I took my SC400 to the Lexus Dealership and ended up paying $146 for basically a car wash - they want $350 to do some diagnostic checks w/o any promises. They haven't found a thing wrong ... so I need some help!

The issue is the motor starts cutting out under WOT after it reaches 5200 or so RPM's. There is no check engine light nor codes in memory. And under normal driving, there are no issues.

Here are the basics of the car:
- 160K miles w/ regular maintenance. Bone stock w/ Lexus replacement parts.
- plugs replaced 30K miles ago. I just pulled out #3 plug and it looked great.
- plug wires, rotors, caps, coils were replaced 80K miles ago - they look good.
- fuel filter replaced 50K miles ago

When the motor does cut out, there is no back firing. It just starts severly bucking and I let off the throttle in fear of doing some serious damage. Until it starts cutting out, the motor is very strong and rev's quickly with no issues.

Anyone have a similar experience and could suggest some things to start with?

 

If I had to guess I would say you may have a problem with a knock sensor throwing timing.

 

fuel pump ecu?

 

It can possibly be the engine ecu.

 

This is not usally a problem on these cars but sometimes thats a condition of a bad or clogged fuel filter. Im willing to bet that this is a fuel related problem somehow.

 

he said he had the fuel filter replaced so i dont see that as being the issue most likely.

i personally havent see a stock toyota one fil but it may be the fuel pressure regulator.

you should also look into the fuel pump ecu. its suppose to provide full voltage to the pump under higher loads and rpm. at low loads it gives a much smaller power source to the pump. if that is an issue then you are basically not pumping enough fuel into the motor at high loads. it can also cause your motor to run lean, and in extreme case on racing engines, burn a hole in a piston...or 2.

good luck.

 

fuel filter replaced 50K miles ago. 50k !

 

when I finished my motor swapped, i didn't have a good enough connection for my igniter and my rpms would start cutting off and on around 5k, at the same time the CEL would blink too until it came under 5k rpm. just a suggestion

 

i know. u said that already. i wasnt talking about your fuel filter.

 

sounds like fuel to me, get a new fuel filter and use up old gas, get new gas and seafoam that shiot!! probably 2 time in a row sill acting up... then could be something more in depth with a sensor. Eve if you did replace it 50k ago doesn't mean something somehow did fall in your tank and get stuck in the filter, and could also be fuel pump, luckly that is all easy changeable and fixable stuff so try cheapest first and hope.

 

Thanks for the info. I'm starting to believe it's the fuel pump or the fuel pump ECU. When I spoke to Lexus, they claimed they have never replaced a fuel filter. I couldn't believe it, but when I asked the parts guy to pull a history on my filter, they confirmed they have never sold one. According to the shop manual inspection procedure, it's indicating a possible fuel pump or ECU. However, I do not have the SSTs to do the flow test so still not sure.

I did do the test on the coils (passed), the throttle sensor (passed), and the VSV on the fuel system (passed). The traction control throttle sensor didn't pass the diagnostic test, but I've turned off the system with the switch and, unfortunately, got the same result. Also, I don't have the equipment to test the VAF meter so that's still a possibility.

Tomorrow I'll do the diag test on the fuel pump ECU.

 

I doubt its the fp ecu .Your symptoms are different from a bad fp ecu .there is a easy way to diagnose the fp ecu . Fp and B+ in the diagnosis port. Most likely its a bad ecm. Ive seen it happen to dozens of sc400's.

 

Have you have a problems trying to start up the car ?

 

don't you just love those "stealership guys". How pathetic. A Lexus stealership never changing out anyone's fuel filter.......pathetic. I doubt that they even used "water" to wash your car. Probably just used a handi wipe....Buddy just do yourself a big favor and track down a good indy shop that works on Toyota products.Forget the idiots at the dealerships. They are ALL pathetic in my opinion. Back to your problem, it is odd that you are not spitting out an engine code. (Autozone will run your codes for free) If it is a fuel pump ecu, they can be had, all day long from the junk yards, for around $30 and can be changed out real easy. Also, are you saying that there is NO PROOF that your old filter was changed to new? Autozone sells them for like $20. Check/replace the simple/cheap stuff first and LOOK everything over real good..ie..vacume lines, electrical connections, grounds etc. Good luck and keep us posted on the fix. It is usually quite simple and "obvious" once you troubleshoot and find it. They are Toyota's remember....

 

have you tried driving the car with the MAF disconnected? It will throw a code when disconnected, but this is an easy way to rule out a MAF related issue.

Also if you caps, rotors, and wires were replaced 80k miles ago it might be time to take a look at them again. One of my wires had a break in the insulator jacket and was causing a slight miss at idle and sometimes would studder on acceleration. The spark was arching on a ground and caused the studder.