Blowing Fuel Pump relay

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Blowing Fuel Pump relay

Postby lumbercis » Wed Nov 09, 2016 7:52 pm

Hey all,

Car has a gen4 engine swap fueled by a 550cc Supra fuel pump. This setup ran fine on the old stock 440cc pump (stock boost), and once i upgraded to the Supra pump it also ran fine for several months on stock boost.

Recently the fuel pump relay blew (car just shut off while driving) and I had it replaced but then it did the same thing again and my mechanic is saying that the second relay has also blown. Their theory is the upgraded pump is blowing the relay and want to try putting in a stronger relay.

Any thoughts on what might be causing the relay to blow? Anything else to check? Seems strange that it ran fine for months but now can only go a day or two before blowing the FP relay again.

Thanks!
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Wed Nov 09, 2016 11:19 pm

Shouldn't be the larger pump. If it was you'd be blowing the fuse, not the relay.

Which side is going? The coil or the switch?
That will tell you where to look.
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Re: Blowing Fuel Pump relay

Postby lumbercis » Fri Nov 11, 2016 4:15 pm

Just to make sure I have my terminology correct, it's the fuel pump relay that's in the small fusebox on the passenger side near the alternator.

I'm not sure what you mean by which side coil/switch. Can you elaborate a little more?

Mechanic called me back and said even a stronger fuse is blowing and they want to drop the tank and replace the pump... :shrug:
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Fri Nov 11, 2016 6:29 pm

That isn't the fuel pump relay, that's the hi/low speed for the fuel pump. Normal driving the current is routed through the fuel pump resistors [which could be your problem]. When you go to full throttle the relay bypasses the resistors and gives the pump full current.

The fuel pump relay is called the [COR] circuit opening relay [it's by the ECU].

Which fuse is blowing? That makes a big difference as to where to look for the problem.
The fuel pump has it's own fuse. If that's not what's blowing I doubt the pump is the problem.
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Re: Blowing Fuel Pump relay

Postby freddie » Sat Nov 12, 2016 2:39 am

Alltracman 78 hit the nail on it's head.

Does your car start and run without the fuse blowing (that is for a good minute or more?. If so it is because the pump gets 12 volts with out the resistor cutting in.

When you turn your ignition on (without starting) can you hear the pump working (bit of a wirring noise)? If so the pump is working.
When you do this, does it blow the fuse?. If so you have a short in the wiring some where or the pump its self.

If it is a yes to the car starting and you can here the pump working, check out the resister, (that's that aluminium thing with all the heat fins around it)
First off check the wiring and especially the plug. If or when the fuse blows, carefully touch the resistor to see how hot it is.

My experience was, my 165 would start and run, drive down the road twenty feet and it would stop. Start it again and the same thing would happen. Turned out the plug had came loose and a pin in the plug would not make contact. Pushed it all together and everything was fine for 6 months. then the problem came back. I again fiddled with the plug and it blew the pump fuse. I chopped out the plug and replaced it with a new one and everything has been fine ever since. That was two years ago. Oh by the way, I also changed the resistor too just to be sure. hah hah

Freddo

PS. Some where on here is a blog on how to get rid of this resistor and bypass it for the ECU to work. So your pump runs 12 volts all the time.
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Sat Nov 12, 2016 4:13 pm

I'm not trying to be a jerk man, but you have a few things incorrect.

1-The fuel pump shouldn't run when the key is turned on. Not even for a second. Unless someone has changed the wiring. Correct wiring has the pump only run when the engine is starting or running. This helps keep the pump from dumping fuel in an accident.

2-If the pump is running the resistor is going to be hot regardless. Resistors turn electricity into heat.

lumbercis wrote:Just to make sure I have my terminology correct, it's the fuel pump relay that's in the small fusebox on the passenger side near the alternator.

I'm not sure what you mean by which side coil/switch. Can you elaborate a little more?

Mechanic called me back and said even a stronger fuse is blowing and they want to drop the tank and replace the pump... :shrug:


Sorry I didn't explain in my other post. A relay has a coil [electromagnet] that opens or closes a switch. Both are inside the "box".
The switch is basically a thin metal tab, so when the coil gets power it attracts the switch [tab], the contact [tip] touches another contact and opens or closes a circuit.
So you have 4 wires into the relay [you can have more or less, but I'm trying to keep it simple]. 2 of the wires are for the coil, 1 power in and 1 ground. 2 Are for the switch.
The relay has 2 separate circuits. 1 Is for the coil and the other is for the switch. They each have their own fuse, power and ground.
So if the switch in the relay is melting [which is highly unlikely BTW] the problem is in the switch circuit [actually the circuit is for whatever part the switch is controlling; in this case the fuel pump, so the "switch circuit" is actually the FP circuit].
If the coil is getting fried the problem is in the circuit for the coil, and the fuel pump is unrelated.

Relays go bad because either the switch contact [the tip] gets pitted/burnt or the coil either has an open [nothing will work, which is what usually happens] or a short [you blow fuses].


You might have a bad pump. If it is, you're fine putting another 550 in there. It's hard to tell what's going on without looking at the car myself. I don't know what's lost in "translation" with your mechanic.
Which fuse is blowing? Is it a fuse or relay?
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Re: Blowing Fuel Pump relay

Postby lumbercis » Sat Nov 12, 2016 11:42 pm

The relay that is blowing is the one that is MISSING in this photo I found online
http://i137.photobucket.com/albums/q202 ... 010005.jpg
Sorry couldn't find a pick of the fuse box with the relay in place.

They said the resistor pack was bypassed when the engine swap was done. So it's there but apparently not doing anything.

They checked the fuel filter and it wasn't clogged.

They said when they tried the more powerful relay it ran for a minute and then blew and it was extremely hot.

They want to put a celica 440cc fuel pump back in. They don't think the Supra pump is necessarily bad but that it's putting too much pressure on the electrical system somehow. They quoted me about $500 for this job.

I probably made a mistake by taking it to a non-specialist mechanic but the shop that did all the aftermarket work is too far away to tow it and tbh most of the modifications they've done have been a problem in some way. I'd either have to tow it somewhere else or just let these guys get it running however they can.
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Sun Nov 13, 2016 2:03 am

Yeah, it's a yellow one that goes where that jumper sticking up is.
Incidentally; that's a jumper for that same circuit for a 5SFE [in the picture].

That jumper is the best way to get rid of the relay.

There are 2 different resistor packs in your engine bay.
One is for the fuel injectors. On the 1-3 gens the injectors are low impedance[resistance] so the resistor is added in to increase resistance in the circuit so the ECU doesn't blow the driver for the injectors. The gen 4 has high impedance injectors [IIRC] so it doesn't need the injector resistor pack.

The second is for that low/high speed relay for the fuel pump. I think this is still used in the gen 4 setup [maybe not?]. If it is, it can be bypassed. Best way is to use that factory jumper in the picture you posted.

I don't know how else to say it; that shop sounds like a bunch of idiots.
Which fuse was blowing? Or was it just that relay that was blowing?
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Re: Blowing Fuel Pump relay

Postby freddie » Sun Nov 13, 2016 2:44 am

Sorry, yesterday I forgot to say my prayer. (Dear Lord please help me to keep my big mouth shut)

When you turn the ignition on to start the car, the ECU turns the fuel pump on to prime and pressure the system.
I just went outside and started both my ST165 and 152 and confirmed this was so. The next thing to try is, disconnect a
fuel hose and turn the ignition on. When trying to do this make sure safety is at hand no naked heat or flames and stand
well back. Some ECU's turn the pump off again (after a few seconds( so not to flood the system during starting.
My last car had a Haltech ECU and when the ignition was on so was the pump and it stayed on until cranking the engine.
As it did not get electrical power while cranking, the pump was off.

The fuel pump resistor does get hot. Any resistance to electrical flow produces heat. that is why the casing is metal and with heat
disbursement fins. However if this unit gets super hot, like you can smell the wire insulation getting hot (starting to melt) and the
paint starting to smoke and if you touch it, it will burn your skin off, most definately something is wrong. I have done this in the past
hooking up a resistor on a ignition coil the wrong way.lol.

By the way. the other day I backed my 162 over a rock and dented in the bottom of fuel tank. So now I have to remove the tank and
knock out the dent. And it is full of fuel. Guess what i have to do? Ok ok you people call it gas.

Cheer
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Sun Nov 13, 2016 1:22 pm

In a word; no.

Toyota's don't self prime. Furthermore, if they did [which they don't] you certainly wouldn't hear the pump; they are very quiet.
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Re: Blowing Fuel Pump relay

Postby lumbercis » Sun Nov 13, 2016 7:23 pm

From what I understood it was only that relay that was blowing. No other fuses or whatever were blowing.
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Sun Nov 13, 2016 9:51 pm

Is the car back in your possession?
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Re: Blowing Fuel Pump relay

Postby freddie » Mon Nov 14, 2016 6:27 am

The attached picture is from the Toyota Celica ST165 Repair manual page FI-23 showing the
fuel Pump and the wiring diagram.

Power is supplied to the EFI Main Relay via a 15 amp fuse.
When the Ignition Switch is turned on (IG2) the EFI Main Relay is opened (well closed actually)
Power is then supplied to the Circuit Opening Relay and the ECU.
In turn the COR supplies power to the Fuel Pump.
Also note the relationship of the COR and a switch within the Air Flow Meter.
Note the wire from the Fuel Pump Relay to the ECU and how it controls the Fuel Pump Resistor.
And the wire from the Starter Relay to the COR.

Summary: When you turn the ignition switch on (to IG2) 12 volt power is supplied to to the Fuel Pump
and the fuel system is primed. How else is fuel pressure provided for the Fuel Injectors to work??

Mr Alltracman 78 I am not a jerk. Apologies please.
If you remove the petrol tank cap and put your ear to the opening, while getting someone else to turn on the ignition, you can hear the pump operating. Mind you it gets hard if the tank is full of fuel. Walbro pumps are noisy (that's what is in my 165)
Attachments
Celica Fuel Pump 001.jpg
Please look at the pump wiring diagram
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Re: Blowing Fuel Pump relay

Postby lumbercis » Mon Nov 14, 2016 4:50 pm

@alltracman78:
Its at a shop around the corner from my house. It doesn't look like they've started work yet but maybe they will today.
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Re: Blowing Fuel Pump relay

Postby alltracman78 » Wed Nov 16, 2016 1:22 am

So you're going to have them replace the fuel pump?
Maybe they're right; I'm not there so it's hard to say they're crazy.
Too bad you're not near me, I'd take a look at it for you.

freddie wrote:Power is supplied to the EFI Main Relay via a 15 amp fuse.
When the Ignition Switch is turned on (IG2) the EFI Main Relay is opened (well closed actually)
Power is then supplied to the Circuit Opening Relay and the ECU.
In turn the COR supplies power to the Fuel Pump.
Also note the relationship of the COR and a switch within the Air Flow Meter.
Note the wire from the Fuel Pump Relay to the ECU and how it controls the Fuel Pump Resistor.
And the wire from the Starter Relay to the COR.

Summary: When you turn the ignition switch on (to IG2) 12 volt power is supplied to to the Fuel Pump
and the fuel system is primed. How else is fuel pressure provided for the Fuel Injectors to work??


Look man, you obviously can't read a wiring diagram [I know I'm being a dick, but it's very frustrating when someone that can't even read a simple wiring diagram keeps trying to tell me I'm wrong].
Go back and look at your diagram. There's only 2 ways the COR works; if the starter is working or if the AFM switch is closed. Neither of which happens when you turn the key to on.
You have to turn the key to start; the starter supplies initial power the COR coil, closing the switch inside, giving the FP relay power, which sends power to the fuel pump.
Once the engine is started the switch in the AFM is closed, it keeps the switch inside the COR closed after the starter is off, and keeps power to the pump.

As far as your 165, either you're hearing something else or someone rewired your fuel pump circuit.
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