Dominic Sorresso

Been doing a tune on a 90 LT5, and been getting an intermittent Code 64. It seems to happen after driving car around, then sits idling for about a minute or so. Looking at the log, the right side (which is a new O2) voltage drops and is below the O2 threshold sufficiently long enough to set the code. Not sure why however this appears to be very intermittent. BLMs are within +3 counts of 128
at idle.
The mods on this motor are limited to headers and freer flowing exhaust along w Fidanza aluminum FW.

ULTM8Z

I can't imagine freer flowing exhaust would have much of an impact on idle mixture.

What is an "aluminum FW"?

Maybe swap O2 sensors and see if the problem shifts to the left side? I've heard of bum O2 sensors new out of the box. When did the problem start occurring? Did it coincide with something else that was done?

Dominic Sorresso

Aluminum FW - AL Fly Wheel, and its single mass vs. the dual mass that the motor came stock with.
Its really not a "problem" since it seems to happen sporadically. Most of the time the car sits and idles fine w no SES. Gotta look at the log again. Other than that, the O2s exhibit no issues and they were just installed.

ULTM8Z

What's the material of the exhaust? My headers are stainless steel and it seems the header construction has a non-trivial electrical resistance. I attached a braided ground strap to the O2 sensor body (crudely with a hose clamp) and then attached it to the back of the cylinder head.

Upon doing that, my BLM's shifted by several points and I had to actually retune the VE a little.

It doesn't sound like something that could generate an intermittent lean condition, but just throwing it out there...

Dominic Sorresso

Thanks ULT. Appreciate the input. The headers are SS and ceramic coated. However, it would not explain a disparity between one side and the other.
Since my last post, one thing I changed was to increase the prop gain at idle.
it looks like that may have eliminated the issue.

Dominic Sorresso

An update to this thread. What has developed in this motor is an apparent oil consumption issue that appears to be on the right side. Not sure if the cause of oil consumption is affecting the right side O2 sensor. This is turn causing the Code 64 Lean O2 Right.

ULTM8Z

Can burning motor oil foul up a sensor perhaps? Did you pull the plugs on the right side to find evidence of oil fouling? How are you speculating that it's consuming oil?

Dominic Sorresso

ULTM8Z

No, I mean the spark plugs fouling.

Generally when I have had problems with spark in a particular cylinder that the O2 sensor sees (say a broken plug wire), my BLM will shoot up into the 150-160 range.

So if you have a bad spark plug due to oil fouling, it could generate a perceived lean condition by the ECM. Basically have raw fuel going out the exhaust valve with a lot of unused oxygen.

Dominic Sorresso

ULT,

You have pretty much described the issue. Yes there is at least one and possibly two plugs that show a sooty deposit and appear a bit oily. They also are on the right side and adjacent to each other, ie #2-#4

ULTM8Z

So then recommend replacing the plugs and see if the error goes away...?

Dominic Sorresso

ULTM8Z

and I take it the error remained?

Dominic Sorresso

ULTM8Z

bad spark plug wire perhaps? Impedance goes up with temperature... maybe you have some sort of intermittent there?

Injector(s) going south?

only other thing I can think of is some exhaust leak that gets worse with temperature. If it's small enough, it may only be sufficient to affect idle. At higher rpm, it becomes to small a percentage of the total airflow that it doesn' register any more.

Dominic Sorresso

The interesting part about it is the Code 63 only shows up after say a 40 mile run, and the car is sitting in the driveway idling while garage door is opened.
Then it pops up. Nowhere else during the drive while idling does it show.
Very curious.

ULTM8Z

Yeah, very peculiar. Though it definitely seems temperature related.

Anythign in the LT5 code that takes oil temperature into account for calculating anything to do with target AFR? Probably a long shot... but the time delay you're describing... on my Camaro, that's the one thing that takes the longest to get up to high temperature... the oil.

Dominic Sorresso