SES light popped on in my LT4 truck the other day. Hooked the Datamaster up and the code was a 64:Rt O2 lean.
Drove around and the DM shows that both LT-int/BLM are maxxed out at 160 and the ST-ints are at 200!
They stay pretty much maxxed out at all rpm and load ranges and idle!!

No vac leaks that I can find, one that big I should be hearing.
The MAP sensor on the DM is reading fairly normal, so it appears that the vacuum is ok.
The MAF readings looked ok, around 7-8 AFGS at idle, I swapped MAFs with my TA just to be sure and it made no different.

So thinking something may be screwy with the PCM, I reflashed it with 25% smaller injector size which should make it run very rich...the Left side went rich at cruise with a 119 BLM and about right at idle at 131 BLM....the Right side remianed maxxed out at 160 lean!

O2s both have alot of x-counts and millivolts switching. O2 are maybe a year or 2 old, about 25k miles.

I have a electric fuel pressure gauge but is very inaccurate, but its reading seemed about the same as its always been..its always been about 10 lbs off and was reading 28-30lbs with vac line on.. I'll check it with a manual gauge Saturday.

Any thoughts as to what I could check next besides getting a manual fp guage on it??

 

Try disconnecting the O2 in question and see if the signal to the PCM goes to around 450.

Then try shorting the signal wire to the ground wire and see if the reading goes to near 0.

 

What were the O2 sensor readings? Were they down in single digits?

Just to clarify what numbers you are posting.... the long term (LT) fuel correction is called the "block learn multiplier", or "BLM" (not "int/BLM"). The short term (ST) fuel correction is call the "integrator", or "INT".

 

A vacuum leak would likely make it run leaner but unless there is a large leak like a brake booster hose blown off, I would doubt it would read so lean. Also it would more then likely read lean on both banks.

At this point what was the left O2 reading?

Just curious. What made you suspect PCM problem first? Did you actually check the O2 connections to see if a wire melted or the plug cracked and is shorting out? Even if it brought the right side down, messing with the injector size wouldn't have solved your BLM split anyway.

Are you saying both O2 sensors are active or are the milivolt readings jumping?

IMO an inaccurate gauge shouldn't ever used in troubleshooting... I would think if it was fuel pressure both banks would be affected.

Like Fred said I would be interested in what the O2 sensor milivolt reading is.

I would suspect the O2 sensor first. Try checking the O2 sensor connection and wires to see if they are damaged. Also if you can, pull a spark plug or two to get an idea how that side is actually running.

 

To answer some of the questions above. It is both banks that are maxed lean. It was not until I reflash with a smaller inj size constant did I get a split blm reading between banks. I only did the reflash just for kicks to see it it could be made to run right since both sides were at 160 blms.
I don't have the scan in front of me but the o2 mv were flucuating between 400 - 50mv if I recall correctly.
Yes I inspected both o2 harnesses for any damage found none.
The only reason the inaccurate fp gauge is being mentioned is because it's been installed in one of the a-pillar pods for years and I have just been too lazy to pull it out since fp is something I hardly ever need on a mild daily driver and didn't want an empty pod hole there. I'll hook up the manual gauge Saturday.
I'll try the other suggestions Saturday also. I have a wbo2 I can also install in each bank to see what the afr really is as well. Won't be able to get to it till then.
Thanks for the help so far, I'll keep ya posted.

 

No way man.
I am the only one that is supposed to have "blow my mind" problems.

 

No Bill, I think we are in the elite club, never an easy to solve issue

Update: Problem solved!!
I hooked up the fp gauge, it read right on 40# with line on and up to about 44-45 under good acceleration...so no prob there.

The O2 mv was very low on the Right side, in the 100-200mv range while driving, in the 2-digits while at idle.
So I swapped out a new O2 in the right bank, the mv immediately looked better, but the BLMs were still maxed at 160.
Started digging around the engine while running and I could hear a little hiss behind the front head light (this is on my truck)....the carbon canister and a air/liquid seperator located there that I run the PCV valve through for a oil catch can. I pulled it off and the vacuum bottle part had split from the top portion, heat I suppose got to it. I bypassed the separator and taaadaaa, the BLMs all came down to the low-mid 130's right where I had programmed them to be.

Threw the old O2 back in and the Rt bank immediately went back up to 160 so I suppose the vac leak jacked up the tune enough for long enough that it ruined the O2 sensor, popped the new one back in and it runs fine now!!! So this explains why the BLMs did come down when I flashed it to run very rich and the Rt side did not.

Thanks for the help...now its off to replace the leaky radiator..at least that one is easy to fix

 

Nice work! I always love the threads with happy endings.