Fuel pump resistor hot like hell !!!

[asylum]

My fuel pump resistor becomes hot like hell ! Normal or defective ?
I ask because I have this power loss between 3500 and 4200 - 4300 rpm that disapears when I bypass the fuel pump resistor (explained in my last thread). And I realised that it becomes hot like hell when it is connected, impossible to touch it with the finger. Is it normal or is it the cause of my problem (defective resistor that delivers not enough voltage under the 4300 rpm switch level between low and high fuel pump speed)?

 

[solidol]

They get hot, but not that hot. Swap with spare good one.

 

[Old Guy]

The resistor should get hot. Haven't been to hell (yet :smile so hotter than hell is a bit subjective. The power dissipated in a resistor is equal to I^2xR and the temperature of the resistor will increase as the current and power dissipation in the resistor increases. The DC fuel pump motor (depending on the characteristic of the mechanical pump load) tends to look a little bit like a constant current devices. Using this rather gross simplification, if the resistance of the resistor were to go out of spec by increasing in value, that could reduce the output of the pump and cause the resistor to run hotter than it should (if the motor current stays constant).

I figured that this would be an easy thing to check because Honda would provide the spec for the pump resistor in the service manual. However, such is not the case. Honda does not provide a spec for the resistor so you will have to find somebody with a resistor that you can do a resistance measurement on and compare it to yours. If you have trouble finding a resistor to test, let me know and I will see if I can do a measurement on my car. However, my car is a 2000 and unless the part # for 2000 and your year is the same there is no guarantee that Honda did not change the resistor value during the production run.

Three other things to factor into this. 1) If you have a non OEM fuel pump it may draw a higher current than the OEM pump (at the same operating voltage) and that will definitely cause the resistor to run hotter than normal. 2) If your fuel pump is failing, depending on the nature of the failure mechanism the pump may be drawing higher than normal current which would cause the resistor to run hotter than normal, although that would be an unusual way for it to fail. 3) What is your car voltage at idle? If you have an overachieving alternator and your car is running 14.5 volts or higher at idle this will also cause the resistor to run hot.

 

[asylum]

Thanks. I have 14v at idle. Stock pump. I will try to swap the resistor with the one of my track nsx to see if it solves the problem. Afterward, I will change the filter. And if this does not solve the problem, I will change the pump.

 

[Old Guy]

I was out this morning doing some mild cruising around. Out of curiosity, when I got home I popped the engine cover and did the finger touch test on my fuel pump resistor. The resistor does indeed get really hot. After the engine had been shut off for about 5 minutes, I could briefly touch the resistor body with my finger; but, I could not leave my finger in contact with the resistor body for more than about 3-4 seconds. I expect that your hotter than hell observation is probably normal.

 

[solidol]

That's right, let's define hot like hell first.

 

[asylum]

Well I swapped the fuel pump resistor between this NSX and my track one and problem is gone ! I am happy that, for the time, the fuel pump is still ok.

 

[asylum]

When I said hot like hell, I could not touch it even a fraction of second. Far hotter than my cylinder head cover...

 

[Jinks]

I imagine this is why the resistor has a heat sink built into it’s housing and a cooling fan right near it. It probably gets very hot.

 

[furinax]

Would be perfect time to use one of those BBQ infrared thermometers...

 

[ralph cerbone]

the resistance value is on the back of the resistor , my car is a 97 , .7 ohms (symbol looks like upside down horse shoe) . Yes they get hot , there is an old thread from Gram about " fuel pressure ", he gets very deep into this , very good info. I shot mine with a thermo gun 120 -130 degrees ,local driving , average threshold of pain is 140 degrees yes , it will feel hot .