I'll try to keep this short. Couple weekends ago I replaced my intake and exhaust manifold gaskets along with the spark plugs. Two days ago the 5.3 started chugging at low RPMs under load. Idle is okay and I don't have any CELs. Here is what I have tried:
1. Had half a tank of gas, filled it with fresh stuff, problem went away. Wheeled it hard today and on the way home it started doing it again.
2. Pulled individual coil plugs at idle and each one made the engine idle rough telling me the spark is okay (at idle at least).
3. Looked at live data through code reader and nothing jumped out at me

It's an '02 5.3 with approx 90K miles mated to an NV4500, swapped into a '67 Bronco.

What should I try next?

 

its got that blue oval sickness??? ok seriously i went through this with my silverado a few years back and found i had a failing injector.

 

What plugs did you use? Did you perchance unseat the MAP sensor on top of the manifold?

 

I just used cheap plugs, but the same that I pulled out and it was running great the last three years. MAP sensor is in place.

Is there a way to go about checking my injectors?

 

Check the fuel pressure while it is chugging. Hook up a gauge and duct tape it to the outside of your windshield.

 

My rig eats fuel filters because of the 46 year old gas tank so I have felt the effect of low fuel pressure many times. I definitely don't think it's a fuel delivery issue as it is not a sputter, a cylinder is randomly dead. So I'm thinking injector or coil pack? The bitch of it is that the problem is not consistent. I never had a single issue with this motor besides a vacuum leak that I fixed by replacing the intake manifold gasket two weekends ago.

Is there any way I can narrow this down without throwing a bunch of new parts at it?

 

keep a timimg gun handy.... when it dose it check each cylinder should be a nice steady flash... then also check the fuel pressure when it happens too. then start up plugging injectors.

 

I wish I could check for spark with the timing gun but the issue only happens when loading the engine down. I don't have any friends small enough to ride under the hood.

I have a spare set of low mileage injectors out of a 6.0 lying around but I have the flex fuel injectors in the motor so I would have to install new pigtails (not a big deal just time consuming). That might be my next step though.

 

Last night I did some more digging and couldn’t track anything down. The motor was still idling okay so it was difficult to determine anything. The rear driver’s cylinder (not sure which #) seemed to affect idle the least so I unplugged the injector and it definitely made it idle worse so nothing conclusive. This morning I went to leave for work and it was definitely down a cylinder at idle but it wasn’t consistent. It would idle like it was down a cylinder for a few seconds and then it would idle normal. The problem is definitely getting worse so this makes me think a coil pack or injector is going out. When I bought the motor with 60k miles on it a few years ago it was missing one coil pack. I got this coil pack off another used motor with mileage unknown and this coil pack is on the cylinder in question so it makes sense. I’ll mess with it more when I get home tonight.

 

check your grounds, my stutters real bad at low RPMs, the radio even crackles and pops. i cleaned them all except the one on the back of the motor which i know is bad i just cant get it. the problem cleared up a little but im thinking about relocating that strap.