CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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Im just about ready to start the wiring on my 89 Iroc. Ive converted it from tpi to carb. Im using a Holley AFPR with the stock electric fuel pump. I want to use the stock fans on the radiator and have them come on at the same time. Please get me pointed in the right direction. Im also using a msd 6al box. Thanks in advance!
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The fuel pump will run as always, it just won't prime as the ECM does the priming and now it's gone. But it doesn't need to prime, since the carb holds plenty of fuel to start the car in the bowls. The fuel pump will now be controlled by the oil pressure sending unit.
However, this setup has a potential for failure. If the OPSU goes bad, the fuel pump will either not run, or will run constantly regardless of the key (depends on how the OPSU goes bad). A work around for this is to disconnect the wiring from the OPSU that runs the fuel pump (the larger 2 of the 3 wires - they are orange and red), and run them through the original fuel pump relay, that way the fuel pump will always run with the key on, and will never run with the key off. I did this with mine so that a bad OPSU didn't leave me stranded or kill my battery.
Thanks for the help on that. I wasnt aware the fuel pump would still run with the ecm and wiring harness out. I knew the osu shuts the fuel pump off if it goes bad but I didnt know you could run it through the relay. Im an idiot when it comes to wiring. Which one is the FP relay and how do you wire the OSU to that relay.
The fuel pump wires are located between the backs of the rear seats.
Find the pump power wire,Hayne's manual,it is the purple or grey.
Cut into the power wire and run it to a toggle switch on the console,I added a relay to mine but it worked fine with just the switch.
Summit,Jeg's all sell a fan switch kit with relay,sensor which goes into head.Wire it to a Batt. outlet in the fuse box and it will cut on and off at a pre-set temp.
Follow directions on MSD
Good luck
Thanks for the help on that. I wasnt aware the fuel pump would still run with the ecm and wiring harness out. I knew the osu shuts the fuel pump off if it goes bad but I didnt know you could run it through the relay. Im an idiot when it comes to wiring. Which one is the FP relay and how do you wire the OSU to that relay.
OK - I'm trying to think this out from memory, but my old brain is failing me. Give me until Friday night 10/2 to look and verify the wire colors/functions! I'll update then, and give you step by step if you like.
On the driver side firewall, between the brake booster and the fenderwell, there is a bracket with two relays mounted kinda inside of it. Use a 10mm socket to take this bracket off the firewall.
The OPSU is located above your oil filter - it will have a 3 wire connector to it - verify that you can find these two things, and they are as I describe (just so I don't tell you wrong tomorrow).
One relay will have a large diameter wire that is black with red stripe = that relay is for the electric fans - the other relay is fuel pump.
What we want to do, is a) have a ground, b) activate the relay with a small amperage 12v signal wire, c) have a larger amperage 12v constant supply available to power the pump, and d) route that 12v supply to the pump. Make sense? Small amp 12v makes a connection with ground only when key is on, so that the larger amperage 12v supply gets "routed" through the relay to the pump.
While you wait on me, make sure you have crimpers, solderless butt connectors, electrical tape, and a volt/ohm meter - and tomorrow night I'll give you a step-by-step.
FIRST - I have a TBI car - so I'm basing this off the TBI setup - but it should be the same for the TPI, as I have no TBI diagrams and I did this all off the TPI diagrams anyway for my car - BUT don't scream at me if it's wrong, I'm just trying to help!
The fuel pump relay - has 5 wires...
Black/white - ground
green/white - signal wire to activate relay
grey - 12v + always
orange - 12v + from battery
red - 12v + to fuel pump
To rig the relay from the OPSU:
1) Make sure the black/white wire is making ground (disconnect relay, run volt meter in connector from grey to black/white)
2) Make sure grey is getting 12v+ ALWAYS - if step 1 worked, this is a given and no need to test
3) Disconnect connector from OPSU - there are 3 wires, two of them are larger, one should be orange, one should be red - cut these from the connector BUT... leave enough wire on the connector to reattach if ever a need - maybe 2 inches. Plug OPSU connector back in.
4) These OPSU wires dangling - if you dig on driver side, back of motor, you'll find the little loom tube that these run in from the engine bay to the OPSU - pull them up through. Attach wires to these two to extend them far enough to reach your relay mount.
5) You should have several pink/black wires left over from the TPI - these should be injector wires, and should have 12v+ on them if key is on. If they don't, or are already gone, find any 12v+ that you can tap into that is only on with the key, and tap into that and extend to reach the relay.
OK - now wire the relay... (where I have "butt" is where you'll cut and use a butt connector to connect new wire)
1) ground to black/white (should be already)
2) the hot-in-run wire from step 5 above to the green/white wire (butt)
3) grey 12v+ constant (should be already)
*** These next two do temporarily - no butt connector until it works
4) Orange wire from OPSU to orange relay wire
5) Red wire from OPSU to red relay wire
See if pump runs with key on - should only run with key on!
If it does, go ahead and use the butt connectors on the last two to make permanent, if it doesn't swap the red OPSU wire to the orange relay wire and visa versa and test again.
This will leave you with a left-over red wire and orange wire from the relay - one goes to the pump, and won't have voltage to it anymore - the other may still have voltage on it, and you'll want to make sure it is protected against the possibility of grounding anywhere and causing a short - put a butt connector on it and tape it up good so it can't bump any ground source, then hide them both back in the harness - maybe someday you'll need a 12v+ for something else, and you'll always have it tucked in there.
Oh yeah - test your Oil pressure guage to make sure it still works.
Clean it all up as you see fit.
Hope that helps!
One final suggestion:
If/when you go to remove the pass side wiring harness, leave the harness in place, with enough leftover wires from the ECM connector to access in the future - it comes in real handy to have access to wires already running from inside the car to the engine bay - just cut the wires off with enough left to access, and tuck the whole harness in the fenderwell where it's unseen. I've used these wires for all kinds of cool stuff, like rigging my foglights on a relay to the switch inside, under-hood superbright LED strips so I have plenty of light under the hood in the event I have a mechanical issue after dark, rigging secret cut-off switches for my fuel pump so even if the ignition is hacked, the car won't go past the end of the block (no fuel), leads to a future power antena I hope, manual switches for my cooling fans, manual switches for my TC lockup, etc. - the possibilities are endless, and thus it's real nice to have a harness in place without having to poke through the firewall every month with a new gadget!
I just replied to a similar issue. Whether you leave the OPSU powering the fuel pump, or power it with the relay, if the relay fails you can still have a no power, or power on all the time condition.
You only need to make one connection from the fuel pump relay terminal "C" to the ignition pink wire which is only on continuously when the ignition switch is in the run position.
hey guys, i'm thinking of doin this swap too but trying to understand one main issue. SPARK!!!! so, the HEI distributor/coil on my 85 z28 305TPI will still work if I go with intake and carb or do I change that too. does the ECU still controll the spark or what. I know I will need a Intake, Carb, Cables, New low volume Fuel Pump, but is there anything else to this list that I'm missing to complete the conversion. thank you for any help. God Bless. My TPI runs like crap and tired of dumping money into it.
PLEASE TRY TO PM ME IF POSSIBLE. THANK YOU
You need a non-computer controlled vacuum advanced HEI distributor - you can use your existing coil. The ECM will no longer control timing - it will get advanced by the vacuum on new distributor.
i`m bussy with the swap from tpi to carb!
i have strip out the tpi harness ,so i only have left some wires that i need!
i have read these thread/post and don`t understand it about the fuel wiring relay!
i have a 1988 iroc-z 5,7 v8 and my wires of the fuel relay are different
and i have no 3 wire oil sending unit but it`s a 2 wire!
there are some letters on the fuel plug
A: Tan/white (that go`s from the plug to the oil pressure sending plug)
B:Black/white ??
C:Green/white ??
D:Orange (smal wire that go into the C100 plug)
E:Orange (big wire that go from the plug to the oil pressure sending plug)
so is here anyone who can tell me what to do for working the intank fuel pump
i`m bussy with the swap from tpi to carb!
i have strip out the tpi harness ,so i only have left some wires that i need!
i have read these thread/post and don`t understand it about the fuel wiring relay!
i have a 1988 iroc-z 5,7 v8 and my wires of the fuel relay are different
and i have no 3 wire oil sending unit but it`s a 2 wire!
FYI: a 2-wire is a Oil Pressure Switch unit, not an Oil Pressure Sending unit, same acronym OPSU for different devices.
One is a 1-wire sensor the other is a 2-wire switch.
A 3-wire unit combines the 2 devices into one.
there are some letters on the fuel plug
A: Tan/white (that go`s from the plug to the oil pressure sending plug) Answer: On a TPI it goes to the ECM, MAF, OPSU and Fuel pump. Do nothing to it other than trimming off the wring that Branch off to the ECM and MAF if you haven't already done that, I'd leave them intact.
B:Black/white ?? Answer: fuel Pump relay ground.
C:Green/white ?? Answer: Goes to the Ignition/ECM for fuel Pump relay control.
D:Orange (smal wire that go into the C100 plug)
E:Orange (big wire that go from the plug to the oil pressure sending plug) Answer: D & E go to the "Hot at all times fuse which powers other things including the ECM.
so is here anyone who can tell me what to do for working the intank fuel pump
dennis
As I said before terminal "C" of the relay is best connected to whatever has 12v when the key is on, starting, or running the engine which for me is the pink distributor power wire.
One connection, that's it nothing more, when you turn the key to On/Start whatever pump is connected in the tank will run.
