it is not a compression problem. the p0148 code is telling you there is exessive fuel beeing returned to the tank. first check the rail pressure.if the shop does not have the equipment your in the rong shop. get a auto meter rail pressure gauge for $150 and set it on the dash. at idle you should have about 5,000 psi drive down the road and you should see up to 20000 under load. if the fca has a problem it usually causes exessive pressure. if you unplug the fca and start the engine it will peg the 30,000 pound gauge. the cascade overflow valve can cause all kind of wierd problems with pressure and return fuel problems. from cummins i think it is $40 just replace it. next go to the leak down test to determine witch component is bad. the prv can only pop off a few times and it will ruin it. if the rail pressure is below 26,000 lbs and you have fuel coming out of it then it has failed. if it failed because of over pressure pops then you must fix the problem before you install a new prv. like i said the fittings is the best way to check but when the cr first came out i just removed the banjo bolt on each and observed the amount of fuel that ran out on the ground

 

looks like i should have checked my spelling before sending but i think you can figure it out

 

wow good info.. i will print this off and take it to him to talk to him about it during lunch.. can you explain more details on the prv and cascade valve on how to test it.. and the leak down test.. the shop i took it for is know for there long history of diesel drag racing to truck pulling over 100 1st place medals in there shop showroom.. and have a 2004 with over 700hp as a shop drag truck... the shop seems to know what they are doing.. but the miss was just so inconsistant that it is throwing them off.. he did monitor rail preassure and if im not mistaken he said it was around 25k under load but i will have to confirm that with him again.. but at idle.. it was only moving +/- 200psi so he said the fca seems to be controlling things well..
I called a few places for my injectors and there is one place that will test them for 25/each but i have to take them out and send it to them..

the P0148 code is kinda intermitting.. it came on in the morning going to the shop.. but went off by the time they took it for a test drive and we drove it so hard trying to get it to go off.. but the code stayed off...

would the cascade valve or prv cause random like once every so 20 seconds misses.. or at certain rpms.. barely slight miss felt?? and cause the excess smoke under acceleration? the truck idles and pulls really hard so i been wiery that its not the injectors.. just thought it be good idea to have them tested with over 500k on them

 

well.. good news today.. even though the rail preassure was showing good numbers.. idling at 5k an rising all the way to 25k under load .... i said screw it... lets start at the most common issue.. the fca and went and grabbed one.. stuck it in.. omg.. huge drop in smoke.. almost back to normal.. took some brake cleaner and sprayed it up in the old one.. and it had this thick black crap come out of the hole in the middle of the sensor.. it still work.. but it was apparently not working correctly.. so... it is running much smoother and much less smoke... i am just wandering were the rest of the smoke is coming from.. im wandering still.. its not perfect still.. i hope the fca preassures didnt screw up an injector.. but the smoke is hardly noticable.. we are going to pull the tank tomorrow and make sure its clean.. then run some strong solvent through lines to try to clean it all out.. if anything is in there.. the thick black stuff bothers me.. cause when i changed the fuel filter a while ago.. there was some of that stuff on it..