Engine bogs or misfires @ 7psi (RB25)

[Iam99x]

I'm running a S1 RB25 with a Garrett T3/T04e, Tial 38mm wastegate, Walbro fuel pump, 3" turbo back straight pipe, Blitz FMIC, and a Nismo FPR.

Okay, so, I've been running a 6psi wastegate spring, and the car runs fine at 36psi of fuel. It's been daily driven on this setup for months and months.

I got bored...so...

I got an MBC to up the boost to 10psi, but it runs like crap past 7psi. I've tried adding more fuel pressure, and it doesn't seem to help the problem. I haven't had the car tuned, yet. I'm currently saving money for a SAFCII, EBC, and a tune.

Anyway, any idea why it runs so badly after I added more boost?

It has spiked up to 8psi before and it didn't bog/misfire.

I can make a video if needed.

Thanks.

[S14-NEO]

wideband?...if not your playing with fire especially seems how your not running the stock turbo anymore and prob still running the stock injectors

[Cjmartz2k]

I just want to make sure I'm understanding you right. You put a turbo capable of 100hp over the stock unit on your car, at way less fuel pressure than stock, with what I'm guessing are stock injectors and MAF, and you wonder why your car doesn't run right?

[Cjmartz2k]

I really need to ask, aside from all the other stupid crap your doing, why the hell are you only running 36psi of fuel pressure?

[Iam99x]

No wideband.

And holy s***...why so harsh? I don't see the need in being an a** when I came here to try to fix my problem. Chill out, man. Anyway...

Yes, you understood me right, but I'm not the one that did any of this. I got the car as it is.

I'm assuming the injectors are stock, as well as the MAFS.

I read online that the stock fuel pressure was 36-38psi. It has been running PERFECT on that fuel pressure for at least a year.

I set it to 40psi with the vacuum line off, and it still does the same.

[Cjmartz2k]

43.5psi base fuel pressure.

There is a difference between running perfect and not blowing up. I'd bet yours is just barely doing the latter.

-Set the fuel pressure to 43.5psi/3 bar with the vacuum off-Screw the SAFC. Get something real to tune with, not a piggy back, and if you can't afford a stand alone EMS, look at a ROM tuned VG30det ECU, or even an ROM'd RB20 ECU with an external switch for the VCT.-Do NOT beat on your car until you get it tuned. Even at 6 psi. Even at 43.5psi of fuel pressure. Just don't.

A stock turbined RB25 is faster than an untuned RB25 running a T3/TO4e at 6psi. Get t running correctly and you will be amazed at the difference.

[Iam99x]

Okay, I'll start from there. I've been thinking about getting a ROM tuned ECU or something similar.

No way a stock RB25 setup is faster than mine. I haven't had it hooked up to a wideband or anything, but I know I get good gas mileage, it cranks every time, pulls hard as f*** in every gear with no issues at all. I'm not saying that I have a perfect 14.7 A/F ratio, but it can't be far from it.

Neejay on here has a completely stock RB25 setup, and he can vouch how much faster my car is than a stock setup. I'm not out to prove anything, but I can get you video proof of it running great with the 6psi setup, then you can make that assumption.

Thank you for your replies, but do you have any idea what is causing it to run s***ty at higher boost?

If not, I'm going back to 6psi. Oh, I drive this car every single day, and I drive the hell out of it. It has honestly been the most reliable car I've owned beside a couple of Hondas.

Thanks again.

[DrifterProdigy85]

Get it properly tuned. Going with a bigger turbo requires the change in timing and fuel maps. At least go with Emanage or try MAP ECU II.

[Cjmartz2k]

No way a stock RB25 setup is faster than mine. I haven't had it hooked up to a wideband or anything, but I know I get good gas mileage, it cranks every time, pulls hard as f*** in every gear with no issues at all. I'm not saying that I have a perfect 14.7 A/F ratio, but it can't be far from it.

A narrow band 02 sensor can give you good gas millage and keep you at 14.7 during light throttle cruising even with a garbage tune. `

Neejay on here has a completely stock RB25 setup, and he can vouch how much faster my car is than a stock setup. I'm not out to prove anything, but I can get you video proof of it running great with the 6psi setup, then you can make that assumption.

Not knocking neejay's setup, but I've seen what untuned RB25's with T3/TO4e's and a fuel pump can do against stock cars. They missed, sputtered, at got beat. MAYBE at 6psi, you were just flowing little enough not to freak out the factory computer. Case in point--full bolt ons, stock turbined RB25, no tune. I made 285hp at .7 bar (stock) and 252hp at .9 bar. That's on the stock snail. The ecu freaks out when it sees to much are, throws a bunch of fuel at it, and pulls timing in hopes of saving the engine. That's probably what yours is doing now to the extreme of making it miss.

Thank you for your replies, but do you have any idea what is causing it to run s***ty at higher boost?

You can't really even say with out at least putting a wide band 02 sensor on it. IF it had a/f ratios in the high 10's to 12 flats, I'd say coil packs, but I'll bet that's not where your a/f ratios are at. My number 1 guess for the missing is lack of tune, and I can't tell you enough times how dangerous that is for your motor man.

If not, I'm going back to 6psi.

Do it until you are tuned--and don't get on it even then. Getting an RB25 tuned is one of the most expensive parts of the build. They aren't cheap computer and injector wise.

[Iam99x]

I don't have much time to reply, but Neejay's setup is completely stock. I'm just going to reset my fuel pressure, and drive it how it was. I'll make a video for you of how it runs for s***s and giggles.

Thanks.