Cars falls on its face at 5k RPM

**powermad** · 02-03-2008, 02:13 PM

I'll keep it simple:

Procharged C5, ran fine on 4lbs 480/420. Broke a timing chain, replaced U/D pulley with stock balancer for more boost. RETUNED. Car made 523/480 on the dyno but does not run right now. Hesitates and makes a noise when it goes over 5k. Under 5k rpm drives fine, decent gas mileage still, no driveability issues. Just got my boost gauge and fuel pressure gauge. Boost shows about 6 lbs at 5k so no leak that I know of. Waiting on an adaptor for the fuel sender. So am I running out of fuel? I hope it is that simple.

This is what I have been told could be my issues:

Boost leak, probably not since 6 lbs at 5k
Fuel- pressure by incorrectly installed BAP, dirty filter, old fuel pump
piston slap- this by my tuner, don't think this is my issue
blowby- broke timing chain trashed valves and marked up the pistons, may have damaged skirts.
tuning in general

Once I get the fuel pressure gauge on I will know better and post up the results. Really want to go forged but just no money for that now....

**Frost** · 02-03-2008, 04:58 PM

You are almost certainly maxing out your MAF at that HP level, and prolly right around 5K. If your tuner kept your AFR to 11.5 across the board in maxed-MAF territory on the dyno, there will be times when it will be too lean up top, since there is no airflow measurement available. Post a prinout of the pull with AFR. Really need a wideband at that level to keep an eye on things. Are you using methanol? My money says the fueling is off up top personally, though it's just a feeling.

Blowby comes from bad ring seal, which is usually from knock/high cyl temps at your HP level, and usually signals the beginning of the end. Start the car and let it idle, pull a breather/PCV out of the valve cover and see if it "puffs" a lot at idle. Outside of that, obviously compression test and leakdown check are in order.

I would be unsettled by being told piston slap is the cause by my tuner; that's a new one on me. Never even heard slap much north of idle before.