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Discussion Starter #1
I finally built my baby. I have an 07 STi that I built (head gaskets blew and consumed a quart of oil every 300 mi) and after a very bumpy road of dealing with "knock" during engine break in and troubleshooting, I finally tuned perfectly on 93 octane. I put one tank of E85 and it felt amazing. The difference was literally night and day... Second tank of E85, it fell apart.

I have a Radium gauge installed on my supply line to easily troubleshoot. The needle does a slight wobble, then will start to shake, then gets faster/shakes bad then stable all in about 3-5 seconds...rinse and repeat about every 20 seconds. To make a long story short, (list of mods at the end) I've replaced my FPR, removed the fuel pulse dampers and I still have issues. Radium mentioned to remove the return fuel line put it in a bucket and see if the pressure stabled. My buddy/builder helped me do that test and I was not there but he said it cleared up the pressure issue.

It runs smooth as butter until I hit double digit boost. Doing some testing today, I never hit over 11psi, but once I got into about 10psi I noticed it was not happy...not super angry, but not feeling it... I captured some datalogs to send to my tuner and I reviewed them a bit, I was a tech for Chrysler for 10 years so I understand a bit.

LTFT are ADDING a steady 12.5 at idle, and while i'm steady cruising on the highway around 2400rpm it's actually PULLING fuel at -17. When I'm about 3200 and higher it's pulling -7.03. I've had a minutes worth of data at each mark so it was definitely sustained for a bit.

One thing to note that was weird, My buddy set the fuel pressure at 42.5 and I replaced the FPR because it dropped to about 38psi and I was having other issues to warrant replacement. I set the pressure at 42.5 myself and when my buddy did the test of the return line in the bucket, he checked fuel pressure and said it was at 50psi so he brought it down. I checked fuel pressure today, it's at 38psi again.....

I'm beating my head trying to figure out what is going on and any and all input would be appreciated. Thank you for taking the time to read this newbie/scrub nugget to the forums, post.

List of mods:
Built short block, Callies rods, CP pistons, and a closed deck block, nitrite treated crankshaft, stock re-worked heads
AEM 320lph pump, Vibrant 6AN lines in the engine bay (about to install from the pump forward supply and return due to this issue to eliminate the lines as a suspect), with Radium FPR, fuel pulse dampers and fuel rails, ID 1050cc injectors
TGV, vacuum pump, and EGR delete
Grimmspeed Intake with box, Grimmspeed up-pipe, Nvidia catted downpipe and SPT catback
NGK 2309 step colder plugs
FP Blue 58mm turbo
Radium AOS
Other irrelevant stuff, STi group N mounts, Perrin turbo inlet, ACT clutch, EBC redstuff with DBA slotted rotors

She's naaasty when running right

Thank you!
 

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Set your fuel pressure with the vacuum line off to whatever base pressure you want. Then scale the injectors to this base pressure.

The ECU has trims for idle and varying loads up to open loop. You're going to need to tune the MAF curve for GS intake or go SD but either way it's going to need to be tuned properly.
 

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I very much appreciate the response Joshua. One thing I did fail to mention which is odd that I just discovered, if I check the fuel pressure right after starting, it's a beautiful 42.5psi. When I get home from work (11 miles mostly toll roads) and check the pressure again, it's 38 to 39 psi. Today when I got home, it was 40psi. It ran flawlessly today. I'm so confused.

I am getting an E-tune and my guy has been very helpful, supportive, patient and knowledgeable we've been working together for about 3 months now. After sending him logs he sent me a map in which he said he set the MAF scaling back to where it should be (I replaced the MAF at the same time as installing the intake on the 4th of July). So I think that is why it drove beautiful today. But doesn't explain why I'm struggling to keep fuel pressure. I ordered the Iwire kit for the fuel pump controller bypass because, with all the demand I have on the fuel system it's silly I haven't bypassed the OEM controller already.

When I feel it, it's a pretty decent bucking and jerking almost misfire type.
 
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