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Discussion Starter · #1 ·
For those who have done the carbed 2.8 to 3.4 swap, where did you hook the power wire to? I know it needs to be hot in the on position as well as start, but dead when the key is in the acc. position. And is a relay necessary for the electric pump?
 

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Awww..you ain't got shit!
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You would be insane to not run the relay and the cutoff switch. No offense man. That's just really dangerous otherwise. Should use a hot wire from the switched power (like ac fan motor or something) and connect that to the energize wire on the relay. Ground the relay, connect a hot to the relay from the battery and then run the hot off the relay to to the power wire on the pump. That's if you are running without the safety switch...I will say that I cannot remember exactly how that wires in there at this particular second. I bought a relay kit and a safety switch from Jegs. Well worth the added piece of mind.
 

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I hate my phone sometimes, I had replay almost complete, and either I hit a wrong button or it glitched and lost the reply....

You should use an oil pressure safety switch, to control when the fuel pump is on. The oil pressure safety switches that the aftermarket supplies usually have 3 terminals. NO is a normally open connection, NC is a normally closed connection, and comm is a common connection. The comm terminal is what will connect to the fuel pump relay coil to control when the relay is closed and open. The NC connection will connect to a start signal, and the NO terminal will connect to a true ignition source. This allows the fuel pump to be on only when the engine is starting and when it is running, much like an OEM electric fuel pump would be controlled.
 

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You are correct. I sure don't recall that...I am looking at the instructions for the Mr. Gasket 7872 which is what I used on my truck. I never hooked the third wire up to this switch. The only caveat is that it will require sawing on the starter for just a second longer till oil pressure comes up....that couldn't be a bad idea though right? Truck starts in about 1.5 seconds no problem. Even stone cold.
 

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Shouldn't change how quickly the truck starts. The carb will have fuel in the bowl and the engine will light off that, even if the start connection wasn't made. The only issue to that is of oil pressure does not raise enough during cranking to energize the fuel pump, and you end up running the carb out of fuel.
 

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That's never been an issue. I think there's enough fuel to run the truck for at least 5-10 seconds in the bowl before it would run out of fuel...at least. The pump is already running by the time the key is let loose from the start, so I know the pump has already caught up delivering fuel, so I am guessing it's a moot point on my pickup. On a truck with a worn engine it might make a difference if the oil pressue is low on starting. I don't think the 3.4 has but about 7K miles on it since the swap. It cost too much to drive it with the 4bb....although it is SHITLOADS of fun to drive!
 

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Discussion Starter · #7 ·
You would be insane to not run the relay and the cutoff switch. No offense man. That's just really dangerous otherwise. Should use a hot wire from the switched power (like ac fan motor or something) and connect that to the energize wire on the relay. Ground the relay, connect a hot to the relay from the battery and then run the hot off the relay to to the power wire on the pump. That's if you are running without the safety switch...I will say that I cannot remember exactly how that wires in there at this particular second. I bought a relay kit and a safety switch from Jegs. Well worth the added piece of mind.
Is this the one you used from Jegs?
http://www.ebay.com/itm/JEGS-Perfor...Parts_Accessories&hash=item48536dea05&vxp=mtr
 

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Yeah, that is basically the same thing. Will do the trick.
 

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The oil switch closes connection at 4 PSI. There will not be any more cranking then the normal starting of the engine. So you will not notice anything different.
The TBI don't have a fuel bowl like carbs. And the switch is factory wired from factory to the relay and oil switch.
That's true mostly. The bottom of each injector has a tiny resevoir in that you could justify as a "fuel bowl", but yeah, it's a pretty tiny amount of fuel compared to a carb bowl filled with a float so that makes plenty of sense why it is there. I put mine on there strictly for safety reasons. Fires are scary. Trust me. I had my truck almost burn up once from a backfiring carburetor. Scared the crap out of me. I also helped a guy pull a damn drunk out of a burning Mustang one night about 5 years ago. I almost had to watch him burn to death. That idiot was very lucky. His BAC (blood alcohol level) was .28. What an asswipe. As a result I keep a a fire extinguisher in every vehicle I own.
 

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That's a good point...I can't swear on that for sure. I'm doing an EFI swap now. My knowledge is very limited.
 

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Tips:
Wire everything to the engine first with the donor harness.
Use starter wire & alt. from trucks original harness. You can use some of the sensor wires that run to instruments as well. However on mine I did not bother since they will all be manual ones.
Then work the rest of the wiring that powers/controls the ECM.
Get schematics for both donor and the truck.
If you get stuck on a wire. Trace it back to the ecm and to the engine if that's where it goes. This will give you an idea what it's for when you try and find it on the schematic.

That's the best advice you will probably get on wiring in this forum. I had only 2 guys on here to even try and help me a bit. One hooked me up with my schematic. The other looked at his harness and replied to me what he seen on his.
 

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Discussion Starter · #14 ·
OK I got the relay kit from Jeg's, in the instructions it doesn't show an oil pressure switch in the wiring diagram. Should it be installed between the switch and relay or the relay and pump, or does it matter? I'm thinking between the switch and pump, the wiring pigtail I got for my pressure switch doesn't have very big wires.
 

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I always install the pressure switch before the relay. Less current used to control the relay. Also the start circuit would have to power the pump directly when starting, if it were placed between the relay and the pump.
 

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Discussion Starter · #16 ·
OK I got the relay kit from Jeg's, in the instructions it doesn't show an oil pressure switch in the wiring diagram. Should it be installed between the switch and relay or the relay and pump, or does it matter? I'm thinking between the switch and pump, the wiring pigtail I got for my pressure switch doesn't have very big wires.
I mistyped pump in above question, should have been relay, just like Raven said. Relays use a low amp signal to control a high amp switch.
 
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