My 2005 CTS-V

[asshanson]

Did a couple quick WOT pulls on Friday afternoon, something feels weird above 4k rpms, so I let off without going to redline. Feels great under 4k, then it feels like it breaks up or something, and gets slower. So I'm going to take it back to Shane to do some street logging to check out what's happening.

Not sure if losing 45lbs off the flywheel changed the load on the engine enough to need some retuning.

[sleepydsm]

Weird. This car is awesome though. How is this thing in snow? (just in general)

[asshanson]

I have blizzaks for the winter, so it's not terrible, but it's not all that great either. Fortunately the traction control works alright, but I still have to be super gentle with the throttle in any amount of snow.

[A//// Guy]

Shane told you not to go WOT until you bring it back to him and do street tuning to finish up the final tune.

Hopefully its nothing huge.

[scheides]

Hopefully it's an easy fix! Car felt solid up to 4k though that's fo sho!

[asshanson]

Well, I've been gone for most of July so I never got a chance to diagnose the high load issue above 4k rpms. Took it to Shane last night for some street logging, and the wideband said it was going super lean, more than 16:1 at WOT. It's fine down low, but goes lean with higher rpms.

Hooked up my fuel pressure gauge to a long -4 line (normally right on the rail) and Shane held it in the car while we were driving. Fuel pressure drops from a normal 55-60psi down to around 25psi.

The funny thing is that it doesn't knock at all, it just gets so lean it can't run. So now I have to figure out whats causing the loss of fuel, we came up with 3 possibilities:

1. Fuel filter is clogged. I recently went to e85, and converted just days before my dyno tune, so maybe the tank was cleaned out after a thousand miles and the filter can't flow enough now.
2. Fuel pump is going out. Hoping this is not the case.
3. It's a physical G force issue where the pump hanger is being starved. I doubt this, since it never had a problem in the past and I didn't mess with the hanger setup. Also it was a completely full tank while tuning last night, so it's doubtful. There was another car on the dyno last night though so we couldn't verify.


On a positive note, I fixed the fueling issue at startup. As several of you know it would take multiple primes and tries before it would start. The wally 310 pump doesn't have a check valve, and all the fuel from the lines would leak back into the tank. I installed an Earl's one-way fuel valve in the tank and problem solved. The car now holds fuel pressure for hours after the car is turned off, and starts with no issues after a day of sitting.

[Matt D.]

Do you think the check valve could be the source of the low fuel pressure under high load?

[asshanson]

That was suggested by Peter as well, but this was happening in June after the clutch break-in. I just installed the check valve two days ago.

[A//// Guy]

But it didnt do it on the dyno while tuning it? The only thing that changed between then and now is the flywheel and clutch, right?

[asshanson]

Well, fuel pumps break and fuel filters get clogged. It's just what they do.

But you are correct, nothing else has changed except the odometer reading.