BasicallyReliable

Cylinder misfire on 1-3-2-4, besides a vacuum leak I have checked valve springs, coils, wires, plugs, and recently had tuned. Tune was fine then after some hard driving I turned it off for 30 minutes and when i started it back up it's had a misfire since. Has some white smoke out exhaust. But no coolant or oil usage. 2003 Silverado

G Atsma

Check all connections and grounds.

pdxmotorhead

You hit the basics, just a few things to check if you havent..
Did you rotate the engine with the valve covers off and watch to see if its opening and closing the valves?
Pressure test cooling system?
Leakdown the engine. (You may have blown the head gasket between the cylinders.)
Instant fails are often sensors on any EFI motor

BasicallyReliable

I have not yet I don't have a compression tester. Maybe I'll go get one. I have no problems with cooling. And oil looks fine, it's only week old so easy to see still.

pdxmotorhead

If there is no electrical or fuel issue, your stuck with a sensor issue or a mechanical issue..
I'm puzzled what items could go bad that would cross the engine side to side on 4 cylinders.

You can blow a head gasket without causing any issues with the oil or cooling circuit.
If you blow threw the thin section between 2 cylinders it misfires, But on both sides at once? that would be weird.
If you have white smoke that's coming from somewhere and white is usually coolant.

You can check the insides with a cheap bore scope that hooks to your phone available off places like amazon.
Less than 100 bucks, handiest shop tool ever. Since I don't know the engine specs, I would check Piston 2 valve clearance?
If the line bore was just a smidge off you could have kissed a valve lightly enough to make a leak not hard enough to kill the motor.
and it would happen likely at one end. Totally wild *** guess here.. just trying to brainstorm.. That's where the bore scope would help.

I'd also buy a leakdown tester,, they tell a way bigger story than a compression test.. Pistons/valves/cracked head all in one check.
Harbor freight sells one for light use, if you need to you can put better gauges on it but the rest is basically just a valve and hoses.
Once you practice its a very fast process, I do a leakdown on a sprint car between sessions..
Of course when you can see the whole engine its way easier to get the plugs out LOL

Its also possible you had a electrical glitch and damaged a coil. Or that your fuel system sucked up some grunge and its clogging injectors. But that doesn't explain the white smoke.

Waiting to see what it turns out to be...

ChopperDoc

I’ve had bad crank sensors cause similar issues. It’s a cheap enough part to replace, but don’t forget to check the wires too. I had a brand new sensor cause half the cylinders not to fire, but it was a bit more random.

BasicallyReliable

I re checked all the valve springs, and rechecked all the connections. Both grounds on back of the heads. Driver side is hard to get to. Forgot to say, I have perfect spark at all 8 cylinders. Unplug them and watch the current jump across. But when I unplug the front 1-2-3-4 cylinders idle doesn't change. As if they are barely firing. The white smoke is very little and has always been there. And I've never had to refill coolant or oil in-between an oil change. So it doesn't seem to be using anything.

pcguy

Any chance you have displacement on demand?

G Atsma

It's a 2003, so no. DOD came in with Gen IV, a few years later.

pdxmotorhead

How old is the fuel.. ? I've gotten a bad load of gas before and the engine didn't like it a bit..
If you idle is not changing when you pull plugs, try it with the injectors.. You have either a fuel delivery issue, or a mechanical issue.

BasicallyReliable

Fuel isnt old same fuel I always run. Same tank of gas too.

I'm running out of ideas now.
Map sensor and pcv are next to check.

BasicallyReliable

Bent valve on cylinder 2, and low compression on cylinder 1.

samckitt

iTrader: (5)

Is it a cast iron block? I can't remember what is in a 03 Silverado (assuming its a 1500). I had a 2003 1500 HD silverado with the 6.0L iron block & had a bad miss fire until the engine got hot. I checked everything, replaced too many parts. Took it to one shop that put over $2k in parts/labor in it but still had the miss, so they didnt charge me. After 2 other shops looked at it, one finally found the issue. They took out the crank position sensory to check for a broken tooth in the target wheel & found rust under the seat of the sensor. It was making the gap between the sensor & target wheel to big & wasnt getting proper signal. Once the target wheel got hot it expanded (i assume), made gap smaller & it worked fine. remove the rust & reinstall sensor & it worked fine from then on.