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acceleration issue at high speed

Old 12-08-2018, 04:58 PM
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Default acceleration issue at high speed

Hi, I have a 1996 buick regal, Olympic edition 204,400 miles, 3800 series 2 engine, no mods. K engine. while at highway speeds I sometimes attempt to accelerate and when I press the gas the engine rpm stays the same but if I release the pedal and press the gas again the engine surges to around 3000 rpm and i let off the gas a little it drops back down to around 2000 and it works fine. It only happens at higher speeds and it doesn't matter if I've been driving for 30 minutes or all day. I have NO error codes at all, no CEL'*

Another issue im having is a slight sound when I accelerate. its not a hissing sound it sounds more like "tsst", kinda like the sound you get if u press the valve stem on your tire for a second.
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Old 12-08-2018, 05:06 PM
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Sounds normal to me. When you gently accelerate, the torque convert stays locked up. But, when the ECU sees the accelerator release quickly and back on it, it unlocks the torque converter, when it unlocks, the engine RPM rises.

Not sure on the sound though.
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Old 12-08-2018, 07:47 PM
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So the engine not revving up when the torque converter is locked is a sign the car is actually doing what its supposed to do to protect the engine?
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Old 12-08-2018, 09:36 PM
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Originally Posted by bmbrelandjr View Post
while at highway speeds I sometimes attempt to accelerate and when I press the gas
Originally Posted by bmbrelandjr View Post
if I release the pedal and press the gas again
It would be important to know how far down you are pressing the pedal for this response. I'm guessing 75% . . . ?

Is the behavior different if you floor it?

Shifting from 2,000RPM in overdrive to third would get you to 2,840RPM, plus some slip from the now-unlocked torque converter and you'd be right around 3,000RPM at the same vehicle speed.

My guess: Sticky vacuum modulator.

How long have you owned this car?

How many miles have you put on it since you got it?

This behavior is a change from what you've noticed is regular behavior, right?

Originally Posted by bmbrelandjr View Post
Another issue im having is a slight sound when I accelerate. its not a hissing sound it sounds more like "tsst", kinda like the sound you get if u press the valve stem on your tire for a second.
Does this sound happen with the ignition off?
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Old 12-08-2018, 09:58 PM
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I don't think I've ever floored it when it happened. 75% is probably accurate, just far enough down to notice nothing'* happened. I've owned it for a few years, probably have put 10,000 miles on it. Yeah its definitely a new issue, but I have a feeling you might be right about the vacuum modulator (or the vacuum system in general). Ive had a few issues with my vacuum lines because some noob screwed them up before I got it.
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Old 12-09-2018, 12:11 AM
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To confirm the Torque converter clutch (TCC) is behaving properly, you can hold throttle still at cruise, and then start dragging the brakes slightly. Once you start to engage the brakes, the TCC should release, causing engine speed to jump. Once you release the brakes, the TCC should reengage soon after, and engine speed should lock back down.

I am also curious what the service history is. If the vehicle is down on power because it needs a tuneup, or as a result of another mechanical or electrical issue, it could cause what would appear to be a deadzone in the power band. When the TCC is locked at cruise, this is typically the weakest point, because the engine is locked with essentially a solid connection to the drive wheels, and often at a speed low in the power band. Think of trying to accelerate a car with a manual transmission up a hill in top gear. Just about anything is going to seem weak at that point.
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Old 12-09-2018, 12:21 AM
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Originally Posted by CathedralCub View Post
It would be important to know how far down you are pressing the pedal for this response. I'm guessing 75% . . . ?

Is the behavior different if you floor it?

Shifting from 2,000RPM in overdrive to third would get you to 2,840RPM, plus some slip from the now-unlocked torque converter and you'd be right around 3,000RPM at the same vehicle speed.

My guess: Sticky vacuum modulator.
I disagree with the sticky vacuum modulator angle myself. Shift points are computer controlled. The modulator simply sets line pressures based on engine vacuum, which ultimately varies the firmness of the shift. If you start getting really cushy shifts that take for ever, difficulty engaging (or missing a gear), or are tired of shattering your teeth every time it slams in to a gear, I would start looking at it, but none of those seem to apply.

If presented with your issues, I would start scanning live sensor data. A bad TPS can cause problems like this. A bad MAF sensor can cause problems. Heck, even a plugged catalytic converter or poor fuel quality can show issues like what the OP is describing.
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Old 12-09-2018, 01:30 AM
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Originally Posted by rjolly87 View Post
I disagree with the sticky vacuum modulator angle myself. Shift points are computer controlled. The modulator simply sets line pressures based on engine vacuum, which ultimately varies the firmness of the shift. If you start getting really cushy shifts that take for ever, difficulty engaging (or missing a gear), or are tired of shattering your teeth every time it slams in to a gear, I would start looking at it, but none of those seem to apply.

If presented with your issues, I would start scanning live sensor data. A bad TPS can cause problems like this. A bad MAF sensor can cause problems. Heck, even a plugged catalytic converter or poor fuel quality can show issues like what the OP is describing.
Good point. I was thinking old-school non -E transmissions. Next I'll point out problems with his carburetor.

Yes, what you said: a TPS, maybe with a dead or dirty spot on it. He presses down to 75% and hits the dead/dirty zone, reverts to previous then back to ~75% again and hits a good spot or clears crud off.

It will be good to find out the history of this car.
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Old 12-09-2018, 03:11 AM
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As far as the service history of the car, I can only tell you what I've done. limited to the engine. I've replaced the intake manifold gasket, intake plenum, PCV valve, evap purge solenoid, all fuel injectors and connectors, 6 spark plugs, spark plug wires, one coil pack, hot soaked with seafoam (wow after that), the usual fluid changes including transmission and filter, fuel filter and pump, flushed the coolant, new alternator and battery. I'm currently averaging about 19mpg, before the hot soak it was 14 or so. New belt, water pump. Replaced the idle pulley'* notoriously bad plastic connectors with the metal ones (did that when I changed the intake manifold). As far as fuel, I usually stick with Royal Farms with 10% Ethanol (its nearby). 87 octane (as recommended).

You have all given me a lot of ideas as far as what it could be.

Could it be a vacuum leak? I've tried tracing the issue maybe Ive overlooked something. I was thinking that 'tsst' sound could simply be the throttle releasing pressure. or the fuel regulator (which I also replaced) its not a constant sound, only the moment I press the gas or tickle the throttle at the throttle body.

Can I clean the TPS with solvent just to be sure? I'm not getting any error codes that indicate a TPS issue. Maybe I didnt align it properly when I changed the intake plenum? I cleaned everything thoroughly.

The catalytic converter works great, never had a problem with it (its a 50 state cat), even meets California standards. No real issue with the exhaust. Looks as though someone replaced the muffler at some point. Both resonators are intact and rumbling away.
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Old 12-09-2018, 09:56 AM
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I wouldn't try to clean the TPS. I believe they are sealed anyway. I would look at live data to check it, or there is info somewhere on how to check it with a multi-meter, but it typically requires breaching the harness.

Could it be a vacuum leak? maybe. The noise could also be a dirty throttle body. The noise could even be normal, and just happen when the throttle blade hits a specific angle.

Honestly, I would scan live data at this point to try and track down the issue, because it'* very easy to start randomly guessing. It could be many things.

Even a dirty MAF sensor.
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