Simple Solution To Hesitation Problem

[mnesbit]

I have a 95 ls400 with serious miles on it. i keep it well maintained but in the last several months i was getting a chronic hesitation from the engine which seems to be a problem with many sc and ls owners. performance has been quite lousy for the last several years.

the cause wasn't the fuel system, electrical, etc. but was caused by the top idler pulley. the bearings in the pulley literally melted this week and caused the belt to break so i replaced the pulley. i think the pulley started to fail many years ago which caused my fuel mileage to become horrible and engine performance to suffer including the hesitation and reduced hp getting to the rear wheels.

i was shocked at the results. the performance on the ls400 is unbelievable now. there is an incredible increase in hp, fuel economy and the hesitation has disappeared. the engine increases from 2000 rpm to 5000 rpm in a fraction of a second now. the ls400 is now powerful and very fast.

it is the best the engine has run since i bought the car 15 years ago.

so if you can't figure out why your ls400 or sc400 sucks and hesitates look at the tension and idler pulleys because the answer may be that simple. if they are old and worn you are putting a big drag on that engine.

[Exhaustgases]

If there was a huge drag from bad bearings the belt would have slipped and squawked. The hp loss to cause a slipping belt would be very small not more than 5 hp at the most. I don't think that was the cause of a hesitation problem. Maybe you wiggled the right wire in the repair process and fixed the real problem. Isn't 95 an obd2 ? When it had the problems you needed to have a decent scan tool to see what the operating conditions were.

[mnesbit]

no wires wiggled..simply replaced pulley.

[landar]

What pulley did you replace? There are two pulleys with the timing belt..tensioner pulley and idler pulley. Are you saying you replaced the timing belt idler pulley only? That does not really compute because, while in there to do that kind of a job, I would think you would also replace the timing belt and maybe water pump, not to mention the tensioner pulley. Something just does not make sense here and I think maybe we are not fully understanding what you replaced.

You are not, by chance, referring to the serpentine belt idler pulley, are you?

[mnesbit]

Hi Randall:

I replaced the top pulley for the serpentine belt not for the timing belt. Nothing else was done. I replaced the timing belt, water pump, etc. summer of 2013.

It doesn't make sense to me either. There was no previous squelching of the serpentine belt other than the morning that it broke. The bearings in the pulley had melted.

All I can say is the hesitation is gone. There is way more power and mpg is up.

The only think I can think of is the serpentine belt pulley started to fail a while back and some how affected the performance of the engine.

The improvement in the performance of the engine was immediate and very obvious. Best it has ever run.

So may the lexus gurus can figure out why.

[Exhaustgases]

Lots of times when R and R ing something you inadvertently touch and disturb other things not related to the job, you could have moved a wire and not even known that you did. There is a coil up front there and other sensors, that the loose belt could have touched when the thing flew off when it broke. So yeah you wouldn't have done it the belt would. There is no way that a pulley bearing and small power loss is the problem that you mention. The problem could resurface and is likely something you didn't know you did when the T belt was changed and then your broke belt fixed it.

[Micah.Berry]

Whatever the cause, I'm glad that it got sorted out. Seems as though you have a new engine! :) Enjoy how it performs now. Please chime back in after a few months to report on whether the engine performance is the same then as it is now. If Exhuastgasses is correct, then the chances of a slightly moved item returning to its prior state are probably good. However, if the pulley you replaced fixed the issue, then I suspect engine performance will be the same.

I am curious if the bearing becoming close to seizing would cause that much drag and possibly !Removed! timing some? A 95 doesn't have variable valve timing, which if I recall started in 98. Just brainstorming, but may be the drag caused the computer to !Removed! timing (like very poor octane gas). Most likely this is not the reason, but as I said, just brainstorming.

Glad that you got it fixed though!

Micah

[Exhaustgases]

To cause enough drag the belt would not last 5 minutes.

[landar]

I have to agree with Bob on this one. In order to drag the horsepower down enough to notice, the pulley or belt would be toast real quickly. That would be a lot of heat to dissipate.

Something else happened coincidentally with this change. Not sure what but guessing it was some wiring disturbed when plastic covers were moved to get to the pulley.