Just a long shot for suggestions on diagnosing the following:

While driving at the track this past weekend, car developed a "stumble" from about 5500 - 6000 rpm during WOT pulls. This started happening on the last two sessions of the weekend, after about 4 laps each time, at which time it occurred with perfect consistency (on every straight, ruining my lap times!)

The car pulls hard to 5500, then "bogs" or "stutters" until 6000, then pulls strong again to red line. No smoke, no overheating etc.

Stock engine with intake, dp, cb, and PFS PMC providing some extra fuel for 11-12 lbs of boost. Was running 93 octane plus octane booster, but was well below a quarter tank when the stuttering began. Coincidence?

Drove car home from track, roughly 4 hours at 80 mph with no problems at all. Unable to reproduce it today, but then again I can't really push it to track extremes round the neighborhood here...

 

first off let me say your a "ballsy" guy! you drive 4 hours to a track, race it, the drive home another 4 hours?! wow your car is tough!

as for the stumble??? could it be as easy as your plugs going bad? maybe you need better ignition wires... im not too sure.

 

check plugs, fuel filter and your map if you have a datalogic..

 

Could easily be what you mentioned. I was at an auto-x this past weekend and I sent the car way to wide, causing me to drift it a bit but enough for the fuel to slosh and hesistate. I would guess that was the cause.

 

I thought this is the norm. I doubt everyone trailers his FD to the track.
You do get tired at the end of the day though.


Back on topic: Dont ever run with that little fuel in your tank. It could be the extra power at transition to push the fuel away from where it gets pumped and you get a fuel starvation (and dangerous lean condition). I always run with more then 1/2 tank of fuel (or at least 1/3).

 

Would have trailered it if I'd had more time to plan, but it was a last minute road trip. It's not often we have a weekend in July 'round here with high temp of 75F!!! Too sweet to pass up!

Thanks for the help - I'll post whatever I turn up in the investigation.

 

Follow-up:

It turns out, apparently, to have been fuel slosh. Both straights were hard left-handers followed by an uphill straight. The cut-out was happening 5 seconds or so after the left-hander.

So I figure: slosh, get a bubble in the line, then 5 seconds later it makes it to the injectors.

Fortunately the car seems to have suffered no ill effects. (I think I am very fortunate!) It ran great at another DE event this past weekend with nary a hiccup. Needless to say, I didn't let it get below 1/2 tank!

 

see my thread about fuel pick-up problems. i've always had problems with less than 1/2 tank at the track...now it is getting worse. i can't even drive around the neighborhood quickly with less than that!

 

I have the same problem and heard it was the fuel pump. So i'm hopefully gonna switch it out tomorrow and see.