Zee man

I am swapping a 98 ls1 into my 94 z. I know the fuel system is different, higher psi and regulator in the tank on the 98. But even worse there are 2 plugs and 9 wires on the 98! The 94 tank has 3. I am not sure what to do from this point. I cant find any info on this part of the swap.
Also the 94 fuel lines didnt survive removal. So I need to use the 98 fuel lines.
If anyone has done this swap has any info I would appreciate the help.

Injuneer

The second connector on the 98 fuel pump sending unit is for the tank (not pump) pressure sensor. That is an OBD-2 system, that you may or may not choose to install. I would assume you are using the 98 PCM. Are you planning to delete any of the OBD-2 diagnostics? The 98 has codes related to tank pressure.

The fuel level sensor wires are black/white (ground from PCM) and purple (signal t PCM). The fuel pump wires are gray (12V from fuel pump relay in underhood electrical center) and black (ground from ground distribution). The tank pressure sensor wires are orange/black (ground from PCM), gray/black (5V reference from PCM), and dark green (signal to PCM).

You should download the 94 and 98 factory manuals to help you out.

LINK: 4TH GEN SERVICE MANUALS; 82-02 PARTS DIAG; 99-02 WIRING DIAG - Firebird Nation

The differences are significant.

-94 system operates at 43.5psi (3 bar), and is vacuum compensated. 98 system operates at 58psi (4 bar), and is not vacuum compensated. The LS1 PCM A/F tuning will be based on non-compensated (constant) fuel pressure.

-94 system is recirculated... line from pump to fuel rails, pressure regulator on the rail outlet, return line to the tank. 98 is a dead-ended system, with the pressure regulator back at the tank, and a single supply line to the fuel rails, no return line.

-You can change the LS1 to a recirculated system, using the fuel rails from a 97 Corvette LS1. Or buy aftermarket rails. Nothing to be gained doing this, unless you are going to a very high HP setup.

Zee man

You have the crux of the problem. I had wanted to keep the evap functional but that is not going to work. So, the new plan is to remove the pump and regulator from the 98 tank and install it in the 94 tank. this way everything is plug and play as long as
1) the lines plug in where they are supposed to
2) the 98 pump will fit into the 94 sender unit.
This way I can run the vented cap on from the 94 and the electronics will play nice.


My backup option is to delete all the stuff I cant use on the pigtail from the 98. Rewire the pigtail to work on the 94. and figure out a way to vent the tank.
I like option #1 best of the 2

Injuneer

94 does not have a vented cap. System is vented through the charcoal EVAP canister.

Why not use the larger, lighter plasric tank from a later year LS1 car?

GaryDoug

Just in case this helps, here is a photo of my 98's fuel filter, supply line, and return line from/to the fuel tank. I presume the short return line is to provide the in-tank regulator with the post-filter pressure (?).

Zee man

Not vented? Well it'll just continue to be vented through the charcoal canister then. I could of sworn I read it was a vented cap..... Oh well....

I would use a plastic one if I had one but the tank from the 98 is steel also. I cant continue to throw money at this opti spark fix, lol.

Zee man

Thanks Gary, wouldnt that also work as a return line? I was thinking it was just a return that wasnt run all the way to the fuel rail.

Zee man

So if I delete the evap function, should I even bother putting the line in place? There wont be a pressure sensor to tell the pcm anything. I suppose I could just put it in to plug the lines, rather than leaving them open.

Injuneer

The 94 and 98 are similar, in that the vapor leaving the tank passes through the canister, where the canister carbon adsorbs the hydrocarbons. Then a stream of air is pulled through the canister, pulling the hydrocarbons into the engine. Both work the same.... it just appears the control system is different. They both appear to have a purge solenoid that is activated by the PCM, but the 94 is very simple, operating the valve solely on engine parameters, with no reference to the canister or tank pressure. The 98 appears to be a bit more sophisticated, using input from the tank to control the purge. The canisters are also quite different - see last comment below.

I know the 98 has a metal tank, that's why I said "later year LS1 car". Used plastic tanks should be available on ebay.

Are you aware that you can totally eliminate the Opti from your LT1 engine, using the 24X conversion from EFIConnection. Your 94 would be operated by the LS1 PCM, and use the 8 coils from an LS1.

EFI Connection, LLC - EFI Connection 24x System

And then there's the Bailey Engineering LTCC system, that only uses the Opti optical cam position sensor to feed a small processor, that fires 8 LS1 type coils. Getting the high voltage function out of the Opti eliminates the problems. I've been running a 7,400 RPM stroker for 14 years using a system similar to the LTCC , and the Opti is flawless, providing an extremely accurate cam position signal, for the ignition timing and injector timing. The engine has actually turned 8,000 RPM (don't ask why) with a reliable cam position signal.

Bailey LTCC setup

The outlet of the filter goes to a "tee", and that allows excess fuel to return to a bypass style fuel pressure controller on the sending unit. The "tee" send surplus fuel directly back to the tank/regulator, and the required fuel forward to the rails.

You already have supply and return lines on the 94. Use the stock supply line to run from the filter to the engine compartment, use an aftermarket bypass type fuel pressure regulator at the rails, and use the stock return line to return excess fuel to the tank.

There will be a pressure sensor but there will not be the electronic connections to the EVAP canister unless you swap that too. The LT1 canister is very simple, with not controls. The LS1 canister has wiring attached to it, leading me to believe it is controlled in synch with the purge valve at the engine.

Zee man

I read your reply Fred thanks.
I destroyed the original lines removing them. But I was able to use the 98 lines to replace those. Here is what I ended up doing.
I removed everything on the 98 sending unit down to 4 wires. purple, black, black with a white stripe and grey.
purple, signal from the sending unit
grey power for the pump
blackw/white stripe is ground for the fuel Gage
black, is ground for the pump
I ended up combining the 2 grounds on the pigtail and using the 94 plug end , soldered it all up. Looks like it should work.
I am just going to hook the lines up to the evap just to keep bugs out out the tubes, it'll vent through the charcoal canister.
Yeah, I know about the 24x systems, I thought this would be easier for some reason,lol.

Zee man

just an pdate to my fuel system woes. The 98 fuel gauge sender will not work in the 94, it just has the wrong resistance values or some such. So I had to drop the tank again and combine the 2 senders. I cut the gauge sender off the 94 bracket and, after modifying the 98 bracket, I welded the 94 sender onto the 98 bracket. Then I had to swap the ground wire for the added pigtail and change the location of the ground wire in the plug going out of the sender. I also removed the extra ground wire.


That is what I ended up with. A 94 gauge sender on A 98 sending unit. Everything seems to work. the gauge is just as inacurate as a stock unit so I guess I did it right.