Older thread but have an interesting one related to this.....
Went to Cobb tuning back in 2009 and my car at 350whp 373wtq with an AVO380 AVO fuel pump and DW 850 injectors was at 100% duty cycle for some reason.
Just went to Cobb this week, I had changed regulator and orings in the tank but still had my 2-3 year old AVO pump in but now have Id1000's.
While at the beginning of tuning right when we got to 360whp 415wtq, still in the rich stages of the tune I was at 97% duty cycle on the ID1000's.
AFR's were in the 12.7 range when they should have been in the 10.5 range at the beginning of the tune.
I changed my pump to the Aeromotive Stealth in the parking lot and the AFR's dropped by a point immediately but I was still at 97% duty cycle on the injectors.
Through some trouble shooting and tearing of my interior apart to get to the fuel pump relay and the fuel pump control module/unit we found part of the problem.
My stock wiring harness was dropping almost 2 volts from the fuel pump relay to the fuel pump module at the back left of the car. It was causing the fuel pump to never get above about 11.7 volts coming out of the fuel pump module/unit.
We bypassed the wiring from the relay to the module and then were able to get 12.7 volts out of the module to the pump and the duty cycle of the injectors dropped to 80-85 % when the pump was at 100%
If we bypassed the fuel pump control module/unit altogether and had 14v battery/alt voltage it would drop the duty cycle of the injectors even more.
We are doing some more testing to find if the fuel pump module/unit is defective or not but it was interesting to see how the pump changed the AFR's as well as how I had a 2 volt drop in my wiring harness.
In my case the fuel pump control module/unit never allowed the pump to go above 11.75 volts on stock wiring and with external wiring it went to 12.7.
Last edited by Scooby2.5; 11-03-2011 at 07:38 AM..