I thought it was hesitation

Tiny
SILLYBOY
  • MEMBER
  • 2007 SUZUKI FORENZA
  • 2.0L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 64,000 MILES
At around fifty mph, when car is at operating temperature, it seems to “hesitate” for a second, then stop, then hesitate again, etc. Until speed is below fifty mph. This has been happening for over six months now.

The engine or, is not hesitating though. I was watching the tachometer and when it seemed to hesitate, the rpm were actually jumping up about 150-200 rpm.

When the engine is cold on the same stretch of road, under the same fifty mph conditions the “hesitating” is not as prevalent.

Parts replaced within five thousand miles:

coil, OEM (Bosch) spark plugs, catalytic converter, both O2 sensors, spark plug wires, air filter

There is no CE light on.
There are no CE codes showing. I am using a Bluetooth OBDII and a tablet with the Torque Pro app.

I was at the dealer and they ran a diagnostic, and came up with nothing but a suggestion, “install the OEM plugs”. I did that, and it did nothing but make my wallet thinner.

I checked the fuel trims (from another web site) also, and was told that they are within the correct parameters.

What could it be?

Thanks, SB
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Wednesday, February 15th, 2017 AT 3:14 PM

14 Replies

Tiny
CARADIODOC
  • EXPERT
I suspect you are way in the wrong area. The glaring clues are the 200 rpm increase, and the speeds at which this occurs. This sounds like your torque converter is unlocking. The torque converter sits between the engine and transmission. The engine spins a fan. The fan spins the fluid. The fluid spins another fan that turns the transmission. This all sits inside the torque converter. There is some slippage in there that allows the engine to keep on running when the vehicle is in gear, but not moving, as in when sitting at a stop light. Chrysler invented a lock-up clutch in the mid 1970's to mechanically lock those two fans together for better fuel mileage. Every manufacturer uses a variation of that today. It will only lock up above a certain speed, typically thirty five to forty mph, only when in the highest gears, only when the engine is warmed up, and only when the throttle is held fairly steady at cruising speed. It will also unlock when the brakes are applied, in anticipation of coming to a stop.

To tell if this is what is causing the problem, drive at highway speed with the engine warmed up, hold the accelerator pedal perfectly steady, then with your other foot, briefly tap the brake pedal. You will see engine speed increase about 200 rpm, then drop back down about two or three seconds later.

If the same thing is happening on its own, the two most common causes are the brake light switch is out-of-adjustment and the rattling pedal is turning the "lock-up cancel" signal on momentarily, or there's dirt or a bad connection inside the throttle position sensor. The torque converter will unlock at wide-open-throttle to provide double the torque, and at close-throttle, to allow the engine to slow down while coasting. An intermittently-lost signal from the throttle position sensor can confuse the computer into thinking it should unlock the torque converter. If the brake light switch is suspect, hold it up with your toes to see if the problem stops occurring.
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Wednesday, February 15th, 2017 AT 3:33 PM
Tiny
SILLYBOY
  • MEMBER
Thank You CARADIODOC for the super quick reply. I am dumping the other site I was going to.

I do have an extended warranty and I am sure that the torque converter is covered. How should I go about approaching the dealer with the info you gave me?

I was thinking to print out your answer and present to the service manager, and let them follow your directions.

Sound like a plan, or is there a better way? The dealer is the only one that will accept the extended warranty, sorry to say.

Thanks again.
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Wednesday, February 15th, 2017 AT 5:23 PM
Tiny
CARADIODOC
  • EXPERT
Most of the time this is not a torque converter issue. It is a lock-up clutch control system issue. The lock-up clutch is just following orders. It is those orders that are wrong.

When I experiment with this on my vehicles, I use the Chrysler DRB3 scanner. That shows the "Inputs and Outputs" associated with the lock-up function. It will show if lock-up is "requested" or "denied". In the rare event you see "requested", but it is unlocking at times, that is due to a defective clutch, low fluid level, or the wrong type of transmission fluid was used. It is more likely you will see it switching back and forth between "requested" and "denied", in response to something. You have to watch those inputs to see which one is changing when the unlocking occurs. My scanner will list the brake light switch as "pressed" or "released". If you see it change to "pressed" when you are not pushing the brake pedal, that will tell you which circuit to look at. If you see it switch to "denied" due to low coolant temperature, you might suspect a defective thermostat that is not letting the engine reach normal temperature, or an intermittent coolant temperature sensor. Those sensors have an extremely low failure rate because there is just one component inside it. It is much more common to have corrosion on the connector terminals.

The point is anything is a guess unless you have a scanner to actually see what is changing and what is simply responding to those changes. Be aware too that only a few models are picky about using the correct transmission fluid. The typical symptom when using the wrong fluid is a harsh shudder that can last from a couple of seconds to non-stop just as the speed is reached when lock-up will first occur. The shudder usually goes away at higher speeds, and it will occur again for a few seconds right after tapping and releasing the brake pedal. That shudder is caused by the lock-up clutch grabbing, then slipping, then grabbing again repeatedly. It is being pulsed on and off to create a smooth, gentle engagement, but the wrong additives in the fluid makes it grab too harshly. That gentle pulsing does not occur at higher speeds. At those higher speeds it is allowed to turn on fully in an instant because you will barely feel it.
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+1
Wednesday, February 15th, 2017 AT 6:46 PM
Tiny
SILLYBOY
  • MEMBER
Thank you again. I got in touch with the dealer service manager. They send transmissions out to be repaired or replaced. I am going to print out all your answers and show them to the transmission guy, an see what he says.

I tried to donate to this site, but the third field, to the right of the Mo/Date fields is not showing. Since I cannot fill it out, it will not let me send it.

Thanks Again
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Thursday, February 16th, 2017 AT 7:46 AM
Tiny
CARADIODOC
  • EXPERT
Let me know what they find.
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Thursday, February 16th, 2017 AT 5:34 PM
Tiny
SILLYBOY
  • MEMBER
I certainly will.

Thanks again
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Friday, February 17th, 2017 AT 3:12 AM
Tiny
SILLYBOY
  • MEMBER
Hello, I took my car to a transmission shop. They have been there 62 years. This is where the dealer sends their cars (and lots of other dealers do too). Was told that the torque converter is going bad. I have an extended warranty that they accept (whew!) Car is in their shop as I type. I was told that there was 17 hours of labor involved.

Thank You so much.

Did anyone get the donation fields fixed for this site? When fixed I will donate.

SB
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Tuesday, February 21st, 2017 AT 6:47 AM
Tiny
CARADIODOC
  • EXPERT
Thank you. I only know the site owners recently did some work on the donation system. I recently shut down my automotive electrical web site due to the cost going higher and higher every year. Seems everyone in the internet business makes money, ... Except me. I'd like to set it up again on a different hosting site, if I can find one at reasonable cost. Donations are greatly appreciated, but I'm happy to help everyone.
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Tuesday, February 21st, 2017 AT 4:38 PM
Tiny
SILLYBOY
  • MEMBER
Thank You for everything. I tried to donate but the field to the right of Month will not expand so that I may enter info. See image, and show to webmaster.
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Wednesday, February 22nd, 2017 AT 3:33 AM
Tiny
SILLYBOY
  • MEMBER
Opps.I mean "Year"
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Wednesday, February 22nd, 2017 AT 3:38 AM
Tiny
KEN
  • ADMIN
Thanks for the image we have our tech guy working on that now. Can you tell us what device and browser you are using?

Best, Ken
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Friday, February 24th, 2017 AT 11:56 AM
Tiny
SILLYBOY
  • MEMBER
Firefox 51.0.1
Ubuntu Mate 16.04
Computer
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Friday, February 24th, 2017 AT 1:50 PM
Tiny
MAXIMILIAM
  • ADMIN
It has been fixed.
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Saturday, February 25th, 2017 AT 2:33 AM
Tiny
KEN
  • ADMIN
Nice work Max !
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Sunday, February 26th, 2017 AT 6:05 PM

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