Re: ls1 swap question fuel tanks
 

Here is a copy from the 87 Factory Wiring Manual , It shows the wire you are talking about (circuit 490) is a switching wire back to the relay and then conects to the "ECM" (engine computer).

I will include the wiring to the "Tank Switching Valve" which show the circuit back to the sender/Fuel Pump

I know these diagrams can be hard to follow , take your time and follow the circuit number.

Hope this helps you out...

Deserthttp://i185.photobucket.com/albums/x...lpumprelay.jpg

http://i185.photobucket.com/albums/x...ingharness.jpg

http://i185.photobucket.com/albums/x...pumpwiring.jpg

Re: ls1 swap question fuel tanks
 

does that mean to get the switching valve for '87 sending units to work i'll need the ecm for an '87 also?

Re: ls1 swap question fuel tanks
 

So if I am following this correctly here, the switching wire in the 2006 harness from the PCM would take the place of the red wire (circuit 490) at the OEM relay?

Usually, when these harnesses and reworked, the fuel pump switching wire from the PCM is wired in to a relay, then from there you are to connect it from that relay to the pump. So it looks like I would remove the relay from the reworked 2006 harness (or just not have them install it) and hook that switching wire to the original relay on the firewall.

Thanks for the drawings! The middle one is hard to read though, I'll see if I can blow it up a little.

Re: ls1 swap question fuel tanks
 

If you decide to stay with the original powerplant, I would say no since you would likely keep the manual pump. Yours is already set up to switch tanks from in the cab, just not to power in-tank pumps.

If you do the LS swap, that PCM will have the switching wire (that signals the relay to turn on) already in the harness. But you would need to configure your truck harness to turn on the proper pump for whatever tank you switch to. You could ether do it using the schematics above, or just get the wiring from an 87 donor truck.

Re: ls1 swap question fuel tanks
 

i understand. i didnt think the new ls harness would have a switching wire for some reason... so i'll need an '87 harness that goes from the plug in the firewall to the sending units to the switching valve. that would probably be the cleanest way rather than wiring the pumps myself?

Re: ls1 swap question fuel tanks
 

Yeah, if you can find a donor that would be the best route.

I don't know if you have this link or not, lots of great LS wiring info!

http://www.lt1swap.com/2000harness.htm

Re: ls1 swap question fuel tanks
 

whoa, thanks for that Bob! that is a good one... saved!!

Re: ls1 swap question fuel tanks
 

Thanks for the drawings! The middle one is hard to read though, I'll see if I can blow it up a little.[/QUOTE]

If it will help you I can rescan the "ECM" wiring and repost it?

Desert

Re: ls1 swap question fuel tanks
 

One thing to note on the 87 TBI setup the sending units are plumbed with a return line from the factory.

What would you use for a Fuel Pump in a "TBI" style sending unit? Does a WALBRO pump go high enough to feed an LS1?
I know their working pressure is like 5 times what a Throttle Body setup needs.

Just trying to get my head around this swap...

Desert

Re: ls1 swap question fuel tanks
 

Nah, don't worry about it. I was able to blow it up enough. I won't be using much wiring from the TBI harness anyhow as a lot of it will be coming out.

Having the TBI sending units in my truck already is helping me to save money. :metal:

I'm using ACDelco EP381 pumps. It's what GM recommends in their LS1 swap manual, and is what S&P uses in-house on the swaps they do. Also, I haven't been hearing much good about the Walbro pumps since Walbro sold their pump unit. That, and the Delcos are inexpensive and are readily available at most any parts store.

Re: ls1 swap question fuel tanks
 

What is the working pressure on your LS1 setup? Do you need to switch it all over to braided lines? or can you use high pressure rubber with good clamps?

Desert

Re: ls1 swap question fuel tanks
 

Still gathering parts right now. I've seen people use the high psi line all the way forward, and braided too, but I am going to use the original steel line for the most part. It's there, and it will save $$.

Plus, it's 3/8", I can tap the filter/regulator into it easily along the frame, and it exits up at the engine in a perfect place. And I won't need the return line so I can remove it all together from the engine to the filter/regulator. From there back to the tanks, I will replace all the rubber lines with high psi hose.

Re: ls1 swap question fuel tanks
 

at least 58 psi. to 60.

Re: ls1 swap question fuel tanks
 

great thread! thanks all!

Re: ls1 swap question fuel tanks
 

Doing an ls swap in an 87, with dual tanks, and a procharger. Anyone know where to find a fuel selector valve that will handle up to 90lbs of pressure?

Re: ls1 swap question fuel tanks
 

* AC Delco EP381 in-tank pumps. $69 each at http://store.getgmparts.com/fe0114.html
* Pollak high psi tank selector valve, this is a direct OEM replacement (JC Whitney p/n ZX812705U) $83
* Fuel selector switch from an 87, replaces existing dash switch (AC Delco p/n D7089C) $11.50 at rockauto.com
* Corvette filter/regulator if running a returnless/1 line system (WIX p/n 33737) $34 at rockauto.com
you will need the Pollack switching vavle

Re: ls1 swap question fuel tanks
 

Ep381 pumps will not produce enough fuel flow/pressure for a procharger. Also read in previous posts that that pollack valve only handls 60 psi???? This would all be great with "stock" LS engine swaps.

Re: ls1 swap question fuel tanks
 

Does ProCharger actually suggest 90lb fuel pressure? Which kit are you talking about?

Re: ls1 swap question fuel tanks
 

The person that is going to do the tuning/dyno when the truck is finished suggested 340lph fuel pump supply which produces 90psi. The procharger is a D1SC.

Re: ls1 swap question fuel tanks
 

Wow-thats some serious fuel pressure!