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**asshanson** · 08-25-2010

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.

08-25-2010	#76
asshanson immune from paybans Join Date: Oct 2005 Location: West Des Moines Drives: poorly Posts: 4,358	Re: My 2005 CTS-V 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.