Aftermarket fuel pump and resistor over heating

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Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

I've read somewhere that after market fuel pumps can overheat the fuel pump resistor. What would be the symptoms of this?
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Re: Aftermarket fuel pump and resistor over heating

Post by warpc0il »

The fuel pump resistor gets too hot :roll:

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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

warpc0il wrote:
Sat Mar 21, 2020 5:24 pm
The fuel pump resistor gets too hot :roll:

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What else happens? Fuel pump cuts out?! Any other symptoms apart from the obvious?
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Re: Aftermarket fuel pump and resistor over heating

Post by warpc0il »

If the resistor burns out then there's no fuel pressure at low revs, so the engine is a pig to start and won't idle.

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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

The fuel pump seems to be cutting out momentarily at low/mid rpm. The Afr's are running a bit lean and I can feel it holding back. It's almost as though the fuel pump is running on 3/4 capacity and then snaps back to full capacity
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Re: Aftermarket fuel pump and resistor over heating

Post by warpc0il »

You could bypass the resistor for a short test.
I wouldn't try it for too long as that could cause other issues, but it's a useful diagnostic step.
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Re: Aftermarket fuel pump and resistor over heating

Post by Phil Bate »

How old is the rest of the pump assembly?
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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

Phil Bate wrote:
Sun Mar 22, 2020 12:40 am
How old is the rest of the pump assembly?
Pump is an AEM unit. Was brand new a couple of months back
New filter installed on bottom of pump
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Re: Aftermarket fuel pump and resistor over heating

Post by Honkytonk »

Paul don't know if it'll fit, but I have a full OEM recall RX8 pump you'd be welcome to have if you want it.
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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

Honkytonk wrote:
Sun Mar 22, 2020 10:44 am
Paul don't know if it'll fit, but I have a full OEM recall RX8 pump you'd be welcome to have if you want it.
Thanks for the offer but it won't fit unless it's a R3 pump.
R3 use the same body as mx5 just with a different inlet.
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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

I'm starting to think either the pcm isn't activating the relay properly and that's why it feels like it's holding back, or there's a fault with the relay. I have swapped these out
I need to find my resistor Bridge I made. Or failing that I may wire up the fuel pump directly
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Re: Aftermarket fuel pump and resistor over heating

Post by casey »

Another option is to remove the relay completely and use a jumper.

viewtopic.php?f=30&t=55420&p=989293#p989293

I've tried this and it works.
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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

I'll have at a look at that thanks.
I've removed the resistor and it's a load better.
My guess is the resistor was dropping the voltage to low
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Re: Aftermarket fuel pump and resistor over heating

Post by warpc0il »

The PCM doesn't check the voltage to the pump, so doesn't care about the current draw or the value of the resistor.

I'd be wary of running long term without any resistor in place, as the pump would be running full speed all the time, even at idle.
However you could replace the original 0.3 Ohm with (say) a 0.2 Ohm of the required wattage to allow your higher power pump to do what it needs.

Finding a suitably package resistor might be a problem, so the easiest solution would be to obtain a second OEM resistor (Bigpete?) and stack them with the connections in parallel - this would give an effective resistance of ~0.15 Ohm with double the wattage capability - which might be a good match to the pump.
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Re: Aftermarket fuel pump and resistor over heating

Post by casey »

That's a good suggestion Dave :thumleft:
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Re: Aftermarket fuel pump and resistor over heating

Post by Paul_13 »

I bought a resistor off said trader and it failed. Might try another