HELP! 1999 silverado 5.3 p0300

[jcj02]

1999 chevy silverado z71

5.3 motor

 

P0300 CODES MISFIRE

MISFIRE ON MOST CYLINDERS

MISFIRE ON #3 CYLINDER VERY BAD

 

CHANGED PLUGS, WIRES, FUEL FILTER

CHECKED EGR VALVE, NOT BAD

CHECKED FUEL PRESSURE LITTLE LOW

AT SOMETIMES 48LBS BUT THEN HOLDS AROUND 55 AT IDLE WHICH IS FINE

 

THE PROBLEM!!!

 

MY TRUCK IS HARD TO START, HAVE TO GIVE IT A LITTLE GAS

WILL NOT STAY STARTED WITHOUT BEING ON THE GAS OR IF IT DOES

IDLES AT 300 OR 500 RPMS

VERY ROUGH IDLE! SHAKING A LOT

 

ABOUT TO CHECK THE CONVERTERS

ALSO WOULD THE CRANK SENSOR BE A PROBLEM. JUST ANY HELP PLEASE

DOING DISASTER RELIEF 700 MILES FROM HOME, NO PAY AND NO WAY HOME

PLEASE ANYTHING WOULD BE GREATLY APPRECIATED

[Butch 02 Denali]

1999 chevy silverado z71

5.3 motor

 

P0300 CODES MISFIRE

MISFIRE ON MOST CYLINDERS

MISFIRE ON #3 CYLINDER VERY BAD

 

CHANGED PLUGS, WIRES, FUEL FILTER

CHECKED EGR VALVE, NOT BAD

CHECKED FUEL PRESSURE LITTLE LOW

AT SOMETIMES 48LBS BUT THEN HOLDS AROUND 55 AT IDLE WHICH IS FINE

 

THE PROBLEM!!!

 

MY TRUCK IS HARD TO START, HAVE TO GIVE IT A LITTLE GAS

WILL NOT STAY STARTED WITHOUT BEING ON THE GAS OR IF IT DOES

IDLES AT 300 OR 500 RPMS

VERY ROUGH IDLE! SHAKING A LOT

 

ABOUT TO CHECK THE CONVERTERS

ALSO WOULD THE CRANK SENSOR BE A PROBLEM. JUST ANY HELP PLEASE

DOING DISASTER RELIEF 700 MILES FROM HOME, NO PAY AND NO WAY HOME

PLEASE ANYTHING WOULD BE GREATLY APPRECIATED

 

<{POST_SNAPBACK}>

 

 

 

Don't think it's the converters, even if clogged, they will usually idle ok but lose performance as the revs go up. If you've determined it's not plugs, wire or coils then I'd lean toward a vacuum leak or a clogged injector, probably #3.

 

Cleaning the throttle body may help. Clean the mafs too.

 

Does it run alright once you get moving?

Could you have gotten a bad tank of gas?

[jcj02]

1999 chevy silverado z71

5.3 motor

 

P0300 CODES MISFIRE

MISFIRE ON MOST CYLINDERS

MISFIRE ON #3 CYLINDER VERY BAD

 

CHANGED PLUGS, WIRES, FUEL FILTER

CHECKED EGR VALVE, NOT BAD

CHECKED FUEL PRESSURE LITTLE LOW

AT SOMETIMES 48LBS BUT THEN HOLDS AROUND 55 AT IDLE WHICH IS FINE

 

THE PROBLEM!!!

 

MY TRUCK IS HARD TO START, HAVE TO GIVE IT A LITTLE GAS

WILL NOT STAY STARTED WITHOUT BEING ON THE GAS OR IF IT DOES

IDLES AT 300 OR 500 RPMS

VERY ROUGH IDLE! SHAKING A LOT

 

ABOUT TO CHECK THE CONVERTERS

ALSO WOULD THE CRANK SENSOR BE A PROBLEM. JUST ANY HELP PLEASE

DOING DISASTER RELIEF 700 MILES FROM HOME, NO PAY AND NO WAY HOME

PLEASE ANYTHING WOULD BE GREATLY APPRECIATED

 

<{POST_SNAPBACK}>

 

 

 

Don't think it's the converters, even if clogged, they will usually idle ok but lose performance as the revs go up. If you've determined it's not plugs, wire or coils then I'd lean toward a vacuum leak or a clogged injector, probably #3.

 

Cleaning the throttle body may help. Clean the mafs too.

 

Does it run alright once you get moving?

Could you have gotten a bad tank of gas?

 

<{POST_SNAPBACK}>

 

 

 

 

 

WHEN I GET MOVING IT STILL DOESNT HAVE THE POWER.

PUT INJECTOR CLEANER IN IT AND NEW TANK OF FUEL SINCE THEN

 

 

TRUCK HAS AROUND 160K MILES

IF THE CRANK SENSOR WERE BAD WOULDN'T IT JUST NOT RUN AT ALL??

ALSO ON THE SCANNER IT READ #3 CYL WAS REALLY MISFIRING BUT ALL CYLINDERS WERE ACTING UP.

 

JUST A LITTLE MORE INFO

 

ALSO NOT ABLE TO LEAVE THE GUAGE ON OVERNITE

CONVERTERS NOT POSSIBLE??

[rdnkcpa]

Clean the idle air control valve, perhaps.

[jcj02]

Clean the idle air control valve, perhaps.

 

<{POST_SNAPBACK}>

 

 

 

 

WHICH VACUUM LEAK WOULD I CHECK NEXT TO CYLINDER #3? OR EVEN CHECK THE CLOGGED INJECTOR?

 

ALSO CHECK MY OTHER POST IN GM TECH AREA BECAUSE THERE IS MORE INFO. IT HAS A P0400 CODE AS WELL.

[97chevy350]

Clean the idle air control valve, perhaps.

 

<{POST_SNAPBACK}>

 

 

 

 

WHICH VACUUM LEAK WOULD I CHECK NEXT TO CYLINDER #3? OR EVEN CHECK THE CLOGGED INJECTOR?

 

ALSO CHECK MY OTHER POST IN GM TECH AREA BECAUSE THERE IS MORE INFO. IT HAS A P0400 CODE AS WELL.

 

<{POST_SNAPBACK}>

 

 

 

 

I know its a long shot, but make sure you wires on the PCM are tight, especially if you have ever had it out. I had a VERY similar problem on my 97 and my dad had a very similar one on his 99, I spent 400 bucks before I found hte problem. Might wanna clean out the EGR too.

[Butch 02 Denali]

 

 

 

WHICH VACUUM LEAK WOULD I CHECK NEXT TO CYLINDER #3? OR EVEN CHECK THE CLOGGED INJECTOR?

 

ALSO CHECK MY OTHER POST IN GM TECH AREA BECAUSE THERE IS MORE INFO. IT HAS A P0400 CODE AS WELL.

 

<{POST_SNAPBACK}>

 

 

 

 

Hmmm, well the P0400 is a EGR code. Usually a clogged or stuck open EGR will run OK at normal driving speeds though.

 

You may very well have a few problems.

As for the injector, the easiest way to check is to swap the #3 injector to another cylinder and see if the problem follows it!