[p-Lovelady]

have a 2000 Silverado with a 5.3 and have a p0300. cylinders 1 & 8 are dead misfires at idle but when you get the rpms up the misfire moves and starts jumping around to all cylinders. have new plug wires and plugs have also had the injectors test and cleaned. tested wires from ecm to each injectors wire and they are good. have swap coils from cylinders. 1&8 are still dead till you get high in rpms then it moves to multiple cylinders. did a crankshaft and camshaft sensors and timing gear and chain. and i still have the dead cylinders on 1&8 till i get high in rpms then it moves to other cylinders and did a compression test on the motor have 150psi across all cylinders. pretty stumped any info or recommendations would be extremely helpful tired of throwing parts at it and nothing working.

 

[OpalLacod]

What's your fuel pressure?

 

[bazar01]

You will need to find a way to scope the crankshaft position sensor as well as the ignition and fuel injector signals on this misfire condition. Anything else is guesswork.

 

[p-Lovelady]

have 49psi at idle and it drops to 45-47 psi on throttle. also bleeds the pressure off when i turn truck off

 

[OpalLacod]

You need to solve the fuel pressure problem, first. Should be better than 57psi. I had this P0300 on mine with poor fuel pressure.

 

[p-Lovelady]

did fuel pump and fuel filter and fuel pressure regulator. have 50 psi at rail. it bleeds off to 0psi when motor is shut off. what else could be the reason for low fuel pressure. injectors leaking by?

 

[OpalLacod]

did fuel pump and fuel filter and fuel pressure regulator. have 50 psi at rail. it bleeds off to 0psi when motor is shut off. what else could be the reason for low fuel pressure. injectors leaking by?

Still too low on the fuel pressure. Upper 50's (57+) at idle or it will not operate properly. These engines verge on prima donna status with fuel pressure, in my experience. I have a 2000 5.3L and a 2004 5.3L, both of which despise low fuel pressure.

I'm going to number these for easy reference.

1. Fuel Pump
   1. When did you do the fuel pump, regulator, and filter?
   2. Was the pump new? New doesn't mean "good"...
   3. What brand?
   4. Did you update the fuel pump electrical connector when you swapped pumps?
2. Fuel Lines
   1. Have you checked for leaks in the lines?
      1. Highly, highly recommend checking the connections at the filter very closely. Flare fittings are very sensitive to improper alignment and torque. Common leak point and would result in low pressures if the leak was significant enough.
   2. Do you smell raw fuel?
3. Fuel Injectors
   1. How quickly does the pressure drain occur?
   2. Were the injectors pressure tested?

 

[bazar01]

My case is different though.
I have 48 psi on my 2001 5.3L on my 2nd 150k miles tired fuel pump and still runs fine. It does not bleed off though when turned off.
Still runs very good at 309k miles.

There must be other causes of your misfires.

 

[OpalLacod]

I have 48 psi

👀

 

[p-Lovelady]

fuel pump was done yesterday along with filter and regulator. did a new tru-grade fuel pump. and I don't smell raw fuel and I checked under the truck by filter and there is no fuel leaking out. could it be leaking air from fittings and its not leaking fuel? because everything is dry. fuel pump connecter was good tested it before I install pump and made sure I had good connections. injectors were taken out cleaned and tested but were not pressure tested. as soon as i turn the truck off it bleeds to 10psi within 5-10 sec of truck being off.

 

[p-Lovelady]

the misfire is 1&8 cylinders when I have it in park at idle but when I'm in drive and cruising down the road i have no misfires at all. when stop at a red light 1&8 when start to misfire.

 

[p-Lovelady]

someone mention it could be injectors leaking down after truck is shut off

 

[OpalLacod]

someone mention it could be injectors leaking down after truck is shut off

Yes, it could very easily be leaky injectors causing all your problems. But before continuing the parts cannon w/ new injectors, I wanted to have you check all the free fix failure modes I could think of.

Move ONLY Injector 1 to another cylinder while leaving everything else alone (including Cyl 8 components). Does the Cyl 1 misfire move with Injector 1 to another cylinder? Did the Cyl 8 misfire change?

Question: Do you have any other codes? I just noticed this was not specified.

 

[p-Lovelady]

will try that next but nope only a P0300

 

[bazar01]

Instead of pulling fuel rails, swapping injectors, then installing the fuel rails back to test, why not just pull the fuel rails with the injectors in place, lay it on top of engine with injectors visible, prime the fuel pump and observe if injector is leaking causing drop in fuel pressure. Fuel pressure gauge must be hooked up.

 

[carlzdooms]

I have 48 psi on my 2001 5.3L on my 2nd 150k miles tired fuel pump and still runs fine. It does not bleed off though when turned off.
teatv

download apk

 

[ttouring]

have a 2000 Silverado with a 5.3 and have a p0300. cylinders 1 & 8 are dead misfires at idle but when you get the rpms up the misfire moves and starts jumping around to all cylinders. have new plug wires and plugs have also had the injectors test and cleaned. tested wires from ecm to each injectors wire and they are good. have swap coils from cylinders. 1&8 are still dead till you get high in rpms then it moves to multiple cylinders. did a crankshaft and camshaft sensors and timing gear and chain. and i still have the dead cylinders on 1&8 till i get high in rpms then it moves to other cylinders and did a compression test on the motor have 150psi across all cylinders. pretty stumped any info or recommendations would be extremely helpful tired of throwing parts at it and nothing working.

What brand spark plugs did you use ? And plug wires

 

[lesholthaus]

have a 2000 Silverado with a 5.3 and have a p0300. cylinders 1 & 8 are dead misfires at idle but when you get the rpms up the misfire moves and starts jumping around to all cylinders. have new plug wires and plugs have also had the injectors test and cleaned. tested wires from ecm to each injectors wire and they are good. have swap coils from cylinders. 1&8 are still dead till you get high in rpms then it moves to multiple cylinders. did a crankshaft and camshaft sensors and timing gear and chain. and i still have the dead cylinders on 1&8 till i get high in rpms then it moves to other cylinders and did a compression test on the motor have 150psi across all cylinders. pretty stumped any info or recommendations would be extremely helpful tired of throwing parts at it and nothing working.

Did you check for vacuum leak?

 

[p-Lovelady]

no vacuum leak and used ac Delco plugs

 

[WorthFlorida]

Questions from me, I know very little about FI rails. Is there a regulator to open up to send excess fuel pressure back to the gas tank? During idle, can gas be squirted into the air intake past the MAF sensor? Can a test light or voltmeter be placed at the fuel injector to know that the injectors are working at idle Or with a finger, feel the injector that it is operating?