chief455

95 LT1 383 D1SC 60lb inj, 10psi pullies racetronix pump/wire, aeromotive boost reference regulator

bought the car this way, solid build, dynoed 560rwhp in 2005
swapped in new walbro b/c lost fuel psi and car died
now it runs awesome except under WOT and boost sweeps up to 10psi
fuel pessure stays at 38psi - does not rise WITH BOOST.
had a stumble during a WOT blast, saw the fuel gage dip to 20psi and let off.
returned to 38psi, car still runs hard - but push it flat out seems it stumbles and drops fuel pressure for an instant - so I stopped not to go lean.

ideas?

Kevin Blown 95 TA

Not enough fuel pump volume, low voltage at the pump, or a plugged filter or other lack-of-fuel-for-some-reason problem

chief455

I was thinking same thing
I wonder if this set up always had the issue

think a Walbro 255 and the racetronix hot wire kit can supply my 383/10psi boost?
what nominal psi should be good for fuel pressure? low 30's cruising, 38psi under load seems like low pressure to me??? although - could be the same issue as the WOT

I'll get the filter changed then keep checking

Kevin Blown 95 TA

Whatever you set your fuel pressure at initially (vacuum line off), say 38psi, it should go up pound for pound with boost. So if you have 43 psi at WOT normally aspirated or 0# boost, then you want 53psi at 10# boost or else you could run lean. Don't forget when your intake manifold is at 10 psi, that pressure is working against the 43 psi in the fuel system as the injectors try to squirt the fuel in there. Your one pump may work up to some level, then it can't supply enough volume past that point.
The Aeromotive regulators that mount on the fuel rail in the stock position, weren't the best regulators and probably not as good as the stock ones, but that doesn't sound like your problem although you would have to test it with a Mityvac that has pressure capability or some other pressure source to verify that it is working the way you think it is.

roguedriver

Sounds like a lack of fuel volume. You probably need to go with a dual pump setup vs the single. Usually if your not increasing psi or even dropping, its running out of fuel. Your injectors should be able to hang with that setup, but i'd be running dual pumps.

Ken R.

chief455

good advise guys thanks

UPDATE: I do not have an aftermarket pressure regulator.

On the rear driver side fuel rail is a factory looking diaphram with a vacuum source.

What I saw on the pass side rear rail is a source to the fuel pressure gage.

I got a receipt in the folder for an Areomtive regulator - but it's not here.

No FMU from Procharger either -

Soo.. D1SC pulling ~ 10lb boost at WOT with a racetronix walbro pump and hot wire kit.

that explains why fuel psi does not rise with boost, correct?

stop driving until I get a boost referenced regulator to pull more fuel psi under boost?

really play it safe and get the twin walbros and a regulator before I apply boost again?

I can't believe they built the car like this - it dynoed 560rwhp after the fuel pump install - I bet it never ran on the street under boost without this isue I'm having though.

how much danger am I in - with the stock reglator, 60lb injectors, the walbro and the pcm is tuned, the car runs real good until the lack of WOT thing occurs.

Kevin Blown 95 TA

Not entirely correct. your problem seems to be volume, not regulation and the stock regulator should work. You don't need the FMU with big injectors, you need more fuel pump. An alternative that might work is a boost-a-pump which jacks up the pump voltage. Otherwise you need to think of adding a second pump and you could turn it on with a pressure switch or other device.

chief455

HMMM...twin walbro 255 pumps are on my $$ list, but i had boost referenced regulator first.
You make sense though - can't regulate fuel that's not there b/c I ran out!

I heard of the 16v boost a pump deals but I think I'm too far on the needing more fuel side of the fence = another pump needs to come first..
If you don't mind - what are you using on your 383??
thanks for helping me think through the issue..

Kevin Blown 95 TA

I have two pumps on the sending unit. I reworked the sending unit completely, though. Where others simply tee'd the two pumps together, I redid the hard lines with larger tubing. I ran separate lines out the sender to a filter, then a larger line up front and a Y then to the back of the fuel rails then a magnafuel regulator, then back to the tank. I used some teflon/braided lines. Here's a couple pics of it, anyway. I have more if you ever decide to do something like this. Other guys get along with much less than I have, though. they are using stock lines and just went the twin in-tank pump route.

chief455

beautiful job!

I just can't afford the big lines right now, I invisioned the same pump mount and wiring on my sending unit - just using a y-fitting and the stock lines.
Another $110 pump, $60 hotwire kit, $25 Hobbs switch and an afternoon plumbing it onto my existing single pump unit. I will nt get an aftermarket regulator yet based on your replies.
thanks for sharing.
you have the return line just dumping into the tank, yes?
How low have you run the tank on gas and how old/ miles are on the set up?

Injuneer

Are you using the standard pressure Walbro, or the high pressure Walbro? As the pressure rises, it's normal for the volume of fuel the pump can move to go down. The high pressure pump doesn't lose as much volume as the pressure rises.

Kevin Blown 95 TA

The return fuel line is that black hose that ends right between the pumps, so it kind of drains over them. It has been up for at least 3 years, but only a few thousand miles. I did set up the pump wiring so that I can switch connectors to make the secondary pump the primary.
There's no sense in spending $60 on a second hotwire kit.

chief455

so - you just ran your own red wire from second pump - from sending unit to alternator power (or hobbs switch?) - tucked into the same plastic shielding? no second relay or anything??
can you show me how you set up the wiring? that is the third time I've heard switching primary pumps. I have an idea but would like to see if it's easy for you to show - pics or diagram. thanks - you're helping alot.

I'm not sure - said to be high pressure from a vendor on the site.

MikeGyver

You need more fuel pump (or fuel pump voltage).
That's exactly where a walbro with a hotwire kit will run out.

Kevin Blown 95 TA

I put two relays in back, one for each pump. One relay is controlled by the fuel pump relay, the other is controlled by the WOT & manual switch. There are two identical connectors coming from the fuel pumps & the relays, so I can switch them every year or when ever I feel like it.

I completely replaced the stock in-tank wiring so that it doesn't go through that *hitty little yellow connector. I ran 14 ga wires through the sending unit and made a separate large gauge ground which you can see in the pics. I have a big wire feeding the fuel pumps/relays, coming off the alternator.