94 Lexus SC400. I've been chasing this issue for a long time now and I've checked everything I can think of. I'm hoping some of the smart peolpe on this forum can point me in the right direction...

Starts idles runs drives fine but it's way down on power. It previously had an ecu issue that was triggering the cel for knock sensors and causing limp mode. It used to run fine unless the cel was on... then at some point it started running sluggishly whether the cel was on or off - felt like limp mode was on all the time (no timing advance). The ecu has been sorted out and no longer has codes but the car is still sluggish and feels like it's in limp mode. It sputters a bit on acceleration and just falls on its face at lower rpms. At higher rpms its less noticeable but if you push it too hard it will start cutting out pretty bad.

The engine has good compression and virtually no leak-down. Fuel pressure is good. Spark strong to all cylinders. Timing has been checked visually and with a light at idle. TPS and MAF have both been swapped out several times. IACV has been cleaned (idles perfectly). Coil packs, distributor caps/rotors, and plugs/plug wires have all been swapped out several times. Catalytic converters have been removed. 2 different ECUs exhibit the same symptoms (the 1 in the car has been professionally rebuilt by Josh @ Relentless).

 

 

Maybe test the ignitors? Assuming sluggish acceleration maybe due to lack of fuel, air, timing. Doesn't appear like your timing belt is worn.

 

Thanks for the reply -- I really appreciate any help I can get. Do you mean test the igniters or the ignition coils? I've got power going to all 8 plug wires (verified with a spark tester) so I thought I could rule out the igniters. Is there a test for the igniters specifically? The ignition coils are new and have been swapped out several times with no change.

On the pictures of the timing marks on the cams -- do they seem slightly off? Is it possible that my timing belt tensioner is failing and not taking up all the slack in the belt and allowing the cams to shift slightly advanced of the crank? The car runs pretty smoothly just doesn't have any power - especially on the low end.

Thanks again

 

I would test the igniters. Mine would run smooth, but as soon as I gave it gas it would stutter and trip over itself, and would not have any power. Overpowering smell of burned fuel, thought it turned into a 78 Chevy, where you have to give it gas to keep it on, except this one I wanted to run away before it set me on fire. Cooked both cats, and it turned out being the driver side ignitor had failed, it swelled and cracked along the leading edge. Once I figured how to pull it out, I swapped both of them out, have the old one as a spare in the trunk still.

 

Here is what it looked like.

 

Yeah that's an ignition coil pack. I just swapped those out recently. Your issue dies sound similar tho so I'll double check the wiring etc. Thanks!

 

Changed this crusty tensioner out but still runs the same

 

30 seconds of run time. Fuel flow looks good (thanks Kelvin). I'm thinking dirty injectors 🤔 I've tried pour in tank fuel injector cleaner many times but didn't change a thing.

 

Well I went ahead and pulled the injectors. Resistance looks good. Was hoping to find them full of crud but they looked pretty clean in the little basket inside... Professional cleaning or diy - any advice?

 

This one maybe up to you and your budget. If you can do it then go for it, if you feel better by sending it to a pro, then do that instead.

 

Thanks for the reply. I decided to do it all on the cheap for now since I don't even know if that's my problem or not. Ordered injector seals and valve cover gaskets. Borrowed an ultrasonic cleaner. I'll post an update of how it goes.

 

Pretty dirty in here and they were leaking so I decided to do the valve cover gaskets, cam plugs and spark plug seals while I've got the throttle body off.

 

 

This thing is lookin good... Should open a build thread and drop your stuff in there.