The car (MY '99) "hiccups" or cuts out when I lift a wheel which is increasingly the case with better grip (245s and 315s) and a stiff suspension set-up (JRZs + GT3 bars, arms etc). Once the car is settled again it drives fine but it seems to last an eternity but in reality maybe 0.5-1 sec. per incident. At RA its about 4 times a lap so the time adds up and its killing the car's momentum.

I'm used to driving older pre-traction control cars so I thought it was a fuel delivery issue but believe now it may be TC. Anyone experience similar?

 

David,

LSD or not? I have a similar setup but likely not as hard a susp. I have an LSD and with TC off never see this kind of hiccup.

Assume you are still on cable throttle as well?

I do notice all kinds of annoyances in the Drive by wire cars which you just have to drive around (ie be smoother)

 

No LSD (yet) and cable throttle. As I get faster (couldn't get slower) the problem is getting more problematic. Used to be just hard turns over rumble strips now its any hard turn and even under the bridge at RA where the car flies briefly.

 

No LSD?????

I do think that would solve your problem.

 

David,

Is the "interruption" electronic? or mechanical as the car simply settles down after a big bounce?

IE electronic: your foot stays in the gas and the power is cut or mechanical: you foot stays in the gas and you are getting wheelspin as the car revs up?

 

Is there early PSM on board and if so did you bypass it?

 

Check your PMs. I am sending you one with two people to contact on this one in the Atlanta area.

 

Power cut. The car is back on all fours and settled but takes a second (seems longer) for the power to come back.

Not sure if the car has PSM- I'll have to send the VIN to a dealer and see.

Thx Seth- YGM too.

 

Open the front hood and check for the PSM connects passenger side near the shock tower trunk area. A couple of club racers with 996's told me they just unplug the damn thing and it shuts off. I have also heard from a local race shop that running the bigger rubber causes weird problems like you described, especially if you tire diameters front to rear are near 4% differential(ABS cutoff). Ask Chris Cervelli as I know one solution if it is ABS related is adding the motorsport ABS system ($$$).

 

The 99 car shouldn't have any of those fancy electronics.

PSM came with E-GAS

 

I run Yokohama cup slicks 240/640 (25.2) fronts, and 280/680 (26.85) rear on my 99'. The delta between the 2 is 6% and I haven't had any ABS interference....

Without any PSM issues (99' car), I'd have to think what he's experiencing is LSD related. I can't imagine trying to drive one hard without a good diff, one of the most valuable parts to 911 based race car. PSM applies braking to a wheel and really slows the car down. That's not how I read his description....

 

+1

 

JR I agree on the diff inside wheel spin, but I also know Dougherty (Colin of CDOC's Dad's Company) has had this issue independent of PSM with tire sizes. Your driving style may be very different and avoids this issue. 315's in back with 245's if running 245/40 there should not be this issue, but with 245/35 it could as the sizes are 1inch different in diam's. I experienced a similar problem on my 993, but Cervelli is convinced it was fuel starvation as it only happens in right hand corners and the stock tank pickup is on the right hand side of the car. Which would be another question if the tank is full and are the corners similar that it happens in.

 

More facts.
It did the same thing with 230/280 and 235/295 but less so. I guess I push it harder with 255/315 tires.
It is worse with a lighter fuel load but I presume now that's a function of weight i.e car lifts more when its lighter.
It "only" happens on right handers (not all) but I have only run clockwise tracks (Road Atlanta, Sebring and Barber) that are right hand oriented.
It is not wheelspin related I don't think.

 

Top the tank off completely. When I looked back at my data, I was running below 1/4 tank and the filter screen in the tank was dirty. I do not know if the pick up for the fuel tank is on the same side as the 993. Is there an rpm change or just seems to slow down? You could add data logging for fuel pressure.