I went from: 19# injectors -to- 24# injectors stock regulator -to- Kirban AFPR 95lph fuel pump -to- 255lph Holly F/P stock coil -to- MSD Blaster stock module -to- Accel Module I did all this at once, which was a big mistake because then it wouldn't stay running, so I ended up pulling it all apart, putting all the stock parts back on and it still wouldn't start, then took it apart, inspected it again, put it all back again, and if fired right up. What I did wrong the first two times, I have no idea. Who cares it runs now. When I put all the new parts back, I did the fuel pump first, cranked it up, then the regulator and injectors, cranked it up, then the coil, cranked it, then the module cranked it. Well, thanks to a bad 02 sensor, it runs richer than a swiss bank account but it runns. All for $400 total. The injectors and fuel pump were used, the regulator I bought from Mamimum Motorsports, and the module and coil from Barnett's. I can't really say weather it picked up any power because I haven't driven it in a month, but the fuel pressure rises alot faster. I'm going to get the new 02's and then put it on a dyno soon, maby have it professionally tuned. It feels great to have it running again, driving that Grand Am as my only car for a month sucks.
Let us know if your fuel pressre drops from the original setting when your engine warms up. Mine would be set @ 40psi cold, then as I drove a few miles the pressure would drop to about 36psi. Still happens every day. Cold=higher pressure Warm= lower pressure. I haven't been able to make sense of it. Maybe someone can help. Kinda funny since I got a Kirban since they are supposed to be so good.
Is it the o/e pump? How old? How many miles? Maybe after the pump runs a while it's gettin tired therefore causing some drop in pressure. Same advice for the fuel filter. Maybe somewhat restricted and causing the problem.
Oh yeah, I swapped out sample tubes with the guy I bought the 24#'s from. It's going to run rich until I get a new 02 sensor. I'm getting the carpet and seats dry cleaned by my neighbor who runs a carpet cleaning buisness, but needs a serp belt for his car, worked out a deal. I have my seats out for the occasion. Going to parts store tomorrow for a serp belt and a 02 sensor.
I have a 255 lph pump. To rememdy the problem I am just setting the pressure so it goes down to 40psi when it warms up.
I'm having the same problem (pressure drops about 10lbs when it gets warm). It has a 255 in tank and I installed a t-rex and new filter and had the car dynod. My guess is a bad regulator. I have an aftermarket one now (blue.. I think its a Paxton). Have 12.5 volts to the pump when its warm. Friend told me to get a Kirban, but I don't want to spend the money unless I know what the problem is????
The regulator controlls fuel pressure. The fuel pump constantly puts out the same output, the injectors do what the computer tells it to, but have no effect on the pressure unless there is a leak, and you would know by now. I would bet money it is the fuel pressure regulator. Get a Kirban. The Maximum Motorsports one is the Kirban one.
The reason you are seeing a change may be due to the coeficient of thermal expansion (Cte). Materials expand and contract with temperature. This can affect pump seals, pump rpm's and overall efficiency and repeatability.
I see about 40 psi when I start it up. The weird thing is that it only drops a few pounds sitting there warming up, but it drops down to 30 after you drive it. I checked the vacuum line to the regulator and there doesn't seem to be any gas in it.
Guys- the reason why the pressure drops is not because the FPR is faulty- it is because the computer is set at a predetermined Air to fuel ratio- so even if you set your pressure to 80PSI once the car starts and warms up the computer will lean down the injector pulse WAY DOWN to get the AFR back to stock settings- for that reason an aftermarket FPR is a waste of time and money- put your stock FPR back on-
all cars run richer - ie more FP - when cold, then when the car is warmed up the computer leans it out slightly for emissions reasons and drivablilty.... what you state is what all cars do- there is nothing wrong about that-
the computer uses injector pulse width (as you stated) to adjust a/f. this will NOT affect fuel pressure, only the actual flow (due to shorter p/w). AFPR aren't meant to do anything while cruising around town, they are used to adjust a/f at WOT where the computer is reading from tables and not sensors. the computer will adjust to the new pressure at part throttle, but for WOT tuning you need that AFPR. true, cars do run richer during warm up, but it does NOT affect the fuel pressure. the only things that SHOULD affect pressure would be the FPR or improper voltage to the pump. on that note: 90mustangGT- have you checked your electrical system lately? it's a long shot but possibly your alternator isn't charging properly. if your voltage dropped enough that could bring down the f/p. just a thought. -steve
so if the FRP is only good at WOT- that is what - <1% of your driving time? bottom line- your computer is programmed to run a set FP and will alter the settings done to it to get it back to those pre-wired settings- when you increase pressure you will richen up the combustion= when the computer realizes that the conditions are too rich it will lean down the pressure by shortening the amount of fuel being fired into each cylinder thus negating any functionality (outside of WOT) of your FPR. in other words- they are a waste of money.
Well, most performance parts you put on a car only help at WOT, so basically with your logic every performance part is a waste of money.
Sorry fella, but the FPR is pretty important. Run your stocker and I'll blow you off the road if we had the same setup. WOT is the most important time for performance and fuel needs. Run a blower motor lean through transition to boost and it'll let go or detonate. I can tailor my fuel pressure so the A/F stays steady until the FMU takes over for boost. Noticed a huge difference in how the car ran with the fuel pressure set up around 44psi. Jamie
