GMC 6.0 misfire only at speed

is misfire code only on one cylinder every time?

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don't know, my scanner wont give me individual cylinders, but the code is for "Random misfire"

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should be a P0300

Without looking at an actual scanner, not a code reader, it can be any number of things. Mass air meter, fuel pump,fuel pressure regulator,crank sensor,cam sensor,distributor(if the truck is old enough to have one)

gm forum are full of this issue, the 99-07 years all had fricked up fuel pumps

something about the fuel pumps being crap and causing issues

the general consensus is replace fuel pump with new one and issues go away, if you dont you will continue to chase your tail after false codes triggered by low fuel pressures at speed

im told the ac delco pump is only like $115 but you have to lift the bed or drop the tank to change it so its a PITA to get to it

This is gonna suck! Can be a number of sensors, solenoids or switches from the engine compartment to th the o2 sensor. Or the cat converter, leaking heads, faulty fuel pump, cracked head, evap system......

Get a fuel pressure test gauge and hook it up to the truck. Look up your year model and what the Fuel Pressure should be for idle and for under power.

Idle the truck for a bit and check the pressure and then take it down the road at speed with the gauge visible to you(I run the hoses up by the cowl and lean it on the windshield and then close the hood to where it latches but not down all the way).

Look the pressures, especially if it misfires. Reference what the pressures should be at idle and under load. If they are off by more than a couple of PSI, you probably have a fuel pump going out.

I had an 03 S-10 once with the 4.3 that started having the same symptoms. It was the pump that causes the problem.

If your pump is bad, it's much easier to unbolt the bed and slide it back or over with a few friends to get to the fuel pump. Much better than draining the tank and then dropping it. I've done both and I'll do the bed move every time if given the choice.

If the fuel pump checks out, I'd look the ignition coil or coils. Pull it and look for carbon tracing on the coil wire and anywhere on the coil itself. That is also a common misfire cause. If you have coil pack per cylinder, you'll have to inspect each one.

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Any suggestions?

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Get rid of the POS GMC?

Do what I do with all GM engines


Ignore the lights and the knocking and rattlings, change oil with 10w-30 no matter what they recommend, and drive the shite out of it.

Got a 2013 gmc on the farm with 200k and it’s been knocking for 3 years now. Done nothing to it, still going