A Toyota factory original fuel shutoff solenoid for a carburetor
measures 90 ohms, but the aftermarket ones I've checked measured 30-35
ohms. Can this low resistance damage the car's computer by overloading
the transistor that drives it? I can add a driving relay between the
computer and solenoid for a lot less than what a factory solenoid would
cost.

I can add a driving relay between the computer and solenoid for a lot
less than what a factory solenoid would
cost.

Or a transistor. Possibly a switching transistor. Or maybe the
aftermarket relay has a diode across the coil to save it from spikes or
to elimate interference to the original transistor/circuit.

Bob AZ

I can add a driving relay between the computer and solenoid for a lot
less than what a factory solenoid would
cost.

Or a transistor. Possibly a switching transistor. Or maybe the
aftermarket relay has a diode across the coil to save it from spikes or
to elimate interference to the original transistor/circuit.

Bob AZ

larry moe 'n curly wrote:
A Toyota factory original fuel shutoff solenoid for a carburetor
measures 90 ohms, but the aftermarket ones I've checked measured 30-35
ohms. Can this low resistance damage the car's computer by overloading
the transistor that drives it? I can add a driving relay between the
computer and solenoid for a lot less than what a factory solenoid would
cost.

JUST BUY A NEW CAR.

"larry moe 'n curly" wrote in message
oups.com...
A Toyota factory original fuel shutoff solenoid for a carburetor
measures 90 ohms, but the aftermarket ones I've checked measured 30-35
ohms. Can this low resistance damage the car's computer by overloading
the transistor that drives it? I can add a driving relay between the
computer and solenoid for a lot less than what a factory solenoid would
cost.

The simplest and most robust fix would be to put a 60 ohm resistor in
series
with the solenoid coil and see if you get enough current from the computer
drivers to activate it reliably. You might not, (and then again you just
might.)
Some solenoids work over a fair range of voltage and current.

If that doesn't work, I would use the factory computer as a driver for an
outrigger relay. As another poster mentions, you could also do it with a
transistor.

larry moe 'n curly wrote:
A Toyota factory original fuel shutoff solenoid for a carburetor
measures 90 ohms, but the aftermarket ones I've checked measured 30-35
ohms. Can this low resistance damage the car's computer by overloading
the transistor that drives it? I can add a driving relay between the
computer and solenoid for a lot less than what a factory solenoid would
cost.

Your CCM (Carburetor Control Module) (just wrote that cause it sounds
funny) is a hearty unit, capable of much abuse. Secondly, I suspect
you measured the resistance of the OEM part that has failed... that
resistance value would be fairly meaningless. My apologies if you got
that measurement from a new unit. 30-35 ohms is a fairly common spec
for Toyota solenoids, I wouldn't be worried.

Toyota MDT in MO

larry moe 'n curly wrote:
A Toyota factory original fuel shutoff solenoid for a carburetor
measures 90 ohms, but the aftermarket ones I've checked measured 30-35
ohms. Can this low resistance damage the car's computer by overloading
the transistor that drives it? I can add a driving relay between the
computer and solenoid for a lot less than what a factory solenoid would
cost.


If its controlled by a transistor then I wouldn't worry as most of those
will have current limiting and heat sensing built in nowadays.

If its a fuel pump I would be more concerned as sometimes these are
PWMed, but a shut off solenoid I don't think I would worry about.

--
Thank you,



"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

30 ohms across 12 volts will draw about 0.4 amps. Your typical
transistor, when fully on, drops about 0.4 volts. So the transistor
will be dissipating about 0.16 of a watt, not enough to cause any major
heating, unless it's a micropower signal transistor, which would be a
ridiculous design choice. I wouldnt worry about it.

Comboverfish wrote:
larry moe 'n curly wrote:

A Toyota factory original fuel shutoff solenoid for a carburetor
measures 90 ohms, but the aftermarket ones I've checked measured 30-35
ohms...I can add a driving relay between the computer and solenoid
for a lot less than what a factory solenoid would cost.

Your CCM (Carburetor Control Module) (just wrote that cause it sounds
funny) is a hearty unit, capable of much abuse. Secondly, I suspect
you measured the resistance of the OEM part that has failed... that
resistance value would be fairly meaningless. My apologies if you got
that measurement from a new unit. 30-35 ohms is a fairly common spec
for Toyota solenoids, I wouldn't be worried.

Toyota MDT in MO

I checked the secondary (1-wire) fuel cut solenoid, and it measured the
same 90 ohms. I was warned that coils can fool digital meters because
they measure ohms by sending out pulses, but the resistance read the
same with an analog meter.

The replacement solenoid is a Neihoff (good? bad?) and doesn't seem to
be built as well as the original.. Its threads were rough (I lapped
them to keep aluminum bits from shaving off and getting into the
carb), and the wires were insulated with common 105 Celcius vinyl that
I'm sure will become rock-hard and crack in a year. I sleeved each one
with high-temp heatshrink to reduce the chance of shorts from this.

larry moe 'n curly wrote:
I checked the secondary (1-wire) fuel cut solenoid, and it measured the
same 90 ohms. I was warned that coils can fool digital meters because
they measure ohms by sending out pulses, but the resistance read the
same with an analog meter.

Resistance checking a coil with no current passing through it will
yield meaningless results in some cases. It won't tell you if the coil
only fails under a load. The part about "sending out pulses" is
generic and IMO wrong. The DVOM passes a very small amount of current
through it's leads and into the tested component and determines an ohm
value based on known current and voltage.

The replacement solenoid is a Neihoff (good? bad?) and doesn't seem to
be built as well as the original.. Its threads were rough (I lapped
them to keep aluminum bits from shaving off and getting into the
carb), and the wires were insulated with common 105 Celcius vinyl that
I'm sure will become rock-hard and crack in a year. I sleeved each one
with high-temp heatshrink to reduce the chance of shorts from this.

Neihoff is decent in general. Typical aftermarket shop stuff that in
most cases would exceed Autozone products. I don't think you have
anything to worry about with using it. I've always tested and reused
the original solenoids on Toyotas. I've never found a bad one during a
rebuild. The heatshrink was a good idea.

Toyota MDT in MO