New guy here trying to help a friend of mine figure his car out. I heard Paul is the guru when it comes to stock A9L with superchargers. So here's a brief description.

A friend of mine put a blower on his car and its running very very lean. Currently it has 30lb injectors w/ an adjustable fmu. At 1500 rpm, the a/f ratio is 20:1. When he up the fuel pressure to 50 psi, then it drops to about 16:1. Timing is set to 8 degrees to dial in a/f ratio. He took a short drive and at 3/4 throttle up to 4000 rpm (about 5lb boost) in 2nd gear, the a/f was about 14:1. We don't know what the fuel pressure was at because he doesn't have external gauge. It must have been kind of high because with the 2 fuel pumps loading the alternator, it died. He's got a 3G coming soon. I'm thinking with the 42's it might run too rich at idle.

Any help is greatly appreciated. Thanks

 

Just throwing this out there. Did you set the fuel pressure with the vacuum line off the regulator? Also make sure the vacuum line that's running off the regulator is running to the vacuum tree or one of the lines to the intake.

 

Yes, fuel pressure was set with vacuum line disconnected from regulator and that line does come from the manifold. Thanks for asking tho.

 

30lb injectors isn't enough really unless you are running a small charger with like 5-6 lbs of boost and no major mods. Ditch the FMU and install 42lb injectors(36's work nicely but they are tough to find anymore...or were a couple years back). Make sure you get a fuel pressure gauge on there...you MUST know what your fuel pressure is.

 

Thanks for the response. I don't know if this is the same vehicle area51 is talking about - but IIRC, it also happens to be a 5.0/302 stroked to 331ci. The 42's still adequate for that application?

 

As hi5.0 mentioned it is a 331ci. I should have added that in. Anyway, thanks for the reply svopaul. So my understanding is that you can run an A9L with 42lb inj. as long as you know exactly what the fuel pressure is.

 

Yes, the 42lb injectors should work fine but it's not as long as you know the fuel pressure...you NEED to know what the fuel pressure is regardless if you are tuning on the car....it's a tool, part of the equation in tuning is fuel pressure and if you have no idea what it is, then you cannot adjust and tune to make it better....it's like being blindfolded.

 

Thanks for your response, Paul! The FMU was removed, 42# injectors on, and fuel pressure gauge replaced - apparently the old one was reading a little high or in any case inaccurately. The vehicle is reportedly running fine (only slight hiccups when cold start/run) and the A/F is in the 11.5:1 range.

 

Great, good to hear!