Pontiac Sunfire (1999) odd tugging when speeding up


#1

Hello, for the last two years my old Sunfire (I’ve been its only owner) has been tugging while speeding up (happens at different speeds) and I have taken it to all sorts of mechanics and none have been able to solve the issue. The car had a faulty injector which was changed with a new original part, the transmission diagnosis have all come out negative, the engine is in great condition according to all the mechanics and the electromechanics I’ve been to have found no problems with the car whatsoever.

The car has around 130,000 miles and runs great, it just has these tugging episodes while accelerating and I have ran out of things to check in the darn car. The car is always up-to-date with maintenance and it’s used for short trips the majority of time.

Any thoughts on what could be wrong with this car?

Hello again, thanks for the replies…

circuitsmith: Nothing on the ignition has been changed, the mechanic said there was nothing damaged there.

jesmed: The tugging feels like misfiring, it is as if the car is running out of fuel, but the fuel pump and lines have been checked at least already twice already and it’s still in good conditions, plus the fuel pump is new. The only problems with the breaks is possibly a faulty sensor on the anti-lock which I just discovered recently.

Another detail is that when the car is full (fuel) the tugging stops, but none of the mechanics have been able to find the relation between the fuel and the tugging.


#2

I think you are going to need a mechanic who is willing to drive your car until he experiences the problem himself.


#3

Have ignition parts been changed? Plugs, wires, distributor cap & rotor etc.


#4

Can you explain more what you mean by “tugging?” Does it feel like the engine is losing power for a moment, like it’s stumbling or misfiring? Or is the engine maintaining power but something else is dragging, like someone is stepping on the brakes for a moment?

I don’t know the specifics of your car, and it may be too old for this, but some newer cars have had problems with the stability control system automatically engaging the brakes because of a faulty sensor.


#5

The problem might be caused by torque-steer.

Torque-steer occurs because one halfshaft is shorter than the other. So when accelerating the longer halfshaft is allowed to twist more than the shorter halfshaft. So the shorter halfshaft applies the torque to that tire faster.

If this suddenly started to happen, I would have the tires, suspension, and steering components inspected for wear.

Tester


#6

Partially plugged catalytic converter ?
An exhaust specialty shop would be able to check that.