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Engine SwapEverything about swapping an engine into your Third Gen.....be it V6, V8, LTX/LSX, crate engine, etc. Pictures, questions, answers, and work logs.
Similar but different topic from my last post.
About wiring up this fuel pump and running it though my computer.
all around this harness is confusing. The fuel pump was straight forward. Easy no problem.
got the 10 gauge wire plugged in the back and ran to front for the alternator easy. What next? If I trigger it off the computer I have to splice? If I run it alone I’ll need a relay and a trigger?
Just want this pump to run of the pcm.
my pcm apparently can handle the load alone according to speartech.
can yall please help me get this thing running
my harness has its own fuel relay but how can I use it since I need better wires for the pump?
As long as your stock fuel pump wiring still works, the hot wire kit will work too. Just need to wire your ECM fuel pump control to operate your stock fuel pump relay in the engine bay.
Basically your stock fuel pump wiring is now used to run the relay in the hot wire harness.
Is that a 255 L/hr pump? And how much power is your engine going to make?
Your username has LS7 in it. It doesn't take much for an LS7 to overwhelm a 255 pump.
yes those are rated for up to 600 hp. I would think it would make atleast 550 or just shy of 600.
but my main concern is getting this pump wired correctly. My harness has a built in relay. It has a wire for fuel. How do I use that as my relay and let the computer control it. I got the Hotwire kit in. What do I do next. I’ve thought over and over and over. I do t think this is going to be plug and play. My stock relays are gone. I could cut one off my old harness?
Hang on.... looking at pictures of your part number harness it appears it might need to plug into the stock tank harness too. That's all redundant wiring, I don't know why they would do it that way.
It could be simplified using similar methods as I show in that fuel tank wiring link. You'd have to pull off all the loom and see where the wires go and figure it out just like I did for the 4th gen harness.
I would have to see the harness myself to really give you detailed advice.
This is really good information but dang it. Why is this simple thing turning into a huge problem. I bought this kit for the sake of keep my sending unit so my level “gas gauge” would work and getting better wires so the pump could perform as it should. What’s the deal with these kits?
I had the rearend out of the car and though I was home free
If you still have your old stock fuel tank harness then you can just plug it in and you won't have to rework the Racetronix harness.
But to me it seems silly to buy a nice brand new harness and then keep the old harness too. Especially on a brand new build like what you're doing. They could have VERY EASILY made the harness a little different to eliminate the stock harness altogether.... but they didn't.
It's up to you whether you use the old stock harness with the new harness, or eliminate by reworking the new harness.
The purpose of the racetronix harness is to eliminate the inadequate thin wire going to the fuel pump from factory with a relayed power source straight from alternator for good voltage. Assuming your LSX harness gets power through adequate wiring it should effectively be achieving the same goal. Especially if you upgrade alternator cable to battery.
Sell me the untouched racetronix harness and then extend the grey fuel pump wire back to the fuel pump from your LSX harness.
The purpose of the racetronix harness is to eliminate the inadequate thin wire going to the fuel pump from factory with a relayed power source straight from alternator for good voltage. Assuming your LSX harness gets power through adequate wiring it should effectively be achieving the same goal. Especially if you upgrade alternator cable to battery.
Sell me the untouched racetronix harness and then extend the grey fuel pump wire back to the fuel pump from your LSX harness.
id have to splice in or just re pin that gray wire? I thought all the weak wire was in the tank. So the weak wiring the bulk head too correct? That gray wire is 10ft. If it’s easy to hook up I’ll give you the harness. Just get me set up properly
I’m pretty sure this is the relay they gave me. Right? That would be the same part number that’s on the bag?
In your picture you've got the Racetronix harness plugged into the connector behind the rear seat. I think maybe it is supposed to be plugged into the fuel tank instead? One connector plugs into the fuel pump, the other connector plugs into the old stock harness?
The racetronix harness FPWH-005 doesn't change anything in the tank, it is an upgrade for the section of harness from the 3 wire connector near the bulkhead to the factory fuel pump relay. It is "plug and play" because it effectively uses the factory fuel pump hot wire in the 3 wire connector as the trigger for their relay. With you not having factory setup it would need modified.
Assuming you are using factory fuel gauge wiring you would leave the factory 3 wire connector at the bulkhead in place for only the fuel level signal wire. Then you would want to connect the grey fuel pump wire to the factory (confirm color) 12v hot wire going to the tank. Cutting it from the tank side of the 3 wire connector. Then the negative wire would similarly get cut but gets grounded to body somewhere. The 3 wire connector and wiring going into the bulkhead would only be using the fuel level signal wire. The other two wires would be dead and unused.
Last edited by dabomb6608; 09-25-2024 at 09:07 AM.
255 L/hr pump probably won't carry that LS7. Neither will stock wiring. You NEED a hotwire kit. Just my advice.
255 pump in my car wouldn't support any more than ~480 RWHP. The wideband O2 sensor never showed a problem but the fuel pressure dropped and plugs showed running lean. Switched to a 340 L/hr pump and picked up a whole lotta power.
255 L/hr pump probably won't carry that LS7. Neither will stock wiring. You NEED a hotwire kit. Just my advice.
255 pump in my car wouldn't support any more than ~480 RWHP. The wideband O2 sensor never showed a problem but the fuel pressure dropped and plugs showed running lean. Switched to a 340 L/hr pump and picked up a whole lotta power.
His new LSX harness is effectively a hotwire kit is it not? It replaces the inadequate factory wiring and (assumedly) has very good incoming voltage from power supply. Combine that with a modern alternator on the LS7 that will supply and maintain proper voltage in the 14s.
His new LSX harness is effectively a hotwire kit is it not? It replaces the inadequate factory wiring and (assumedly) has very good incoming voltage from power supply. Combine that with a modern alternator on the LS7 that will supply and maintain proper voltage in the 14s.
I put a 150amp power master on it. I’d like to use my harness If possible. Keep my sender for gas gauge utilize my harnesses built in relay, and let the pcm control the gas. 2nd delay on that pump would be nice. Does the pump stay on constant with a Hotwire kit? Some ppl would argue about the fuel pump but this is my first rodeo so I’m all ears how to get this thing running.
I put a 150amp power master on it. I’d like to use my harness If possible. Keep my sender for gas gauge utilize my harnesses built in relay, and let the pcm control the gas. 2nd delay on that pump would be nice. Does the pump stay on constant with a Hotwire kit? Some ppl would argue about the fuel pump but this is my first rodeo so I’m all ears how to get this thing running.
All the hotwire kit does is use the factory fuel pump wiring to trigger a new relay that is getting its main power straight from the alternator through a thicker than factory gauge wire. So the fuel pump functions just like factory.
Oh dang, I didn't even notice the other harness. I thought he had installed the Racetronix harness.
At this point I'm lost without seeing a wiring diagram.
His LSX harness has the following built in.
It is effectively an upgraded fuel pump harness compared to a factory setup. It looks to be made with plenty thick gauge wire and likely utilizes a better main power supply scheme than the factory harness did.
I personally see little reason to try to modify a hotwire kit to use that thick grey wire as simply a trigger to the hotwire relay. You would basically just be using a relay to trigger yet another relay.
All the hotwire kit does is use the factory fuel pump wiring to trigger a new relay that is getting its main power straight from the alternator through a thicker than factory gauge wire. So the fuel pump functions just like factory.
but if I take the Hotwire kit off I’m back to factory gauge wiring. I’d have to run my gray wire from the harness to the power side of the plug(splice) would I still be on factory wiring at that point too?
but if I take the Hotwire kit off I’m back to factory gauge wiring. I’d have to run my gray wire from the harness to the power side of the plug(splice) would I still be on factory wiring at that point too?
You would run (extend with same gauge wire if required) the gray wire from the harness to the fuel tank side of the 3 wire connector. From that point on you would be on factory gauge wiring. Just like you would even if you installed the hotwire kit.
Like I said, the hotwire kit doesn't modify in anyway the wiring from the 3 wire connector near the bulkhead to the fuel pump itself. That all remains factory gauge regardless of which direction you take.
It is all right there accessible by the fuel tank. From the factory the tank side three wire connector is what plugs directly into the bulkhead wiring pass-through. See below.
Arrow #1 is the bulkhead connector. Arrow #2 is the fuel tank harness with a 3 wire connector that plugs into to the bulkhead connector. This connector has a thin wire (fuel level signal wire) and two thicker 14awg wires. One should be tan (12v hot to fuel pump) and the other black (ground to fuel pump).
#2 is what would get modified to work with your LSX harness. First you remove the racetronix harness from the car completely. Then you would connect the 3 wire connector (#2) directly to the bulkhead (#1). Next you would cut the Tan wire and black wire going to the tank. The tan wire would connect to your gray fuel pump wire from LSX harness. The black wire would have a ring terminal installed and then grounded to body somewhere around there. You "could" leave black wire alone as it does ground elsewhere, but I would just do a body ground.
Thats what I’ll do. Remove the hot wire kit. Cut the brown and solder it in. Gonna do that tonight hopefully. I’ll get some extra 14 gauge Incase my gray comes up short. Painless has some good txl wire in looms. I came here for answers and yall didn’t let me down.
Excellent clear answers so I can confidently modify that 3 pin and use this harness as intended.
If all goes well and you definitely don't end up using that racetronix kit, I actually do need one if you'd sell it lol. I've needed to install one (or make one) myself for a while now. My setup is far from ideal.
[QUOTE=dabomb6608;6544258]If all goes well and you definitely don't end up using that racetronix kit, I actually do need one if you'd sell it lol. I've needed to install one (or make one) myself for a while now. My setup is far from ideal.[/
You are more than welcome to it. Help is a great thing to receive. I feel tons better
Yes, that GREY wire in the Speartech harness could be wired to the B+ side of the pump. Need an equal size ground wire from pump to chassis though. And the fuel gauge level needs to be wired to gages too. Can be done by someone willing to build out their own fuel tank harness from scratch.
If not wanting to build from scratch, then the Racetronix Harness has the building blocks.
Yes, that GREY wire in the Speartech harness could be wired to the B+ side of the pump. Need an equal size ground wire from pump to chassis though. And the fuel gauge level needs to be wired to gages too. Can be done by someone willing to build out their own fuel tank harness from scratch.
If not wanting to build from scratch, then the Racetronix Harness has the building blocks.
so if I use my speartech harness that will cause the gas gauge not to work? I thought there was already a ground. It’s a 3 wire. Power, ground, fuel sender in the plug
Yes, that GREY wire in the Speartech harness could be wired to the B+ side of the pump. Need an equal size ground wire from pump to chassis though. And the fuel gauge level needs to be wired to gages too. Can be done by someone willing to build out their own fuel tank harness from scratch.
If not wanting to build from scratch, then the Racetronix Harness has the building blocks.
I believe he still has his factory fuel tank harness in place. Assuming all the photos he supplied are his own it is #2 in the photo I edited above. If that is the case, the ground wire is present as well as the fuel level sensor. The racetronix kit doesn't change anything on that section of the wiring from fuel tank sending unit to bulkhead connector.
He could certainly remove this section of wiring and build from scratch starting from the fuel tank sending unit but it isn't necessary.
Stock fuel pump ground is 14 AWG wire and it meanders through the vehicle. You will want a larger Ground wire for the same reason you want a larger B+ wire.... minimizing voltage losses in the circuit to improve pump flow. If you inspect the Racetronix harness you will see it has a big *** ground wire that you have to bolt to the vehicle chassis. You can either cannibalize the Racetronix harness for the parts you need, or build your own custom harness.
A 255 pump can run on stock 14 AWG wire size, just not to peak performance. In your case you will need EVERYTHING that pump can possibly give and maybe more. Lay some big wires, minimize voltage drops in the circuit. If you end up upsizing to a 340 pump then the current draw of the pump will increase to the point where you must use larger wire anyway.
Not to throw another new thing at you, but if you're looking for the cleanest way to do this, it would be the concept in Post #4 of the thread I linked earlier. I normally don't suggest that but you've got the car blown apart so now is time if you're going to do it. You'll have to decide that based on your skills and desire to learn. I linked you that thread and pretty much every question you've asked can be figured out from that thread. I can tell you haven't taken time to soak it in yet because of the questions you're asking.
Stock fuel pump ground is 14 AWG wire and it meanders through the vehicle. You will want a larger Ground wire for the same reason you want a larger B+ wire.... minimizing voltage losses in the circuit to improve pump flow. If you inspect the Racetronix harness you will see it has a big *** ground wire that you have to bolt to the vehicle chassis. You can either cannibalize the Racetronix harness for the parts you need, or build your own custom harness.
Hence the recommendation to forget the ground through the bulkhead and just ground to chassis straight from the fuel tank harness ground wire. Cause end of the day, racetronix harness or not, the juice is still traveling through the 14 awg wires from the tank to the 3 wire connector.
The racetronix kit doesn't change anything on that section of the wiring from fuel tank sending unit to bulkhead connector.
I think the Racetronix harness has a 10 AWG ground wire at the pump connector, and terminates at the ring terminal you bolt to the car body. That grounds both the pump and the fuel sender.
However, inside the harness another smaller wire is spliced to that which follows the stock ground path through C313 connector. So it looks like there are two grounds, but really it is just one common wire terminated at two places in the car. The stock ground path becomes redundant, you could disconnect it and everything will still work.
Edit: LOL! We're replying to each other faster than I keep up with the conversation.
Okay great. Let’s start over. I need a bulk head with bigger wire. Yeah it hasn’t soaked in yet. It keeps changing! I’ve done a lot of work to this car and this is by far a confusion killer. Please feel free to elaborate more for this from scratch. Break it down like algebra. Everytime I search around it’s something different so let’s put the solution in here
Okay great. Let’s start over. I need a bulk head with bigger wire. Yeah it hasn’t soaked in yet. It keeps changing! I’ve done a lot of work to this car and this is by far a confusion killer. Please feel free to elaborate more for this from scratch. Break it down like algebra. Everytime I search around it’s something different so let’s put the solution in here
Yeah I know, sorry, we're throwing a lot of stuff at you. And it didn't help that I misunderstood some things from the beginning.
The problem is there are many different ways to whip this problem. In other words, you have choices.
Please read that thread I linked earlier to get more familiar with some of the basics of stock wiring and a Hotwire harness. Then we'll talk again.
Yeah I know, sorry, we're throwing a lot of stuff at you. And it didn't help that I misunderstood some things from the beginning.
The problem is there are many different ways to whip this problem. In other words, you have choices.
Please read that thread I linked earlier to get more familiar with some of the basics of stock wiring and a Hotwire harness. Then we'll talk again.
Yeah I know, sorry, we're throwing a lot of stuff at you. And it didn't help that I misunderstood some things from the beginning.
The problem is there are many different ways to whip this problem. In other words, you have choices.
Please read that thread I linked earlier to get more familiar with some of the basics of stock wiring and a Hotwire harness. Then we'll talk again.
I think one problem to keep in mind is the link is regarding 4th gen fuel tank/sending unit and the corresponding hotwire harness for 4th gen cars. This differs slightly from the 3rd gen fuel tank and hotwire harness specific to 3rd gens. He has a 3rd gen specific hotwire harness.
Last edited by dabomb6608; 09-25-2024 at 02:34 PM.
This is the FPWH-005 (now FPWH-035?) harness for 3rd gen cars. If you look closely you can see how it is wired.
The male 3 wire connector on the right side of photo connects to the bulkhead connector on the car. The gray wire takes the vehicles factory 12v fuel pump signal and uses it to trigger the new relay mounted nearby. The black wire is simply a ground wire. The purple wire is for the fuel gauge and comes from the female 3 wire connector. The purple wire is simply jumpered between the 3 wire connections.
The relay is powered via the red heavy gauge wire going from the ring terminal at the alternator, through a fuse, and to the relay. The relay then has a red wire that goes to the female 3 wire connector.
The female 3 wire connector connects to your harness coming from the fuel tank sending unit. It has a red wire, black wire, and purple wire. The red wire comes from the new relay included in the kit and explained above. The black wire is spliced with the ground coming from the male 3 wire connector as well as the relay and terminates at a ring terminal. This is your chassis ground for the harness and fuel pump. The purple wire comes from the fuel sender/fuel level sensor and goes to the male 3 wire connector as explained above.
1) Where is the Speartech fuel pump relay going to be located in your car? Engine bay, inside under the dash, trunk area?
2) Is it possible for you to run the Speartech GREY wire through the interior of the car to the back seat area? Yes or No is all I need to know for now.
3) Is the C313 connector still riveted to the body of your car behind the rear seat? Or have you drilled the rivets and made it removable?
4) Do you still have the stock fuel pump wiring (all 3 wires) on the interior side of the C313 connector? Or has it been cut up in some way? And if cut up, then how much length is still attached to the C313 connector?
5) Do you still have the stock fuel tank harness and is it in good condition? I think the answer is 'Yes' based on your photos, but I want to hear you say it and make no assumptions on my part.
6) Can you show me pictures of the connector on your stock harness that plugs into the fuel tank? top, bottom, side, and front (showing the ends of the pins so I can see if it is male or female).
I'm trying to evaluate what would be the best solution for you, and if I can maybe make something to help you out.
1) Where is the Speartech fuel pump relay going to be located in your car? Engine bay, inside under the dash, trunk area?
2) Is it possible for you to run the Speartech GREY wire through the interior of the car to the back seat area? Yes or No is all I need to know for now.
3) Is the C313 connector still riveted to the body of your car behind the rear seat? Or have you drilled the rivets and made it removable?
4) Do you still have the stock fuel pump wiring (all 3 wires) on the interior side of the C313 connector? Or has it been cut up in some way? And if cut up, then how much length is still attached to the C313 connector?
5) Do you still have the stock fuel tank harness and is it in good condition? I think the answer is 'Yes' based on your photos, but I want to hear you say it and make no assumptions on my part.
6) Can you show me pictures of the connector on your stock harness that plugs into the fuel tank? top, bottom, side, and front (showing the ends of the pins so I can see if it is male or female).
I'm trying to evaluate what would be the best solution for you, and if I can maybe make something to help you out.
1the computer and relay is going under the dash.
2Yes
3answered
4yes stock wiring car is mint, stock length
5stock fuel tank harness, great condition
6 jack and stands are on the way. I can try and crawl. Squeeze in between the rear. Yes eventually.
that would be amazing if you helped.
1the computer and relay is going under the dash.
2Yes
3answered
4yes stock wiring car is mint, stock length
5stock fuel tank harness, great condition
6 jack and stands are on the way. I can try and crawl. Squeeze in between the rear. Yes eventually.
that would be amazing if you helped.
I know exactly what you need for a SUPER CLEAN install. It's something I've always wanted to do but never had the right car.... until now.
I will have to do some research to find part numbers for the fuel tank connector, and make sure I have all the right tools to do the job. What I need from you in the interim is to know if that GREY wire is 12 AWG or 10 AWG size. I will PM you my phone number to discuss more.
QwkTrip had a lot of great insight on how important voltage and wiring is. I don’t want to skip ahead of his plan but I am curious to ask what it would take to run a 340 LP\h pump with all the proper harness, grounds, wiring, and inside the tank setup.
My setup runs a 255 pump with plenty of headroom, so I never needed to research going bigger. I would not be able to answer that one in a way that I would feel confident to say "use this".
Here are my thoughts however....
Looking up a 340 pump, I see AEM specs it "requires in excess of 17 amps" for their replacement pump. Assuming 80% safety net for max amperage capacity that means minimum of 10 awg wiring for battery to pump and to ground. (10 awg max 30 amps x 80% = 24 amps)
The factory wiring from pump to the bulkhead connector definitely isn't 10 awg. Same inside the tank. So all of that needs upgraded. Personally for "overkill" I could easily see your gray wire being used underhood for a heavy duty relay that sends 12v through a 8 awg wire back to the tank. Even if you then go 10 awg from there to the pump. Mainly due to the losses associated with the extra length of wire.
09-24-2024, 11:57 PM
