting problems)=starts within 2seconds, no heater
13. During hard acceleration, do you have excessive black smoke? Yes/no=no
14. Do you have any unusual exhaust smoke issues?=no
15. Turbo check out (http://dieselplace.com/forum/showthread.php?t=39368)- pass/fail=turbo fine, had previous cracked vacuum line issue, fixed awhile ago
16. Do you have an EGR on the engine? (An F or an S engine code 8th VIN digit)=no EGR
17. Indicate if you know if it’s a 1500, 2500, 2500HD, 3500, 3500HD=2500.
18. Indicate fuel that you are using: Bio-diesel, #2 Diesel, #1Diesel, SVO/WVO, other=not sure, whatevers at the pump, summer blend
18a. If running a VO (Veggie Oil fuel) setup, indicate details of your conversion (homemade, or packaged system)
19. Are you using any fuel additives? If so, please list=no.
20. Please indicate geographic region you are in: (example: Texas or Canada)=canada
21. Do you have any service history available that might pertain to the problem you are having?=started stalling several months ago, wouldn't run for 2 minutes, changed PMD and that seemed to fix it
22. Please indicate any modifications to the vehicle that might help us diagnose better=bone stock, just moved PMD.
23. Upon unscrewing the fuel cap (http://dieselplace.com/forum/showthread.php?t=42338), do you have a large vacuum formed in the tank? yes/no=a bit of vacuum, yes. tried driving it with cap loose, still jerks
24. Location of PMD/FSD (http://www.dieselplace.com/forum/showthread.php?t=39436)? On the pump/remoted over intake/remoted out of engine bay (please specify placement specifically)=behind grille
24a. If remote mounted, describe wiring harness (homemade or purchased from a vendor?)homemade, soldered connections, 12 gauge wire
24b. Indicate the location and condition of the FSD/IP grounding wire.=on inj pump
25. Are ALL glow plugs in=glow plugs ok, starts well

got er fixed fellas. Took it to my diesel pump guy, found the poppet closure time was way out of spec, as was the timing. Kinda looks like the last pump changed out on warranty was not set properly by the dealer. Thanks for the help.

More information, MORE INFORMATION...

Is this a fix you can do yourself? How do you set the poppet closure time, or test it for that matter? Mine does the bucking thing at that same rpm area.

unless a person has the scan tool, i think one is captive to a dealer or a injection shop (which i would recommend the injection shop if u know a good one, they seemed to be wayyyy more knowledgeable about the engine, easier to deal with and cheaper than a dealer) From what i understand one needs that scan tool to check or set the poppet closure and the TDC offset. After fighting with this problem for months, it was well worth the money, i was inches from trading it off and taking a beating on it just to end the pain.

Poppet valve is set on the work bench. Pump has to be disassembled.