I have a stock fuel pump with an additional 255 Walbro in-line pump on my Trans Am. I went to the dyno and recorded a 11.1/1 A/F across the board. When I hit the 125 shot (NX wet) with the proper jets I jumped to 13.5/1 across the board It acually dropped near 13.0 in the upper rpm range. I put a larger fuel jet to compensate, butthe A/F stayed the same. I had my tuner adjust the car to 12.6/1 N/A with LS1-Edit, but I am afraid that I am going to be leaner on the NOS. What to do? If I had a fuel pump problem, why would the A/F stay constant and even drop to a lower A/F at the higher rpms? Wouldn't it start getting leaner up top if the fuel delevery was the problem? BTW I have a stroked 382ci LS6 with a mild cam most of the bolt-ons.


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Changing to a bigger fuel jet will drop the A/F ratio down. You might have to go with a bigger one than what you first selected. Going from a .030 to a .032 is not going to drop the ratio that much.

 

It does not seem to affect the A/F with the larger fuel jet.

 

If the jet size increase doesn't help then there must
be another upstream restriction in the fuel path.
Some solenoids look kinda small in the orifices, long
skinny fuel line might add up, etc.