ol' paddy

I am almost finished with my Lt1 swap in my 92 rs, but im having some trouble with the fuel pump relay.

when i turn the key to run the fuel pump works fine, fuel is getting to the fuel rails and the injectors are getting a signal, it will fire up and then die within seconds. the fuel pump is not running while the engine is. i have the relay wired according to the factory diagrams with

ORN -> Battery
RED ->
GRY -> fuel pump
BLK -> ground
DK GRN/WHT -> LT1 A7

Does that look correct? i havent seen an oil pressure switch on my LT1 before so im not sure if i need to wire one in to the relay?

any help would be great thanks

chevyowner02

iTrader: (3)

That's how I wired mine up, could be VATS?

John in RI

iTrader: (167)

I've got

Pink: Pole '30' on Relay ( HOT in RUN, BULB TEST, or START,
Black/White: Pole 86 on relay (ground)
Grey: Pole 87 on relay (from relay to FP)
Dk Grn/White: Pole 85 on relay (from relay to PCM 'A7')


Power shouldn't not be HOT at all times to the FP relay. The PCM fuse is "switched power" and was the factory power source for pole 30 on the FP relay.

Don't know if the VATS is still active in your set-up but I'm guessing that it could be VATS related. If you've still got active VATS you could check the 'A25' Pin on your PCM for the VATS "Fuel Enable" signal from the VATS module to the PCM (Dk Blue wire).

89rs454

correct me if i'm wrong it's been a while since my swap. The lt1 pcm kills the injectors, so you will need to tune out vats or get a vats delete on ebay for 15$ and it does the job believe it or not i think it's a 15hz signal, and the vats delete on our cars is in the left panel under the dash a yellow and green wire needs spliced together and vats will get got.

89rs454

This may help you this is from my thread https://www.thirdgen.org/forums/ltx-...stock-lt1.html

----------------------------------------------------------------------------------
----------------<<<<<<<<<<<LT1>>>>>>>>>>>-------------
And here is the Guts of the wiring this will get you started and on the road!

c100
PIN A-Power feed from injector fuse 9 going to a switched 12v source
PIN G-Power feed from ignition fuse 11 to a switched 12v source
PIN K-Power feed from injector fuse 10 to a switched 12v source

c105
Power feed from Fuse #10
(injectors 1995/eng sensor 96-97)

c210
PIN A-Starter 12v source to B4 C100 Starter wire(purple)


C220
PIN J-Fuel Pump Relay Control to G4 of c100 Fuel Control gray wire


C230
PIN G-Power feed from ecm ign fuse 5 to switched 12v



And here is the end result.

vetteoz

iTrader: (13)

The pump running is not VATS related
If you had a OP switch wired up and working it would run the pump independent of the pump relay as soon as you have oil pressure when cranking the engine over

The Op switch supplies power direct to the pump , it doesn't operate the relay

IIRC ,
the LT1 uses a 3 wire unit similar to the late 3rd Gens that combines the OP switch for the pump and the OP gauge sensor .You could have just reinstalled your original OP switch into the LT1 and used the stock wiring

vetteoz

iTrader: (13)

Fire up and instant cut off is typical of a VATS problem but he states
" the injectors are getting a signal "
so it is not a VATS problem
Appears the ECM is not continuing to run the pump after the initial 2 sec prime

89rs454

if you want to make sure hotwire your fuel pump up hot and see if it runs if it does the same thing. I'm right?

LT1 Vats will let the engine run for 3-5 seconds, it let mine run for 3-5 seconds i was so happy to hear it run off prime i hooked up that bypass and it idled even with the brake booster vacuum unhooked, which tells me he needs vats tuned out or get a http://www.ebay.com/itm/GM-VATS-or-P...-/281179660936 it's 20$ and all it does is feed your pcm a 50hz signal. A cable to hook up to a laptop is 40$ and lt1 edit is free program.

your choice but that ebay piece does work because i used it for two months before i tuned mine out. Hell i would sell you that for cheap if i could find it, but you will want to tune your pcm at some point that's a fact ol' paddy.

ol' paddy

i definitely appreciate the help on here guys.

the previous owner had done the Lt1 swap in the car before i had it, but i had to rebuild the engine and in the process bought a new Lt1 harness to modify as his was some of the shittiest wiring id ever seen. but the car did run in the past, the vats was bypassed and i do have the yellow and green wires spliced together under the dash, so i think ill try out lt1 edit and try to tune out the vats.

but it is the same PCM that the previous owner used so im not sure how he had it running if it would be vats, because wouldnt it already be turned on the PCM?

89Z28LT1

Hoping to get some info here as well. If I read this correctly, the grey wire at the c100 needs 12v from the relay to run the pump. Is that correct?

John in RI

iTrader: (167)

I would have to say no: I don't know what GREY wire @ C100 you're describing, but the only GREY wire shown on the 89 C100 diagram is for the Wipers.


This is the factory schematic for the 95LT1 fuel pump: You'll have to wire the fuel pump relay into your existing wiring the same way it's shown here. (LT1 harness GREY is voltage out of relay & to the fuel pump.)



Here is the C100 schematic for the 89:

89Z28LT1

I got the information for the grey wire from this diagram below and from an earlier post. Please see screenshot. Can you tell me which wire is the power wire to the fuel pump?

89Z28LT1

Sorry, I didn't see the third gen c100 diagram before my reply, looks like I need to hook my power to tan/white at g4. Is that correct? I have applied 12v to this wire before and the pump did not come on, is the fuel pump grounded through the c100 as well??

John in RI

iTrader: (167)

I'm GUESSING that you're not using the TPI wiring to control the LT1 - Right ?? If you're using an LT1 harness you'll need to follow that LT1 fuel pump diagram I sent to you. If your trying to use the TPI harness to control the LT1,.... I'd GUESS that the fuel pump wiring is still intact.

89Z28LT1

I'm running the stock lt1 harness and ecu. Yes, this means I'm using the lt1 for relay to drive the fuel pump. And yes, I'm getting 12v out of the relay. Yes, that also means the body harness is still intact. (I had already made a previous, detailed post about this and had no responses, so I didn't feel like going into detail unless I got someone willing to try and help.) Now I'm GUESSING you know the color of the wire that powers the fuel pump in the body harness and I'm also GUESSING you know whether or not you had to provide an external gound to run the fuel pump or if you just hooked up power to (insert color here) wire..

John in RI

iTrader: (167)

My car was VERY different ( 84 factory Carb ) so I had to add EVERYTHING !

Your's being an 89 I don't have the schematic for that exact year,... but I do have one for an 88 and that might help.



Looks like you nailed-it: voltage from relay to fuel pump = Tan/White @G4 of C100 !

If I'm not mistaken,...... looking at the LT1 fuel pump diagram it appears as if the 4th gen FP relay's ground passed thru the body to the interior and to a grounding location inside the cockpit. In any case; you can ground the relay pretty much anywhere and you should be G-T-G.

89Z28LT1

Right on, I do appreciate the information. That's how I thought it should have been ran, but got nothing to happen when I hooked it up.. I'll be checking the plug going into the fuel pump and more then likely, replacing the pump. It's been an interesting swap, I pulled my lt1/4l60e from a Cadillac hearse, which had its own wiring that doesn't even match gm diagrams for that year lol
Thank you.