Posted by PeterW on November 30, 04 at 14:25:02:
Hey guys,
Thought an update was in order. I posted that my stumble problem on acel. in my 91 R2500,7.4L with trouble codes 33,42 and 86 recorded was cured when I discovered the MAP sensor vacuum line disconnected. WRONG, only a partial fix. The stumble returned. Following Dave's02LT advice I replaced the ignition module(p/n GM 10482827). TA-DA stumble and code free. One "attaboy" goes out to Dave! Thanks Dave! I also replaced the MAP for good measure based on Traveler's advice. He made a good argument for doing so and it was the original as far as I knew. Traveler was also spot on with the code 86 being 4L80-E related. Found the reference in the manual.Thanks Trav!
My guess, both TC 33 and 86 were triggered when the ignition module failed. BTW, this failure was intermittent for a few days, followed by complete failure and a no-start condition.
PeterW