@roadtrip appreciate all that. i didnt see anything unusual about the maf readings although i didnt check a log under load to see what my engine load is reading. but if i can unplug it and force it to run off map that might give me some indication as to weather its an issue or not.
My thought process for including the MAF was A) Not a part of the TBI setup, and B) since it's
so easy to prove/disprove that it's part of the problem vs
not part of the problem why not see
how your Vortec engine runs without it? (A good part of troubleshooting a computer-controlled engine
is figuring out for yourself just how good/how bad the VCM's internal diagnostics are at sussing sensor errors,
especially after this many years of service?)
FWIW, I'm assuming that you will disconnect the MAF sensor and you will experience no real change with the #2 & #3
misfires. Then again, the hallmark of a successful troubleshooter is *proving* that something is not contributing to
the error, as opposed to *assuming* that it can't be.
Let's just say that in the beginning I did a lot more assuming...and towards the end of my career I did a lot more proving.
Some hotshots from other units watching yours truly may have felt that I was plodding, but I always insisted on proving
my theories to the rest of the repair team. Done correctly, when it was time to declare the diagnosis, it was the lowest stress
time of the entire process. And I discovered that it was easier to convince others that the rudder ISA had to be replaced
(ie: lots of effort by others) if *I* was
already convinced. :0)
In English, sometimes when it's difficult to prove a specfic part is malfunctioning, you have no choice but to prove to
yourself that
all other parts are still working properly. And every once in awhile a part that I wasn't considering was
either the root cause -or- it had a overlapping failure that was obscuring the fix of the failing part I was suspecting all along.
Definitely the more I learned...the less I knew kinda thing.
i had some curiosity in crank sensor, unusually it throws no dtc code so i dismissed it. good to knwo it can cry wolf without triggering the CEL. ill look into it. i think when i get back from vacation im gonna try to get the distributor closer to 0 instead of the 1.7 its at. then mess with crank sensor, do a relearn and probably reset tps, ltfts etc so im starting more fresh
I like your plan of attack. If you were to give your CKP sensor a good visual inspection, verify that the
clearance between it and the reluctor is within spec, and then accuratize the engine/sensor/VCM with
a CASE relearn you may either clear up the rough running -or- attain more accurate misfire info? Either one
is a win in my book.
those manuals are an absolute bear! lots of useful info i think i have them at work somewhere in the ancient GM depositories
I've found the online .pdf files are unsurpassed for quick research of everywhere a specific DTC or wiring circuit # is
sprinkled throughout the 4 phone books that cover my '99 chore truck. But other times there's nothing better than
sleeping on a problem, then enjoying the morning coffee while paging through the book(s) and acquainting myself with
stuff that I had never stumbled across before. I have experienced the 'Aha' moment more than once doing just this.
(In the attached is some of the very best money I've spent to date on my well used GMT400.)
Best of luck with the hunt for the root cause of your rough idle. And please be sure to come back and
share what it took to get the final fix implemented.
Cheers --
