I changed some stuff on the truck this winter, among them being the hotside and turbo location. I also added a kenne-bell 17.5v transformer for the fuel pumps (walbro400lph X2).

I've gone from 58psi at idle to 44psi without touching the regulator spring. It's seems to have happened kind of slowly. I can I identify the scan log where it might have started since all of them idled at 58psi before that one and it started off fine and by the end the base pressure had dropped to about 52psi. The next log (same day maybe 30min later) its down to 48-45psi. Next log which is a couple days later (wasn't driving it in between) it now at 40psi at idle... But the 10+ logs before this were all fine. The fuel pressure was consistent.

I feel pretty stupid for not noticing the pressure dropping while I was adding 20% to the airflow table, I didn't make note of it until I literally couldn't make the same boost anymore. But now I'm stumped on the cause. I saw some wet around the sending unit and figured the line to be loose or something and had a leak but I didn't know if it was water or not and could only see it with a flashlight between the cab and bed. So i let it dry in the garage and cycled the key a few times to pressurize the system...nothing dripped or got wet around the area but the key cycle before startup is only 15psi. I didn't idle it again yet.

At some point around this starting I added a PWM signal generator to my alternator and starting having it make 14.8v instead of the default 13.5v I had been getting. But I don't see how that could matter.

It's taken probably 25-50miles for it drop from 58psi to 40psi.

I'm not totally sure but I think I head both pumps running still, they're mounted about 18" apart in the tank so you can kind of hear both independently. Even if one went out, the check valves are still functioning so...could it bleed off from a bad pump?
Maybe the regulator spring was bound up or something and it's righted itself and now settled into a position with less preload? I did add the kenne-bell booster so maybe the extra pressure moved something?
It kind of seems like it's lost about 4psi each day I took it out. Pumps are basically new, <3k miles.

Thoughts and suggestions appreciated.

 

Since really th only thing you did that would effect it is the kb boost a pump bypass the bap and see if the pressure comes back. Double check your electrical connections at the bap. I've seen cheap crimp connectors cause a voltage drop. So check voltage going in and coming out of the bap with the fuel pumps pumping. Also check grounds. That's where I would start anyway.

 

^^^ this , grounds are just as important as power in , check voltage into pumps (as close as you can ) using the ground that the pumps use. Are you making more power than 2 400s can feed at say 13.5 - 14 volts ?

 

The alternator stops making juice at about 5500RPM so the BAP was my attempt at keeping a higher voltage to the pumps when the Alt stopped making power.

I'm not really sure though, it's a VSR 83X75 T4 1.10 on a 5.3 with summit stage 3 and some tube header log style manifolds made for a F-body. 80lb dekas 3/8" feed line to stock rails, aeromotive regulator. Factory truck intake. So I doubt it? It is easily more than Deka 80's can handle at 44psi though on the two pumps. The IDC is maxed out by 11-12psi at 44psi. I was squeezing about 15psi out of it starting from 58psi but once the alt's charging voltage dropped from RPM the most it was making was about 46-47psi fuel pressure. I was hoping to maintain 58psi at 15+psi of boost. It's still run out of the hat of the factory sending unit so I couldn't make the feed any larger.

Connections were all tight when I checked under it looking for leaks but I'll put a meter to it tonight. Maybe the BAP is putting out low voltage or something when it's in input voltage mode.

 

So I took the voltage to the pumps and it was exactly what ever I set the PWM to make it put out. I then bypassed the hobbs switch for the BAP and made it put out 17.5v. You can hear the pumps gain power noticeably when you turn the BAP on. I also cranked down the fuel pressure regulator to try and force some more pressure.

So matter what I did, it would not gain any fuel pressure at idle, it was 44-43psi at 12v and 17v and at both voltages with the regulator spring cranked all the way down.

The bulkhead fitting with the wiring going through is leaking fuel up through it like the tank is pressurized so I'm now assuming something in the tank has let go and I'm spraying fuel around in there. So out comes the tank tomorrow.

 

Have any exhaust/hotwire near a fuel line or is it possible the pumps are overheating the fuel?

 

There have been quite a few threads on the alternator/rpm problem. IIRC the fix is a good original gm alternator or high quality reman and /or slowing the alternator rpm with a bigger pulley . I haven't had these issues but I only spin it to 6000 , the bigger pulley would be my first choice but what you're attempting should work although more complex and expensive. Sounds like you are probably correct about an in tank leak

 

If filters are clear and reg working, sounds like pump supply issue. Never hurts to measure dead head pressure to know what pump(s) are capable of. Additional info - measure fuel volume through reg at defined pressure (idle and boost referenced) i.e. Measure flow out return with reg oulet capped.

 

It ended up being a bad hose connecting the pump to the hat. I replaced it and just left one single 400lph pump in there because the way I had the two rigged up was pretty sloppy. It's working great now.

At 12v before it couldn't even make use of the referenced regulator. Now I build all the way up to 75psi and the injector duty cycle is down to 50% at 19psi...on a single pump. I'm happy about that.


I'm getting some back firing in the exhaust at higher boost levels though, 17psi+. The reference making the fuel pressure climb so much made it a lot richer, and I've retuned it several times now. But it's not liking making RPM under 17-19psi past about 5800.

I'm not sure if the new setup just likes a different AFR than last time which was 10.9. Seems to sputter on it. But I'm only running 90 pump and water/meth.

 

Maybe try tighter plug gaps just to rule that out?

 

I added a 5gph nozzle in addition to the 10gph for the water/meth anticipating having more fuel for more boost. I had that sucker maxing it's ramp in rate at 15psi. The same setting I used on the single nozzle. I started setting the ramp from 9psi-15psi to 9psi-17psi, then 9psi-22psi and I'm going to try 9psi-30psi tonight. It's progressively getting better and better. Just too much water/meth I think.

 

I think you're on the right track, too much water will put the fire out. Did you get it dialed in ?

 

I need to gap the plugs like you were saying. I got it dial enough that I can adjust the boost right the point it starts and it starts doing it at exactly 16.8psi. The plugs are Br7's and they have the gap they came with, they are blowing out... The extra water/meth was making it worse though and with both nozzles going it would blow out at 15psi, gets about 2psi more with just the one nozzle on. So this weekend I'll pull and re-gap them. I have to remove the waste gate and maybe even the down pipe to get the back plugs out of the passenger side. Kind of a pain in the ***, also makes it so I can't check plugs at the track on those cylinders...

 

I feel your pain on changing plugs, esp my #8-I tried building in room during the install, but the pipes gotta go where they gotta go, lol. One thing I found that helps, they make a 5" plug wrench, who knew, slide it on, 3/4" open wrench, helps.

 

Whole damn manifold, turbo and down pipe had to come out to get the passenger side ones out. It only takes me 30min to remove that stuff and 30min to put it back on but I won't be checking the plugs on that side at the track anymore lol.

 

plug gap from .0028 to .0020 and two plug wires were burnt and grounding...it runs like hell unleashed now at 24psi.

 

Great , were you able to do something to prevent the replacement wires from getting burned?

 

there must have been a crap batch of submersible hose last year. ive fixed 3 this month. thank goodness for the crinkly straw things walbros ship with now

 

New routing and a heat sleeve. Trouble is I have normal wires for a truck 5.3 on the drivers side and LT1? plug wires for the passenger side that are longer and meant to go to a distributor. I need to find some that are like the factory ones but with a nice angle off the plug cap instead of the straight style.

 

You should be able to make what you need for the passenger side from a cut to fit set with the boot angles you need. Could also put angled boots and terminals on your current wires, msd used to sell boots separately or you could probably source them at a JY . Seems like a lot of boost on 90 octane, gives me a bit more confidence in my sbe