Hey guys, brand new here but not to forums. Searched high and low, all I find in relation to this is clear fuel pressure issues with codes to match. I don't have those problems, and I'm at my wits end, spinning in circles for 2 weeks now. I'll try to keep it as short as possible, any details you may need and I left out I'll gladly fill in. I'm a fleet mechanic with 100's of GMC/Chevy Duramaxs from 2009-2019, so reference material is not an issue, and we're all stumped.
Got a 2009 GMC 2500 Duramax won't rev over 2k. I'm familiar with fueling issues, and this feels and sounds exactly like a limiter on a gas engine feels like, 2k rpms on the button. Other mechanic said he had it last month, only did it during regen and then it was fine. He replaced cmp sensor and ckp sensor and did an egr job also.
Now it does it all the time, park, neutral, drive, don't matter. No codes. Will throw a ckp code if you lay into this limiter but that's it. Everything on Tech2 checked out except 2 things. #2 balance rate was wonky, and my desired fuel pressure will not go over 13k on it's own. I can command it no problem, but will just dead end at 13k when it hits this limiter at 2k rpm.
I replaced #2 injector, no change. I ruled out exhaust/intake restrictions/leaks, swapped in known good ecm and tcm, no change. Wiggle tested the harness and the main harness failed by the ecm connections. replaced the main harness, no change. Hardlined cmp and ckp sensors to pcm and ruled out the injector harness. I ran it from a bottle and no bubbles, not even when it's bucking. Checked the FPRV, not a drop comes out, not even when it's bucking. I did a injector return test, replaced #8 for slightly failing, and #3 was fubar'd removing the return fitting, no change, and now those 2 injectors AND #2's balance rates are all wacked out. I now change the fuel filter just cause, and find my primer won't harden up. Other trucks I can essentualy stand on the plunger, this one I can push through and keep pumping. I start pinching lines, and when I pinch the fuel pump return right off the pump, the primer stiffens up and holds pressure. I'm not 100% sold at this point as it really doesn't feel like or check out as a fueling issue, so I start off with a regulator. No change, surprise.
Now my boss isn't 100% sold that it's a bad pump, and neither am I for that matter. My gut is telling me a check valve in the pump but all signs are steering me away from a fueling problem, mostly because of it's consistency at 2k rpm. You can sit at 1950rpm right as rain, then it hits a wall the second you touch 2k. We discovered that if you disconnect the cmp while it's running then try to do it, it shits down dead at 2krpm. Doesn't flutter, doesn't break up, 2k rpm, thump stall. Not sure what this means, but more reason I don't feel it's a pump with no answers. We have even scoped the cmp and ckp cause we came across the drive gear pin shearing issues, and we didn't see anything to say for certain the pin sheared.
We don't have a vacuum gauge, and i'm not even sure if it would help me here. I would gladly buy one but don't even know if it would help, truck starts up right as rain, even with the fuel primer staying soft.
Any input or help is greatly appreciated. My next orders are to tear down the front of the engine for visual inspection of the gearing, then do a pump on the way out, but if I can nail this down before I go in would make my day.
Got a 2009 GMC 2500 Duramax won't rev over 2k. I'm familiar with fueling issues, and this feels and sounds exactly like a limiter on a gas engine feels like, 2k rpms on the button. Other mechanic said he had it last month, only did it during regen and then it was fine. He replaced cmp sensor and ckp sensor and did an egr job also.
Now it does it all the time, park, neutral, drive, don't matter. No codes. Will throw a ckp code if you lay into this limiter but that's it. Everything on Tech2 checked out except 2 things. #2 balance rate was wonky, and my desired fuel pressure will not go over 13k on it's own. I can command it no problem, but will just dead end at 13k when it hits this limiter at 2k rpm.
I replaced #2 injector, no change. I ruled out exhaust/intake restrictions/leaks, swapped in known good ecm and tcm, no change. Wiggle tested the harness and the main harness failed by the ecm connections. replaced the main harness, no change. Hardlined cmp and ckp sensors to pcm and ruled out the injector harness. I ran it from a bottle and no bubbles, not even when it's bucking. Checked the FPRV, not a drop comes out, not even when it's bucking. I did a injector return test, replaced #8 for slightly failing, and #3 was fubar'd removing the return fitting, no change, and now those 2 injectors AND #2's balance rates are all wacked out. I now change the fuel filter just cause, and find my primer won't harden up. Other trucks I can essentualy stand on the plunger, this one I can push through and keep pumping. I start pinching lines, and when I pinch the fuel pump return right off the pump, the primer stiffens up and holds pressure. I'm not 100% sold at this point as it really doesn't feel like or check out as a fueling issue, so I start off with a regulator. No change, surprise.
Now my boss isn't 100% sold that it's a bad pump, and neither am I for that matter. My gut is telling me a check valve in the pump but all signs are steering me away from a fueling problem, mostly because of it's consistency at 2k rpm. You can sit at 1950rpm right as rain, then it hits a wall the second you touch 2k. We discovered that if you disconnect the cmp while it's running then try to do it, it shits down dead at 2krpm. Doesn't flutter, doesn't break up, 2k rpm, thump stall. Not sure what this means, but more reason I don't feel it's a pump with no answers. We have even scoped the cmp and ckp cause we came across the drive gear pin shearing issues, and we didn't see anything to say for certain the pin sheared.
We don't have a vacuum gauge, and i'm not even sure if it would help me here. I would gladly buy one but don't even know if it would help, truck starts up right as rain, even with the fuel primer staying soft.
Any input or help is greatly appreciated. My next orders are to tear down the front of the engine for visual inspection of the gearing, then do a pump on the way out, but if I can nail this down before I go in would make my day.
