Alright guys, new to this forum although i have logged many many hours viewing very educational threads which led me to join to get your help. So to give you some backround info I have had a 99 GMC Sierra with a wornout 4.3 that i dropped a 2006 low milage 5.3 in. I blew the stock tranny and had a built one put in. Last weekend i installed a Magnacharger on my truck. This is where i started having my problems. I took it to get it dynotuned and using the inline pump magnuson includes in their kit and the stock intank pump I was running super lean at 4500+ rpms no matter what my tuner did. We installed a fuel pressure guage while on the dyno and the fuel pressure dropped to 30psi at 5000 rpm. It was running 13 and 14:1 at 5000rpm but just fine at idle and lower speeds. We installed a 255 intank and still ran the inline and dropped the AF to barley 12:1. My tuner was shocked that it was starving for fuel with the dual pumps and 43# injectors. My next step i guess is run a new bigger less restrictive fuel line to the motor? Not sure what to do next, Please help and let me know if i left anything out or have any other questions. Sorry for the long post, just wanted to include as much as possible. I am just hoping the v6 fuel lines are smaller and are too restrictive. My tuner says with forced induction he likes to see around 10:1. I just don't want to melt or blow anything up.

 

Oh also it wont hold fuel pressure at all for more than a couple of minutes. The local guys at AZ TPI who are like the rocket scientist of Fuel injection are puzzled because both of the walbro pumps have a check valve. Do i have a bad regulator or something. Oh and i already replaced the filter first thinking that it was clogged. I have just been babying it around at under 3000 rpm where the AF mixture is safe.

 

How high does the AFR get when it maxes out? It does sound like a possibility that a smaller fuel line could be the issue, but I can't imagine the 4.3 having much smaller of a fuel line because pretty much everything on that engine is a bolt on to the 5.7 as well...

 

What size pulley u runnin?I run a 3.0 and my IDC is at 95%.You may be max out your injectors with a smaller pulley.Also you should be looking for 11.8 afr not 10.1 as that is too rich and you will lose power and kill cats like that.

 

I am running stock pully that comes on the maggie although i would love to change pulleys but don't want to until i get this fuel thing under control. Not sure on specific numbers but it ends up around high 12 to 13:1. Before the intank 255 it was around 14:1

 

The stock pulley is a 3.6, right? Should be around 6psi on a 5.3
Are you using the stock maggie injectors?
Is this a mp112 or tvs1900?
Whats is the injector duty cycle when it goes lean?

One 255 should be plenty of pump for that setup...and 10:1 afr is way too rich for FI, 11:1 is better, but still very safe.

 

not sure whether it is a mp112 or tvs1900 although i would love to learn what i have and what the difference is. I just ordered the radix kit and yes the 43# injectors that came with the blower. Not sure of the duty cycle but I dont think the injectors are the problem because the fuel pressure drops to 30 psi vs around 50 or 60 where it should be. My tuner did everything he could but the injectors arn't getting the fuel to begin with so even if i had 100# injectors it wouldn't make a dif because they aren't getting the fuel they need.

 

Have you changed your fuel filter?? Are you running the factory FPR on the rail??? I would think that the pump you received with the maggie is plenty for what your doing. Also the line in the fuel tank, going to the orig pump might be broke or rubbed through.. 10.1 afr is really rich.. Needs to be in the 11.8 range.. I would check them few things out before anything else.. Also the lines that was on the v6 are the same size( i do believe ) never heard of them being smaller..

 

Thats not actually correct, as long as there is ANY pressure, it is possible to inject enough fuel, but obviously the higher the pressure the easier it is. Bigger injectors put in more fuel in a given time. However I agree I dont think the injectors are the issue...

Is the blower black or silver? Does it look like a big waffle maker or have a big J shaped tube coming out of the back?

This is a great time to upgrade the fuel pumps wiring to 10gauge to prevent voltage drop...

 

Start by checking the regulator, since it's easiest to get to. Another possibility is in your tank. The line from the pump to the bucket may have come loose. Seen that many times.