Acceleration Hesitation

[dopefishzzz]

Hi !

I've got a 94 ES300 with 200,000 miles on it.

Air filtter and fuel filter have been changed recently.

When accelerating under WOT (Wide Open Throttle), the car hesitate, only between 3000rpm and 4000rpm. Below & Above, I get normal acceleration.

When I say hesitate, I mean that the car lose about half of it's power, but still has enough to go pass the 4000rpm mark.

Gas mileage is fine and I've got no check engine light. Engine runs smooth, no strange noise and no shaking.

What could be the problem ?

(Note that I have a small exhaust leak, just behind the muffler, could It be affecting THAT much ?)

Thank you.

[wwest]

Hi !

I've got a 94 ES300 with 200,000 miles on it.

Air filtter and fuel filter have been changed recently.

When accelerating under WOT (Wide Open Throttle), the car hesitate, only between 3000rpm and 4000rpm. Below & Above, I get normal acceleration.

When I say hesitate, I mean that the car lose about half of it's power, but still has enough to go pass the 4000rpm mark.

Gas mileage is fine and I've got no check engine light. Engine runs smooth, no strange noise and no shaking.

What could be the problem ?

(Note that I have a small exhaust leak, just behind the muffler, could It be affecting THAT much ?)

Thank you.

Might be somewhat SOP at 200,000 miles...

Valve float due to weakened valve springs, slight backfire, etc.

[dopefishzzz]

Then why would the engine runs great at a much higher RPM ? Power is great at 5000rpm, 6000rpm etc..

Doesn't make sense to me,

but I'm no expert at all.

[wwest]

Then why would the engine runs great at a much higher RPM ? Power is great at 5000rpm, 6000rpm etc..

Doesn't make sense to me,

but I'm no expert at all.

Many cars have two springs on each valve, a heavy one and a lighter one inside of that.

I cannot explain the engineering aspects, I just assume it takes both springs to cover the wide range of frequency, 500 to 6000 RPM, of valve opening and closing operation.

I could see how one spring might begin to allow the valve to float, say at 4000 RPM, before the second, lighter(??) spring comes into "play".

Many years ago I would have suggested a valve job, but at today's labor rates and with 200,000 miles....

[dopefishzzz]

Then why would the engine runs great at a much higher RPM ? Power is great at 5000rpm, 6000rpm etc..

Doesn't make sense to me,

but I'm no expert at all.

Many cars have two springs on each valve, a heavy one and a lighter one inside of that.

I cannot explain the engineering aspects, I just assume it takes both springs to cover the wide range of frequency, 500 to 6000 RPM, of valve opening and closing operation.

I could see how one spring might begin to allow the valve to float, say at 4000 RPM, before the second, lighter(??) spring comes into "play".

Many years ago I would have suggested a valve job, but at today's labor rates and with 200,000 miles....

Do you think a compression check would reveal if you are right ?

[SKperformance]

check for an egr problem as it open around that range.

[dopefishzzz]

Thanks for the tips,

but wouldn't an EGR problem cause the check engine light to turn on ?

[dopefishzzz]

Compression check done.

Nothing unusual.

[vetmx1]

I have a '00 that has a hesitation with a pop/backfire.

You're in the gas a little, let off, and immediately press it to the floor.

Runs fine otherwise.

[wwest]

I have a '00 that has a hesitation with a pop/backfire.

You're in the gas a little, let off, and immediately press it to the floor.

Runs fine otherwise.

Sure sign of burning/leaking intake valve(s), you need a valve job.