I have a 2008 f250 2.5"lift, trutrac rear diff, 12v cummins zf6 south bend duel disk clutch, 160 pump, rebuilt engine, arp head studs, Dap 5x12 inj, Hamilton tow/ef cam, manton HD pushrods, 4gsk w valve springs, torktex adjustable return valve and snubber, pre boost elbow, 3" dp to 5" straight exhaust, bhaf, afc adjusted, fuel plate ground down to a 10, engineered diesel aluminum freeze plugs, 3" intake horn, gauges. I previously had a worn out 12v w a 180 pump with a bunch of blow by and low power so I rebuilt another engine and added studs, injector's, and cam and it didn't change much at all besides cooler egt and better mpg. My problem is no low end power both 12vs in this truck feel like my 01 f250 with a 5.4 gas engine. Truck struggles to pull my 7k pound camper. I can't even spin the tires without reving up and dropping the clutch. I have to ride the clutch a good amount just to take off in first gear. once I'm about 1500 to 3000rpm it runs fairly good and will pull 30+psi fairly easy, turbo spins freely and feels nice and tight play wise. Iv pressurized intercooler tubes from turbo to intake with no leaks. I have new fuel filter and lift pump and cleaned heater screen. Digital fuel psi gauge jumps around but usually stays around 20to 35psi under wot. Iv also seen it jump between 5 to 65 psi but I think the snubbed valve ain't the best. Iv adjusted the AFC to where it chugged smoke and to no smoke, right now I have it at a good haze but still just no power. I'm out of ideas please help. Iv read and done tons of homework but I'm out of ideas besides going to a fasts fuel system and adding twins.

 

How fast does it build boost from 0-15psi? If it builds like 7 psi then kinda hangs there a little until motor revs pick up then starts building boost a lot faster then your starwheel could be too tight or your smoke screw isn't far enough in to close the gap between preboost and when the AFC spring takes over.

Also what is your timing set at? Too high/too low can cause power problems on bottom end.

 

Thanks for the reply It takes a sec or two for the boost to kick in but then just climbs straight up and I have no clue on the timing of my old engine but I timed my new engine to 16 degrees or at least I believe but I'm thinking of pin timing it back to stock to verify I didn't mistakenly regard the timing I just know between my old and new engine I barly seen any improvment. Iv been messing with the preboost screw and star wheel to get the most power without putting out alot of smoke. But my trucks still just a dog off the line. Could I put out tons of black smoke but still have almost no fuel psi? I am new to the Cummins world and not sure if its just me cuts iv never ridden in a good running truck with a Cummins and always heard there torque monsters but just to get rolling in my truck with all my mods I feel like in driving a small gasser. I know with my modes a should be around 600+ ftlb to the wheels and it doesn't feel anything like that Iv driven 7.3 and6.0 fords and id say 0 to 15 they would blow me away. if I'm on a steep incline even without a load I use superlow just so I dont ride the clutch to much.
anybody in the stl area with similar mods I can compare my truck to just make sure in not crazy!!!!

 

Also I don't think this matters but I do have to tap the gas pedal to start otherwise it will crank for a few seconds and puts out a puff of smoke. Also both engines did that. Could my delivery valves be worn causing no torque under 1200 rpm

 

The problem you're having sounds more like a fuel delivery problem than a fuel supply problem. Especially if your fuel pressure gauge says you have good fuel pressure.

The having to tap the pedal to start the truck probably has to do more with your idle not being set quite right.

Also delivery valves don't really wear out. There's nothing to wear out that would cause your truck not to have low end torque. Delivery valves just control how fuel is injected, how much to a point and sort of when it gets injected. So I wouldn't suspect delivery valves.

Where is your afc positioned? Is it full forward, all the way back towards the cab, or somewhere in between?
What have you done to your afc? Different spring? Foot grinding?

Hopefully this gets figured out

 

My afc is positioned closest to the front or radiator I did the gourd foot mod and Fender washer but the spring is stock. I also have the mack plug I first had it set up using a regulator and shop air but have adjusted around since then, also my afc is getting it's boost psi from a port on the intake of the head, not sure if that's were it usually gets its psi from. Yea hopefully, If I'm not around 1200 to 1300rpm taking off normal from a stop light I'd kill the engine and that's riding the clutch for about 3 or 4 seconds just to keep it around that range on flat ground. Does that seem about right. I would think u could lug this engine taking off at around 1000 rpm np. I have 3.73 gears and stock tires but there equivalent to 34" my old 5.4 gas with 250000 miles 35x12 tires and 410 gears had more torque to get going. Are my expectations too high for this engine

 

Today I added some diesel kleen cetane booster and shortly after adding it I was going to take off from the light and I noticed I had no power at all cus my truck was smoking the whole intersection out it looked like a truck pull event but I was barely on the gas then it cleared up and took off as normal this is the first time it's done this on the new engine but has done it multiple times on the old engine but only when the air is hot out it never did it below 60 degrees. Engine temp didn't matter. And ideas on that as well.

 

I had a coworker that owns a newer cummins and has owned a 12v as well and his current cummins is a manual and he killed it twice just trying to take off from a stop he said the top end was about right but he couldn't be leave how easy it was to kill. He was thinking maybe my intercooler is too big but it looks equal to the Dodge intercooler. I was thinking maybe it could be clogged so I pulled it off and looked inside and it looked fairly clean, I'm think my next step would to be bypass intercooler. And run it. Do you get and boost around 1000 rpm this low end torque issue is just driving me nuts

 

I got it figured out for the most part I tightened my gov springs 2 clicks I originally had them set at .047 as directions said and now it's way larger gap the that but I have good torque again but still seems like it defuels around 3000 but I'm not to worried about that. I'll work that problem out later

 

OK so since all that iv had my 180 pump rebuilt with 13mm barrels and plungers and gone threw. And that seemed to help alot supposedly it's retimed so when it's pin timed it's set at 13 degrees and advances to 19 under excelleration I also added the afc live for tuning and am now running a he351ve iv raced a few trucks and know I'm good in hp, iv raced a couple 6.4 and 6.7 ford's and won as long as I could keep my egts in check but truck still seems low in torque. Iv had a few people drive my truck and everyone had killed it trying to take off in 1st (not super low) since it doesn't have the torque and have to ride the clutch to get going iv put prob 15000 on since rebuild and still get a 1 inch spot of oil below the breather tube when parking for a while and am thinking my low torque may be do to crappy sealing in the cyls also been getting higher egts. Here's my question would (ok) compression in the cylinders ca use normal hp but crappy torque when I rebuilt the engine i reused the the old pistons with new cummins rings and honed the cyls good. But I'm thinking not good enough and I might rebuild the other engine w new pistons and bore 10 over