2001 Buick Century occasionally stumbles, more rarely dies.

Bought a 2001 Buick Century in April 2017 with 23K miles on it, in near perfect condition. Classic "Grandma's car". Aside from a battery and new tires, haven't done a thing to it since. But in July it started stumbling and sometimes dying. No codes to speak of - there was a P0446 but a vent control solenoid and new gas cap may have fixed that - don't think a full evap test has run yet. The car currently has 39K miles on it.

I am new to ScannerDanner world and I am definitely not a technician by any stretch (though I wanna be! DIY in the driveway type.) The vacuum at the fuel regulator is 17 in Hg and it regularly pulses low to 16.5. I notice that when I have a scanner connected and I am watching the O2S, when I accelerate to ~4000rpm the voltage of the O2 sensor suddenly collapses to near 0V and stays there until the rpms fall some or until I lift off the gas. If I don't lift off the gas the engine rpms rise and fall in a regular fashion, first 4K then 3.5K etc. When the rpms are high the O2S voltage is near 0.

Please excuse the ignorance here, I am literally only on Chapter 1 of Mr. Danner's book, and though I have done a lot of mechanical DIY repairs over the years, I am over my head here for the time being.

I have not even looked at the spark plugs/wires etc yet.

Any guidance will be appreciated. I do not have a scope yet and have only a Blue Driver ODB2 thingy and an old Genysis OTC SPX scan tool. I do have the usual DVM and a Power Probe and a garage full of mechanical tools etc. I have mostly been a parts changer.

Thanks,
Dave Day

DaveDay wrote: I notice that when I have a scanner connected and I am watching the O2S, when I accelerate to ~4000rpm the voltage of the O2 sensor suddenly collapses to near 0V and stays there until the rpms fall some or until I lift off the gas.

It sounds like a fuel delivery problem. All O2 sensors should go full RICH and WOT. What is your fuel pressure at idle, and during a WOT acceleration.

If I don't lift off the gas the engine rpms rise and fall in a regular fashion, first 4K then 3.5K etc.

Are you in Park, or Neutral, when you are doing this. If so, that is the rev limiter preventing OVER revving. It is better to do a test drive and wrap out 1st, or 2nd gear, while watching your O2 sensors...they should go full RICH.

Hey Dave! It'd be helpful to know more about your symptoms. How intermittent is this stumble/stall? Once a day? Week?

When exactly does it happen? During acceleration, coming to a stop, idling?

Besides the stumble/stall, does the engine run well?

I notice that when I have a scanner connected and I am watching the O2S, when I accelerate to ~4000rpm the voltage of the O2 sensor suddenly collapses to near 0V and stays there until the rpms fall some or until I lift off the gas. If I don't lift off the gas the engine rpms rise and fall in a regular fashion, first 4K then 3.5K etc. When the rpms are high the O2S voltage is near 0.

Does this happen while stopped in park, or driving down the road? :huh: Because it kinda sounds like you're describing the rev limiter.

I do not have a scope yet and have only a Blue Driver ODB2 thingy and an old Genysis OTC SPX scan tool. I do have the usual DVM and a Power Probe and a garage full of mechanical tools etc.

Those will work just fine.

Thanks!

I am just in park in the driveway. I'll test drive it and get back to you.

I haven't checked the fuel pressure yet, I'll do that tomorrow. I did change the fuel filter.

Dave

CHAD GET OUT OF MY HEAD.

Tyler wrote: CHAD GET OUT OF MY HEAD.

I will take that compliment.