billy-94z28

Here is a situation my 94 6spd, z28 has recently developed.
I have what feels like a miss or sputter, but only in 6th gear with relativelly low rpms ( 1500 to 2000) and the accelerator 50% or more then you downshift and accelerates smoothly.
It only shows in 6th gear or possibly if you are really "lugging" when you need to downshift in other gears.

I have replaced the original optispark with the aftermarket dynaspark distributor and I am running seafoam through the fuel system with the current tank of gas.

Car is a one owner with a good fuel filter and 79,000 miles and up to date maintenance. Currently running reqular gas.

Any help appreciated.

Kevin Blown 95 TA

See if a change of gas helps it - its trying to do a lot of work at high gear like that and it might be detonating a bit or retarding the timing or something. Maybe it's carboned up a little or EGR isn't working so well any more. Could be a few different things liek that.

NJ-LE

billy-94z28:
"Kevin Blown 95 TA" has nailed it. If you scan the PCM you'll almost certainly see spark retard. 10° or more of timing being pulled wouldn't be unusual under the conditions you describe ... even under light throttle some timing will sometimes being withheld. The sensor and PCM knock circuit are more sensitive than our ears. They will "hear" pinging that we can't. (5th gear is your friend!)

Sick97SS

I had a weird stumble when underload. usually in 6th gear.

Turned out i had a cracked spark plug (#5) from water dripping off the windshield and directly onto the plug in heavy rain. Hot plug + cold water = big crack in the porcelain.

I would never of found it if i didn't remove the plug wire boot.

just something to check if you havent already.

billy-94z28

thanks for the replies,

kevin, are you suggesting that i run premium gas instead of the 87?

moparman

You should run 93. Try it and see what happens.

I had the same problem in 6th gear. Turned out I had two bad plug wires. It would run fine at a steady speed/rpm, but give it some gas and it would miss. Check the plugs and wires. Don't forget to check the coil wire as well. A spark checker comes in handy. Just touch it to the wires and watch what it does.

Injuneer

Have you ever read your Owner's Manual, regarding fuel recomendations?

maddog05

If you are running 93 octane then, Your problem is electrical... I would start with wires -especially coil, then look for water in, or, hitting the opti-spark; then the plugs and you may want to check the wires visually at night with the engine running to see if there is arcing anywhere under the hood. A sputter under a load is usually electrical

shoebox

If you have an ignition problem (sounds like it), it's there all the time (not just 6th gear). It is just that the higher gears (and lugging) make it more noticeable.

jsetzer

My $.02 - I've had blown head gaskets stumble in higher gears when pushing water.

If you don't find anything with the ignition you might do a compression check.

billy-94z28

Injuneer, I have read the manual regarding fuel.
I am currently using the car as my daily driver and was trying to save a few dollars on gas since I have a 90 mile round trip for a daily work commute.
I intend for the next tank to be premium, which is almost back to $3.00 per gallon in my area. I really think it is just the gas, all plug wires are secure and protected and I definitely do not have a blown head gasket (no mixing of oil and coolant.)

Thanks for all the views and replies.