There are some fpr that do lower fuel pressure with vacuum. One example is the Buick GN; once base fuel pressure is set with vacuum line off, re-attaching the line with the engine idling under vacuum results in a drop in fuel pressure. It then rises with decreasing vacuum and (obviously) increasing boost.

 

I'm not talking about using AFR as a trigger. I'm talking about using it as a feedback sensor; real-time monitoring of actual AFR at that instant and using it to adjust fp on-the-fly to maintain whatever AFR setpoint is requested. That way there is no guesswork (dyno run, log data, scratch your head, make adjustments, etc). It would be a closed-loop scheme with fp being varied to regulate changing AFR due to changing conditons.

 

THis closed loop is currently being done with the Zeitronix wideband controller. Actually I first hooked it up for a trial about a year ago. Woody

 

the older cars do that, since they didnt have such precise control. The aftermarket fpr's such as aeromotive might drop 2-4psi but its nothing dramatic.

 

My aeromotive FPR is one psi fuel boost per psi signal sent to it. It will also DROP the fuel pressure at the rail one psi per psi, (thats -15 psi drop at -30" of mercuryvacuum ). THe factory crossfire regulator has the same response for both positive and negative 'boost' signal, I have done a bit of testing on these over the last year. Woody

 

Hey you guys running lean!! - - show us your spark plugs....

 

That's what I was asking about. That's good news.

 

We've never had problems with the aeromotives dropping that much pressure on our applications

 

here is a datalog we just recieved of a customers car, this is NOT where we want to be air fuel wise!!!!!!!

so this is the before datalog identifying the issue, now time for the fuel tweaks to this car. most cars arent going lean until over 5k rpms but this one has such a lean tune that it is lean from the time the pedal hits the floor until they let off.

its tough to stress enough how important a wideband gauge is when tuning these cars. dont be an ostrich and bury your head in the sand thinking that since your motor hasn't grenaded yet that your fueling is adequet running over 18psi. widebands used to be $3000 10 years ago, they are now less than a 1/10th the cost so there shouldnt be any excuses, protect yourself with knowledge!

 

Worth repeating!