kusee pee

Hi all, my SC track car has picked up a slight hesitation above 4000rpm. It pulls no problem up to that and will rev to the limiter when in neutral no problem. I have a feeling it may be linked to lack of use as it's hardly had a good run for a couple of months. Any suggestions? TIA.

ron mcatee

Put in some Techron and see if that helps.

Steve Weiner-Rennsport Systems

I would:

1) Check the distributor's advance mechanism to ensure its functioning properly.

2) Check the system and control pressures. A failing fuel pump, plugged fuel filter will display low system pressures.

PIXXI

Just a thought, could it be a bad O2 sensor, leading to overly rich mixture?

Brian
'87 Carrera Targa (newby)

Droops83

Even if the original poster's car is an O2S-equipped car, which it is likely not (he is in the UK), it would most likely not be the cause due to the fact that the O2S-eqiupped 911SCs have a full-throttle switch that causes the control unit to ignore the signal from the O2 sensor at wide open throttle (which a track car will be at most of the time).

Pretty much any car with an oxygen sensor since the beginning of time has the means to ignore the O2S signal at WOT as a safeguard to the engine: a 14.7:1 air/fuel ratio is great for emissions but far too lean for full throttle acceleration. The A/F ratio at WOT will likely be in the 12:1 range for max power and to safeguard the engine from overheating and detonation.

I would agree with Steve on checking the basics first

kusee pee

After a run today I can give more information. It seems it will pull fine to the red line if I accelerate gradually on a half-throttle but if I put my foot flat then the stuttering occurs. Any more ideas?

User 4221

I would check the coil. I say this because at gradual acceleration, the coil can recover and provide energy to the plugs. Under hard acceleration, the coil cannot recover fast enough and will not provide enough energy to the plugs.