INTERMITTENTLY CAR JOLTS, ENGINE LOSES POWER

  • Tiny
  • MissAshlee
  • 2001 Mazda 323
  • 174 miles

Hi,

A few days ago, I was driving at 100 kilometers per hour and the car jolted, lost a bit of power, than jolted again and seemed ok. Took it for a long drive and didn't happen again.

The next morning driving on the highway to work, at the same speed, the car repeated this jolting, though lost any guts. I was driving at 80 kilometers in 3rd gear but was sluggishly accelerating but didn't help with change of gears. Every time I was at a stand still, the car would idle vigorously, feeling like it was going to cut out. Than I gave it a good rev at the lights and it jolted again back to normal. I took it to the mechanic and the Knock Sensor was melted, they replaced it although this has not solved the problem. Same thing happened at 40 kilometers.

This after noon I turned the car on in the driveway and waited for it to happen again, without actually driving it. After about 6 minutes, the engine was shutting down (though did not cut out), vibrated when acceloration, it struggled to gain power. Very deep sounding rev's and strong smell of fuel out of exhaust. When car is started, RPM's sit around 2000.

Already Tried:
Replaced Knock Sensor. Spark Plugs and fuel filter apparently ok. Fan Belt replaced 2 months ago. Battery repaced. Minor service 2 months ago. Getting clutch replaced this week, though problem seems to be within the engine!

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Monday, August 13th, 2012 AT 6:09 AM

6 Replies

  • Tiny
  • mhpautos
  • Expert
  • 30,561 posts

Did the mechanic run a diagionstic scan? Not all faults will set a check light, I would also be checking the ignition coil as often if they are faulty they will over heat and cause very similar problems to what you describe, re post when you have had these checked.

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Monday, August 13th, 2012 AT 8:48 AM
  • Tiny
  • MissAshlee
  • Member

The mechanics did run a diagnostic scan, that's how they found the melted Knock Sensor. If the codes weren't cleared on the ECM, could that still have an effect on my car? What would cause a Knock Sensor to melt?

Also if there was a fault with the Ignition Coils, would this read on the scanner?

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Monday, August 13th, 2012 AT 9:08 AM
  • Tiny
  • mhpautos
  • Expert
  • 30,561 posts

If codes not cleared they just sit there, will in itself do nothing, the knock sensor is attached to the block either an electrical short or engine over heating, only systems driven by ECU functions are coded, the knock sensor will advance and retard ignition timing through the ECU, the coil is not controlled by any ECU function.

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Monday, August 13th, 2012 AT 9:48 AM
  • Tiny
  • MissAshlee
  • Member

Great. Thank you for your help. I'm taking it to the mechanics tomorrow so fingers crossed it's only the coils.

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Monday, August 13th, 2012 AT 9:53 AM
  • Tiny
  • MissAshlee
  • Member

Hi,

So I had my car at the mechanics the past 2 days. They couldn't find any fault with it. When they hooked up the ECU, the code from the previous fault of the Knock Sensor was still in memory and wasn't cleared. They have now cleared it, I took it for a 50 minute drive and the car didn't play up. Could that have fixed the problem?
I still feel my car idle's a little rougher than I remember when stationary, what could this be from? It use to be very smooth to the point you couldn't feel the car was acrually running.

Your help is appreciated

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Wednesday, August 15th, 2012 AT 11:04 AM
  • Tiny
  • KHLow2008
  • Expert
  • 41,997 posts

What is the idling speed at operating temperature?
If idling speed is within spoecs, have the engine mounts checked?

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Tuesday, August 21st, 2012 AT 11:35 AM

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