Im posting this for my friends car it's a 2001 z28 6 spd with a rear mounted turbo and he's having trouble with the car it goes lean over 4k rpms his afr reads in the 14s to 15s under boost after 4000 rpms the car has an intank walbro brand new it was replaced thinking that was the problem, it has 8psi and 42# injectors car was in the mid 11s afr but it started going lean about 2 weeks ago, I helped him do a fuel pressure test and it's right about 55 to 60 psi but I noticed when I purged the tester after the car was off it pushed a lot of air pressure out along with gas, so I tested it again and when I
Did I got a lot of air pressure coming off the fuel rail again this time it felt like it was a big air bubble, I'm not sure if this has anything with the car going lean or not but I've never seen it before, usually when I test fuel pressure you get only gas coming out not air, we filld up the tank thinking it was low on gas and still same problem sorry about the letter and thanks for your help.

 

Any air should immediately leave the system when the car is started.

As for the car leaning out, you may be exceeding the limits of your pump depending on your power level.

Feel free to give me a call & I will work with you to get the proper pump for your application.

 

Changed the fuel filter and didn't make any difference, the car made 418 hp at 4000 rpms but then it leans out bad so he had to let go, I thought a single 255 walbro was enough for 8psi specially in a rear mount setup but I might be wrong? we will be checking all the hoses here in a couple days see of there's any kinks or something like that. If anyone else has any other suggestions please let me know thanks.

 

What is your fuel pressure when the car leans out?

 

I didn't even get to check it with the car running that was gonna be the next step but today my friend pulled the pump out and we figured out that when he did the walbro swap he cut the hose from the pump to the plastic unit too long so when the pump was compressed the hose was collapsed that's why he had air in the lines go figure, anyways he removed that hose and replaced it with a shorter one and problem fixed no more air, his afr went back down but now it's somewhere in the 12s cause they had been messing around with the tune, I think as soon as they get the tune done it should be good thanks for your help.