Mechanics

CHEVY MISFIRE

2000 Chevrolet Silverado

Engine problem
2000 Chevy Silverado V8 Four Wheel Drive Automatic 65000 miles

Code p0300
engine is misfiring on #2 and #7 cyl at idle
So far I have checked compression 155 & 160
switched coil, plug wire, plug and injector
Checked fuel pressure 55-60 psi
Checked egr
Checked for plugged exhaust
Changed both rear o2 sensors
Compared all scanner data with another truck that is known to be operating properly
The only difference noted being bank#2 sensor#2 is staying down around 100-200 mv
At 1 point there was a map sensor code
I suspected a possible cracked or leaking upper intake
but when I called the dealer they told me they had never sold one or even priced one before
I'm running out of things to check.
Does anyone have any more ideas?
Thanks in advance
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Rowtiear
January 23, 2008.



Hello !!
Cyl #3 and #7 are in the same side..

not next to each other...


http://www.2carpros.com/forum/automotive_pictures/576_0_13.jpg



On the same side on the distributor cap...
Did you replace the "cap"

How about the spark plugs?

When did you replace them?

Are the correct "heat"?

Did you check the pick-up coil?

could be "missing" at low RPM`s

Let me Know and I`ll be thinking about it..

BTW thanks a Lot for your donation!!

Tiny
Fisherman
Jan 23, 2008.
Hello and thanks for responding
The spark plugs are approx. 2 months old and installed by myself at the shop where I work.
I am also a tech
The 5.3 litre is d.I.S. &Quot; one coil per plug" #2 cyl and #7 cyl are the problem cyls
I am aware that they are on opposite ends of the engine.
The only thing I have found is that they follow each other in the firing order but I can't see the crank sensor causing the problem on just the two cyls.
Any other input would be appreciated.

Tiny
Rowtiear
Jan 23, 2008.
Replace the intake gaskets, not the intake. That should fix your problem. You were getting a MAP code because the engine is sucking unmetered air, more that what the computer thinks should be. Basically, your computer is confused. It is taking the readings from the TP and O2 sensors and says that the intake should be sucking a certain volume of air, based on MAF. When you have an intake leak, it produces a lower vacuum that what the computer thinks it should, making the computer think that the MAP is bad. This also explains the O2 sensor reading (which is lean). The engine is sucking more air than what the computer can compensate for. Hope this helps. If you need any more info, don't hesitate to ask.
Dave

Tiny
Flexy5
Jan 23, 2008.
I`m sorry about the mistake on your engine,

well if the cylinders 3 and 7 are close on the firing order check the crankshaft position sensor. Could be " missing' at that point, I saw that all the commun " missfire causes" were checked already but I have the " feeling" that is an spark issue, also be sure that the sensor has the correct gap.
Here is a little trick that will literally show you if a DIS ignition module and its crankshaft sensor circuit are working: connect a halogen headlamp to the spade terminals that mate the DIS module to the coils. A headlamp is recommended here because it puts more of a load on the module than a test lamp. If the headlamp flashes when the engine is cranked, the DIS module and crankshaft position sensor circuit are functioning. Therefore, the problem is in the coils.

If the headlamp does not flash, or there is no voltage to the module or coil pack when the engine is cranked, the problem is most likely in the crankshaft sensor circuit. On most vehicles, a bad crank position sensor will usually set a fault code, so use a scan tool to check for a code. Or, check the crank sensor itself.

Check the cyl. 3 and 7 with the light ans see if there is a " miss" .
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Tiny
Fisherman
Jan 23, 2008.

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