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cloudmaster
Senior Member
Posts: 980
Loc: Arrowsmith, IL
Reg: 01-30-02
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 06-15-12 02:11 PM - Post#2237510
So, on a dual-tank '87 model with TBI, how are the in-tank pumps wired? Are there two relays connected to the tank switcher which switch the fuel gauge and the pumps, or do the pumps just run constantly, or is there another thing hooked up off of the in-dash switch?
Anyone got a service manual with the wiring diagram? Wiring the fuel pumps is about the last thing I have to do in my HP Avenger TBI setup (on my dual-tank '85), and I figure that GM probably had a decent idea when they did theirs...
And "yes, I want both tanks" for the healthy 454, followed by "no, I can't run a suburban tank" 'cause my DMI bumper's in the way. 
'71 Malibu: 350/200-4R/3.73 Eaton posi
'75 Elky: 350HO/TH350/3.42 peg leg
'85 C20: 454/TH400/3.73 locker
'95 Caprice Wagon: LT1/4L60E/3.42 posi
'95 BMW 740i: untouched, but a V8
'04 Grand Marquis: 2V4.6/3" pipes/SCT flash |
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 Vaughn
"11th Year" Gold Supporting Member
Posts: 13637
Loc: Colorado Springs, CO
Reg: 08-08-04
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06-16-12 01:33 PM - Post#2237883
In response to cloudmaster
Because running both pumps would be a significant current draw (we know this because there is a relay powering the pumps) - it is more than likely that the power to operate the pump is switched between the tanks. Since there is no more than one relay powering the pump(s), the power has to be switched between the tanks - or at the switching valve.
You can set up two relays to feed the pumps - and then just switch the relay activation wires (less current draw, so switch will last longer) when you want to switch between tanks. If you use the stock GM switching valve to switch between tanks, this will prolong the life of the electrical portion of the switch.
Don't assume that the way GM did things is the most "proper" way of doing things - they did things to save money all the time. Like in this instance - they should have used two relays and switched the relay activation wire at the switching valve, instead of using one relay and switched the main power at the switching valve.
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 gchemist
Senior Chevytalk Moderator
Posts: 20885
Loc: Austin, TX 78748
Reg: 05-09-00
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06-17-12 04:53 AM - Post#2238138
In response to Vaughn
You can find TBI fuel tank wiring here: http://forum.73-87chevytrucks.com/smforum/index.ph...
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS |
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cloudmaster
Senior Member
Posts: 980
Loc: Arrowsmith, IL
Reg: 01-30-02
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06-25-12 09:44 PM - Post#2241371
In response to gchemist
Awesome. Specifically, "http://forum.73-87chevytrucks.com/smforum/index.php?PHPSESSID=vor841m1h6i 6behk979p0htl34&actio n=dlattach;topic=23791.0;attach=19852;image" is what I was looking for.
Looks like they switched directly through the switch at the dash. I'm not cool with pulling the fuel pump power through the dash switch, but I also thought the dash switch was momentary. Since it's constant, that'll be an easy place to activate the relay to power the individual pumps.
Since I apparently only need one pump at a time (which was the biggest question), I can just use 87/87a on a regular SPDT "automotive" relay, activated by either the grey or tan wire on the dash switch. 
Thanks again.
'71 Malibu: 350/200-4R/3.73 Eaton posi
'75 Elky: 350HO/TH350/3.42 peg leg
'85 C20: 454/TH400/3.73 locker
'95 Caprice Wagon: LT1/4L60E/3.42 posi
'95 BMW 740i: untouched, but a V8
'04 Grand Marquis: 2V4.6/3" pipes/SCT flash |
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