Having the same issue and still doing a ton of research and testing... Looking for advice in hopes I am on the right track.

93 SC400

Fresh plugs and cables
New fuel filter
New Air filter
Unplugged the MAF and issue didn't change.
Jumpered the fuel ECU, no change.
Bought a new coil, swapped out each side in turn and no change, returned new coil
Replaced Engine Coolant Temp sensor
replaced caps and rotors
checked all plugs and cables
swapped out ECU with known good one, no change
Replaced MAF sensor with known good.

Issue persists.....

 

I have a '95 SC400 and I've had hesitation issues since I got the car in 03. Can anyone tell me how much the Fuel Pump ECU runs, and the part #? I think I rather buy a new fuel pump ECU than bypass it or buy used.

Mousiee

 

You can probably pick one up off flea bay for under a $100. Hit up Aliga. Have you narrowed it down to your fuel pump ecu.

 

I have not. I replaced my plugs, wires, caps and rotors early this year. I bought a new MAF sensor in '07. I had the IAC checked when I first got the car also. I'm gonna have my mechanic check the IAC, TPS and this soon.

 

I think this thread should be stickied in the maint forum based on how many people deal with this and how much info it actually contains!

 

I just picked up a 154 swapped sc400 and the motor runs perfect but under load it's giving me issues. I figured it was just poorly tuned with an safc causing the issue...So this problem occurs in most 400s ?

I'll have to spend some time with her next weekend and try and figure the tune out a little better.

 

I gave up, took it to a shop and got a free diag, turned out one of my injectors was just bad enough to do this but not bad enough to totally fail or cause a code.

 

Well it's good you know now. Are you going to yank your injectors and have them serviced. If so I sent mine to a guy in Washington state named witch hunter.

 

after factoring in the cost of one injector at retail cost ($240) and the amount of time and backache I would be looking at, not having ever dug that far into my engine, I decided it was worth the $400 to have a shop do it for me and know that it was done right and the work was warranted. They said my other injectors tested fine but recommended I use something called Berryman's Injector Cleaner in a tank of gas about every other tank for a couple months and also only use gas from Texaco or Chevron since they have the cleaner stuff in their gas (I have been buying gas at my local grocery store station so god knows what brand it actually is).

 

I'll be doing all this this weekend....95 sc400. Great diagnostics.

 

how do u jump it from the pins under diagnotics under hood im a little slow lol but i need help cause my sc400 sound like it was running out of gas and i know that sound and i put gas in it and it still wont start i replace the fuel pump and still nothing u can text me the info 267 393 5739 r email it to me ikeim23@gmail.com

 

I think I found my hesitation cause. Looks like I have a bad Idle Speed Control valve. When I hook up the leads and go through the pin sequence, the mushroom tries to move but won't. Took it apart and cleaned it up, but still the same result. Cannot get it to open and close. Found one on fleabay for $55 that is in functioning condition. Better than the $504 to $850 that I could find at parts dealers and the Lexus dealer. Sure hope it works. What bugs me is I have less than 50,000 miles.

 

Great info !Thanks for taking the time with the pics and text.

 

FIXED MY HESITATION ISSUES!!! yay...

Ok so i did fuel ecu mod (got a lil better), replaced upstream O2's with universal bosch units. The seafoamed and replaced plugs, caps and rotors. It worked for like a min but my cold start problems came back (rough idle until warm). So i got fed up and stopped driving it, then i ran into an old mechanic buddy of mine who found the problem. I eventually replaced the maf (just to be sure) and i installed new OEM denso upstream O2 sensors. After this the car was almost there...after digging further the PO did a timing belt and water pump install.

Well as it turns out the driver bank and crank were at TDC but the passenger bank was almost 2 teeth off. We fixed that and boom, car was fixed and boy does it have power. I also had him do a complete fuel system treatment. If anyone in San Diego needs work on their car my buddy will do it on the cheap. He is ASE cert and will do it in your driveway.

As of know car is in shop for paint and bodywork and next my r154 swap and i dunno...maybe a turbo!

CHECK YOUR TIMING FELLAS...even 1 tooth off will allow it to run and idle smooth but under load will hesitate!

 

I just fixed mine as well. I bought the car a few months back with a blown piston ring. Stored it at a buddies place for the last few months and finally worked on it today. No typical symptoms of blwn rings, so we did a compression test first. All around 170-180psi. Then decided to check spark. Bam, drivers side distributor was not giving any spark to the plugs. So decided to check if the actual coil was giving anything to the distributor because it looks to be a pain to change and checking spark at the coils was easy enough. Sure enough, it was the coil. Swapped the 2 coils around for verification and sure enough, when the drivers coil swapped to passenger, no spark. So I'll get a new coil and left the bad coil on the passenger side since it is a lot easier to swap in the new one.
Woot woot, I'm excited. Don't need a new motor and I can focus my funding on my r154 swap. Have everything except the quantum kit now, so I should be 5speed fairly soon.
So I guess the moral of the story is, don't listen to what everybody tells you
and check for spark and fuel
Charley