2003 silverado, chasing mysterious power loss

Discussion in 'Maintenance' started by L_Dillinger, Dec 21, 2016.

  1. ron7000

    ron7000 GMFS Member

    Posts:
    677
    Likes Received:
    8
    Joined:
    Feb 5, 2012
    Location:
    CT
    Either "Engine Management Advanced Tuning" or "Designing & Tuning High Performance Fuel Injection Systems" both by Greg Banish is worth reading.
    It will give you a sense of respect for all the conditions which the EFI parameters and tables have to control. Aftermarket tuners when they modify these don't understand everything that happens while driving on the street and screw it up, sll they do is modify for max power on an inertial dynomometer which is not real world conditions.

    To my knowledge the algorithms in an engine computer are proprietary and protected. Tuners do not modify this part of the computer, instead they only modify numbers/parameters which have been set by the manufacturer that the algorithms use to make the engine run optimally.

    Without having access to the actual programming code to figure out the far reaching affects resulting from changing the values that they do,
    or having instructions published by the source (i.e. manufacturer),
    tuners are guessing and assuming.
    And in doing what they are doing is technically saying they know better than the manufacturer... on modifying something there is no way they can have complete knowledge of. I am unaware of any car automaker publishing any kind of instruction how to modify an engine computer. Furthermore i'm pretty sure it is against federal law to modify an engine computer because of emissions laws- that is for a registered vehicle driven on public roads.
    Like most things automotive aftermarket it is a scam.


    2 basic examples of how tuning can be scam,

    a tuner can sell you on a tune and it actually feels like your vehicle has more power or get up and go, when all they really did was remove the torque management feature where in an electronic gas pedal type vehicle you can mash pedal instantly to floor the throttle blade does not open as fast; there are parameters which govern the rate which the throttle body opens to protect the vehicle; my 8.1L with allison along with many other trucks has this tq mgmt feature for a reason to prevent drive train failure. And you can also observe this in rental cars where mash the pedal and the car takes off like grandma driving. By making the throttle blade open faster in relation to how much you push the gas pedal down deceives the driver that the vehicle has more power.

    the most common is making max wide open throttle horsepower by leaning out the A/F tables from the oem 11.5 to 12.5 range up to 13.0. That's what everyone does when they buy EFIlive or HPtuners. This does increase max hp if done right, but it was not done by the auto maker because the resulting high exhaust heat then reduces the life and kills the catalytic converters. there are a few ways to achieve this leaning of the A/F tables and what happens is it'll work for the narrow operating condition of 1/4 mile pedal always on floor, but it can and usually does screw up many other things that make the vehicle run well on the street under varying loads.

    Does a tuner tell you exactly what he/she changed?
    Any do they offer a means to go back to the oem / original settings in a way you are sure they are not lying or deceiving you?
    If not then what does that say about your tuner?
     
  2. SLEEPER VAN

    SLEEPER VAN GMFS Member

    Age:
    54
    Posts:
    35
    Likes Received:
    3
    Joined:
    Jan 1, 2017
    Are you sure that you don't have a TPS switch? I'd look at your throttle housing and see exactly what triggers the truck that you are giving it more throttle. Just a suggestion.

    Sent from my Moto G (4) using Tapatalk
     
  3. L_Dillinger

    L_Dillinger GMFS Member

    Posts:
    49
    Likes Received:
    1
    Joined:
    Jul 26, 2012
    Location:
    Viola, Ar
    It has a little servo type motor thing in the throttle body the opens the throttle acording to the postion of the pedal. Im pretty certaim it has no tps or need for one. And to ron7000, yes i totally agree, i have called the tuner and he is real cool. Said if wasnt satisfied he could put it all back stock which i prolly will.. After it warms up some ill swap the knock sensors/harness and intake gaskets. And if that dont fix it ill go back to the stock tune. Ive got p0327 & p0332 codes now.
     
  4. John Clark

    John Clark GMFS Member

    Posts:
    96
    Likes Received:
    3
    Joined:
    Feb 1, 2011
    Location:
    Wesley Chapel, NC
    Electronic throttle body units do have TPS sensors but it's all built in to the electronic TB servo assembly. You can easily check TPS reaction voltage with a live data scan tool. I doubt that has anything to do with the current problem, though.
     
  5. L_Dillinger

    L_Dillinger GMFS Member

    Posts:
    49
    Likes Received:
    1
    Joined:
    Jul 26, 2012
    Location:
    Viola, Ar
    Yea ive been runnin live data to and from work all week (30+miles one way) and the tps % is fine, changes exactyl with the pedal. I noticed the long term fuel trims are pretty high. Between 10 & 20% on both banks at idle or drivin, and i have hardly any timing advance under any type of acceleration. Im leanin towards knock sensors and leakin intake gasket combo. I thought it was odd with the knock sensors unplugged it still ran the same with no codes. I got codes days later with em plugged in. Is it true the pcm sends 5v DC to the sensors? Cuz i checked and was gettin less than 1v. Nevermind, Jus checked my wifes truck and it was the same as mine and her truck has zero issues. Was just a thought, the pcm would be the very last thing id change
     
    Last edited: Jan 7, 2017
  6. John Clark

    John Clark GMFS Member

    Posts:
    96
    Likes Received:
    3
    Joined:
    Feb 1, 2011
    Location:
    Wesley Chapel, NC
    If your fuel trims are up in the plus 10-20% range then you still have a bit of a lean condition. It's not enough to set a P171 or P174 code yet but it's a bit lean and the computer is adding fuel to compensate. Vacuum leaks usually cause high fuel trims at idle and closer to normal at 3000 RPM. Mass air flow problems or low fuel pressure could cause overall lean conditions. The thread is long and I didn't go back and look but do you have an aftermarket air filter? I've seen those cause lean conditions. Like this one:

     
  7. L_Dillinger

    L_Dillinger GMFS Member

    Posts:
    49
    Likes Received:
    1
    Joined:
    Jul 26, 2012
    Location:
    Viola, Ar
    No, i put a stock air box on it with a stock dry filter. Ditched that "cold" air open filter junk. Since i have changed all the fuel system parts (pump, filter, regulator, i havnt goten any 171 or 174 codes but the trims are still high, i think the codes trip at 25% maybe. So maybe it dropped them down some, but did not fix it. The trims are kinda high all the time. Almost 20% at hot idle, runs about 8-14% cruisin. Heres a hot idle

    IMG_20170106_014516639_HDR~01~01.jpg
     
  8. ron7000

    ron7000 GMFS Member

    Posts:
    677
    Likes Received:
    8
    Joined:
    Feb 5, 2012
    Location:
    CT
    read through this article
    http://www.autoserviceprofessional....-works-and-how-to-make-it-work-for-you?Page=1

    i mentioned previously it can be a faulty solenoid somewhere in the evap system, someone made a good point that for diagnostic you should remove/plug/clamp all external means of air being able to enter the intake or the exhaust- this will cause other DTC's but it would quickly rule out if there is some kind of vacuum leak as you should see fuel trims go back to the normal +/- 10% range if this is the cause.

    The one thing you can't plug is the PCV system otherwise crankcase pressure would build and you'll start pushing oil out various places the worst being the crankshaft seals, so make sure the PCV system on yours is not leaking.
    On my 8.1L for example the aluminum intake manifold has an orifice on the bottom of it and it sucks directly from the valley of the block, input air back into the block so you don't suck in the crank seals is air coming through the air filter box then metered by the MAF then passes through a side hole in the throttle body which then enters a separate passage in intake manifold connected to the valley/crankcase of the block (very near where the oil fill is). So in my case if my oil fill cap or dipstick is not sealed, air will enter into crankcase this way bypassing MAF sensor, this air will eventually be combustion air and since it is unmetered by the MAF will cause a lean condition and high fuel trims. So you need to understand your PCV system and make sure something like a bad o-ring on dipstick tube or something anywhere else on block is not letting unmetered air into the crankcase. That is if it matters for your engine, I know it does on mine.

    If none of this fixes the LTFT, then you simply need to go back to the OEM programming in the engine computer to rule that out.
     
  9. L_Dillinger

    L_Dillinger GMFS Member

    Posts:
    49
    Likes Received:
    1
    Joined:
    Jul 26, 2012
    Location:
    Viola, Ar
    Yes i totally agree. Stock programming is another step i will take along with KS, KS harness and intake gaskets. I have unhooked the purge valve wires and hose and plugged it and been drivin it like that for weeks with no improvement. I noticed my oil fill tube was not seated to the valve cover, the O ring on one side was sticking out, so i cleaned and re-seated it properly also to no improvement. Idk what the max amount of knock retard is for these trucks, and my scanner dont read knock retard specificly. If have learned anything it is that AC Delco is your friend, and aftermarket is not. At least when concerning parts that give very crucial feedback to the pcm.
     
  10. L_Dillinger

    L_Dillinger GMFS Member

    Posts:
    49
    Likes Received:
    1
    Joined:
    Jul 26, 2012
    Location:
    Viola, Ar
    Today i checked the knock sensor resistance all the way back to the pcm plug and was exactly the same as it was at the KS plug on the intake. 99.5 & 99.7 ohm. I should note that unplugging the knock sensor harness at the intake and driving it shows absolutly ZERO difference in timing being pulled back like crazy. It runs exactly the same.
     

Share This Page