HELP my RB is leaning out after 5500 rpm??

[b00stinbmx]

so yea, haven;t changed my tune at all, can;t smell a fuel leak. im just running 14.5 psi but its happening at any boost levels. im thinking it could be my walboro? i have a tomei type s FPR with a gauge. its set at stock fuel pressure 43.5 with no vaccum. Basically what happens is the car will hit boost 15 psi by like 4500, pulls good at 11.0 ish then leans right out to like 12.8-13 ish around 5500 rpm . tried messing with my tune but it didn;t help, has to be something mechanical. I have hard wired a new relay to my fuel pump right off the battery and never had any issue with it at all. looking for some suggestions to keep trouble shooting this issue. thanks

[Cjmartz2k]

Motor? Turbo? Injectors? Tuned?

I'm going to make a WAG and say RB20 on stock turbo? Stock RB20 injectors aren't good for very much.

[b00stinbmx]

no, rb25 with 35r i have my setup and dyno graph posted in a recent thread.

[b00stinbmx]

tried a new walboro pump today, didn;t help at all. i set my entire map under boost to be a 10.5 and it stays there then jumps up to 13 at around 5500 rpm. not sure what the hell else it could be.

[Cjmartz2k]

no, rb25 with 35r i have my setup and dyno graph posted in a recent thread.

Ah, okay. Fuel pressure gage? Other things could cause low fuel pressure like small injectors, clogged filter, vacuum leak, etc. Do you have a Power FC? If so, any really high peak values?

[b00stinbmx]

im using nistune. going to do some datalogging to see what the injector duty cycle is like and whatnot. i have a fuel pressure gauge hooked up to my tomei type s regulator but thats under the hood and can;t see it during pulls. the base fuel pressure looks fine set at 43 without vacuum and theres no vacuum leak to it i don't believe. im going to try another fuel filter and see if that helps. also going to replace the fuel injector o-rings but i don;t see there being a leak at all.

[b00stinbmx]

did some logging in nistune, as you can see i let off the gas around 5100 rpm and you can see the cursor where it is in the fuel map. i tried richening it up and sure enough right when i let off it jumps up to around 13.5+ afrs so i don;t think its a tuning issue.

if you can' see let me know heres a link to my picasa theres a screen cap of my nistune log there

https://picasaweb.google.com/1016243590 ... 4938296946

[Cjmartz2k]

Need to know peak injector duty cycle.

[Yellow4g63]

Stock RB25 injectors? If so your prob maxing them out at the boost level with that turbo. Or could be that you need to rewire the fuel pump with a 12v from the battery vs the stock wiring. I had a problem like that too, after the rewire stayed rich the whole rpm.

[Darius]

No, that can't be true. You're not running the stock injectors are you??

[b00stinbmx]

guys im not stupid, just stumped. i guess nobody cared to check out my thread before but heres the set up and what i have done

rb25det gt3582r
detschworks 740cc injectors
walboro 255 lph pump (tried 2 they both work) also hard wired to battery with a relay z32 fuel filter
tomei type s adjustable FPR with gauge, set to stock fuel pressure 38 at vaccumm and 43 ish without
nistune z32 ecu with type 2 board


everything has been like this for the whole year with no problem till now... going to try a new fuel filter and hopefully find a way to get the small fuel pressure gauge in the car so i can log that while im doing pulls.

[Yellow4g63]

Are you hitting the burn to rom button after you make changes to the nistune maps?

[b00stinbmx]

^^^ really?

[Yellow4g63]

Yes really if your not hitting it the new changes and old changes mix and cause all sorts of problems.

[Cjmartz2k]

WHAT IS THE INJECTOR DUTY CYCLE? Knowing this number would be helpful in fuguing out if it's a fuel pressure problem or not.

[RRRRB]

Perhaps the MAF sensor is reading incorrectly or got oil on it from your air filter etc..

Having a fuel pressure gauge in the car would be great, fuel pressure dropping off sounds like the issue..

Hows battery votage while problem is occuring?

[Darius]

guys im not stupid, just stumped. i guess nobody cared to check out my thread before but heres the set up and what i have done

rb25det gt3582r
detschworks 740cc injectors
walboro 255 lph pump (tried 2 they both work) also hard wired to battery with a relay z32 fuel filter
tomei type s adjustable FPR with gauge, set to stock fuel pressure 38 at vaccumm and 43 ish without
nistune z32 ecu with type 2 board


everything has been like this for the whole year with no problem till now... going to try a new fuel filter and hopefully find a way to get the small fuel pressure gauge in the car so i can log that while im doing pulls.

Sorry if we are insulting your intelligence with stupid questions, but you never know what someone has or has not already checked. It is just cheaper and easier to verify that all the "free" possibilities have been checked first.

Your setup looks good. Is the car breaking-up or missing before 5500? If it is missing, it will give you a false lean condition and the problem would be ignition related. Likely coils.

[b00stinbmx]

no breaking up. its not ignition i promise you.... i finally did get it figured out in nistune though.... injectors are around 35% duty cycle at 5100 rpm when i let off, does this seem really low?

[Darius]

That sounds really low and in need of a large fuel correction up top.

[b00stinbmx]

i think i found the problem, nistune is saying my voltage is 11.4 when under load. that dosen;t sound right at all and about 2 volts too low.... can anyone chime in? im going to try to find/try another alternator.

[Yellow4g63]

maybe check the harness grounds make sure they are good or reground the maf.

[mrflip69]

Yup, for sure your alt is the culprit if its 11.4 under load. I had the same symptoms when mine died. A lot of missing, and could barely get into boost and would break up over positive pressure. Stock alternator I presume? Take the chance and upgrade to a Quest. Glad you figured it out (hopefully)!

Weird how you said you were sure its not an ignition issue. Maybe the injectors/fuel pump were first to run out of juice.

[b00stinbmx]

yea its weird cause its still running fine for the most part besides it leaning out, and its a stock alternator that i had rebuild over winter and the amps raised up but apparently the dude did a s*** job. im just going to go find a quest alternator in the junkyard tomorrow hopefully and give that a try.