This just started in the last 200 mi or so... on WOT or even about 70% throttle, the ally seems to be calling for an extended defuel at 2-3 (and maybe 3-4 to some degree)The power cuts out instantly to nothing and it doesn't want to shift unless I back off. Under normal accel the truck drives flawlessly, but merging or uphill hauling is problematic. I did oil/fuel/fuel filter changes withing the last 1000 mi. The trans fluid was within a quart of max, appears new and smells fine. I did full fluid and spin-on 35K ago.
The truck gets driven pretty easy - only using the power potential for merging or occasional towing (no burnouts or drags). :confused:

That usually means it's not getting enough fuel and isn't a trans problem.

That usually means it's not getting enough fuel and isn't a trans problem.

I'm having very similar problems with my '05 gasser (8.1l). Fuel pressure is showing 56-58 at idle and 54 key on engine off. It does seem to have some trouble holding prime, it bled off 8lbs in under 2 minutes while I was watching it.

Would you give the same advice about my truck?

Saratoga, A fuel issue could be anything after the CP3 (as I'm not losing prime), or an obstructionanywhere on the system (blocked filter)?

That would include filter, CP3, injectors or a command problem?

FWIW, no codes at all... Also, I confirmed today that it occurs on stock power levels as well as the tuner.

Thanks

For what it's worth mine proved to be the fuel pump. Pressure was good at prime and engine idle but with the fuel pressure gauge on you could see a huge drop in pressure when someone jumped on the go pedal. It swung down from 58lbs to 40! :eek:

No CEL / SES lights or codes either. :confused:

I'd check your fuel delivery pressure, both the static test that everyone does and test with someone hopping on the accelerator.

Oh, and I had someone explain to me WHY the low fuel pressure / volume causes the shifting issue (mine was doing this as well), here is what they sent to me:

"“Filter plugging, Fuel starving, Fuel rail pressure doesn't come up to match demand of the throttle pedal. ECM picks up the problem, *limps engine* to stop farther damage, flips a P1093 code and limits engine RPM to 2000, not always a CEL.” (CEL = check engine light)

Then you jump on the go pedal, the TCM picks up that high RPM is needed and holds the shift until somewhere over 2500 RPM.

BUT.....the ECM is holding the max engine RPM at 2000, it never shifts.

Lighten up on the throttle and you can sometimes get the trany into 5th (60 MPH) and keep the engine below 2000 RPM to get home on.”"

sounds like a good place to start. I think I'll swap out the fuel filter and check for codes to begin, then go on to the FP testing. Thanks!

On a ally diesel, low fuel rail pressure may not set the CEL. The codes will be stored in history. A restart will clear the code from active memory to history. Not all code readers will see the code.
Better readers or a Tech2 should see it. Maybe a P1093, low rail pressure. You throttle up and stop the up shift to higher RPMs that are not there because of lack of fuel.

Fuel filter swap cleaned it up (the easiest, cheapest of all possible fixes?.. I didn't know that I was living that good a life!) FWIW, it was a Wix/NAPA Gold, old-style and had ~3000 miles on it. Every gallon of fuel was out of the same pump... I must have got some diesel at the wrong time:( Thanks for the assistance:)

im having this exact same problem. I am over due for a fuel filter change now anyways, so hopefully by changing it, i get the same result as you. I can't pull out in front of traffic right now cause i top out in second gear and can't get any more gears to come in. Fluid is red and smells brand new, no codes what so ever, hope this solves it. I am going to change the filter tonight for sure.

im having this exact same problem. .......... I can't pull out in front of traffic right now cause i top out in second gear and can't get any more gears to come in. .

Keeping it floored it will not shift:(.
Lighten up on the power, don't push it over 1800 RPM, let it shift into high gear. You limped it floored, change the fuel filter:D. What more can I say.

I was having the exact same problem with my '03 and luckily I came across this thread! New fuel filter solved the problem :-D This forum rules, life is good with a healthy D-max.

Yup, I had the same problem back some months ago. Changed the fuel filter and problem disappeared instantly.