before i get flamed lol, i did a search and i only found threads the seem to dead end. even searched on google


specs;
3.4 60*v6
ported irons
crane solid cam(250801)
howards solid lifters
ported heads
roller tip 1.6 rockers
115# closed 340# open valve springs
7747 ecm with 4.3 APAB 5spd bin
4.3/5.7 tbi with 55# injectors
walbro 255lph fp
adjustable fpr at 15 psi
calculated BPC to 94

now the problem. im fresh in tuning so im learning lol. i just got the truck on the road the other day and started dialing in the BLMs, everything looks good around 128. then i started taking the rpms up little by little, eventually got the rpms up to 3500 to 4K and it lost all power and started breaking up real bad, popping out the exhaust and intake. i tried backing off a little timing and adding fuel to the VE adder table. no change. the O2 says its lean but im not sure if its lying to me since the engine is breaking up so bad. engine is brand new, everything is brand new. im not sure if im missing a setting somewhere thats fighting me every step of the way. even read bruce plecan's tuning tips stuff and BMonte's thread too. i set the WOT tps enable to 80% so i can get the blms dialed in the 70-90 kpa range. when i try to punch it, it breaks up alot sooner, like 3200-3400 rpms. i even bumped the fuel pressure up just to see if that would help, same end result. so can somebody tell me what im missing? id really appreciate the help. thanks!!!

 

Check the fuel pressure while under load.

RBob.

 

yep that was it, good call RBob. dropped off to damn near zero as soon as it hit 3500. will grap another pump ASAP. thanks!

 

OK, but it is better to check out the pump/feed in the tank first. It is very possible that the hose between the pump and outlet tube is split.

And, a BTW, I've never known a 255 LPH pump to be able to be lowered to 15 psi on a TBI setup. There is just too much fuel to be bypassed.

This drives the pressure up.

Better off on a mild TBI to use a GM TPI pump, or maybe a 190 LPH pump.

The reason is that at lower pressure a pump flows a lot more fuel. Which can't all be returned to the tank.

RBob.

 

well it makes sense if i was using an in tank set up. this is an 85 s10 blazer that was originally carb'd, so the sending unit never had a pump. i have the in line pump mounted on the frame rail. i took the sending unit out a few years ago before i started it up and the initial inspection looked good. ill check it out again and check to see if theres a break or restriction somewhere in the fuel system. i literally just got it on the road last week, for the first time since i bought it in 2006. engine wasnt in until 2008. the pump started to whine really loud when i started driving it, so i suspected it was going bad. in my experience, walbro's are hit or miss anymore.

 

welp, im an idiot the fuel filter was clogged, replaced it and it runs alot better. thanks for the replies!