Hello all!
does the fuel pump ecu have failing capacitors like the engine ecu in the 1994 lexus ls400??
I have a jerking problem under load. Its like a "fishbite" effect. Help!!!

I've already addressed these issues with oem parts replaced:
engine ecu, maf sensor, tps, coils2, ignitors2, coolant temp sensor, plugs wires caps rotors, timing belt, air filter, cats3, fuel filter twice, trunk wiring harness is just fine as well.

 

Hello,

Any check engine lights? If so, what are the trouble codes?
Did you check the fuel pressure? Is it normal at the whole RPM band? An old fuel filter can also cause those issues.
Are you sure that the engine itself is good? Is the compression in specs? Any smoke?
What exactly do you mean by "fishbite" effect? Is it a misfire, stalling, etc?

To diagnose issues like that, I would suggest you to use a diagnostics tool described below and a free software like Car Tester 8000; that will allow you to see and log live parameters of your engine. With that device connected, see if you can recreate a described issue, that should give you some useful information.



Hope this helps and best of luck!

 

There are only a fuel pump relay and a resistor between the fuel pump and the main ECU. Some people say there is a fuel pump ECU but there isn't anything like that. I imagine your problem can be checked measuring the fuel pressure. A weak pressure often causes your type of problem caused by the badly clogged fuel filter or a failing fuel pump. In case of a fuel pump, the problem tends to happen when the pump is warmed up after running some.

The fuel pressure is not monitored by the ECU and it is not possible to read the code, I must add.

 

Thank you Yamae,
There is no resistor on a 94 LS400. There is a Relay on my car (CA emissions car) and a fuel pump control module...located in the trunk on the right.
I'm asking if the module has capacitors like the ECU that fail in time.

93-94 Lexus LS400 OEM 219000-0010 Fuel Pump Control Module 89570-50010

also,
ive put my eyes and hand on the Relay and it wiggles when connected. Curious if this is supposed to be a firm fit like the a
Air Pump relay next to it in the same compartment. AP relay is firm when connected and no movement.

 

There isn't any capacitor inside. It only contains a resistor about 0.7 ohm inside the box. The heat sink is used to dissipate the heat.

Correction! My apologies. Above my statement was not correct. See this my new post. There is a PWM circuit and capacitors are used.

 

It looks easy enough to access. Remove the 4 screws, open it up, and take a look for yourself.

 

It do have one

Nippon 820uF 50v 105c Radial Electrolytic Capacitor .

 

Morning Yamae, on a different but related matter it appears to be extremely difficult to get to measure the fuel pressure for these engines. It seems to require a particular specialized kit of some sort with an elongated banjo fitting. The designers could have made it easier imo - but it is what it is anyway. Thanks for your input.