Fuel pressure help!
 

Ap1 s2k with a walbro 255 and rc750's and STOCK FPR at 54psi with vacuum line on. I just installed the e85 walbro 450 and the SOS wiring kit preparing for a retune with Id1300's soon and now my fuel pressure is way high at 80psi at idle and the car is running extremely lean in the 17-18afr range. I thought it should be exactly the same. Wired it correctly as far as I can tell double checked 3 times. Do I need an aftermarket FPR?

Something is wrong. You should see ~55psi with the walbro 450 on the stock FPR. Aftermarket FPRs are unnecessary. Maybe your return is kinked or blocked somehow? That's the only way I can think you would be able to achieve that kinda pressure unless you somehow increased the voltage to the pump which isn't possible on that cars electrical system..

I am running that exact setup. walbro 450, id1300s, stock FPR, my own pump rewire.

possible that the Injectors are failing or something? You know how RC Injectors are (they suck) that's why I'm going ID1300 and switching to e85.

More often then not, u have to start at what changed. Soo, you did the re-wire and pump.

You have 80psi at idle (cant check it when cruising)
but your running lean.

This is where i get confused (extra psi and running leaner)

i would start at the assembly (pump hanger) and re check everything. I know i dont speak for everyone but for me, a gremlin usually ends up being something i overlooked.

check everything! Fine tooth comb.

only thing I can see that it's running leaner is the RC Injectors are locking up with that high pressure. I pulled the pump a second time last night and everything was perfect. I'm gonna check the wiring and relay I have.

It would be wise to get an adjustable FPR. Sometimes you can get by without one, sometimes you can't. Either way, it is a valuable tool when tuning the car. The stock one sometimes can't handle the flow of the larger pump, thus the pressure spiking high. Every setup is different. if you have a 320lph pump with stock wiring, it may be ok. Upgrade the wiring and now you've increased the flow. I originally had an AEM 320lph pump with the SOS wire kit and the diaphragm in my stock regulator couldn't handle the extra flow causing the pressure to drop in boost. I installed an AEM FPR with the largest orifice since I upgraded to the Walbro 450. But, your install could have gone wrong too. I'd go over everything to make sure its all in order.

As to why it's running lean, that's another story. The issues may be related...what tuning stratagies are you running?

kpro v4
I have a flex fuel sensor in the return line. It was there before I did the pump. On hot startup the car always ran lean because the tune was off from a half as tuner on the island but this was on a cold start so it should be fine. I think it's 100% related to the pump or the regulator. I have an appointment with Jeff evans on the September 13th I have a AEM FPR coming from another member. Should be here Friday

Does the pressure go up around 10psi when you pull off the vacuum hose?

yes it increases

I'm still leaning towards a FPR if you have gone over everything else. Mine would increase as well but under boost it would not hold and actually drop.