Bucking and misfiring at low rpm. Direction needed.

[Young1]

I am helping someone prepare their car for NCRS performance review judging in February. 1993 9k mile beautiful.
Fresh fuel.
Vacuum system is tight.
Secondaries function normal per pink wire black stripe test.
Idles well. Will idle down the street in 4th gear smoothly!
Revs well.
No D/M flywheel knock.
No check engine or other lights on screen.
For instance when performing the 1st to 4th Skip shift and apply even moderate throttle it will buck and misfire considerably. It can be heard in the exhaust.
Will occur in any gear between 1-3k rpm. Above this runs normal.
A fórum search reveals many different responses.
What do I test or replace next?
O2 sensors?
Primary fuel pump?

[Paul Workman]

FUEL - AIR - SPARK

Nothing like a dynamic scanner to sort out a plethora of parameters: what is or isn't normal.

That said, and assuming you don't have a scanner to do a dynamic scan, and knowing the secondary pump is triggered at different levels of throttle and rpm, depending on MY, you can verify (at least) both fuel pumps are drawing the right amounts of current - indicative of their function. But, also measuring the dynamic fuel pressure (gauge taped to the windshield while test driving) can provide very useful data.

And, eventually or as a matter of being comprehensive, I'd want to verify the fuel system and filter/lines are clean; a topic for another time, perhaps.

Anyway...I'd focus on fuel delivery first; starting with dynamic pressure especially in the low rpm/throttle region where its having the issue.

[Young1]

OP update. Fuel pressure is 52 and 43. Static tested. Perfect. I think I found the issue. #7 plug wire was routed by GM alongside a bare braided ground strap. There was some carbon discoloration on the original plug wire. Of course it would misfire on #4 as well with the dual plug coil. Rerouted and re insulated. No time yet for test drive. Looking for the simple!

[Young1]

Original platinum tip spark plugs had .050-.060 gaps. Not good. A set of Delco 41-602 did the trick. Missing resolved.

[dredgeguy]

Original platinum tip spark plugs had .050-.060 gaps. Not good. A set of Delco 41-602 did the trick. Missing resolved.

Well done Steve.....Congrats!