Ignition, valve springs, or what now???

[streetknight]

Car runs very good. Noticed after recording with scan tools @ WOT the car was shifting at 4000 RPM's. My other car shifts at 5000 RPM. We messed with the TV cable to get it to shift higher, BUT anything above 4K it breaks up spits, sputters, etc. Like weak valve springs. Heads don't have that many miles on them and put the car in Manual 1st gear and eased the car to 5K RPM and it didn't miss.

What should I be looking for?

 

[83ttypecooled]

misfire

Hi,
Do I understand you, misfire, but when you brake torque it, there is no miss? Unless you are using an 8" torque converter, I can't imagine you spooling up to 5K rpm in that situation. Even then, no way. So I must be misconstrueing your message.Ignition is ALWAYS the main culprit in misfire scenarios. More info, please!

 

[VadersV6]

Hi,
Ignition is ALWAYS the main culprit in misfire scenarios.

Not really. There are quite a few different scenarios. An extremely fat A/F will cause alot of misfire problems and all the voltage you can throw at the spark plugs is not a cure. Exhaust popping seems to be caused by lean mixtures alot more often than rich ones. Intake popping is usually an excessively rich mixture, but that doesnt really apply to these setups. Weak floating valve springs can cause backfiring into the intake. Imagine the intake valve is in the middle of a float situation, and we are also in the middle of the compression and combustion cycle....the intake valve is cracked open slightly cause the spring was too weak to close it, and this combustion finds its way into the intake tract.

 

[streetknight]

Ok, here's something I forgot. Picture this. Your at WOT on a pass. the car goes for the 1-2 shift. The car noses over and starts breaking up. AND the car will NOT make the 1-2 shift UNLESS you back off the throttle a little then it shifts and is clean until it reaches that RPM range again and the same crap on the 2-3 shift.

 

[trbojo]

comp cams 980 springs. had the same problem, replaced with these and problem was gone. they will usually nose over with weak springs, and sputter with a bad coil pack.