[weirdbeard]

I would just like to know how the left bank on this 1998 vortec 350 runs fine and the right bank is running lean some of the time. What besides the o2 sensor could cause this? It uses sequential fuel injection. I am trying to learn more about this engine and I can't find the info I am looking for. Thanks.

[schnitz]

Not an engine pro by any stretch, but could it be somehow related to a weakened injector pulse? I'm not even sure how to test that, but it's a thought.


In a while, Chet.

[weirdbeard]

I thought of that. I pulled the plugs and all for are black and sooty on the right bank. It seems to me if it was a weak injector or injectors the plugs would all be a lil different looking on the right bank.

[schnitz]

I was thinking more along the lines of the signal voltage (sv) to the injectors on the right side being higher than the sv on the left side. Then the o2 sensor would signal to send more fuel, and that's what's causing the rich condition in the right side. I'm just not really sure how that sv is controlled.



Other thought, though, if you don't mind another o2 sensor thought. How many o2 sensors do you have? My '97 has 3. One on each side of the y-pipe, and one by the cat. Could the right side one be fubar'd ?


In a while, Chet.

[oldbogie]

Originally Posted by weirdbeard

I would just like to know how the left bank on this 1998 vortec 350 runs fine and the right bank is running lean some of the time. What besides the o2 sensor could cause this? It uses sequential fuel injection. I am trying to learn more about this engine and I can't find the info I am looking for. Thanks.

A vacuum leak or a leaking exhaust could admit enough air to fake the O2 sensor into thinking that side was running lean as well as a failing O2 sensor or the wiring to or from it.

OK need to explain myself a bit. If additional air is getting into the engine at the intake side or if being drawn into the exhaust, the O2 sensor will read this as a lean condition and throw more fuel at the side with the apparent lean A/F ratio. Since it adjusts by side of the engine, even if only one cylinder is running lean, all on that side will be adjusted causing the normal cylinders to go extremely rich.

Bogie

[weirdbeard]

Originally Posted by oldbogie

A vacuum leak or a leaking exhaust could admit enough air to fake the O2 sensor into thinking that side was running lean as well as a failing O2 sensor or the wiring to or from it.

OK need to explain myself a bit. If additional air is getting into the engine at the intake side or if being drawn into the exhaust, the O2 sensor will read this as a lean condition and throw more fuel at the side with the apparent lean A/F ratio. Since it adjusts by side of the engine, even if only one cylinder is running lean, all on that side will be adjusted causing the normal cylinders to go extremely rich.

Bogie

If that was the case it seems like the cylinder that is lean would have a cleaner looking plug then the good ones that are getting to much fuel. All four on the right bank looked the same. No exhaust leaks. That was my thinking too. I fixed that last week. But I will check for a vacuum leak anyway.
Still the problem seems to come on after driving a bit. And when it happens its like somebody threw a switch. Bad idle, terrible hesitation random cylinder misfire, black smoke. The trans is even effected. It will start running at higher than normal rpm in overdrive.

[ernkazern]

Can you read the #1 O2 sensor output on the right side? If so is it fluctuating roughly between .2 and .8 volts? If it is I would look for anything that would make those 4 cylinders lean. If it isn't is it stuck above or below .45 volts? My guess is that it's stuck below .45.

[oldbogie]

Originally Posted by weirdbeard

If that was the case it seems like the cylinder that is lean would have a cleaner looking plug then the good ones that are getting to much fuel. All four on the right bank looked the same. No exhaust leaks. That was my thinking too. I fixed that last week. But I will check for a vacuum leak anyway.
Still the problem seems to come on after driving a bit. And when it happens its like somebody threw a switch. Bad idle, terrible hesitation random cylinder misfire, black smoke. The trans is even effected. It will start running at higher than normal rpm in overdrive.

Your last statement takes me to the other thing I tossed out at you which is a wiring problem. If you're running at cruise in 4th and suddenly the revs go up a 100-200 rpms with no gear change it tells me the converter is coming out of lock up.

Bogie

[weirdbeard]

I replaced the pre cat. o2 sensors. The heck with it. I have not driven far enough to tell if they were the cause.
I just had the converter replaced because it was slipping bad. It seems very intentional when it comes out of lock up and starts missing and running bad. Just like something told it to do that. I hope I don't sound like a clown.

[mr27t]

Check for vacuum leaks!!!