TWS

iTrader: (63)

I have a '98 Z28 with a D1SC, FMIC, blower cam, exhaust, etc.etc. Car had dual walbro GSS340's (255 lph each). It was running fine last year and putting down 550 RWHP @8.4 psi. I swapped heads and headers and retuned and it put down 590 RWHP @ 7.1 psi (lost boost due to better flowing heads and exhaust - normal). Anyway, when we tuned it last New Year's Eve, everything was fine. I took it to the track in March and car was breaking up a little. Pulled plugs and they looked lean. Did another pass and noticed my fuel pressure was falling from 60-61 psi to 43 psi (!!) Put it on the trailer and went home.


Since then I have tried multiple things. 1. changed fuel filter 2. changed regulator. 3. installed Racetronix hotwire kit (surprisingly the car ran great without it for years ) 4. Finally, dropped the tank again and removed the dual Walbros and swapped in dual Deatschwerks pumps yesterday thinking that maybe the Walbros were dying and not keeping up when put under demand.

Took her out for a couple "test passes" just now and damn it, the fuel pressure still drops under heavy throttle/boost!

Pumps prime just fine and idle fuel pressure is ~62 psi. Cruising around it is 60 psi. Put my foot in it and it drops into the 40's.

What I noticed when wiring in the new Deatschwerks pumps is that the factory wiring inside the tank from the top of the bucket to the pumps is about 2 sizes smaller than the gauge of the wiring that came with both the Walbro and Deatschwerks pumps. The factory harness that runs to the top of the bucket (external to the tank) looks to be one size smaller than the Deatschwerks/Walbro supplied wiring and the wiring from the plug leading down into the tank is two sizes smaller. I am starting to think that may now be the problem. I may be getting a substantial voltage drop (?). I had checked battery voltage at the battery and then back at the body mount when the factory harness plugs in and voltage was a match, but wonder what is happening further down the line leading to and inside the tank.

My question is are members doing a rewire of the stock wiring all the way from the pumps to the factory harness plug at the top of the bucket?

BTW, I checked for fuel leaks and detected none.

Burken01

iTrader: (88)

Check out my thread from a few weeks ago


https://ls1tech.com/forums/fueling-injection/1679903-10-awg-hotwire-setup-ohm-s-law.html

It's a good idea to change the in tank wiring and the wiring that goes to the top bulkhead to 10 awg to match the Hotwire kit..

TWS

iTrader: (63)

Exactly. That is my concern. I don't know if it's the reason for the problem, but it's an idea I can't get out of my head since wiring in the new pumps yesterday.

Burken01

iTrader: (88)

Yea it can't hurt, and wire is cheap enough

josh414

You can always consider instaling a relay independently ran directly to the batt and using the factory pump wiring as the signal for the relay. thats the configuration we utilise in almost all external pump systems. That way you are able to retain any built in safety features such as inertia swich cuting the power in the event of impact.

Burken01

iTrader: (88)

That's what a Hotwire kit is that he Installed, still didn't fix his issue..

josh414

now I see that

Old Geezer

iTrader: (3)

If the wiring size was to blame, I'd think the issue would have been there, from the git/go.

Burken01

iTrader: (88)

Unless wire is wearing away somewhere, these cars are getting old.. Sad to say because they feel new to me still..

TWS

iTrader: (63)

That's what I am thinking too, which is why it is puzzling.