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1999 Chevy Malibu Check Engine Light

Tiny
BKSFLYESTPAPI333
  • MEMBER
  • 1999 CHEVROLET MALIBU
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
I have a P0300 Random/Multiple Cylinder Misfire Detected. I also have a P0420 Catalyst System Efficiency Below Threshold (Bank 1). I would like someone to help me out with these two issues because I have a bunch of mechanic shops in my area that obviously can't fix a flat tires correctly. Please help me out with this. Thank you.
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Sunday, March 9th, 2008 AT 4:22 PM

20 Replies

Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
You probably need a coil and or tune up. Pretty basic stuff. I dont really see weird problems with the running just normal tune up stuff. Dont worry about the cat converter code until you fix the running problem.
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Sunday, March 9th, 2008 AT 4:26 PM
Tiny
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There are various misfires happening, not exclusive to any cylinder. There is probably excessive fuel not being burning and making it's way into the cat converter. Or the converter is plugged and causing the misfires from excessive back pressure.

Have the spark plugs and wires been changed out of curiousity?

How is it running?

I would try to nail down the misfires. Pull a couple plugs and see if they are fuel soaked. Smell the oil, does it appear thin and smell like fuel?

Have you been losing any coolant?

Has the intake manifold gasket ever been replaced?
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Sunday, March 9th, 2008 AT 4:30 PM
Tiny
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I have changed the spark plugs and wires about three weeks ago. It runs poorly, as far as giving gas and not really going anywhere. I was loosing coolant and experiencing small amounts of smoke during start up in the morning at one time and I refilled the coolant so I wouldnt be driving without any and it hasnt lost any since the refill. Intake manifold gasket has been replaced before like in november 07. The misfiring was only on three at first, P0303 and then it went to P0300. The car has also turned off on me four time in the last month, that seemed like
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Sunday, March 9th, 2008 AT 5:39 PM
Tiny
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Assuming there isn't a coolant breach, I would test the fuel pressure next. The fuel pump wave pattern would be anther thing I would want to know is good.

The po420 concerns me a little more, but I think I would still focus on the misfire.

Pull a couple plugs and see if they are fuel soaked. Smell the oil, does it appear thin and smell like fuel?

I assume silicone dielectric grease was sprayed at both end of the wires. I would also assume the plugs are the correct ones. The bosch splitfire for example have been trouble from my experience.

One plug I would pull it the 3rd one and swap it with another cylinder.
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Sunday, March 9th, 2008 AT 6:52 PM
Tiny
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I had the coils looked at and I was told they are in good condition. The electricity is flowing through the spark plugs just fine. What do I do next?
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Wednesday, March 12th, 2008 AT 2:17 PM
Tiny
RHALL77
  • MECHANIC
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First off I agree with all the above, does the car loose power when it warms up going up a hill. One thing you can do is disconnect the exhaust then drive it. See if all your concerns are gone. GM cat converters go out all the time.
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Wednesday, March 12th, 2008 AT 2:33 PM
Tiny
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The car loses power, sounds like it wants to turn off. It turns off sometime. It takes long to start up. The engine shakes a little bit. It eve makes this wierd sound like if its shifting gears or something all by itself. That last noise I mentioned is a little hard to describe what it really sounds like but I thought it was a transmission problem at first because I sound real wierd. So you think the cat converter could be causing the misfire? Is that what you are saying?
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Wednesday, March 12th, 2008 AT 3:38 PM
Tiny
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It can be. I think both codes are going to be related to each other, it is determineing which one is causing the other. Like rhall77 suggested, that will be telltale if it stops after the disconnecting.
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Wednesday, March 12th, 2008 AT 3:42 PM
Tiny
BKSFLYESTPAPI333
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Where do you actual disconnect it? Do you think I should do it myself or have a mechanic do it? Can they just test the temperature of the cat to see if it is bad or not?
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Wednesday, March 12th, 2008 AT 3:47 PM
Tiny
RHALL77
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Disconnect at the engine
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Wednesday, March 12th, 2008 AT 3:54 PM
Tiny
BKSFLYESTPAPI333
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Do I drive the car like that for a while or just a quick ride? What exactly should I do. I dont want to go about doing this the wrong way?
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Wednesday, March 12th, 2008 AT 4:08 PM
Tiny
RHALL77
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Drive it up and down the street it will be loud but you will be able to tell a major difference
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Wednesday, March 12th, 2008 AT 4:27 PM
Tiny
BKSFLYESTPAPI333
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Ok I will try that. Going back to what I had asked before, wouldn't I be able to take it to a mechanic shop and have them check the temperature of the cat and know if it's bad by the reading of the temperature?
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Wednesday, March 12th, 2008 AT 4:38 PM
Tiny
RHALL77
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You can ask them to, they might be able to
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Wednesday, March 12th, 2008 AT 5:05 PM
Tiny
BKSFLYESTPAPI333
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I took the car to get the cat checked and they just looked at it and told me to replace it. Anyway, I did the diagnostic test on the engine. The test results were 4 misfires, 2 clogged fuel injectors, oily spark plug, leaking gasket and damaged cat converter. I'm not sure if the oil is in the spark plug because of the leak or because I have oil in the piston. This soubds like $$$$$. What do you guys thing?
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Thursday, March 20th, 2008 AT 7:35 PM
Tiny
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The cat and the intake manifold gasket isn't surpizing.

$650-750 on the gasket, cat. Not sure.$400?
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Thursday, March 20th, 2008 AT 7:55 PM
Tiny
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That is more than what I was told by the mechanic over here.
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Sunday, March 23rd, 2008 AT 4:58 PM
Tiny
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So have him do it. Not sure what to say other than a rough number for what it costs in this area to do the job right. Pure guess on the cat.
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Sunday, March 23rd, 2008 AT 7:35 PM
Tiny
MASTERTECHTIM
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Ive seen those intake jobs price out at 800 to 1000 and converters from 300 to 500.
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Sunday, March 23rd, 2008 AT 7:56 PM
Tiny
MASTERTECHTIM
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Thats in the boston area
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Sunday, March 23rd, 2008 AT 7:56 PM

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