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Discussion Starter #1
Hey guys!
I’ve looked at possibly all videos and write ups on the 12v mod. Decided to do it myself. Especially since I have free time from the Corona Virus to do work on the car.

It is a 1988 Turbo. It still has the OEM fuel pump. On all the other forums and videos they seemed to be 89+ Supra’s with all grey connectors. Mine are a clear yellowish and a bright yellow (For the one you mod) If any of that that matters. Will be doing a Walbro in the future.

But anyways, I’ve had three friends work on this with me and even they are scratching their heads. Power is going into the relay and out the ground. But nothing to the actual wires that go to the car. We went through 3 brand new relays. A 4 prong and tried a 5 prong as well.

We also bypassed the relay in the engine bay. Nothing.

In honesty, I don’t know much about electronics or wiring. But there was no resistance/breaks in wiring.

I was wondering if maybe the relays I used require you to not put it into the same numbers as the write ups?

Any help would be appreciated.
 

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Sorry man but why exactly are you doing this "mod" to begin with?

I ran a 87 (from 94-2010) without this mod for 225,000 miles on a Greddy TDO6 turbo without the fuel pump or fuel system causing ANY issues.
 

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Discussion Starter #4
@figgie Honestly, with the corona virus keeping us at home I’ve been doing small work to the car. Mostly cleaning up the engine bay (A/C lines, fuse box, and battery relocation..etc). The relay bypass was one of the last things. Plus I’ve heard it gives a slight boost in power and I’ll be doing a Walbro 255 soon.
 

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Discussion Starter #5
After looking at the relay I was pretty sure the way it was wired up was wrong. I had a friend verify through another friend.

So I tried it:
#30: 12v constant and inline fuse.
#87: Fuel Pump (Black/red)
#86 Connector side (Black/red wire)
#85: Chassis Ground.

Car still wouldn’t start. I measured -12.34 volts from 12v constant to all the other pins on the relay.

When wired the way everyone else’s says to do it:
#87: 12v Constant
#30: Fuel pump (Black/red wire)
#86: Connector (Black/red)
#85: Chassis Ground.

The readings were 0.00 from #87 to #30 and #86. But read +12.34 from #87 to #85.
249759
 

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Well, point blank,

bumping the fuel pressure will not add power.
Adding fuel even in a standalone will not add power UNLESS you are running lean as hell.

Without adding air and with the stock tccs, all it will do is take away the added fuel putting you exactly were you started.

in short, your line of thinking is absolutely incorrect.
 

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man I'm of the opinion the oem wiring / relay / awful resistor setup all needs to go

on my car a 255hp pump was dropping 1 entire volt. 14.6 at the battery, 13.6 at the tank connector. this was after I did the new rivet / wiring in the tank (along with new 255hp pump). also run a deans type (rc hobby style) connector at the tank now.

I replace all that oem mess with 1 new high amp relay, and big + power cable and the pumps got full 14.6 v and is noticeably louder. if thats possible for a 255 lol

the oem computer still grounds out the new relay (just as oem). just the dual speed provisions are now gone. the pump only runs with the engine running. key on/engine off = no pump running (just as oem has it for safety)

I think bigger pumps stress the oem wiring with more amp draw. and also that resistor must just glow with a bigger pump pulling more amps through several ancient connectors

I did all of this instead of adding larger 550 injectors. sort of wanted to max out the fuel delivery setup before going larger inj, im running +10psi over factory spec
 

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Discussion Starter #9
@figgie I’ve got a Lexus MAF laying around with an aftermarket air filter. Along with some 550cc injectors. If those are added along with my Walbro when it arrives I’d still have that issue with the fuel pump not kicking on.
 

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The fuel pump not turning on is a wiring or fuse issue.

Check the tsrm and specifically the TEWD portion and verify the fuses.
 

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Discussion Starter #11
All fuses are working. I actually drove the car today and when wired normally without the 12v relay it works perfectly fine. But I’m pretty sure it has something to do with the way it’s wired. I’ll bring out the old tsrm and verify which wires are which.
 

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Agree on the lack of power increase. The fuel pump on any car has more than needed (generally 20-50% more) and the fuel pressure regulator chokes it down to what is specified at the injectors. So you could double the pump's output and accomplish zippo. Unless your fuel pump is on the way out, in which case your efforts should be to replace that. Be sure your filter is in good nick before messing with pumps and such.
 
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