New to me 2000 K2500 missing at idle, occasional stalls

[RokRoland]

Not going to comment on 454 grounds, someone else should know better. A really ghetto hack to investigate the issue is to put a jumper cable from battery negative to both the frame as well as the engine as extra grounds and see if anything improves (note that they don't like to stay put when driving about). Use at your own risk.

However to elaborate on the previous, the purpose of the lambda or O2 sensor is to provide the engine control module feedback about the combustion event, whether the fueling is rich or lean. Obviously, if the sensor gives faulty readings, the fueling will be adjusted the wrong way. Again this sensor is not used on a cold motor, or when you are at wide open throttle, because a normal O2 sensor is unable to get a reading in this condition (a wideband sensor is needed).

Looking at the Vortec 454, it may be that you even have three O2 sensors (left bank / right bank / downstream) so if there's a discrepancy between these it may cause a bunch of issues too. I am not sure how many there are because seems like there are variations. Then again, your problem could be something completely different.

 

[454cid]

Looking at the Vortec 454, it may be that you even have three O2 sensors (left bank / right bank / downstream) so if there's a discrepancy between these it may cause a bunch of issues too. I am not sure how many there are because seems like there are variations. Then again, your problem could be something completely different.

Nope...we have 4 O2 sensors! The rears don't effect the engine, Though. It's my understanding that they are there to monitor the effectiveness of the cats.

Exception: Model year 2000 trucks did away with the 2 post cat sensors, I'm told.

I get to change my front sensors soon.... I have a dead one on the driver's side.

 

[454cid]

The oil pressure switch would also be 3 wires, and "right next door" to the distributor. But you'd know if that were unplugged, your oil gauge would be at 0 and the "Check Gages" light would be glowing.

He may have a 1-wire oil pressure switch..... I do on my 99.

 

[454cid]

Good news? I could not find CMP offset in Torque, but the app called Car Scanner on Android seems to have it. It was at 4.9 at 1,000 rpm.

That's out of spec, but not horrible. Spec is +/- 2 degrees.

 

[Schurkey]

He may have a 1-wire oil pressure switch..... I do on my 99.

My '88 has a one-wire sending unit (for the gauge) and a two-wire switch (for the fuel pump.) Later vehicles used a combination switch/sending unit with 3 wires.

If GM is no longer using oil pressure as a bypass for the fuel pump relay in '99, I didn't know about it. So I guess I learned something today.

 

[Supercharged111]

2 things:

1) The engine does not enter "limp mode" with the camshaft position sensor unplugged. It reverts to batch firing the injectors, nothing more. These motors are notorious for injector and FPR issues.

2) To the O2 sensor comments, watch the data to see if your sensors are hanging at the top or bottom instead of rapidly cycling. You could also just unplug one and see if the truck runs better. Of the 2 sensors that I've had fail like this (one lean, one fat) the truck would always snap out of it when subjected to open loop. On a stock tune, I don't think you can instantaneously will it into open loop like I can, but if you unplug one it ignores both sides and you'll know right away whether or not it was the cause. In neither instance did my trucks throw a code for an O2 sensor.

 

[454cid]

1) The engine does not enter "limp mode" with the camshaft position sensor unplugged. It reverts to batch firing the injectors, nothing more. These motors are notorious for injector and FPR issues.

Until this thread, I had no idea the distributor (cam sensor) could be unplugged, similar to the MAF.

 

[Supercharged111]

Until this thread, I had no idea the distributor (cam sensor) could be unplugged, similar to the MAF.

I did it as a science experiment on my 1500 to try and narrow down its misfire. Truck drove exactly the same and never threw a CEL. The guy who did the 4X LT1 411 swap was the one who first mentioned it.

 

[Nicman201]

Well I found some grounds attached to the frame right underneath the AC condenser. One ground went to the firewall and had rotted away and was no longer connected. The 2nd ground, I'm assuming went to the back of the cylinder head but it wasn't connected to anything so I just put it on the stud for the exhaust manifold for now.

So far, the weirdness has stopped. Will keep updated.

Also wanted to say thank you, turned into a very informative post.

 

[someotherguy]

Well I found some grounds attached to the frame right underneath the AC condenser. One ground went to the firewall and had rotted away and was no longer connected. The 2nd ground, I'm assuming went to the back of the cylinder head but it wasn't connected to anything so I just put it on the stud for the exhaust manifold for now.

So far, the weirdness has stopped. Will keep updated.

Also wanted to say thank you, turned into a very informative post.

Those grounds are pretty critical.. most are, but those especially. Good catch and let us know how things go from here on out.

The typical arrangement of those grounds is indeed one from rear of cylinder head to the firewall, then another from same spot on the firewall down to the frame.

Richard