Hi all, OK i own a 91 350 TPI Speed density car. Now, i just got a hold of and installed a ported and polished plenum off of an 88 iroc.Ok, the front of the plenum looks a little different on the 88, it has a triangle shaped air inlet (i am assuming for the IAC valve. So, i used an 88 gasket. I also noticed there is only two vacume ports on it instead of the three that my 91 plenum had. Ok, no problem i just got a t connector and reconnected the map sensor vacum hose. No problem right? Well, ie also installed a DIY AFPR. Just drilled a hole in the stock one , put a quarter on the top of the diaphram ,and got a nut professionally welded into the top of the thing and now i can use a 1/4 inch stud in the top of it to increase fuel pressure. Ok, put everything back together and the car ran fine around town, but when i floor it there is NO POWER!!!!!!!!!???? WtF? Haven't checked fuel pressure yet, but the screw is backed out all the way anyway. Should be stock i presume? Now, there are a few things that i could have done wrong here. When i took the throttle body off i did spray it pretty heavily with carb cleaner. Inside all of the holes on the throttle body,etc. Did i spray the **** out of my IAC valve? or TPS? Also,did i go wrong using the 88 gasket that has the triangular hole in the front of it? My 91 stock gasket was just flat and had no triangular cutout. I am thinking that maybe i should have used teflon tape around the fuel pressure regulator screw. Could it be leaking through the screw area? upon WOT? Man, i really need some advice here, this car used to break the wheels loose at 35 mph, now it is slower than a small economy car! OH, and i have no codes, no vacum leaks either. Also, i have been told that 91 and up SD car's TPS is not adjustable.

 

Ok, figured it out , when i built the diy afpr. I used a quarter under the cover and on top of the diaphram. That automatically set my fuel pressure to 50 psi at idle (vacum hose removed). Way toooo much! My car already has 24 lb/hr ford injectors. I put those in last year when my stock 22 lb ones died. I got them free so, hey. Anyways, I took the quarter out of my afpr and just left the bolt in it and left the bolt backed out all the way. Still kind of hitting the plenum, but now the car is back to the factory 38 psi at idle(vacum removed) and i suspect it may run a little quicker with the pressure backed off even more. I would suggest to anyone to just go and buy the holley afpr, It has a nice dial on the top that can be turned with no plenum space issues. I have heard that it does require a little fabrication though. I think it hits the fuel rail assembly. Anyhow, my car is now back to the stock fuel pressure setting and again it is breaking the tires loose at 40 mph!