Bypass fuel pump resistor (1 Viewer)

[brandonatx13]

I just installed a new denso fuel pump and my 80 finally runs great, but the resistor didn't ohm out right and i think the fuel pump relay contacts are pitted, i just jumped the relay so it's at high pressure all the time, can i just leave it like this, the denso fuel pump cross references to may other applications, some use a fuel pump resistor and some don't, i'm pretty confident the fuel pump can handle running at 12v all the time, and the fuel pressure regulator just lets the extra pressure go back to the tank, is this just an emission thing or just over engineering?

 

[Parsnip]

It is my understanding that the pump used for carbs ran slower and made little noise. When multi-port fuel injection came onto the scene cars/trucks needed a higher pressure pump and that meant a pump that passengers in cars and SUVs could hear it. As a customer satisfaction solution, to stop the "I hear something grinding" service calls, a resistor circuit was added for times when the engine did not require full pressure from the pump. The engineers simply made the injector pulse wider at the lower pressure and therefore less noise in the cabin. It has nothing to do with emissions. It is my opinion that the cooling effect of the fuel on the pump is greatly reduced when the tank gets below 1/4. YMMV contents my settle in shipping. Special lighting used for TV. etc

 

[brandonatx13]

Makes since, seems like a waste of $160 to replace the resistor and relay...

 

[97 greenmonster]

I'm going threw a fuel issue myself. I can tell u I just drove around with resistor jumped out with no ill effect. Also my resistor all had odd ohm reading when testing. Temperatures seem to change the reading. I thought mine was bad and tried testing green and red wire going to fuel pump in driver kick panel. The voltage is what it's suppose to be. There for in my understanding relay, resistor and such working ok. You might want to give it a try. Good luck

 

[Parsnip]

These ceramic resistors (called ballast resistors in some circles) exist in a lot of other applications outside of Toyota. $160 seems awfully dear. You may find one that meets your needs cheaper looking in the world of Jeep, for example.

 

[97 greenmonster]

I think he's talking about price of fuel pump relay and resistor there about 160$ for both. 55$ for resistor and 95$ for relay

 

[brandonatx13]

Well I bought a new fuel pump relay and a nice used resistor, the resistor ohm's the same as my old one so i know that wasn't the problem, now it will just idle for a min or so and just die, today it just died in traffic, let it cool down for a sec and it drove home, the resistor is extremely hot, and when i check the data link it's at 10.5 volts at idle on the fuel pump voltage, should i just get rid of the fuel pump relay and resistor, it was running fine with a jumper in the relay socket...I through it would be good to put it back to stock, maybe the circuit opening relay is weak too? Any ideas?

 

[9780LC]

Can the old, stock, relay/resistor you're using handle the Amp requirement of the new Denso fuel pump? The Denso pump that I am using is capable of pulling over 20 Amps in 12v mode. Is the wire going back to the fuel pump a thick enough gauge? Are your grounds good? Your problem sounds like a combination of a under rated relay and thin wire. Add high temps to the mix, which adds more resistance, you might have a fire. I fought this issue myself recently. I melted a relay but had no fire.

Bypassing is dangerous. I would not leave it this way.

 

[brandonatx13]

Is the aftermarket denso fuel pump way different from the oem one? It does make since if it's more powerful it pulls more current and the existing relay/resistor isn't isn't rated for it, the thing is it worked just fine bypassing the relay/resistor, and I can't even hear the pump running even when the tank on empty.

 

[9780LC]

It working in bypass makes sense. You're bypassing the problem.....the relay and decreasing resistance. What model of Denso are you using? The one for the Supra.

This one?

Check this out......

http://realstreetperformance.com/Fuel-Pump-Comparison-Test.html


http://www.supraforums.com/forum/showthread.php?591845-Advice-for-those-who-have-the-12V-relay-mod

 

[brandonatx13]

I'm using denso 950-0133

 

[9780LC]

I wonder what it's upper AMP requirement is.....the information is not easy to find. What does your meter say the pump requires AMP wise at idle and at @ 2.5k RPM? What is the relay you're using rated to in Amps?

 

[brandonatx13]

Been working great bypassed, also the Efi relay isn't as hot, looking at the circuit everything goes through the Efi relay, and it's known for having problems and overheating causing it to turn off on hot days