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Huh, I never dug that deep into it honestly, it doesn't seem like the type of the resistor makes that much of a difference unless you are the one actually designing them. It is likely some kind of a Metal Film resistor, since it is a relatively cheap, yet still reliable enough under constant temperature fluctuations and a pretty hefty load among other things, though it is only my wild speculation..
As for the heat, the average draw of the fuel pump is about 6-7 amps, so there would be a fair bit of power going through that resistor when it is engaged, though it will be quite a task to calculate exactly how much power is flowing through it without measuring it.
Huh, I never dug that deep into it honestly, it doesn't seem like the type of the resistor makes that much of a difference unless you are the one actually designing them. It is likely some kind of a Metal Film resistor, since it is a relatively cheap, yet still reliable enough under constant temperature fluctuations and a pretty hefty load among other things, though it is only my wild speculation..
As for the heat, the average draw of the fuel pump is about 6-7 amps, so there would be a fair bit of power going through that resistor when it is engaged, though it will be quite a task to calculate exactly how much power is flowing through it without measuring it.
Hope this helps and best of luck!
Composition of resister element determines service life..
Unlike 1990-1997 LS400, the 1998 - 2000 LS400's are return - less fuel systems (fuel.returning to tank apparently increases emmissions(?)) so the ECU controls the voltage to the fuel pump..and the fuel pump resister plays a role.
Still no answer on resistor composition...
Numerous posts on 1998-2000 LS400 with too low idle RPM.
Cleaning the throttle body and air mix paths oftentimes resolves this.
Mine are clean, the fuel pump, fuel pump regulator, in tank and external.filter are relatively new (soft failure of pump), the fuel pump relay is new, the MAF sensor is new OEM (trouble code... improved part throttle response and fuel efficiency) I may try an aftermarket NTK.
My negative battery cable and engine to chassis ground wires are new 4 gauge marine grade and all ground points on engine and chassis have new OEM fasteners.
So am.focusing on the fuel pump resistor, hence question on its composition.
The wire wound resisters are durable, and so tend to fail open circuit.
Other resistor compositions may exhibit age or use related degradation before critical failure.
Have noticed an occasional up/down hunting at idle coming to a stop which suggests the ECU is attempting to self correct idle speed...perhaps the ECU is toggling the fuel pump relay between fuel pump resistor and full pressure ?
The commonality of this low RPM issue may concern fuel pump voltage sensing or regulating circuit on engine ECU. (Mine has all new capacitors)
Whatever the cause, have ordered a new fuel pump resistor from Lexus and will report results.
So what kind of issue are you having?
Where did you get a brand-new karman-vortex sensor?
Sorry for an obvious question, but did you try testing the IAC valve on the front of an intake?
On 1989-1997 LS400, the ECU neither checks nor controls the voltage sent to the pump, it just engages it through the relay, from 1998, however, the resistor was phased out in favor of a separate control unit, which is indeed controlled by the ECU. Not sure about 1993, but a 1994-1997 has two Fuel Pump relays, Circuit Opening Relay sends the current through the resistor, the Fuel Pump Relay goes straight from the battery, so you can diagnose the resistor by either removing or shorting the Fuel Pump relay to see if you can spot any difference. If your setup is different, you can simply disconnect the resistor, it runs in parallel and is there only to prolong the life of a pump. With that, the only way to exclude fuel supply completely is to get a pressure gauge.
One common flaw on those engines is a Power Steering Load Switch, it opens a channel in the intake to raise the RPM when there is a high load on the pump, like when the steering is turned all the way to one direction. What happens is it either develops a vacuum leak, or the PS oil starts leaking through that valve straight into the engine, making it appear as if the piston rings or valve seals are on the way out, so it is important to check it once in a while.. Other place that develops leaks is a PCV valve that often gets clogged with sludge and can't close all the way, I would recommend checking it every oil change.
Other way to diagnose a pre-OBD2 car is to make yourself a tool described here, which will allow you to pull engine live data from the car, though it does have a refresh period of about 1 second, a part of an obsolete Toyota OBD1 protocol, there is nothing to do about it..
So what kind of issue are you having?
Where did you get a brand-new karman-vortex sensor?
Sorry for an obvious question, but did you try testing the IAC valve on the front of an intake?
On 1989-1997 LS400, the ECU neither checks nor controls the voltage sent to the pump, it just engages it through the relay, from 1998, however, the resistor was phased out in favor of a separate control unit, which is indeed controlled by the ECU. Not sure about 1993, but a 1994-1997 has two Fuel Pump relays, Circuit Opening Relay sends the current through the resistor, the Fuel Pump Relay goes straight from the battery, so you can diagnose the resistor by either removing or shorting the Fuel Pump relay to see if you can spot any difference. If your setup is different, you can simply disconnect the resistor, it runs in parallel and is there only to prolong the life of a pump. With that, the only way to exclude fuel supply completely is to get a pressure gauge.
One common flaw on those engines is a Power Steering Load Switch, it opens a channel in the intake to raise the RPM when there is a high load on the pump, like when the steering is turned all the way to one direction. What happens is it either develops a vacuum leak, or the PS oil starts leaking through that valve straight into the engine, making it appear as if the piston rings or valve seals are on the way out, so it is important to check it once in a while.. Other place that develops leaks is a PCV valve that often gets clogged with sludge and can't close all the way, I would recommend checking it every oil change.
Other way to diagnose a pre-OBD2 car is to make yourself a tool described here, which will allow you to pull engine live data from the car, though it does have a refresh period of about 1 second, a part of an obsolete Toyota OBD1 protocol, there is nothing to do about it..
Hope this helps and best of luck!
Mine is a 1999 LS400...
The PCV valve, PCV grommet and right/left bank vent tubes/clamps are new as are all other engine vacuum hoses.
The "steering load switch", vacuum lines and clamps are new.
Thanks for input.
P.S. 1999 LS400 has installed a 3UZ-FE (4.3 liter)
Mine is a 1999 LS400...
The PCV valve, PCV grommet and right/left bank vent tubes/clamps are new as are all other engine vacuum hoses.
The "steering load switch", vacuum lines and clamps are new.
Thanks for input.
P.S. 1999 LS400 has installed a 3UZ-FE (4.3 liter)
Ow, your account states that you have a 1993 model, so I was going off of it, though a 1999 one makes things a lot easier frankly.. Do you mean that your engine got swapped out for a 3UZ? I thought Toyota did away with the vacuum pressure switch with introduction of VVT-i, even a 1997 SC400 already had an electronic switch, reducing one of the more common issues with that engine.
What about the Live Data, Engine Load, MAF Readings and Fuel Trims in particular?
Installed new fuel pump resistor, new mating connector shell (wiring harness) and bolt.
The fuel pump resister is a ceramic block encased in a finned Aluminum case which appears very well made, so unlikely the issue, but will drive it some to see if any improvement.
Part numbers for fuel pump resistor and wiring harness mating connector shell..
Fuel Pump Resistor backside...solid piece of ceramic.
11-25-21, 12:23 PM
Fuel Pump Resistor
