Mechanics

WHY DOES MY CAR STUMBLE WHEN I INCREASE RPMS?

1998 Chrysler Sebring • 75,000 miles

I have a 98 chrysler sebring convertible with a 2.5 v6 engine. For a few weeks now my car would drive but at highway speeds on an incline my engine would lack power and wouldnt go over 40 mph until I went back downhill. I checked under the hood and found that the egr valve was broken and the vacuum lines were broken. I replaced the valve and solenoid/transducer and checked the lines to make sure they were not clogged. Everything is working fine. Now for some reason I can not drive the car over 5mph down the street. I try revving it in my driveway in park and the car sounds like it is bogging and loses power. The car runs fine in idle but bogs if I rev it at all. I know it could be a number of different things but I just don't know where to start. I did the spark plugs and wires not to long ago. I used a scanner to see if there were any codes and got nothing.
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Alexbail07
November 21, 2011.



Sounds like you might have a plugged catalytic converter. If it is, the exhaust at the tail pipe will sound more like a hissing instead of the normal "putt putt" sound. If you work the throttle under the hood, you might hear some popping through the intake / throttle body, especially at higher speeds.

A failing MAP sensor can cause bogging too. On the older cars from the late '80s and early '90s, it commonly caused the engine to stall when the accelerator pedal was held steady. The engine would continue to run, (poorly), as long as the gas pedal was moving. That sensor can fail to report the correct manifold vacuum readings but as long as its signal voltage stays within its acceptable limits, (0.5 to 4.5 volts), no fault code will be set. A quick check for the MAP sensor is to disconnect the plug. The Engine Computer will recognize the failure and substitute a known good value to run on based on approximations from the other sensors. It still won't run well but if it runs better, suspect the sensor. The MAP sensor has the biggest say in how much fuel enters the engine.

Caradiodoc
Nov 21, 2011.
I did notice that there is a hissing sound coming from the exhaust when I was trying to diagnose it and thought that was weird. I will check the MAP sensor too but I have a feeling it probably is the catalytic converter. If I put a new converter in couldn't it just get clogged again from whatever caused the clog in the first place? Or is this just a routine thing because the car only has 70,000 miles on it.

Tiny
Alexbail07
Nov 23, 2011.
Not routine. My rusty trusty '88 Grand Caravan with 230,000 miles still has the original converter and it's working fine. I don't know what causes some to become blocked and others don't. Leaded gas will do it but you can't find that anymore. Overheating it is probably more common. That melts the substrate into a block the exhaust can't get through. Overheating is due to too much raw unburned fuel entering the exhaust system. That is monitored by the Engine Computer on '96 and newer models and will result in a flashing Check Engine light when it's severe. Even a slightly too-rich mixture will eventually be detected by the computer resulting in a stored diagnostic fault code and the Check Engine light turning on.

In the absence of overheating, I suppose it's possible for the catalyst material to crumble apart and cause blockage. I never autopsied one to see what happened.

Caradiodoc
Nov 23, 2011.