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Thread: Just started finished engine swap, trying to tune 4.8 (wont run right)

  1. #21
    Tuner in Training
    Join Date
    Jun 2014
    Posts
    35
    Anyone else take a look at my logs and see if you can tell if it was a bad MAF. vacuum leak or bad injector....

  2. #22
    Tuner in Training
    Join Date
    Jun 2014
    Posts
    35
    So I replaced MAF and got ahold of another 4.8 truck and compared readings, MAF is good. Smoke test is good. Not a vacuum leak but maybe bad injetor? Or low Fuel pressure? (Or O2 SENlSORS are reading wrong? in which case I have a WideBandO2 and will be hooking that up shortly to confirm O2 readings.)
    But when the truck uses the MAF sensor, it is really, really LEAN.
    And fuel trims are 'dumping fuel' and this is the STOCK MAF table.
    But when I use speed density, the fuel trims are within normal range, or sometimes subtrack the fuel that it was trying to add from before (if i dont reset it)
    I try 'reading' about it but my mechanic calls me an idiot for having an 'internet' education and that knowledge doesn't count.
    Now I have a log of the speed density run again but with 3.73s and after solving all of this stuff I still don't understand why the computer runs SO LEAN on stock tables?
    and the engine is ASKING and STARVING for fuel.
    Or run speed density and its a happy camper.
    And this doesn't even TOUCH the timing issue I have.
    Anyone can take a stab at either.
    Timing is off because it doesn't give high timing under load (look at graph, maybe 23-26) degrees when I only use nice gas and should be getting 29 degrees at least.
    And when I punch it, timing goes up and down for a split second and because of the tall gears I have, I can feel it. Feels like power being cut on and off and you can see this in the log as well.
    So I am confused.
    Last edited by agentruley; 07-07-2014 at 08:45 PM.

  3. #23
    Senior Tuner
    Join Date
    Feb 2009
    Posts
    1,931
    I see nothing wrong with your scans tuning wont fix. Your tables are stock, for stock maf with stock ducting. As soon as you relocate or reclock the maf the table is wrong. Do some reading, put it into maf mode, and tune it. Also, wot open throttle runs are usually the last thing you do. I suggest reading some how too's, and doing some tuning, and working your way up to wot.