Question about 2006 Chevrolet Express

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2006 chevy express 2500 4.8l......misfiring bad. Changed plugs, wires, catalytic converter, muffler, o2 censor and mass air flow censor. Major misfiring and running horrible. I am at a loss here.....HELP!

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Please make sure you gapped the plugs to specifications. ( probably 35 thou' of an inch ) gap gages are very inexpensive. Also suspect the spark plug wires, check teher integrety as well the correct firing order. To check for short, in the dark watch for arching to ground ( visually ).

Hope that helps.

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Posted on Sep 17, 2010


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Where are the O2 sensors? I found one directly behing the spark plugs on the back.

The O2 sensor (2 on V engines) are in the exhaust system pipes before the catalytic converter, the next sensor is the efficiency monitor for the catalytic converter system it looks like a O2 sensor but performs a much different function as far as testing goes. The codes you have follow.

P0420 - Catalyst System Efficiency Below Threshold Bank 1
What does this mean? In most cases it means the catalytic converter is worn out and that is sensed by the catalyst monitor I spoke of earlier.

P0102 - Mass or Volume Air Flow Circuit Low Input
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No, the catalytic convertor does NOT sound right.
Normally with a random misfire a tune up takes care of it. What has also caused a misfire on those early motors is the popet injectors. They were prone to having problems and have been updated back around 2000 or so. But usually its a cyclinder or two or three or... misfire. All popets going bad is unlikely.
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Take the car to a muffler shop (not to one of the big national chains).

They will replace it for around $50~$70 and not charge for additional services like the big muffler shops.

They will keep the old catalytic converter (it has platinum in it).

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2001 chevy blazer multi cyl misfire, fuel trim @ -30, all inj seem to drop about 5psi on inj balance test, o2 sensors switching

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Loss of power on acelaration

There's a lot on any car that can cause loss in power.
A few of them are:
Mass air Flow sensor
Bad O2 sensors
Old oil or sludged oil
Bad Gas
Clogged catalytic converter
Loss of cylinder pressure or compression

I would start with the cheapest tests/fixes first
oil: if you haven't already and don't know the condition of your oil, change it. If your oil has sludge in it then you could have a leacking head gasket.

Next up, If your gas is bad fill the tank about half way and use lucus oil octane booster, and for a second half a tank pour in some seafoam engine cleaner. It will clean your fueling system, injectors, and pistons/chambers.

If those too don't help: get a compression test on the cylinders. Not expensive to have done, but could be expensive to fix if there is something wrong or the compression is leaking.

Next, go to a muffler shop and have your catalytic converter checked. A clogged or bad Catalytic converter may trap exhaust and keep it from exiting your exhaust system.
While your there you can have your O2 sensors checked.

If all of that is fine, replace the O2 sensors and the Mass air flow sensor. These components control the air fuel ratio. If they are going out your engine won't ever get the right amounts of gas and air to run properly.

It's a lot, but my general rule of thumb for trouble shooting any issue with a car is to start with the cheapest fix and work your way up.

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