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I have a 2000 Silverado with about 145k miles on it. It has the 5.3 Vortec and I'm having MASSIVE problems with this pos.

Started about as soon as I bought the car 1.5 years ago. It had 138k when I bought it so I haven't been killing the thing. As soon as I pull into the drive from the dealership, the check engine light comes on. O2 sensors are bad. Easy fix, I replaced them but the problem continued. The truck started misfiring. I replaced the plugs, wires, and the fuel filter. Normal routine stuff that the truck needs at 140k.

Problems continue but they're intermittent. Life got busy for about 8 months and I drove it for a while with minimal problems and just the occasional random misfire. After things slowed down a bit, I decided I'm going to fix this thing once and for all. I replace the O2 sensors again and run some diagnostics. The truck is running rich and I took it to a trust mechanic. They told me that one of my injectors are dumping fuel into the engine. I buy 2 injectors and start swapping around. Nothing works and I decided to replace all the injectors with some brand new ACDelco injectors.

Truck starts running like absolute garbage. Running on only 4 cylinders. Misfiring on 2, 4, 6, and 8. I give up and take it to the mechanic (who has 40 years of experience). After he ran compression test (checked out), replaced the O2 sensors again, and ran some other diagnostics, he can't figure it out. He thinks that it's the computer giving out but he can't be sure. He quotes me for $525 to put in a used computer and to flash it. I'm reluctant to pull that trigger because it might not even be the right solution.

Can anyone please lend me a hand? I'm about to give this truck to a dealership for next to nothing and go lease a Ford or a Ram...
 

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What is your fuel pressure? Did mechanic rule out vacuum, compression, bad EGR, plugs or wires and ignition as well as camshaft position sensor?

have you cleaned the MAF?
 

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Discussion Starter #6
What is your fuel pressure? Did mechanic rule out vacuum, compression, bad EGR, plugs or wires and ignition as well as camshaft position sensor?

have you cleaned the MAF?
Fuel pressure is fine. Around 45psi I think. Mechanic did compression, that checked out. Didn't do vaccuum but the problem is sporadic, not continuous. It'll run fine once minute and terrible the next minute. I replaced the EGR about a year ago when I was first having problems. Replaced plugs and wires. I'm not sure about ignition or camshaft sensor. MAF has been cleaned recently
 

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It's a bit weird that it's only affecting cylinder 2, 4, 6, and 8 which are all on the same cylinder head. (Passenger side I believe). I would look for something that could only affect that cylinder head. I suppose the ECM could be messed up in a way thats only messing up that side, possibly interpreting the cam or crank sensors wrong. Usually what I've seen when an ecm fails is you get an array or random issues that don't seem to have any pattern, so it's a big strange that it's only messing up on one cylinder head. Perhaps looking at injector pulses on the left head compared to the right head might help see if the ecm is throwing the right pulse/voltages. The same idea might be possible with the ignition coils. I would check any vacuum lines/PCV stuff that could be pulling vacuum from the manifold thats chambered from that side.


I did lookup GM's fuel pressure spec for your truck at work, it needs to be 55-62psi. If it is in fact only 45psi then you have a fuel pressure issue going on.
If it drops more than 5psi in 10min something is leaking down when it shouldn't be. This is with the key on to prime the pump for a few seconds and not started or cranked. Just priming the fuel system.

When the ignition switch is ON and the fuel pump is running, the fuel pressure indicated by the fuel pressure gauge should read 55–62 psi. The spring pressure inside the fuel pressure regulator controls the fuel pressure.



A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:

The fuel pump check valve
The fuel pump flex pipe
The valve or valve seat within the fuel pressure regulator
The fuel injectors

A fuel system that drops more than 2 psi in 10 minutes after being relieved to 10 psi indicates a leaking fuel pump check valve.

Fuel pressure that drops-off during acceleration, cruise, or hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or misfire. You can diagnose a lean condition using a scan tool. If an extremely lean condition occurs, the heated oxygen sensors will stop toggling. The heated oxygen sensor output voltages will drop below 300 mV. The fuel injector pulse width will increase.
 

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Also, next time it's running good, spray down some of the wiring harnesses with water and see if it makes it run poorly. That would indicate a bad harness or electrical connection.
 

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If it's one side (bank 2, even number side), I'd suspect something like a leaking intake manifold.

Pull the plugs on the passenger side and inspect.
The plugs should all look the same, a nice like brown (by the way, mark them so you know what cylinder they came from).

And, your fuel pressure is low!
 

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Fuel pressure is fine. Around 45psi I think. Mechanic did compression, that checked out. Didn't do vaccuum but the problem is sporadic, not continuous. It'll run fine once minute and terrible the next minute. I replaced the EGR about a year ago when I was first having problems. Replaced plugs and wires. I'm not sure about ignition or camshaft sensor. MAF has been cleaned recently
your not doing the work .. I own a 2000 LT silverado 5.3L ..purchased it in april 2000.. 175K miles.
you stated 45 PSI well I am surprised it is still running.. if the pressure is below 53psi , then it will miss fire.
what is the fuel trims ? +25 or -25 ? plus trims are lean ..
your fuel pressure must be 57psi at idle speed. the other problem also can be if it is running rich the fuel regulator does leak ..
you should install iridium plugs not plats. the plug wires do get damaged on removal .. have to use a tool to remove the spark plug wire from the plug.check for any manifold bolts also that have the heads rust off..
 

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tilt the bed then check for wiring connector issues and the ground straps on the fuel pump ..replace the fuel pump relay .too old.
 

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Bad fuel pumps can cause issues that seem unrelated to the pump. My neighbor just had this same problem with his Ford ranger. Took him forever to figure out all his odd intermittent gremlins were caused by a failing (for about 6 months) fuel pump. Same for a friend with a 2004 suburban. There are also threads here with the same issue. This is not a GM issue, it is a common high mileage vehicle repair.
 

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Discussion Starter #13
It's a bit weird that it's only affecting cylinder 2, 4, 6, and 8 which are all on the same cylinder head. (Passenger side I believe). I would look for something that could only affect that cylinder head. I suppose the ECM could be messed up in a way thats only messing up that side, possibly interpreting the cam or crank sensors wrong. Usually what I've seen when an ecm fails is you get an array or random issues that don't seem to have any pattern, so it's a big strange that it's only messing up on one cylinder head. Perhaps looking at injector pulses on the left head compared to the right head might help see if the ecm is throwing the right pulse/voltages. The same idea might be possible with the ignition coils. I would check any vacuum lines/PCV stuff that could be pulling vacuum from the manifold thats chambered from that side.


I did lookup GM's fuel pressure spec for your truck at work, it needs to be 55-62psi. If it is in fact only 45psi then you have a fuel pressure issue going on.
If it drops more than 5psi in 10min something is leaking down when it shouldn't be. This is with the key on to prime the pump for a few seconds and not started or cranked. Just priming the fuel system.

When the ignition switch is ON and the fuel pump is running, the fuel pressure indicated by the fuel pressure gauge should read 55–62 psi. The spring pressure inside the fuel pressure regulator controls the fuel pressure.



A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:

The fuel pump check valve
The fuel pump flex pipe
The valve or valve seat within the fuel pressure regulator
The fuel injectors

A fuel system that drops more than 2 psi in 10 minutes after being relieved to 10 psi indicates a leaking fuel pump check valve.

Fuel pressure that drops-off during acceleration, cruise, or hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or misfire. You can diagnose a lean condition using a scan tool. If an extremely lean condition occurs, the heated oxygen sensors will stop toggling. The heated oxygen sensor output voltages will drop below 300 mV. The fuel injector pulse width will increase.

I could be wrong on the psi, I know I checked it a while ago and ignored the test because it checked out. it's not leaking. The pressure holds nicely. I've replaced the fuel pressure regulator and the injectors like I said. The truck is running more rich than anything which tells me that it's getting gas but not firing. Or perhaps getting too much gas.
 

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Discussion Starter #14
If it's one side (bank 2, even number side), I'd suspect something like a leaking intake manifold.

Pull the plugs on the passenger side and inspect.
The plugs should all look the same, a nice like brown (by the way, mark them so you know what cylinder they came from).

And, your fuel pressure is low!
They did a compression test and told me that nothing was leaking though. The plugs look like fine but they were also replaced not too long ago. Nothing super black about them

Fuel pressure number could be wrong. I remember it was testing fine whenever I did test it a while ago. Once I get my truck back from the dealership diagnostic, I'll test the pressure again to let everyone know.
 

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Discussion Starter #15
your not doing the work .. I own a 2000 LT silverado 5.3L ..purchased it in april 2000.. 175K miles.
you stated 45 PSI well I am surprised it is still running.. if the pressure is below 53psi , then it will miss fire.
what is the fuel trims ? +25 or -25 ? plus trims are lean ..
your fuel pressure must be 57psi at idle speed. the other problem also can be if it is running rich the fuel regulator does leak ..
you should install iridium plugs not plats. the plug wires do get damaged on removal .. have to use a tool to remove the spark plug wire from the plug.check for any manifold bolts also that have the heads rust off..
Don't tell me I'm not doing the work. I've spent days working on this thing and so have other mechanics. The fuel pressure number is probably not right. I remember testing it and it was up to the correct pressure and wasn't dropping in pressure either.

Fuel trims are fine on bank 1 but on bank 2 the O2 sensor isn't fluxuating like it should. It's staying between 1.0 and 1.2 but they're all brand new. Even swapped sides to make sure I didn't get lucky with bank 1.

FPR is brand new also. Replaced that when I replaced the injectors.

I have iridium plugs in. plug wires are also new. I used the correct socket with rubber fitting to remove the plug. Truck is completely rust free including the bolts around the manifolds. It's a southern truck that probably hasn't seen snow. Surprisingly completely rust free and the cleanest vehicle I've worked on.
 

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Discussion Starter #16
Bad fuel pumps can cause issues that seem unrelated to the pump. My neighbor just had this same problem with his Ford ranger. Took him forever to figure out all his odd intermittent gremlins were caused by a failing (for about 6 months) fuel pump. Same for a friend with a 2004 suburban. There are also threads here with the same issue. This is not a GM issue, it is a common high mileage vehicle repair.
I thought it might be the fuel pump too. I really didn't want to replace that thing since it's such a pain in the butt to get to. I had to do that to my 93 camaro and it was a nightmare. I'll likely replace this next if they can't find the problem. I just hate to keep guessing and throwing parts at this truck that is quickly becoming more expensive than it's worth.
 

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you say it is running rich what is the fuel trims STFT also LTFT...
NORMAL STFT IS IN THE 5 RANGE THE LTFT IS IN THE 10 RANGE when the engine is at normal temp.
miss fires are a large amount of components that can cause this. if just the P0300 ''''only''' then fuel delivery is most times a problem. fuel pumps can be an intermittent failure .. internal electrical in the pump motor or an idiot improperly changed the fuel pump that had to also change the connector.. the wires on this connector has to be soldered.. if not then this can be your problem..

you have the tools and ability correct .. ? then post on here what the fuel pressure is and put your scan tool to post the diagnostic test on the fuel trims LT/ST ..drive it with the pressure gauge on it see how it holds up .. must be above 52 PSI...

O2 sensors with throw a code in a micro sec if it is NOT working ...the mechanic did this to rip you off .IF the O2 sensor was bad or improperly installed then this is gonna throw a O2 sensor code NOT a P0300.only...

he also did the injector replacing just a guy that just has no ability to properly diagnose your problem.
fuel filters need replacing every 30K miles on these... also only use TOP TIER gas.. if not then fuel system damage and corrosion in the tank/pump/reg/injectors/fuel piping.

good luck .
 

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They did a compression test and told me that nothing was leaking though. The plugs look like fine but they were also replaced not too long ago. Nothing super black about them

Fuel pressure number could be wrong. I remember it was testing fine whenever I did test it a while ago. Once I get my truck back from the dealership diagnostic, I'll test the pressure again to let everyone know.
A compression test will check the head gasket, I'm talking about the intake gasket.

If your only getting a random mis-fire code, how do you know the 2, 4, 6 and 8 cylinders are mis-firing?
 
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