Do I need a fuel pump relay

Tiny
JWM1120
  • MEMBER
  • 1987 HONDA ACCORD
  • 4 CYL
  • FWD
  • MANUAL
Do I have to have a fuel pump relay in fuel system wiring? If I connect my fuel pump to a toggle switch that I can turn off and on, will everything work ok? What stops the fuel pump from overflowing the carb bowl and continuously pumping? Is that what the relay does? I have an 87 Honda Accord DX but have removed the factory carb. I have a Weber 38 on it instead.
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Thursday, August 25th, 2011 AT 5:05 PM

13 Replies

Tiny
HMAC300
  • EXPERT
Yes you do it's under the dash on left side pic included.
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Thursday, August 25th, 2011 AT 5:16 PM
Tiny
JWM1120
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So does the relay control the fuel flow? Does it turn it off and on based on different rpm conditions? I thought the relay was more of a large fuse. Is that not the case?
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Thursday, August 25th, 2011 AT 5:27 PM
Tiny
HMAC300
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It's a relay and if you are jumping it and the pump works then it sounds as if the relay isn't working. Usually the oil pressure switch takes over after initial start up with the engine.
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Thursday, August 25th, 2011 AT 5:44 PM
Tiny
JWM1120
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I swapped out the relay and it still didn't work. If I jump it, it does work. If I run a seperate wire from the ground terminal to a ground spot nothing happens. The relay has 4 terminals +, -, Fuel Pump, and Ignition. I'm not getting power to the ignition terminal. That's why I wanted to wire a switch in seperately. Could it be my oil pressure switch is malfunctioning? It is a carb car, no ecu. How does the fuel pump get a signal from oil pressure?
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Thursday, August 25th, 2011 AT 6:51 PM
Tiny
HMAC300
  • EXPERT
Ok yours is a little different. In the pic i've included the yellow wire goes to the fuel pump. The blue comes form the ignition coil and balck to ground. The other wire goes to fues 1 and should power up with thekey on. If one of these aren't working like the power up an dignition coil your pump wont' work. You can test these with a test light. It may be a bad connection or broken wire on any of these.
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Thursday, August 25th, 2011 AT 7:20 PM
Tiny
KHLOW2008
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For carburetted engine, there is an ECU, Emission Control Unit, which controls the various solenoids and valves but is not related to the fuel pump relay.

If you do not have any power from the ignition terminal, that is the problem you need to address. Ignition terminal receives its pulse from the ignition coil and would only work while engine is being cranked or is running.

Oil pressure switch is not related to the fuel pump relay operations.

Check the continuity of the Blue wire from ignition coil. If the tachimeter is not working, the ignition coil could be faulty.

Using a toggle switch works but is not safe as the fuel pump would not cut off when engine stalls and that is a safety hazard.
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Thursday, August 25th, 2011 AT 7:31 PM
Tiny
JWM1120
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What keeps the fuel from continously flowing? If the pump has constant 12 v power and is always on (like with a toggle)? Would the carburetor flood out the intake? Is there some sort of pressure cutoff in the pump or in the plumbing?
I do see how this is a safety hazard.
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Thursday, August 25th, 2011 AT 8:00 PM
Tiny
HMAC300
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You obviously don't understand a lot of mechanical things. The flow rate is set at the factory for thefuel pump. When you turn the key off it no longer flows. There are other safety things that will shut the fuell off as well. It is not a safety issue. Only when you put a switch in teh system like you have to jump the system then it becomes a safety issue
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Thursday, August 25th, 2011 AT 8:03 PM
Tiny
KHLOW2008
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When the fuel pump is working, the carburettor float would stop the flow of fuel into the carb when the fuel level is attained. When pressure builds up, the pump piston would be held in the pressurised position and that would not allow the contact points inside the pump to meet and that would cut the current flow and stopp the fuel pump from working.

Keeping the fuel pump running would not flood the carb unless the float or needle valve is faulty.

In cases of accidents, if the engine had stalled and the fuel pump is running with a ruptured fuel line, fuel would continue to be pumped out and spews out of the ruptured hose, that would be a safety hazard.
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Thursday, August 25th, 2011 AT 8:16 PM
Tiny
JWM1120
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Gee thanks for the kick in the crotch. Quite the contrary, I do understand many mechanical things. This is an instance where I am trying to figure out exactly how the system works. Maybe my problem is I haven t given as much detail as needed. Yes, obviously the flow rate is set by the factory and when you turn the key off it no longer flows. However, with the switch powered up & the car not running, just on, the pump will flow fuel to the carburetor. Is there a check valve in the system that would stop it from flowing in this condition? This would be without the relay in the system. And yes, I know it s a safety issue the way I currently have it jumped with the switch. I m basically trying to get my car runnable while I sort out the electrical gremlin in the wiring. Can I the car with the jumper switch as a Band-Aid until I can find the source of my electrical woes?
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Thursday, August 25th, 2011 AT 8:21 PM
Tiny
JWM1120
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KHLow2008 - Bingo, that's what I was looking for I think.
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Thursday, August 25th, 2011 AT 8:22 PM
Tiny
KHLOW2008
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Problem resolved?
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Sunday, October 21st, 2012 AT 5:04 AM
Tiny
HMAC300
  • EXPERT
Your carb should stop the fuel from overflowing like KH said, if not your needle and seat or float is out of adjustemnt. Also the pump you have may have to much pressufe for your system. A carb type engine on ly uses 7psi MAX. So you woul dneed to add a regulator for it or disconnect the fuse you have going to teh relay so thepump won't run while you tinker with your electrical problem.
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Monday, October 22nd, 2012 AT 10:18 PM

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