Mechanics

CHEVY RUNNNING RICH

1999 Chevrolet Silverado

Engine Performance problem
1999 Chevy Silverado V8 Two Wheel Drive Automatic 102000 miles

I have a 99 truck with a 4.8 and it is running rich on #4 cyl. I replaced all the plugs, a new set of wires, and a new coil as well as a new injector for that cyl. I get a 300(engine misfire) code and it appears to be flooded when you start it. But why would this affect just 1 cylinder. Any ideas? Thanks
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1999 chevy dude
August 27, 2008.




Is the spark plug wet or something. How do you know its rich on #4. Is #4 where the misfire is?

Tiny
Rhall77
Aug 27, 2008.
The plug is black and the others are clean. I replaced the plugs, coil, wires, injector, and the problem is still there. The previous plug was black on # 4 also. Only 1 cylinder black ( rich ).

Tiny
1999 chevy dude
Aug 27, 2008.
It either has a bad spark plug or a bad igniter coil, each cylinder has it's own igniter coil connected directly to the spark plug, remove the black plastic cover to get to them, this is the most common problem, in some cases, but less common a bad fuel injector or low engine compression could be the cause but I would try just replacing the spark plugs to see if it helps if not replace the coil next.

Tiny
Khooper
Aug 27, 2008.
Did you check this with a scan tool. Is cylinder #4 misfiring? You might just have a vacuum leak at the intake manifold. Also what is your fuel pressure, you might be low on pressure or volume causing a p0300. One way to check is drive the vehicle and see what your fuel trims are when it is under a load using a scan tool

Tiny
Rhall77
Aug 27, 2008.
I do not have a scan tool that will give me this info. But if it was a vacuum leak at or around #4 the plug would not be black (rich). The same situation with fuel pressure. The pressure would effect all cyl. Not just one. The only plug that is black is #4. All of the others are burning clean.

Tiny
1999 chevy dude
Aug 27, 2008.
Ok, well then does your truck burn oil?

Tiny
Rhall77
Aug 28, 2008.
No, it uses just a bit but not an abnormal amount

Tiny
1999 chevy dude
Aug 28, 2008.
1.


http://www.2carpros.com/forum/automotive_pictures/166241_dia_oilfouling_1.jpg


2.


http://www.2carpros.com/forum/automotive_pictures/166241_dia_carbonfouling_1.jpg


whick plug does it look like

Tiny
Rhall77
Aug 28, 2008.
#2, the picture that you have of #1 is a oil control problem (rings/. Valve seals)and that is not what I am dealing with. My situation is #2, a rich condition. Thanks

Tiny
1999 chevy dude
Aug 28, 2008.
Check your thermostat and make sure you are running at a good operating temperature. Do you have coil over plug. Check for terminal tension make sure you have good contact. Or do you have a distrubitor and the timing is off. Stupid question, did you check your fuel pressure regulator, is it leaking. You fixed everything else, theres not much more it could be. Did you install factory plugs back in it.
AD

Tiny
Rhall77
Aug 28, 2008.

AD