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Thread: LT4 High side help

  1. #1
    Tuner in Training
    Join Date
    Oct 2007
    Posts
    20

    LT4 High side help

    Ok so still having issues with the high side pressure. Truck is going into Reduced Power Mode, Codes are as follows

    0x7E8: P0089 - Fuel Pressure Regulator Performance (SES, Pending, Current, Old, History)
    0x7E8: P0106 - Manifold Absolute Pressure/BARO Sensor Range/Performance (Pending)
    0x7E8: P228C - Fuel Pressure Regulator Control Performance - Low Pressure (SES, Pending, Current, Old, History)

    Below is a list of things I have changed. Truck ran fine stock. I added a Whipple, 103mm TB, LT4 HPFP, Injectors, and added the low side feed pipe without the check valve......... After the install it has the High Side fuel pressure issues

    1. New LT4 HPFP replaced with a different NEW LT4 HPFP. no change
    2. Replaced Fuel Rail Wire harness Verified Good. no change
    3. Replaced Fuel Rail Pressure sensor with a New GM part. no change

    the only thing I havent touched was the New LT4 fuel injectors that were installed. They were bought from a vendor as new.

    Would a set of injectors that are bad cause the Low High Side Pressure???

    Things i cant figure out. Ive posted 2 logs as well as the tune.

    Why is the injector pulse with so damn high???? I thought any thing over 5-6ms is bad. Im seeing 19-20ms on light throttle as seen in the around the block log file

    Also any clue on the rev up file, the HPFP started making pressure above approx 2500 RPMS but just matches the low side at any other RPM????

    Ive been fighting this low high side fuel for 2 weeks wrenching on the truck after work, and im beyond frustrated and ready to take the whipple and LT4 stuff off just to be able to drive the truck.

    Id Gladly Pay anyone that can figure something out and make this truck drive able again
    Attached Files Attached Files
    Last edited by 1993 sle; 01-13-2021 at 06:15 PM.
    2003 SSEi SUPERCHARGED
    WHP=Top 5 on Stock Cam chart
    Pullied, Intercooled, Stalled, Geared

    2014 Sierra Denali,
    Whipple Supercharged
    LT4 fueling
    Kooks LT's
    Corsa catback

  2. #2
    Tuner evolmotorsprt's Avatar
    Join Date
    Aug 2018
    Location
    Salt Lake
    Posts
    115
    I've been dealing with the same issue on a 2014 Corvette. We did a LT1 to LT4 conversion and the company that sold us the kit gave me some good info that helped. The 2014's, for some reason, will have no high side pressure if you copy all of the LT4 tables into the fuel system parameters. I set all of these tables back to stock and I was able to get my high side back. I need to go back and one by one go through the fuel system tab to figure out what table causes the issue. Goodluck!

    BTW, in my case the problem was NOT the injector data. Only the Fuel system.
    Last edited by evolmotorsprt; 02-26-2021 at 01:41 PM.

  3. #3
    Advanced Tuner
    Join Date
    Aug 2014
    Location
    Central, LA
    Posts
    737
    You didn't mention changing anything in the low side, so I set some stuff that's only related to the low side back to stock in this tune. As well as undid a few things that cause trouble on other vehicles.
    Attached Files Attached Files

  4. #4
    did you change your MAP sensor? , because I have looked onto your log file it shows at KEY ON Engine OFF show 200 KPA on the other side it should show around 90 to 102 KPA

  5. #5
    any update on the changes suggested?

  6. #6
    Advanced Tuner
    Join Date
    Jun 2018
    Posts
    603
    I ran in to this before with a 2014 model and Janetty helped me so I am paying it forward.

    On the 2014 only, you can NOT modify the High Pressure Pump/Peak Duration table when loading all the LT4 data, return it to stock and all will be well.