Chugging or miss fire

Snowbum said:

2000 Yukon Denali 160k direct injection weird carburetor thing I don’t think it’s flex fuel , zero codes ,L31 5.7

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iamdub said:

Ah. It's the pre-LS "Vortec" tree-fiddy. Definitely not direct injection. It's a throttle body mounted like a carburetor with all the injectors inside the intake manifold with little nozzles that shoot the fuel into the intake runners. So many possibilities for a misfire on these and many that the PCM won't "see" unless it's really bad and, therefore, not throw a code. Can you get your hands on a scan tool that shows live data? How about a fuel pressure gauge?

You said it started "out of nowhere". What happened immediately before it started acting up? Where you driving and it started this or was it from a cold start after sitting, like parked over night?

How old are the ignition components?

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exp500 said:

Spark test at distributor cap and at Coil, Fuel pressure test. Key on eng off#/ idling#/Driving#/ when missing#/.
When was the last time you changed dist cap/wires/plugs?

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Snowbum said:

I had driven it around throughput the day and things were fine. Then it sat for about a hour and a half. That’s when it was kinda like a cold start, idle was rough, when I rev it up it shakes.
Yes scanner has live data
I would assume the ignition parts are original

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iamdub said:

If you can't approximate the age of the ignition components on one of these engines, then they're likely due for replacement. Not saying this is your problem, but I can't say that it isn't and it very well could be a problem later on. If it's your only vehicle, go get a new cap, rotor wires and set of plugs. DO NOT get the store's house brand for electronics and especially ignition components. You want AC Delco or Delphi. There are a few aftermarket ones that are okay, but I can't recall the brand names at the moment. When you get back home, pop the hood and let it cool. Then, remove the cap and inspect. I say to have the replacement parts on hand since pieces such as the cap or rotor can be cracked and get worse once you start messing with them. Plug wires can fall apart and people often find ways to break spark plugs when trying to remove them.

Does it smooth out when you rev it past a certain RPM?

If you've tried it, does it pull like normal or mostly like normal up to its shift point if you floor it?

Being as the problem recently started, it might not have happened long enough or frequently enough for the PCM to set a DTC. The older PCMs tend to be relatively lax.

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