Hello Everyone,
My 1991 LS400 runs fine when engine and air temps are cold. But when warmed up, the voltage to the fuel pump will all of a sudden drop and go down below 5V (~4.7V). Of course the engine barely runs as fuel pressure is compromised, and either surges or stalls. If the gas pedal is pumped at just the right time, the engine will come to life and the voltage to the pump will shoot up above 12V (I hooked a meter up to watch voltage to pump as I drove). If the engine rpms remain high long enough (over 2500-3000 rpm) the vehicle will accelerate and run fine until the gas pedal is released. Then the voltage drops down below 5V and engine idles sporadically and/or dies.
Most of the time the it would restart but now that outside temps are higher, engine must cool off before doing so.
When running voltage to pump is around 8.8 to 9.6V at idle and low acceleration or at low engine load, but as engine warms to normal running temperature, voltage going to pump slowly and steadily drops down to about 7V before dropping off instantaneously to below below 5V.
Any information regarding this issue will be greatly appreciated. Thank you in advance.
Sincerely, Craig
P.S. - Bypassing the fuel pump resistor did not correct this issue. I had to wait for engine to cool down before car would restart so i could make it home. No cel codes stored or reported by ecu.
