2002 Pontiac Grand Prix 6 cyl Two Wheel Drive Automatic 60000 miles
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OK, so heres what was wrong, My car was running reall bad and could not figure out what was wrong, there was a major loss of power. after doing an oil chamge, cleaning the air filter, changing the plugs and the wires, and changeing the fuel filter we decided to bring it into a shop. The shop told me that my "cat" needed to be cut out and replaced.....and at the time i could not afford that, so i just had them cut it out and put a pipe through. I was told that because my o2 sensor was after my "cat" i would get really bad gas millage. So after A month or so i was fialally able to afford to get a cat instaled, it was installed and my check engine light is still on and the error that is still reading is engine missfire. and my car is still getting bad gas mileage....can someone please help me

From the point of the cat, a misfire usually is caused by the ignition system such as plug/wires/coil pack...not to mention the timing and parts of....even a burnt valve. The shop that did the job in the first place should take the responsibility of the repairs he tried to do and the cat converter probaly wasn't at fault in the first place....By law the temp. fix was illegal and second those used cat converters are worth a $100.00. There are two or four 02 sensors on the newer vehicles one before the cat and one after.

Not certain but the cat may be covered under warranty! Retro check on that. 60K and a 2002 car shouldn't be needing a converter just yet - if left running poorly it could have killed it. Is it running ok now? Is there only one converter and one o2 sensor? Sensor could have been wrecked too with letting it run poorly too long.

You should get a full code reading now and if running well now ask them to "reset" it. It may still be in it's current memory.

I'm surprised a shop would "straight" pipe where a converter was and I do understand the expense but it's part of the system in cars of this vintage.

Was an OE converter installed or what really happened with that?

T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/

If the cat was plugged; the new plugs you installed, may have become damaged, due to the excessive heat from the exhaust not being able to get out of the engine?
Is this a P0300 code (random/multiple misfire) or is it a 301, 2, 3, 4, 5, or 6 code identifying a particular cylinder?
If it’s a P0300 look for things that are common to all cylinders, such as vacuum leaks, low fuel pressure, an O2 sensor that didn’t like the AC voltage that it may have seen during the welding of the exhaust system.
I’m pretty sure if you cure the cause of the misfire code your power & fuel mileage will come back all on their own.

Sorry for being so vague but without being there, with a scanner connected; the possibilities are almost endless.

Dan.

Canadian "EH"

Guess we were all responding at once!

T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/

The code that it is giving me is P0300...and i checked my plugs agian just to be sure and none of them were foweled up....how will i be able to find a vacuum leak if that is the problem,or how can i tell if the fuel pressure is low..

I use carb cleaner spray....others use propane and some use wd40, all have same affect. Spray around the engine while its running...the idle will rise if there is a vacuum leak...CAUTION THESE SPRAYS ARE FLAMMABLE so try not overspray on the exhaust manifold.The fuel pressure tester can be rented from autozone.

I’ve been in the trade for over thirty years and I still can’t tell if a spark plug if firing properly just by looking at it. Short of seeing physical damage, as in cracks in the porcelain, bent/smashed electrodes; you can’t tell what its going under load, not without an oscilloscope.
It’s like looking at a frosted light bulb, wondering if it’s burnt out.
I guess what I’m saying is, take the car in and have it diagnosed; pay whoever for that; bring the car home and go on their advice. At least you won’t be throwing parts at this car, completely in the dark?


Dan.

Canadian "EH"