The SC was running great and today I did an oil and filter change put in 5 quarts of oil which is just under the full line as well as put in a new OEM air filter. Well after all of that the car has a loss of power under full throttle. it starts and idles fine it also revs just fine well in park, Its only when im driving that it will lose power and surge but like I said only under full throttle. I am new to this car so any suggestions would be appreciated. I should add the car already has new plugs, wires and caps prior to these problems

 

Check the IACV, MAF, clogged cats (4), and report back. Any codes?

 

The only code showing is 71 which has been on for ever and never caused a problem in the past. The SC does not have any cats on it they have been hollowed out. As for the IACV and Maf Ill check it tomorrow. The car also has a slight backfire right before it bogs down but like I mentioned earlier only under full throttle.

 

I have noticed that the car is experiencing fuel cuts similar to what my VW GLI did after a software flash when the fuel pump was unable to supply enough fuel under full throttle. It starts and idles fine and it also drives fine when you are just putting around but when you go full throttle it kicks down but then its like the engine freezes in time, The car doesn't accelerate nor does the rpms increase it just holds where it is. The fuel pump ECU is already bypassed so i'm not sure if the pump itself may be on its way out again.


1992 Lexus Sc400

Completely Stock
Factory exhaust with cats hollowed out

New

Timing Belt
idler pulleys
belt tensioner and serpentine belt
valve cover gaskets as well as oil and Trans pan gaskets
crank and cam seal
water pump and thermostat
wires, caps and plugs

 

It is possible that the ECU decided to dump. Also, could be your o2 sensors.

 

I will throw another ECU in tomorrow and see if that corrects the problem.

 

New ECU in today and still the same issue. Im thinking its a fuel problem.

 

did you do the rotors in the caps? I would also check both coils.

 

It sounds like the fuel pump is the issue may also be the regulator. Check fuel pressure at idle, 5000rpms, and driving @ 5000rpms. Also check the voltage going to the pump.
If it where a Ign. issue it would do it to you in park as well.

 

I was thinking the exact same thing. My next day off i'm going to replace the fuel filter as well as check the pump.