O2 sensor readings '96 Astro V-6

[4xcrazy]

I'm working on Jenns dads 1996 Astro van, 4.3 Vortec v-6.

Has several issues with it, one thing at a time though.

Been sitting for 2 years due to front end damage, that was recently fixed, I replaced the fuel filter first thing. It was very sluggish, popped out the intake a couple of times and at times, acts like something is hitting the electrical system or fuel is being cut at an instant and the engine stumbles for a bit and sometimes almost dies while hitting the throttle, it finally gets up and goes after fighting with it for a few seconds.

I just pulled the mass air flow sensor out and cleaned it along with the sensor behind it, cleaned out the air filter, scraped out all the carbon build-up on the terminals inside the distributor cap.

It seems to run a bit better now, unsure about the near stall issue though, haven't driven that far just yet to find out.

It originally threw an O2 sensor lean condition (both banks) I figured the very restrictive fuel filter, and it was very restrictive, ran much better right after that, but still with that sputtering deal after it gets warmed up.

On the way back from his house yesterday, it again, threw the O2 sensor lean condition (both bank)

I plugged in the ELM327 scanner, reading different readings of what the engine is doing, nothing seemed weird really, except for the readings from both O2 sensors.

Since I'm pretty new to reading live information from one of these, I honestly don't know what I'm looking at.

BOTH O2 sensor readings jump from 0.2v to 0.9v constantly. They level off around 0.9v for a few seconds when I rev the engine up, but the start fluctuating again shortly after if I hold that throttle.

I guess I'm just looking for a bit of info, or ideas as to what else I should be looking at before I go replacing O2 sensors.

Thanks.

 

[Russell]

The fluctuating is call crosshatching and is evidence of correctly operating oxygen sensors.

I'd be checking my fuel pressure and making sure none of the injectors are sticking.

 

[4xcrazy]

Yeah, I checked the fuel pressure while the old filter was off, before the new one was installed, it tested within range at 13.5 and went up to close to about 20psi when rev'd.

I haven't driven it yet since the few things I did earlier, but already it does seem to start and idle a bit nicer.

I'm taking it back to his place tomorrow for some other things to figure out, I'll see how it does then.

The other thing I was thinking was maybe the new fuel filter was plugged up with something already, this vehicle was sitting for a hair over 2 years and just recently restarted after body repairs were completed.

I dunno, tomorrow will tell me more.

 

[Russell]

Vortec 4.3L engines require 58-60 PSI of fuel pressure.

 

[4xcrazy]

Yeah,,, major brainfart there

I was thinking this thing was similar to my mothers 4.3, it's a Vortec style, but not this year and is running TBI....

UGH..

 

[Russell]

Any exhaust leaks? I somehow don't believe your ECM when it says that it is lean enough to throw a code...

 

[4xcrazy]

A slight one at the donut gaskets, yes, but that lean code usually comes on when under a good amount of acceleration, or when it tries to stumble and I essentially force the throttle down to get it movin, it'll stumble, sputter and hesitate, then it'll just snap in a go.

 

[4xcrazy]

Well, driving around today, no CEL, no sputtering or spitting out of the intake.

what I did so far was clean the mass air flow sensor and the little sensor behind it, reseated the intake tube on the throttle body, it wasn't flush, removed and scraped off all of the carbon build up on the terminals inside the distributor cap.

That alone made a big difference in the way it ran, haven't had any of those seemingly electrical hit to the system where it almost cuts the engine off and stumbles,,, yet..

Still sluggish with throttle it seems to me though, but doesn't fall on it's face anymore,, so far.

Gonna hook up a different fuel pressure gauge to it tomorrow in a different location and see what it reads just to be sure the other gauge was getting an accurate reading and go from there.

 

[Russell]

The intake tube leaking would cause all kinds of trouble. Un-metered air is never good! I'd make sure and get that exhaust leak fixed as well. Extra O2 in the exhaust stream is no good either. It does not take much to screw with the O2 indications.

How many miles on the engine? When was the last time the cat was changed? What have you got for vacuum in the intake manifold? Has the timing been messed with?

What do you spark plugs look like?

 

[4xcrazy]

175k miles, I haven't checked the vacuum, almost impossible to get to the plugs, so unsure at the moment, wires have AC deco on them,

I don't think this thing was maintained all too well.

 

[4xcrazy]

It's gettin there, I still have several more things to check or replace, worked most of today on his boat, trying to get that stupid carb'd 350 to even idle, I can't remember the last time I had this amount of trouble working on a carb'd engine. Annoying, but I think there may be something internal going wrong.

Anyways, originally I was just curious about that swinging reading on the O2 sensors, never knew they did that, never had a live fees of sensor activity either though.

 

[Russell]

Have a look at this link:

http://www.picoauto.com/applications/lambda-sensor.html

 

[Blue85]

The ECM is going to adjust fuel until it sees the O2 voltage swinging up and down. That's what they do at stoich. Anytime it's stuck high or low you don't really know the AFR.

A wideband sensor is actually a narrowband sensor with additional stuff on it. It can manipulate the oxygen level inside the sensor. By controlling temperature carefully and knowing how much oxygen is needed to bring the (internal) narrowband back to stoich, it calculates how far you are from stoich. That's why the WBO2 sensor always has a controller with it. The NBO2 just generates a voltage on it's own whenever it's hot, so it routes directly to the ECM.