7845

iTrader: (1)

lets see im having 2 issues and i cant figure them out. first one is my fuel keeps bleeding down. my fuel system consists of..... 2 walboros intank using -6 to a Y block then -8 to a checkvalve to a inline filter then to the speed inc fuel rails. i crossover at front of motor and goes into my Magnafuel regulator [2k hp model] then returns with -6. im using motron 60s. now at idle my fuel psi is right at 55 and 58 at 0 vaccum. now my problem with fuel is i cycle key and i build pressure and lose it as fast as i build it. now if i hurry up and start truck and then use throttle i can get it to run and idle. now if i cycle key and dont react fast enough truck wont start for a few more tries and when it does i ahve to have throttle 100% and then im excessively rich. this doesntmatter if im warmd up or not. my commanded AFR can be 14.7 and still have rich condition after this happens. if i catch it on first cycle of key its fine. my oil is soaked with fuel. today i removed plugs and dissconnected the harness from injectors. i ohm'd injectors and they read 12 ohms. i also cycled the key and installed a plug in 1 cylinder and i noticed some fuel on the threads of the plug. i did other cylinders and didnt notice any on the threads. i wiped the threads clean did it again and got little more on the threads............any ideas on the fuel issue? i was thinking of installing a set of stock injectors into truck to see if pressure stays


other issue is this...... other day was out logging and working on tune and motor accidently spiked to 25psi at 50% throttle, i instantly let off throttle. little later i went for a another log after i made some changes to tune. it hit 19psi at wot in first and i broke the rear end. well i get everything fixed a few days later and i go to drive it and i notice my truck from time to time drops 1in of vaccum and starts to idle funny. it then goes away. well i pull truck in and do a compression check. it reads from 140 to 147 across the board. no oil in coolant no coolant in oil. no coolant on fenders or anything. oil psi still good. also plugs looked good. i pul my fast and notice the floor of it where it had been repaired was cracked again. i guess the spike blew apart the epoxy on the intake's floor. so i swapped to the ls2 intake i had laying around. started truck up had 10in of vaccum. as it warmed up i lost vaccum to 9 again. im still scratching my head on this. well i figured out why i overspiked. Tial 60mm gate springs are rated wrong. installed the 5 psi spring and im seeing 8psi. ok this is livable. so i go out and start tuning again for this intake. first thing i notice truck is rich but with the ported fast tune was spot on at 14.7 for out of boost. i also notice my right bank and left bank was opposite. one was calling for fuel other was trying to lean out. so truck wasnt happy with running out of boost. the W02 read richer then target. i drove some more and logs keep looking rich, no matter how much fuel i pulled i was still rich according to W02. i did get into boost for a short time and seemed fine once inboost after this truck the truck started to idle badly and only at 3in of vaccum. i pulled plugs and did comp test all checked out fine again. motor doesnt smoke, no oil in coolant or coolant in oil. motor isnt noisey, still have good oil psi.. i went to start it yesterday after taking days off and i got it to run again and had to use throttle and had no vaccum this time. today i pulled plugs oncei got truck home and plugs were soaked in fuel. can the vaccum be related to a fuel issue? or soemthing else?


setup is 02 silverado 4.8 with 241 heads. 8.8cr , 230/236 115lsa, PT88, Tial 60mm. when it first was running it would idle with 10in of vaccum. the drop to 9in doesnt make sense but that happend after the motor spiked to 25 then to 19. the 19 was WOT and since has been giving me issues


thanks and sorry for long post but i have no more patience and cant seem to figure this out

7845

iTrader: (1)

update. i used a snap on compression gauge. i did only driverside for now. it read 150, 145,150, 150. seems like motor is in check

OLD BULL

iTrader: (1)

Sounds like you have checked everything out thoroughly. Not sure if the fuel issue is related to the vacuum problem. Could it possibly be that the cam is a little agressive for the 4.8 and vacuum is dependant on rpm? As far as the fuel issue maybe it's the tune. I'v herd horror stories about idle tuning larger injectors. Sorry I couldn't be more help, good luck.

philntx

iTrader: (8)

Running 6-8lbs of boost on a cammed 4.8 motor, you shouldn't require the 60's. Is there a reason you went with the larger size rather than 42's (like what comes with the Magnuson kits. Same boost levels as a maggie)

That might be a starting point.

Is the regulator "boost referenced"

I also agree with Old Bull, you might want to "cam-down" a little for that 4.8

Wheel to Wheel did a stock 4.8 with 42's, a 67 mm inlet Garrett and 8 lbs boost and got 542HP at 5,100 RPM/603tq at 4,500 (engine dyno)

BlackGMC

iTrader: (31)

Have you done a leak down test? Maybe that is the next step...

TXsilverado

iTrader: (19)

fast intake, 60 lb injectors, boost, dual pumps, big cam...all on a 4.8. i say he is getting ready for a BIG motor and is running the small motor during the mean-time getting everything squared away.

krambo

iTrader: (4)

Did you happen to log battery voltage during the cycling of the key-on? How about voltage at the injectors during the same cycling (not cranking)?

7845

iTrader: (1)

i could have truck on charger or not and it still does it. no voltage to injectors and it still bleeds down. the harness is currently unplugged

7845

iTrader: (1)

exactly, thanks!!! all this was to learn and see how much a 4.8 can handle. no need to hurt a good motor

7845

iTrader: (1)

not yet no access to one