New guy
 

Hey guys. New to the forum and new to having an ls motor that requires my attention.

Short story about my truck. I was given an 01 Chevy silverado 3500 with a lq4 mounted to a nv4500. about a year ago. This was my dad's truck that he bought used back in 02 or 03. It sat for some time only being started every once and a while and driven less than that. I have since cleaned it up, running good, and it is now my daily driver.

The engine light came on and (i forget what code exactly) told me that the knock sensors needed to be changed. It ran fine as far as I could tell with the exception of hard starting every so often. I went ahead and changed them along with the harness and the intake gaskets. Now it's throwing p0332 (knock sensor 2 circut low bank 2), p0327 (knock sensor 1 circut low bank 1 or single sensor), p0171 (sytem too lean bank 1), and whatever the code is for system too lean bank 2. I can clear the codes and drive around for a while with nothing, but as soon as I shut it down and turn it back on, new code get throw and not always all same at one time (either knock sensor, or too lean, or both).

I only have a scanner that will read and clear code. it will also read freeze frames, but that's it. I'm looking into getting a better one.

I've done a bit of research as i'm new to having to work on an ls motor. I'm thinking that I have a vacuum leak somewhere. after sitting for so long, I can only imagine that most of the vacuum lines and rubbers are very brittle and when I removed the intake to change the knock sensors, I must have cracked something. It's either that or a frayed wire leading to or from the knock sensors beyond what I have already replaced. I'm planning on looking around and trying to find something obviously damaged tonight when I get home.

My question to you is there something that notorious that goes out as far as vacuum components that I can check first? I can't hear a leak while the truck is running, but that's not to say it's just a small one. I am going to get a vacuum tester (not sure what they are really called), and check everything out. I'm also going to inspect the wiring to the sensors and see if there are any breaks or frays.

Other that exhaust that my dad had installed, this truck in bone stock.

Thanks in advance for any help.

It's possible the new harness you got is bad too, seen it happen. Or it's the wires in the longer harness to the computer.

If you have vacuum leaks to both banks at the same time I'd lean towards the intake gaskets not sealing right or one big vacuum line leak somewhere.

The too lean code only comes one at a time. This time it's bank 1. Last time it was bank 2. They never come on at the same time. I would think if the intake gaskets weren't sealed properly, the motor would run horrible if it even runs at all. At the moment, the only noticable difference is at idle. It idles around 600-700. The only other thing it's now doing is when you shift into neutral while costing to a stop sign, the rpms rev up to 1800 and fall off to idle until your almost to a dead stop. I may be wrong get and it might be a bad gasket seal. I'm looking into the wiring also.

If you had a live data scanner you could see which bank is more lean than the other by viewing the fuel trims. One would be far more positive than the other. Small intake leaks won't make it run that bad.

Stopped by the parts house this morning and bought a scanner that reads live data.

Short term fuel trim bank 1 is at 52.3
" "bank 2 is around 40
Bank 1 holds strong at 52 and bank 2 fluctuates from 36 to 46

I also noticed the o2 sensors are all different
O2s11 0.185
O2s12 0.000
O2s21 0.580
O2s22 0.060
They all fluctuate too

Not l00% sure what all this means. I'm sure the o2 sensors and fluctuations get due to the lean condition. I'm just not sure if they would cause the condition. I do recall seeing an o2 sensor code a while back, but it just popped once.

I was thinking that the truck would run bad with intake gaskets not sealing right because of previous experience with the old 350 in my c10. The carb gasket developed a hole and it was not drivable. Of course I didnt take in to consideration that it's not controled by a computer. I cleaned the sealing surfaces on both the intake and heads and torqued the bolts to specs. What else should be done to ensure proper sealing? I wish I knew somebody who has one of those smoke pumps so I can find the gap in one shot instead of taking everything apart.

All those reading were at idle

Those are some way positive numbers on the fuel trims, meaning very large leak somewhere for sure. The fuel trims on a normal running motor should be less than +5% on avg for the most part.

o2 sensors will always move around and the front sensors more than the rear. The front o2 sensors will alway switch lean and rich of stoich (450mv) when running correctly. The rear o2 sensor once warmed up and the cats are nice and hot will stay somewhere around 600-800 give or take some and normally stay there. If they start bouncing all over the place and swinging like the front sensor that is a starting sign that the cat converters aren't working as good anymore and on their way out.

The rear o2 sensor don't mean much on the early trucks though, they would run just fine without them and the cat converters.

A smoke tester or making your own would help you a lot here, with fuel trims like that pin pointing the leak is needed for sure.

As far as smoke testing, where would be the best point of entry? I'm in the construction field and I might be able to borrow one from my hvac guy. If not, I could rig one up. Would dry ice vapors work or would that be a bad idea? My c10 only have one vacuum linew going to the vacuum advance. Pretty easy to find. I don't want to hook it up where it's going to push smoke through the cylinder and out an open exhaust valve. That is assuming the valuetrain on these motors operate similar to an old 350. I guess I could block the exhaust at the tailpipe to keep the smoke from going that route.

As far as the o2 sensors. I did notice while poking around that the exhaust system is true duals. My 02 silverado did not have this set up and I'm not sure if this is stock or was modified when the old man had it installed. Would that cause problems with the o2 sensors?

6.0's in those truck has single pipes all the way back to the muffler, that's a factory thing.

Just use the brake booster vacuum line if the truck doesn't have hydro-boost. Or just pop the MAP sensor off and feed the smoke in through there. You want to cap the throttle body off while doing this and that too could be a spot to feed the smoke in if you wanted too to.

It's got hydro boost. I'll see if I can get my hands on or rig up a smoke tester in the next couple of days and let you know what I come up with.

One thing I did notice when I was taking the intake off. I watched a video of a guy doing this repair and he pointed out a big vacuum line that plugs into the back of the I take. Mine does not have this line, only the port with the push to connect fitting. With the truck running, I felt of the fitting and didn't feel any suction. I assume it's blocked off from the inside. Just thought I'd add that.