Chugging or miss fire

[Snowbum]

Snowbum​

TYF Newbie​

Ok so yesterday out of no where I got a semi rough start, and rough idle. Lots of vibration when I Rev it Maybe not chugging but felt as if not all cylinders were firing. Couldn’t get any codes off of it. I had a fuel filter on hand and that’s why I was/am changing it out. I’m not sure by any means that the filter is the problem.

Due to current fuel prices I have been keeping her filled. That said if it’s the fuel pump, well that going to be a nightmare, but whatever. So my question is has anyone else had this happen? Should I be looking at plugs and wires, maybe CSP ? Or is this a sign that the pump is the problem?

Zero codes

Any info would be appreciated

 

[Fless]

Info about your rig? Year, miles, flex fuel or not, maintenance history, any codes showing up with a scan tool?

 

[Snowbum]

Info about your rig? Year, miles, flex fuel or not, maintenance history, any codes showing up with a scan tool?

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

 

[Snowbum]

Info about your rig? Year, miles, flex fuel or not, maintenance history, any codes showing up with a scan tool?

 

[ratled]

Try this https://www.tahoeyukonforum.com/threads/real-rough-idle-at-start.133875/#post-1672830

 

[Snowbum]

Try this https://www.tahoeyukonforum.com/threads/real-rough-idle-at-start.133875/#post-1672830

O2 won’t throw a code? That seems odd

 

[S33k3r]

Is it possible you got some gas that was too cheap (i.e. a little water in the gas)?

 

[Snowbum]

Had that thought to, but due to gas prices I’ve been keeping it topped off. I use Costco gas which is a very busy station, was also wondering about vacuum lines

 

[S33k3r]

Had that thought to, but due to gas prices I’ve been keeping it topped off. I use Costco gas which is a very busy station, was also wondering about vacuum lines

I've seen people take something relatively flammable (i.e. carburetor cleaner or the like) and spray around the engine while it is running. If you have an intake leak, that should cause the idle to change in the engine -- though I'm sure I am mangling my description on this one. You might want to search youtube for "rough idle" and get some other ideas.

 

[Snowbum]

I've seen people take something relatively flammable (i.e. carburetor cleaner or the like) and spray around the engine while it is running. If you have an intake leak, that should cause the idle to change in the engine -- though I'm sure I am mangling my description on this one. You might want to search youtube for "rough idle" and get some other ideas.

Yeah I might give that a try

 

[iamdub]

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

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?

 

[exp500]

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?

 

[Snowbum]

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?

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

 

[Snowbum]

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?

I just recently got this. I haven’t done much to it other than brakes and getting the fuel filter half off. Yesterday was a dust storm and today it’s snowing pretty heavy so I’m not going to touch it till it dries up

 

[iamdub]

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

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 for long enough or frequently enough for the PCM to set a DTC. The older PCMs tend to be relatively lax.

 

[Snowbum]

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.

Yeah I’m probably just going to toss all the parts at it next paycheck. Thanks for the insight

 

[Tonyrodz]

I had a similar issue with my 01 Express van that had the 5.0 motor. Turned out to be the spider injection. I don't remember if it threw a code tho.