Help from the GM techs, plz...

[-stew-]

2000 Sonoma, 2.2L Auto, 2WD, 85,000 miles.

Driving along, all is good. Stop at a light, foot on the brake. Light goes green, take my foot off the brake and hit the gas (gently, I drive like an old lady) and the truck starts spitting and sputtering, making that hollow sound like the throttle blade is open, but no air is moving, truck is barely moving. More gas makes it worse, bogging, tach dropping down to around 500 RPM, voltage guage drops, oil pressure starts falling, lights dim. CEL never came on. I dropped the gear selector down into "1" and ran it back through the gears back to "OD", nothing changed. Stopped, put it in reverse, and backed up a lil bit, put it back in drive. No change. I did these things thinking maybe it was stuck in OD and this would move things and help. Went 500 feet and it returned back to normal. Went two blocks and it did it again. Parked, turned it off, and restarted, same deal.

Last night was the second time it did this. First time was on a clear and dry winter day (six or seven months ago), so I don't think the rain had anything to do with anything.

Runs and drives fine this morning.


Anybody got any thoughts? Something sticking in the trans? Fuel pump? I'm gonna see if I can get my hands on a scanner tonight and see if the computer can tell me anything, But like I said, no CEL during this. CEL is there during startup bulb check. Truck has been driven gently it's whole life. Still has OEM plugs and wires that will be getting replaced this week. Had a CEL a year or so ago for the airpump, I never fixed it and the light when away.

The only issue (other than a few batteries and brakes) with the truck since new was a trans line went bad and I think it got ran dry at ~25,000 miles. Don't know if they just replaced the line, and refilled it, or if they rebuilt the trans, too.


Thanks in advance,


-stew-

[88Nightmare]

for starters, I'd say it would need a tuneup after 85k miles.


perhaps its a vacuum issue? The 2000 may have dexcool in it, and if thats the case, perhaps a intake gasket was eaten away causing a vacuum leak.

If you could get it over here in OC I could hook my scan tool up to it just to see if there is a stored code of some sort, or hook my vacuum gauge up to it.

[WickedSix]

You check the charging system?

[BAD LS1]

It needs to get scanned to see what its doing while it fails, it really could be anything but the trims should show big + numbers if its correcting for a hella lean condition. Could be just a failing o2 sensor giving an eroneous reading think its either lean or rich and is adding or removing fuel. The bogging and no responce can be due to too much fuel as well. W/o doing some simple checks to verify if its correcting for something you will be just guessing and throwing parts at it. The lights dimming etc are all part of the RPM dip and the PCM dropping the alternator to prevent extra load from stalling the engine.

[-stew-]

for starters, I'd say it would need a tuneup after 85k miles.


perhaps its a vacuum issue? The 2000 may have dexcool in it, and if thats the case, perhaps a intake gasket was eaten away causing a vacuum leak.

If you could get it over here in OC I could hook my scan tool up to it just to see if there is a stored code of some sort, or hook my vacuum gauge up to it.


It will be getting plugs and wires this week, LOF and fuel filter tonight. IDK it the 4cyls use coolant passages in the the intake. I don't think it's a mechanical problem because it's done it twice in 5-6k miles, and runs like a top other wise.


You check the charging system?

I will for shits and grins, but it should run fine initially on battery voltage, spins over and starts up great, had no issue on the coldest days this winter.

[-stew-]

It needs to get scanned to see what its doing while it fails, it really could be anything but the trims should show big + numbers if its correcting for a hella lean condition. Could be just a failing o2 sensor giving an eroneous reading think its either lean or rich and is adding or removing fuel. The bogging and no responce can be due to too much fuel as well. W/o doing some simple checks to verify if its correcting for something you will be just guessing and throwing parts at it. The lights dimming etc are all part of the RPM dip and the PCM dropping the alternator to prevent extra load from stalling the engine.


Doing this only twice, is going to be reflected in the trims? I put the post up to avoid throwing parts at it. I was (am) hoping one of the dealership types here knew of a TSB, reflash, or oddity that would cause this. I know this may be impossible to diagnose with out it doing it again, and with out being able to look at the datastream while it is acting up.

Does this sound stupid: if it does it again, pop the hood and unplug something (TPS, ect) in order to set a code and get the ECM to take a snapshot?


Also, thanks.

[BAD LS1]

No you need a OBDII scanner that can display realtime data and just watch what stuff does. The trims were just a thought, those things can react very quickly. A sensor could be defaulting momentarily as well which would make it puke like it did. This just not a cut and dry thing esp since its so sporadic. Something Air pump related could mess with it, i know it does on trailblazers where the check valve sticks and allows spent exhaust gas back into the intake which will cause huge running issues, also EGR could be acting up too. If you read the PCM with a good enough scanner you will see if there is any pending codes that arent quite ready to turn the SES light on.