Trouble codes and lamp is on

[John B Kobberstad]

1996 Chevy C3500 Silverado 1 ton Dually 2W RWD 454 Vortec Extended cab 2DR 269,000 miles

I’ve got 3 codes coming up on the scanner –

P0134 – Bank 1 Sensor 1 Low voltage (no activity)
P0171 – Fuel System Too Lean Bank 1
P0175 – Fuel system Too Rich Bank 2

O2 B1-S2 is at 4 mv and does not change

The other 3 O2 sensors all are changing and none go any lower than 350mv and no higher than 900mv

Exhaust smells out the back from the driver’s side pipe and white smoke comes out at idle and pipe throws out black soot on my white garage door if I rev it up.

Vehicle goes into closed loop momentarily a couple minutes after it is cold started and then goes back into open loop.

MAF sensor was cleaned recently. Had MAF code come up and cleaning it solved that code problem.

Should I replace the downstream O2 sensor or check something else first before replacing it?

Topic

[college man]

Here is a way to test if the o2 are working or not. With no activity sounds like
a bad o2 or wiring.

http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-oxygen-sensors-1

[none]

Just to clarify, your P0134 code is saying there’s a problem with the upstream sensor. It’s the one before the cat on the driver’s side. If you do find that the upstream O2 sensor is bad and replace it, you might wind up gaining code P0172 later. Deal with the O2 code before you put any consideration into the other codes.

[EricTheCarGuy]

I’d start by looking at the sensors to see if there’s an issue there. They should switch rapidly back and forth from rich to lean. Also check for vacuum leaks. These can upset the mix and cause O2 sensors to freak out. Also any exhaust leaks near the sensors can throw them off at times. It’s probably also a good idea to check your plugs and fuel delivery to see if those are working properly. More info on solving these issues here.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

Keep us updated on what you find and good luck.

[John B Kobberstad]

Thanks for the replys and the useful advice

Just tested the fuel pressure at the rail Schrader valve. Engine cold Key On Engine Off = 48 psi Cold start at idle = 48 psi , 2000 rpm = 48 psi , 3000 rpm = 48 psi sitting parked. The pressure bleeds off and within about a minute it was down below 30 psi and still falling. Since FSM indicates it should be 60 – 66. I guess that I should start looking for a new fuel pump. I’m not too familiar with GM but can you rebuild the GM fuel pump module with a new pump motor and some new fuel pump strainers/filters. I’ve rebuilt Chrysler fuel pump modules and never had a problem with that. Where would be the best place to purchase a new pump motor w/strainers/filters? As I have an almost full 34 gallon tank, I think the best way to get to the tank to fix this would be to lift the bed up on the driver’s side to get to the tank. How difficult would this be? and would this be the preferred method?

[John B Kobberstad]

Update

I realize that the bleeding off of the pressure is definitely a problem here. Replacing the pressure regulator or replacing leaking injectors (or their O Rings)or both may be necessary also. Because the pump spec calls for 60 – 66 psi and this is much lower, at 48, I think it’s time to think about replacing it also though, even though it starts fine and seems to run all right. Can’t tell how the gas mileage is because the truck is new to me and I have yet to run it through a full tank of gas and I am aware that I can expect to get about 8 miles/gallon with it, not much more than that.

I finally got a chance to do some checking on this truck.
Took the O Scope out yesterday and although I could not get a trigger set right to stop the waveform and hold it steady so it wouldn’t keep tracing across the screen, I did find that at the VCM pins I got a negative square wave —-_— pulse on each of the output pins for the control of the injectors. They seemed to all be the same about 14V + going down to 0V then back up to 14V + only getting the negative pulse when the injector was fired, so most of the time voltage was at 14V +

Today I checked under the truck and to my surprise Adam,there are no catalytic converters in the exhaust system. However there are 2 – O2 sensors in the pipes connected to the exhaust manifolds about 4 inches from the connections and 2 more farther on down the exhaust pipes about where the cats should be. I could only get what would be considered the downstream one on driver’s side (Bank 1 Sensor 2 I believe) removed. The other 3 would not budge. When removed the threads were really bad and there was no compression ring washer attached to it. It was covered with black soot at the sensor tip so I cleaned it and wire brushed the threads and put never seize on what was left of the threads and re installed it in the hole with s bit of difficulty but eventually got it in.

I had reset the codes just after I posted this and the P0134 and P0175 have returned.

Put fuel pressure gauge on the rail this AM. Powered up fuel pump with the scanner. When pump was turned off pressure immediately dropped from 55 psi substantially. Powered it up again and clamped the fuel feed line from after the fuel filter. No change, pressure dropped again. Fired up again and clamped the return line which is next to the feed line. Pressure dropped again. Fired pump up again and clamped both feed and return lines. Pressure dropped. Conclusion is that there is nothing between where I clamped the lines off and the fuel pump/gas tank fuel return that is causing the fuel pressure bleed. Guess my next move is to remove the upper intake manifold to get to the fuel injectors and the fuel pressure regulator.
I will try to keep this updated as things progress.

Thanks for all the suggestions

[Author]

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