1999 Pontiac Sunfire Car skips/jumps intermitently

Tiny
CANADAINCYNOSURE
  • MEMBER
  • 1999 PONTIAC SUNFIRE
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 300,000 MILES
1999 Pontiac Sunfire 2.2L
When driving, the car intermitently jumps 200-300 rpm.
It occurs at various speeds - but more so on the highway.

Driving 50-60km/h it occurred, as well as at 90km/h
It's been occurring for a number of months but gradually becoming more frequent especially at around 100-120km/h. The car feels like it is lurching or skipping a beat, the rpm spike from 2500rpm to 2800rpm for approximately 3-4 seconds and settle back to normal.

Engine temperature seems good.

Since noticing the issue I have replaced Coil packs, spark plugs, wires, air filter, and the fuel filter.

A mechanic visually inspected the exhaust and the only note was the bracket was broken near the catalytic converter which he tied up with some mechanics wire.

The only things I can think of next are:
1. Air Temperature sensor
2. M.A.P
3. Maybe fuel filter?

I don't think it's the transmission because it occurs at different speeds.
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Monday, March 29th, 2010 AT 5:25 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
Sounds typical of a torque converter unlocking. They've been using a lockup design since the early 1980s to improve fuel mileage. It will unlock when letting off the gas or when tapping the brake pedal in preparation for coming to a stop. It will also unlock below a preset speed, typically somewhere between 35 - 45 mph, or your kph equivalent.

If you can make the same symptom occur by tapping the brake pedal while holding a steady speed on the highway, this is likely what you are experiencing. Things to check include the throttle position sensor, speed sensor, and brake light switch. If the brake switch is the culprit, it might stop acting up if you hold it up with your toes. If that works, it could just be out of adjustment. I'm not familiar with your car, but if the cruise control is on the same part of the brake switch, it might cut out too if the brake switch is misadjusted or has pitted contacts.

Your mechanic can also drive it with a hand-held computer called a scanner, to watch the sensor readings. It will also display whether torque converter lockup is requested or not by the Engine Computer.

Caradiodoc
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Monday, March 29th, 2010 AT 10:20 PM
Tiny
CANADAINCYNOSURE
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Thank you Caradiodoc - I'll give that a shot.
On a side note, the ETS light does pop-on when I initially move the car. I read somewhere that sometimes that can be related to the Torque converter. Is that true?

Additionally don't have cruise control - pretty standard model in terms of extras.
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Tuesday, March 30th, 2010 AT 12:45 AM
Tiny
CARADIODOC
  • EXPERT
Sorry, I'm not familiar with an ETS light. What does that refer to? Sounds like something out of my area of expertise.

Caradiodoc
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Tuesday, March 30th, 2010 AT 1:41 AM
Tiny
CANADAINCYNOSURE
  • MEMBER
My apologies - more details to give you a better picture. I also added some more to the donation for all your help.
It's a 2.2L 99 Pontiac Sunfire
Automatic 4 speed transmission
Standard options - only extra is AC

I appreciate your help - if it is the Torque Clutch - I want to be super sure since it's likely going to be the end for my car due to costs to repair (It's 10 years old)

ETS is the Sunfire's name for the Electronic Traction System.

I took the car out on the highway for an hour. Naturally it behaved itself this time. I pressed on the brake and low and behold I was able to reproduce EXACTLY what occurs.

I played with the brake pedal with - pressing it as much as half an inch to see if it was a switch issue, but I did not achieve any results.

Based on the fact that I was able to reproduce with by engaging the brakes - Is this then most certainly the Torque Converter?

1. Could it be the Selinoid - and is that easier to fix?
2. Does replacing the converter usually involve disassembling the transmission?

Thank you again.
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Wednesday, March 31st, 2010 AT 12:34 AM
Tiny
CARADIODOC
  • EXPERT
To replace the torque converter requires removing the transmission but not disassembling it. It sits between the engine and transmission.

The torque converter is doing what it is supposed to do as evidenced by the fact it is locking up. If it had failed, the lockup would never occur or it would cause a shudder as the clutch plate slipped. The intermittent unlocking is usually due to a sensor problem. As one example, if there is a "dropout" in the signal voltage coming from the throttle position sensor, the engine computer might think you took your foot off the gas pedal. When the signal voltage returns to normal, the computer will energize the lockup system again within a few seconds. Where you might notice this under normal conditions would be after coasting down a hill with your foot completely off the gas pedal. You might feel the converter lock up a few seconds after you resume pressing the pedal. On some cars, Chryslers for example, if you watch the tachometer, you will see it drop in two steps, the first step is when transmission fluid starts to apply pressure to the lockup clutch, and another drop when the clutch is fully locked. Each step drops engine speed by 100 - 200 rpm.

The fact that you can press the brake pedal half an inch before the converter unlocks tells you the brake light switch is not misadjusted. It still could have arced or pitted contacts, but that would not be real common because there is just a tiny signal current going through them. That low current isn't very hard on switch contacts.

What might be the easiest way to narrow this down is to have your mechanic drive the car with a hand-held computer, called a scanner, to watch the sensor readings and the "inputs / outputs". Most scanners also have a record / playback function that can record about five seconds of data. Because that data is stored momentarily as it passes through the scanner, the recording actually starts a couple of seconds before the "record" button is pressed.

When the recorded data is played back frame by frame, the mechanic can watch for incorrect sensor values and the inputs that affect lockup. Lockup should not occur if engine temperature is too low, vehicle speed is too low, or the transmission hasn't shifted into 3rd gear yet. The "output" will be displayed as "TCC" for torque converter clutch, "yes" or "no", or "on" or "off". If the display says the computer is requesting the lockup clutch to be energized when in fact it is not, the sensors and switches can be ruled out. That would indicate an electrical problem between the computer and the transmission. The most probable suspect would be a corroded or loose pin in an electrical connector. The solenoid could also cause the same problem, but on most cars, a break anywhere in that circuit will be detected by the computer which will memorize a fault code. Any fault that could adversely affect tail pipe emissions must turn on the Check Engine light. Since fuel mileage would drop if the converter wasn't locked up, emissions would go up. If that light is not on, there still could be other fault codes in the computer, but if there are no codes related to the torque converter, that would suggest the intermittent unlocking is due to the computer requesting it to unlock in response to the sensors or switches.

Thank you for the donation, but you don't have to keep adding to it. I'm happy to help people who are appreciative. The dollars go toward constantly repairing three laptops I use. I still have an old tank I built about ten years ago for a backup, but that one will never need repairs. It's too bulky to accidentally tie to the trailer hitch of my minivan!

Caradiodoc
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Wednesday, March 31st, 2010 AT 2:14 AM

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