2000 silverado misfiring #3 Help

I have a 2000 silverado 5.3 with a p0303 code. #3 misfired 600,000 times and #1 24,000 times. I have changed the plugs no help, changed the wires no help, changed the air filter no help, added injector cleaner no help, changed the fuel filter this helped tell the truck got warm then some. No power check engine blinks all the time. The exhaust sounds different when this happens.

Welcome to AF.
Check fuel pressure for up to par.
What are the fuel pressure redings?
Good hot spark to plug?
Good Ac plugs?
Good compression?

New dubble plat.plugs champion. Any idea where to get a good presure gage? What do I use to check for a intake leak carb cleaner is bad on rubber

New dubble plat.plugs champion. Any idea where to get a good presure gage? What do I use to check for a intake leak carb cleaner is bad on rubber

Pitch the champion in the trash can and get some good AC plugs.
AZ and some parts places loan /rent /sell fuel pressure gauges.

New dubble plat.plugs champion. Any idea where to get a good presure gage? What do I use to check for a intake leak carb cleaner is bad on rubber

throttle body cleaner would be safe...starting fluid ...with a straw to direct flow...My favorite is propane...small torch with hose on the output direct the hose in the area suspected and the idle will increase....

your problem appears to be more a low fuel pressure....random miss fires...if the pump is bad get delphi pump ...

Checked fuel pressure 54 psi with key on and 52 with the truck running. Changed coil packs #3 with #4 still #3 misfiring p0303 code still.

Checked fuel pressure 54 psi with key on and 52 with the truck running. Changed coil packs #3 with #4 still #3 misfiring p0303 code still.

why are you replacing all these parts? It's your money...

the fuel pressure is too low! many,many , many. times this proceedure is decribed in detail as to how to determine if you have fuel delievery problems...on this vehicle.................

you need 60psi minimum and it should hold this pressure within 5psi of what you got....for 15 min...

since you will need a pump make sure its a delphi pump...NO airtex....

5.3s do have problems with intake gaskets,blowing out and sucking in air causing the missfire.Spray carb cleaner near the intake gasket area and if there is a change,bad intake gaskets

5.3s do have problems with intake gaskets,blowing out and sucking in air causing the missfire.Spray carb cleaner near the intake gasket area and if there is a change,bad intake gaskets

he's only getting 53psi of fuel pressure....

Well i moved one coil and found the problom bad coil 49.99 fix and gave my truck a tune up.
fuel pressure 50 to 60 psi is dealer guide lines. I saved 600 bucks by not going with that idea thanks any ways

Well i moved one coil and found the problom bad coil 49.99 fix and gave my truck a tune up.
fuel pressure 50 to 60 psi is dealer guide lines. I saved 600 bucks by not going with that idea thanks any ways


As in post 2 we asked about the spark.
But
Bad coil is another reason to pitch them champion plugs in the trash.

On fuel pressure.
DEALER GUIDE LINES IS NOT SPECS ON IT.

You should have around 57 idle full vacum and 60-61 under load.
Always check fuel pressure regulator vacuum line for fuel in it.


You fuel pressure is to low.
Specs on it is 55/62 lbs of pressure
Here is some guide lines of fuel pressure checking.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 55-66 fuel pressure.
Cold start should be 55/62 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 55/62 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
If pressure does not come up with return line pinched or blocked off.
Go to fuel filter and hook a gauge direct to a line at fuel filter.
Pressure should come up to 75 or more and will hold after fuel pump is turned off.
If it leaks down there after fuel pump is turned off it is LEAKING BACK THREW PUMP CHECK VALVE OR PUMP MODULE LINES.
Post back your fuel pressure readings.
MT

Well i moved one coil and found the problom bad coil 49.99 fix and gave my truck a tune up.
fuel pressure 50 to 60 psi is dealer guide lines. I saved 600 bucks by not going with that idea thanks any ways


the fuel pressure gauge you used must be out of cal. their is no way your vehicle will run properly with 53psi...

dealer guide lines???never heard that one...oh! you mean bull shit. be prepared for more problems...these pumps have an intermittent nature....

I would listen to these guys on here. They know what they are talking about. You can get your truck fixed on here cheaper then at a dealer.

Well bull shit or what ever changed the fuel pump STILL MISSING even better I know have p0300 code

Proper testing before throwing parts at it.
Did you run the fuel pump pressure test before and after replacing fuel pump?
Go threw the repair flow chart for missfire codes.

Well bull shit or what ever changed the fuel pump STILL MISSING even better I know have p0300 code

the dtc 300 is generated by the crankshaft position sensor...when the crankshaft changes speed that is improper it will send data to the computer to cause this code to be created...

the fuel supply pressure is the #1 item that will cause this...then you could have a bad injector ground...if the injector ground is loose corroded it will cause some cylinders to not get the full amount of fuel...grounding of the coil causes the injector to open...the longer its grounded the more fuel is injected into the cylinder...so this is something that must be checked after fuel pressure....

then it is possible especially if this engine has more than 100,000mi that the ckp crank sensor is dirty or bad or connections ...this is mounted under the starter motor...this has been a cause of this problem but not that often,,,

this is a problem that you must follow the proper troubleshooting procedure ,, that way you fix what is the problem with the least amount of expense....